IN-SITU SOIL AND GROUNDWATER BIOREMEDIATION TECHNIQUES AND APPLICATIONS.

IN-SITU SOIL AND GROUNDWATER BIOREMEDIATION TECHNIQUES AND APPLICATIONS.
TAMPERE POLYTECHNIC
Environmental Engineering
Final thesis
Laitinen, Jarno
IN-SITU SOIL AND GROUNDWATER BIOREMEDIATION
TECHNIQUES AND APPLICATIONS.
Supervisor: Senior lecturer Viskari, Eeva-Liisa
Commissioned by: Doranova Oy
Tampere 2006
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TAMPERE POLYTECHNIC
Environmental Engineering
LAITINEN, JARNO
In-situ soil and groundwater bioremediation
techniques and applications.
Final Thesis
Supervisor
Commissioned by
April 2006
Keywords
84 pages + 6 appendices
Senior lecturer Viskari, Eeva-Liisa (PhD.)
Doranova Oy, supervisor Dy. MD. Laitinen, Ari (MSc.)
bioremediation,
biodegradation,
contaminated, soil, groundwater
micro-organism,
in-situ,
Abstract
Current and previous polluting activities have caused our urban nature to become
ever so more contaminated with various pollutants, some natural, some xenobiotic.
Many of these contaminated sites today are located within heavily constructed
urban areas where activity cannot be seized without economic losses or on areas
which are already re-zoned and have pressing need for their development. Old
remediation technologies are not able to offer solutions that are environmentally or
economically acceptable in many of these cases and therefore the focus has to be
placed on novel technologies.
The aim of this thesis is to focus on one field of these novel soil and groundwater
remediation technologies, namely in-situ bioremediation, meaning biologically
oriented technologies conducted in the site, without excavation and removal.
Bioremediation is based on the basic principles of biotechnology and microbiology,
with special focus in in-situ with site biogeohydrochemical processes and
engineering principles. The technologies themselves require diverse basic
background knowledge on many fields of science; therefore a multidisciplinary
approach is commonly required in full scale applications.
This paper gives an overview of the main topics in and around bioremediation.
Literature survey features a short overview of the role of bioremediation in the field
of environmental biotechnology and its global and national economic perspectives,
and presents key player in bioremediation, the micro-organisms, and their
metabolism and environment requirements. The technical section defines the
border conditions for a successful remediation, outlines and defines the currently
acknowledged in-situ bioremediation techniques and their applicability and
suggests tools for verifying and monitoring the process along quality control. In
addition, a documentation of a real-life in-situ pilot scale field trial is included.
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TAMPEREEN AMMATTIKORKEAKOULU
Environmental Engineering
LAITINEN, JARNO
Maan ja pohjaveden in-situ bioremediaatio
tekniikat ja applikaatiot.
Tutkintotyö
Työn ohjaaja
Työn teettäjä
Huhtikuu 2006
Avainsanat
84 sivua + 6 liitettä
Lehtori Viskari, Eeva-Liisa (FT)
Doranova Oy, valvojana Vtj. Laitinen, Ari (DI)
bioremediaatio, biodegradaatio, mikro-organismi, in-situ, pilaantunut,
maaperä, pohjavesi
Tiivistelmä
Nykyinen ja aiempi ympäristöä pilaava toiminta on aiheuttanut kaupunkiympäristömme maaperän ja pohjaveden pilaantumisen erinäisillä kemikaaleilla,
joista osa on ympäristölle luontaisia, osa vieraita. Monet näistä saastuneista alueista
sijaitsee laajalti rakennetuilla kaupunkialueilla, joissa nykyistä toimintaa ei voida
keskeyttää ilman taloudellisia menetyksiä tai alueilla, jotka on kaavoitettu uutta
käyttötarkoitusta varten ja rakentamisen paine on suuri. Perinteiset
kunnostusmenetelmät eivät kykene tarjoamaan taloudellisesti ja ympäristön
kannalta kannattavia vaihtoehtoja useissa näistä tapauksista, ja siksi huomio
tuleekin keskittää uusiin, innovatiivisiin tekniikoihin.
Tämä lopputyö keskittyy yhteen erityisalueeseen maan ja pohjaveden
kunnostukseen keskittyvien tekniikoiden joukossa, nimellisesti in-situ
bioremediaatioon, joka sisältää biologiseen toimintaan pohjaavia menetelmiä jotka
toteutetaan maaperässä tai pohjavedessä, ilman maaperän kaivamista tai
pohjaveden poistoa. Bioremediaatio pohjaa vahvasti biotekniikan ja
mikrobiologian perusteisiin, erityishuomio on kuitenkin kunnostuskohteiden
biogeohydrokemikaalisten
prosessien
tuntemisella
ja
insinöörityön
perustekniikoilla. Tekniikat itsessään vaativat laajaa perustietoutta monilta tieteen
aloilta ja siksi poikkitieteellistä lähestymistä vaaditaan lähes poikkeuksetta
täysmittakaavaisissa sovellutuskohteissa.
Tämän työn tarkoituksena on antaa yleiskatsaus aihepiireihin bioremediaation
ympärillä. Kirjallisuuskatsaus kuvaa bioremediaation roolia osana biotekniikkaa ja
tarkastelee sen kansainvälisiä ja kansallisia taloudellisia näkymiä, lisäksi se
luonnehtii bioremediaation avaintekijöitä, mikro-organismejä, sekä niiden
metaboliikkaa ja vaikuttavia ympäristötekijöitä. Teknillinen osuus työstä
määrittelee reunaehdot onnistuneelle kunnostushankkeen toteuttamiselle, sekä
alustaa ja määrittelee nykyisellään tunnustetut in-situ bioremediaatio-tekniikat ja
niiden käyttökelpoisuuden. Teknisen osan päätteeksi esitetään metodeja
onnistuneen kunnostuksen todentamiseksi, monitoroimiseksi ja laadun
varmistamiseksi. Edellisten lisäksi, lyhyt kuvaus pilot muotoisesta in-situ
bioremediaatio kenttäkokeesta on sisällytetty.
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Acknowledgements
An era of engineering studies in Tampere Polytechnic is now over and the
culmination, my final thesis is finished. This thesis was not so much ordered as it
was inspired and encouraged by Doranova Oy, for whom I have been working
during the last year of my studies concentrating on issues of soil and water
remediation.
The thesis was supervised on behalf of Tampere Polytechnic by Eeva-Liisa Viskari
and on behalf of Doranova Oy by Ari Laitinen. Both have shared significant
amounts of their expertise and taken the time and effort to aid me in my questions
concerning the thesis. For Ari I owe special thanks for numerous insightful
discussions and for giving the confidence on the field that allowed me to learn
more and faster.
In addition, I would like to thank Outi Kankaanpää from Doranova Oy, who
continuously brought me new articles and studies concerning my thesis and J.F. de
Kreuk from Biosoil R&D B.V. (NL) for being a big inspiration and for teaching me
the simple complexity of these issues.
Last, I would like to thank my parents, brother, friends and loved one for their
understanding and support, without them nothing would be possible.
Thank You!
Jarno Laitinen
Tampere, 19.4.2006
TAMPERE POLYTECHNIC
Environmental Engineering
FINAL THESIS
Laitinen, Jarno
List of abbreviations
Acetyl-CoA
ATP
Aw
BATNEEC
BS
BTEX
BV
DDT
DNA
DNAPL
ESB
FAD
GAC
GW
HDPE
Kow
LC50
LD50
LF
LNAPL
MCL
MNA
MSW
MWW
NAD
NADP
NAPL
PAH
PCB
PEP
POP
PR
PVC
REDOX
ROI
RTDF
SE EPA
SME
SVE
SVOC
SVOC-Cl
SYKE
TNT
TPH
UN CDB
US EPA
UST
VOC
VOC-Cl
VTT
€
Acetyl Coenzyme A
Adenosine triphosphate
Water Activity
Best Available Technology Not Entailing Extensive Costs
Biosparging
Benzene, Toluene, Ethylbenzene, and Xylenes
Bioventing
Dichloro-Diphenyl-Trichloroethane
Deoxyribonucleic acid
Dense Non Aqueous Phase Liquid
Enhanced Saturated zone Bioremediation
Flavin Adenine Dinucleotide
Gas Activated Carbon
Groundwater
High density polyethylene
Octanol-Water Partition Coefficient
Lethal Concetration 50
Lethal Dosage 50
Land Farming
Light Non Aqueous Phase Liquid
Maximum Concentration Limit
Monitored Natural Attenuation
Municipal Solid Waste
Municipal Waste Water
Nicotinamide Ademine Dinucleaotide
Nicotinamide Ademine Dinucleaotide Phosphate
Non Aqueous Phase Liquid
Polycyclic aromatic hydrocarbons
Polychlorinated biphenyl
Phosphoenolpyruvate
Persistent Organic Pollutants
Phyto Remediation
Polyvinyl Chloride
Reduction-Oxidation Reaction
Radius Of Influence
Remediation Technologies Developer Forum
Swedish Environmental Protection Agency
Small-Medium sized Enterprises
Soil Vapour Extraction
Semi Volatile Organic Compounds
Chlorinated Semi Volatile Organic Compounds
Finnish Environmental Institute
Trinitrotoluene
Total Petroleum Hydrocarbons
UN Convention on Biological Diversity
US Environmental Protection Agency
Underground Storage Tank
Volatile Organic Compounds
Chlorinated Volatile Organic Compounds
Finnish National Research Center
1 € = $ 1.19 = £ 0.68 = 138.12 Yen (06.03.2006)
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Environmental Engineering
FINAL THESIS
Laitinen, Jarno
v
Table of content
Abstract ................................................................................................................i
Tiivistelmä.......................................................................................................... ii
Acknowledgements............................................................................................ iii
List of abbreviations ...........................................................................................iv
Table of content ...................................................................................................v
1.
Introduction..............................................................................................1
PART I Environmental biotechnology ................................................................3
2.
3.
Defining biotechnology ............................................................................3
Environmental biotechnology...................................................................7
PART II Microbiology......................................................................................14
4.
5.
6.
Taxanomy and structure .........................................................................14
Microbial metabolism.............................................................................19
Conditions for growth.............................................................................25
PART III Bioremediation..................................................................................32
7.
8.
9.
10.
Pollution control and role of bioremediation...........................................32
Data requirements ..................................................................................43
In-situ bioremediation techniques ...........................................................45
Monitoring and quality control ...............................................................64
PART IV Case study: Biowall -pilot .................................................................70
11.
12.
13.
Project information.................................................................................70
Operational principles and construction ..................................................74
Monitoring .............................................................................................77
REFERENCES ..................................................................................................79
APPENDIXES
APPENDIX 1. Pictures from the biowall installation and process equipment
APPENDIX 2. Biowall site geographical map, geological cross section and
geohydrological data
APPENDIX 3. Biowall well installation diagram with specifications and data
APPENDIX 4. Biowall piping and process instrumentation diagram with parts list
APPENDIX 5. Biowall monitoring results
APPENDIX 6. Biowall project budget
TAMPERE POLYTECHNIC
Environmental Engineering
1.
FINAL THESIS
Laitinen, Jarno
1
INTRODUCTION
Biotechnology has been under fast development in the previous decades and
expectations towards the benefits it is able to offer are high. In environmental field,
both nature sciences and engineering, it is opening new questions and offering new
answers. It increases our knowledge of nature and the processes within ecosystems
and gives us new tools for working in the environment by using naturally occurring
processes.
Bioremediation is one of the new fields of technologies benefiting from the
research that has been conducted multidisciplinary. It offers a new, (cost-) effective
means for soil and water remediation. Interest towards it has been developing
constantly as research and field trials have been able to show its potential in
degradating harmful substances.
Thought much is known about the subterranean microbial systems and
biogeochemistry, complete and coherent information on bioremediation is not
widely available. The multidisciplinary research on various fields has contributed
to the development but only some programs and literature have aimed in discussing
solely bioremediation, and hardly any on engineering perspective. The combined
information on bioremediation and field methodologies would be valuable for
engineers dealing with environmental remediation projects.
This study will discuss the issues around bioremediation, from perspectives of
economics, natural science and engineering. It will cover the basic theoretical
background, give descriptions of feasible technologies and offer solutions for
monitoring and quality control. It will also present a case study of an in-situ
bioremediation field trial conducted in Finland during year 2005, describing the
design and construction process as well as monitoring. Results and discussion on
the achievement of field trials goals will also be attached. Some material
concerning the field trial is defined classified and not available in the public
version of this thesis.
Theoretical aim is to give insight on the historical development biotechnology and
explain the terminology used in bioremediation. Processes and systems necessary
for the pollutant degradation are to be covered through biogeochemical framework.
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Environmental Engineering
FINAL THESIS
Laitinen, Jarno
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The goal is to give insight on the theoretical background of bioremediation and the
biogeochemical and engineered processes that undertakes during the remediation
process.
Besides clarifying the theoretical background, various in-situ bioremediation
technologies are presented and their applicability is discussed more thoroughly.
Not all technologies are feasible on all sites, therefore understanding the
background behind the biogeochemical processes and pollutant properties is
important in selecting the right approach. When remediation is conducted, there is
need for monitoring the status and development of the process. Solutions for
monitoring as well as discussion on quality control for in-situ bioremediation are
presented.
The field trial case study will offer more technical information suitable for
engineering purposes. It will present a thorough description of a field trial
conducted Finland in summer-winter 2005. In the field trial a permeable
biologically reactive barrier was made to study the possibilities to constrain the
pollution dispersion of the contaminated site without hindering the natural
groundwater flow.
TAMPERE POLYTECHNIC
Environmental Engineering
FINAL THESIS
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PART I
Environmental biotechnology
2.
DEFINING BIOTECHNOLOGY
Biotechnology can be viewed as a group of useful, enabling technologies with wide
and diverse applications in industry, commerce and the environment /15/. One of
the widest definitions used is the one by the UN CBD (Article 2. Use of Terms),
which states that “biotechnology means any technological application that uses
biological systems, living organisms, or derivates thereof, to make or modify
products or processes for specific use”.
2.1.
History of biotechnology
Historically, biotechnology evolved as an artesian skill rather than a science /15/.
When considering biotechnology through the framework provided by the UN CBD,
the history of biotechnology can be traced to 8000 BC, when people begun to
collect seeds and domesticate wild animals, thereby starting selective breeding
without accurate understanding of the molecular mechanisms. Biotechnology
evolved quickly due to lucky errors in the 4000-6000 BC to include brewing of
beer, fermenting wine and baking bread with the help of yeast and making yogurt
and cheese with lactic-acid producing bacteria /7, 15/.
In latter times, the development of biotechnology has been very rapid. The first
micro-organisms were discovered in 1676 by a Dutch plainsman called
Leeuwenhoekusing who used primitive equipment far from microscopes and
opened the amazing world of micro-organism by finding protozoa in a sample of
pepper-water /4/. By the change of millennium (2000 AD), the human genome was
mapped. /42/
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Environmental Engineering
2.2.
FINAL THESIS
Laitinen, Jarno
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Biotechnology today
The quest in going deeper on details of life itself has kept the development
continuous and today the biggest constraints on experimenting arise from
legislation. The speed of innovations and new possibilities has lead to a counter
effect, causing public criticism on the subject. Biotechnology is usually seen as a
sect of genetic engineering, assimilated with the ‘artificial’ production of new
plants and species, or furthest, cloning of animals or even human embryos. Modern
consumers and industrialized societies are demonstrating concern, as Ratledge
(2001) states, about the ‘unknown’ health risks, possible deleterious effects on the
environment and the ‘unnaturalness’ of transferring genes between unrelated
species.
The difficulties in usage of biotechnology are much a part of the public perception
of the issue. In 1997 an Eurobarometer study on public perception of
biotechnology /15/ noted that (i) the majority of Europeans consider the various
applications of modern biotechnology useful for the society. The development of
detection methods and the production of medicines were seen to be the most useful
and considered the least dangerous. (ii) The majority of Europeans tend to believe
that we should continue with traditional breeding methods rather than changing the
hereditary characteristics of plants and animals through biotechnology. Less then
one in four Europeans think that regulations are sufficient to protect people from
any risk linked to modern biotechnology.
The public perception is clearly distorted due lack of knowledge on the scientific
basis and history of biotechnological applications and its relation to natural
development, e.g. evolution and gene transfer. The Eurobarometer answers show
that people are afraid of biotechnology when they have to be dealing with it or it is
in contact with their own ‘environment’ or ‘living area’. On the other hand, if
applications are developed in laboratories under scrutiny of scientists for the better
of humanity the usage of biotechnology is widely accepted.
Today, new legislation is passed nationally and internationally to constrain the
fields of research, implementation of applications and sale of genetically
engineered products. Governments and international co-operatives have made
TAMPERE POLYTECHNIC
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FINAL THESIS
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legislation on the environmental issues since the 1960s, with main focus on
pollution control. In the previous decade also issues on biodiversity have been
acknowledged. The strict environmental legislation has opened new possibilities
for biotechnology in environmental field, mainly in the fields of ‘clean
technologies’, pollution control and waste disposal.
Modern biotechnology can be divided into three main sectors including medical-,
agricultural- and environmental biotechnology. The most advanced fields of study
are medical and agricultural, due to the amount of money available for their
research.
Agricultural biotechnology concentrates in both traditional and genetic breeding of
living organisms to make or modify products and to improve plants and animals.
Medical biotechnology concentrates designing organisms to produce xenobiotics
for medicine and genetic engineering to increase human health. Environmental
biotechnology concentrates on pollution prevention and control by utilizing
properties of living organisms and natural systems.
2.3.
Legislation
Environmental pollution has been aimed to be controlled by international
conventions to minimize the pollution effect to ‘global commons’ as soil, water and
air. A short list of legislation that has been imposed is shown in table 1.
Table 1. List of selected international conventions and protocols concerning
pollution and biotechnology (Data from: UN treaty collection)
Year
1972
1972
1979
1982
1987
1997
1998
2000
2001
International convention and protocols
Convention on Prevention of Marine Pollution by Dumping of Waste and Other Matter
Convention Concerning the Protection of the World Cultural and Natural Heritage.
Convention on Long-Range Transboundary Air Pollution (LRTAP).
Law of the Sea
Protocol on Substances That Deplete the Ozone Layer
Protocol on Climate Change
Convention on Prior informed Concent
Protocol on Biosafety
Convention on persistent organic pollutants
NOTE! The 2000 Biosafety protocol is an addition to 1992 Rio Convention on Biodiversity
The conventions presented in table 1 give implications on the developmental path
of the legislation in international field. The first international conventions focused
around issues as air- and waterborne pollution and aimed at regulating the release
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of waste to these common areas. In 1980’s and 1990’s scientist begun observing
changes in the earth’s atmosphere, changes in gas composition and holes in the
ozone layer.
The 1987 Protocol on substances that deplete the ozone layer (often referred as the
Montreal protocol) was a huge victory for environmental lawmaking and
international co-operation. Science had been able to show evidence that there were
changes in the atmosphere that were man made and threatened life on the earth.
Consensus was gained fast, and nearly all nations eagerly signed the protocol and
begun working for the common goal.
It was long hoped that the same joint concern would continue in the field of climate
change due to increasing greenhouse gas emission, but the hope was useless. The
1997 Protocol on climate change was officially not enforced until 2005 when
enough member nations had ratified it, and still, the single largest polluter in total
and per capita (USA) has not ratified the agreement and informed that they will not
do so.
The new development on the international legislation has been the focus on
biodiversity. The year 2000 convention on biological diversity, in addition to 1992
Rio convention states in Article 1. Objectives: “The objectives of this
Convention…are the conservation of biological diversity, the sustainable use of its
components and the fair and equitable sharing of the benefits arising out of the
utilization of genetic resources, including by appropriate access to genetic
resources and by appropriate transfer of relevant technologies, taking into account
all rights over those resources and to technologies, and by appropriate funding”
/23/.
Biotechnological innovations have been extensively researched in the last decades,
and as a new development, companies have begun to patent rights for organisms or
genes, found in nature /16/. There is a question that has been raised more often
these days; what is the individuals right to own something that nature has created?
A company might patent a gene found in Amazon from a plant able to produce
antibiotics, hence having an overseeing right over that gene. The indigenous
peoples of the area have probably used the plant for centuries and possessed
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previous knowledge on the healing properties. Today, there are already cases where
companies have done so and gained a right for something that they have not
created themselves and are not required for any technological or economical
compensation.
3.
ENVIRONMENTAL BIOTECHNOLOGY
Environmental biotechnology is not as glamorous field of study as medical
biotechnology, which promises to cure cancer and remove genetic diseases.
Environmental biotechnology in contrast to medical is different as it is dealing with
high volumes of low-value wastes, products and services /19/ when the latter deals
with low volumes of high value products and services.
Environmental biotechnology is fundamentally rooted in waste, mainly concerned
with the remediation of contamination caused by previous use and the impact
reduction of current activities Dealing with waste and cleaning up pollution are in
everybody’s best interest, but most people would rather not recognize the issues, as
they are easier to be ignored. They are problems people feel they do not contribute
to themselves and rather would have them not exist in the first place. /9/. Even for
industry, thought the benefits may be noticeable on balance sheet, the likes of
effluent treatment or pollution control are more of an inevitable obligation than a
primary goal themselves /9, 19/.
3.1.
The scope for use
Key intervention points for environmental biotechnology are waste management,
pollution control and manufacturing processes, which are often referred as clean
technologies /9, 19/.
3.1.1.
Waste management
Waste management is one of the most fundamental and commonly applied fields of
environmental biotechnology. The applications can be divided into solid and sludge
treatment. High amounts of biologically degradable waste in both forms are
produced domestically, industrially and agriculturally /19/. Biowaste is a modern
term introduced to simplify the existing terminology used for classifying waste
from organic-origin. Before there has been numerous waste labeling schemes
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where biodegradable material has been defined as green, yard, food, manure and so
on, mainly biowaste falls in one of the three categories feces, raw plant matter or
process waste /9/, smallest common denominator being their characteristic high
carbon content.
Evans (2003) quotes a study by Lemmes (1998), noting that in EU (note, before the
new membernations) the annual amount of biowaste was 2500 Mt, of which 1000
Mt was of agricultural origin, 550 Mt of garden and forestry waste, 500 Mt of
sewage, 250 Mt from food processing industry and only 200 Mt from the MSW.
In waste management commonly acknowledged basic concept is the Reduce,
Reuse, Recycle. Biotechnology can offer an important step for this process. Firstly
it can offer a change to produce more with less, and secondly it can help reusing
the once produced organic components. All biowaste can be reused by microbial
processes. One popular and effective process is anaerobic sludge treatment, where
sludge is anaerobically transformed to energy intensive ‘by-products’ like biogas
and the material is transformed back to soil-like amendment which can be used
again.
The possibilities for environmental biotechnology in dealing with biowaste are
enormous and technologies have already found their place in everyday operations
of most municipal institutions. There is also constant development in the field of
small scale biowaste management. In Finland e.g. there are plans for co-operatives
of agroindustries and municipalities to begin collecting human and animal origin
sewage combined with agricultural waste for small scale energy and heat
production.
3.1.2.
Manufacturing processes
Industrial processes always produce some amount of waste, or scrap, which on
economy wise means extra internal and external costs. An industrial process can be
divided into a number of basic stages as Scragg (2005) does; the following figure 1
represents the stages of industrial production process and the possible stages where
biotechnology can be applied cost effectively (BATNEEC).
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Figure 1. A basic division of an industrial process
showing the needs for energy and sources of waste /19/
The main objectives for sustainable industrial process include low consumption of
energy and non-renewable raw materials and elimination of waste /19/. The
optimization of industrial processes has been a key factor in process and factory
design for decades. The main tools and models for this category come from the
field of total quality management, a philosophy which mainly originates from
Japan and USA.
Main reason for industries to aim for ‘clean technologies’ is the economical
benefits they offer both in reducing scrap and in fulfilling the ever tightening
environmental regulations that have increased the cost of waste management
manyfold.
Biotechnology can be utilized in achieving cost effective results in achieving clean
technologies. Renewable energy sources can be used instead of non-renewable
fossil energy, and in some cases also the waste can be re-used as energy. Raw
material extraction can utilize microbial cultures; e.g. microbes have been used for
metal extraction and oil recovery. Raw material processing with biotechnology can
also replace the inorganic catalysts with micro-organisms and enzymes /19/.
Compared to chemical processes, manufacturing industries can also benefit from
the applications developed on basis of whole organisms. Microbes and enzymes
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usually operate with lower temperatures and pressures, hence less energy
consumption and safer conditions for workplace and environment /9/.
3.1.3.
Pollution and pollution control
Pollution is one of the most prevailing topics in today’s environmental discussions
and a subject of continuous legislation.
The awakening to existence of chemical pollution took place in the 1960’s in the
USA through the book of Rachel Carson, entitled “The Silent Spring” (1962),
where she wrote about the dangers of chemical usage, especially DDT and it’s
bioaccumulation in the food chain. Carson concluded that we had already
irrevocably harmed birds and animals and had contaminated the entire world food
supply.
In the following decades mankind experienced other alarming ‘events’ that lead to
tightening of the legislation. Examples include the Love Canal case in USA, which
climaxed in 1978, when the New York State Department of Health announced a
medical emergency and President Carter declared a national emergency for the
area. The Love Canal area had been used for 50 years as a municipal and industrial
waste landfill and in 1950’s the current owner sold it to the city for $ 1 which
started immediately filling the area with housing projects, schools and industries. It
took a while for the inhabitants to notice the effects of living in the area; not the
fact that their children started to born defected was enough, but it required the
chemicals to start flowing freely into cellars and full canisters of toxic chemicals to
surface due to erosion and heavy rains. The company responsible for the operation
of the site was sued for $117,580,000 /38/
In 1984 the Bhopal disaster of India, claimed by many as the worst industrial
disaster in history. It was caused by the accidental release of 40 t of methyl
isocyanate from a pesticide plant located in the heart of the city of Bhopal. The
accident lead to the instantaneous death of 4000 people and the gases also injured
anywhere from 150,000 to 600,000 people, at least 15,000 of whom later died /41/.
Accidents have been happening constantly, like Chernobyl nuclear reactor 1986
and Exxon Valdez oil-spill in 1989. Thankfully the last decades have been quieter
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in the field of pollution accidents, partly due to international legislation and
conventions, hence increased knowledge.
A goal of environmental biotechnology is to control existing pollution when
another is to aim towards pollution control at source. Industries producing waste or
wastewaters that contain high concentrations of organic waste or biodegradable
contaminants, have found biological treatment methods very effective in their
pollution control operations. “Biotechnology stands as a particularly cost-effective
means of reducing the pollution potential of wastewater, leading to enhanced
public relations, compliance with environmental legislation and quantifiable costsavings to the business” /9/.
Pollution contaminated land and groundwater is a large concern for today’s
industrial societies. Previous operations have contaminated sites around the world
and at some parts due to economic reasons or lack of knowledge or caring, land
and water are still contaminated by poor process operations or by simply dumping.
The short industrial history of mankind has already contaminated large, primary
areas. The contaminations are due to previous industrial operations on site, like
mining, refining or storage. The usage of these sites is a hot topic today for
community planning and construction industries. Most sites are though too
contaminated to be usable in construction until large scale remediation has
occurred.
Järvinen & Salonen (2004) from Ramboll Finland Ltd. have estimated in their
memorandum for Finnish Environmental Institute; “Remediation costs of
contaminated sites in Finland”, that in Finland there is 20 000 contaminated sites in
Finland, which is twice as much as in the previous estimation conducted within the
framework of SAMASE-project in the beginning of 1990’s /30, 22/.
Previous methods for soil remediation have mainly been focused around removing
the contaminated soil and storing it to a landfill elsewhere. Biotechnology has
brought new possibilities for completely removing the contaminants from the
polluted soils and water. “Bioremediation technologies provide a competitive and
sustainable alternative and in many cases, lower disturbance allows the overall
scheme to make faster progress” /9/.
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It is estimated that some 60 000 to 70 000 chemicals are in use today, of which 80
% is actively being used in industrialized countries. Many of these chemicals are
classified as xenobiotics; substances that are foreign to the biological system they
are found from, but can be produced or occur elsewhere naturally. An example is
antibiotics, which are naturally produced by bacteria but do not occur naturally in
humans.
3.2.
Market for environmental biotechnology
Evans (2003) has researched for figures on the biotechnology market size
worldwide and in Europe. He writes that the estimated size of environmental
biotechnology products and services worldwide is $ 75 billion (63 G€) (2000 est.,
OECD) accounting for 15% to 25% of the whole environmental sector. He also
gives figures from UK’s department of trade and industry, which estimated 1520% of the world environmental market was biotech-based.
Naturally most of the biotech based market is due to medical and agricultural
sciences, which can afford the constant R&D operations. Following the line of
results that Evans presents, it could be estimated that environmental biotechnology
makes approximately 20% share of the global environmental markets. This portion
can be expected to increase in relation to traditional environmental sector as well as
in total, due to increase in environmental products and service markets.
As noted earlier, environmental biotechnology is a diverse industry, including
everything from waste management and manufacturing to pollution control. In
Finland the biotech markets are dominated by pharmaceuticals, where 2 out of
three employees are working. In 2001 number of Finnish biotechnology SME
companies was 106, with sales 141 M€, R&D costs 114 M€ and profits -96 M€.
Out of the 106 companies working in the field of biotechnology, only 3 are
working primarily in the field of environmental biotechnology /25/.
According to calculations made by Järvinen and Salonen (2004) on the basis of
various reports, between 2003 to 2025 in Finland there will be approximately 330
soil remediation projects annually with 60 M€ annual costs. They estimate that the
cost structure in a remediation project consists of 5-20 % investigations, < 5 %
planning, 30-50 % excavation, transportation and quality control and 30-50 % of
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treatment and final disposal. They have only taken in consideration the possibility
of excavation as a remediation technique, as according to their memorandum: “Use
of in situ techniques abroad seems to be increasing. In Finland, this will not be the
case to the same extent because, for example, of the cold climate. In contrast,
isolation of contaminated soils in situ will probably increase. This is likely to
reduce total costs even if the costs of surveys and planning will rise”.
A quick calculation, estimating that 10% of these projects were remediated
biologically (as in UK 12%, /9/) and that the 50% of the costs which is reserved for
excavation, transport, treatment and disposal is used for bioremediation, gives for
the market size of bioremediation in Finland 3 M€ annually for the next 20 years.
In reality, the total annual in-situ market has been remarkably lower.
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PART II
Microbiology
4.
TAXANOMY AND STRUCTURE
4.1.
Taxonomy of organisms
The sequence of taxonomy runs from domain, kingdom, division, class, family,
genus and finally species. The genus/species level of names is the one usually used
to identify different organisms.
There are differing methods for classifying living organisms. One of the simplest is
the divisions is into domains of eukaryotes and prokaryotes, where the difference is
in the cell structure. Eukaryotes have larger cells, but most importantly their
nucleus is formed from DNA molecules and they have a membrane protecting their
nucleus. Prokaryotes are smaller in size and do not have a clear nucleus, only a
nucleus area with a single DNA molecule, not protected by a membrane /10/.
A more evolutionary division is the three-domain system into eucarya, bacteria
and archaea. Previously both bacteria and archaea were classified as prokaryotes,
but in the last decade due to genetic analysis, there has been found differences in
the ribosomal RNA, mainly in the 16 S rRNA /19/. The differences found imply
that the archaea are in fact closer to eucarya than bacteria, which means that
archaea have at some point in evolution diverged from bacteria and developed as a
unique domain. See figure 2 for illustration on the development of life on earth.
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Bacteria
Archaea
Green nonsulfur
bacteria
Purple bacteria
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Grampositives
Cyanobacteria
Flavobacteria
Eucarya
Methano- Methanosarcina
bacterium
Halophiles
MethanoThermoproteus coccus
Pyrodictum
Animals
Entamoebae
Slime
molds
Fungi
Plants
Ciliates
Flagellates
Trichomonads
Thermogales
Microsporidia
Diplomonads
Figure 2. Development of life on Earth and classification into the three domains.
(Data from: /2, 15, 27/)
4.2.
Microbial structure
Micro-organisms are defined as microscopic organisms that are not visible to naked
eye. In reality they include species from all three domains, mainly from bacteria
and archaea, but also from eucarya, namely fungi, algae and protozoa.
In terms of structure, archaea are closer to bacteria than eucarya. They both have
simple prokaryotic structure; single DNA molecules, no nuclear membrane nor
chloroplasts or mitochondria. Eucarya are a more diverse group (shape wise). They
have multiple DNA molecules, a protective nuclear membrane and mitochondrion
and chloroplasts /10, 19/.
4.2.1.
Prokaryotes
Bacteria have three general physical appearances and their sizes range from 0.2 to
250 µm, with normal range of 1-10 µm. The simplest shape is the single bacterial
cell, or coccus, which occurs singly, in pairs and in chains. Not all cocci are
perfectly spherical and can vary greatly in shape from spherical to almost square.
The next common shape is the rod or bacillus, which can also occur singly, in
pairs, and in chains. Less common are spiral shapes, the spirallum and organisms
that consist of thin threads. The thin threads are called hyphae and the mass of
hyphae is known as a mycelium. Typical examples of this group are streptomyces,
which are found in the soil and often produce antibiotics, such as streptomycin.
There are also other shapes, such as the stalked bacteria like caulobacteria, but
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these shapes are less common /19, 10/. Some bacteria are motile which is achieved
by using one or more flagella which are hair like filaments extending from the cell
wall. The flagella can be single, bipolar or multiple. Other filaments do occur on
bacteria, known as fimbriae and pili. Pili are involved in cell-to-cell adhesion and
attachment to surfaces during biofilm formation /19./
Bacteria are classified using physical, chemical, genetic, and metabolic
characteristics. Genus and species are assigned on the basis of shape, chemical
makeup and genetic characteristics /10/.
Bacteria are the most abundant group of organisms present in the soil. The number
of bacteria present and the predominant species present is a function of soil
characteristics and the specific environment (e.g. temperature and moisture) /10/.
Because of their diversity, bacteria are usually found in heterogeneous
communities. Some species will be primary degraders; that is they will initiate the
degradation of organic materials in the soil. Other species will grow on compounds
resulting from partial degradation of complex organics or waste products of
primary degrader’s /10/.
4.2.2.
Eukaryotes
Eukaryotes are micro-organisms that include the higher plants and animals, namely
algae, fungi and protozoa. Their importance for bioremediation is not very high,
but in general, yes. Different forms of algae are used as nutrients, fungi and
bacteria in food and drink industry and protozoa plays a large part in wastewater
treatment. The diversity of eukaryotes in their cellular structures as well as cellular
organization and metabolism makes their domain too wide for quick overview
here. The main uses of eukaryotes in bioremediation are white-rot fungus and
plants used in phytoremediation.
Algae
Algae are photosynthetic eukaryotes that can be both micro- and macroscopic in
size and are generally found free living in fresh and salt water. Algae structures
vary from unicellular to colonial, and some are filamentous or coencytic. Some
algae have plantlike structure, with multi-cellular growth but no real difference
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between cells /19, 10/. Algae are generally photosynthetic but some can utilize
different organic or inorganic compounds for growth /19/. On land algae are found
in the soil and on the surface of plants and rocks in a symbiotic relationship with
fungi in form of lichens.
Algae are not important players in the field of bioremediation. In a few cases algae
have been used in the bioremediation of aquatic systems either by bioaccumulation
of hydrophobic compounds in their lipids followed by harvesting of the algal
biomass or by degradation in the presence of sunlight. Algae are also sometimes
used in on-site nutrient removal systems but are extremely difficult to separate
from the water and often become troublesome contaminants themselves and
possibly start forming blooms /10/.
Fungi
Fungi are immotile filamentous organisms that consist of branching structures that
are called hyphae, forming networks known as mycelium. They generally have cell
walls separating fungal hyphae into individual compartments, hyphae are generally
branched and growth occurs in the tip of each hyphae. Hyphae without cross walls
are generally known as coencytic /19, 10/.
Some fungi are aquatic, living in freshwater, but most are terrestrial, living in soil
or on dead plants. Fungi uses organic compounds for both energy and carbon
source. Some of the better known fungi include moulds, yeasts and mushrooms.
Relative to bacteria, fungi are generally less numerous, grow at considerably lower
rates, and do not compete well in most engineered environments. Additionally,
metabolic processes of fungi are generally less diverse than those of bacteria /19,
10/.
Protozoa
Protozoa are eukaryotic predators that mainly feed on bacteria or other organisms,
thought some use dissolved organic substances for food. They are heterotrophic
motile or non-motile unicellular organisms that lack cell walls. Protozoa require
water to carry out metabolic activity. However, there exists many species of
protozoa and a high number are typically seen in the microbial communities’ /10/.
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In biological treatment systems, protozoa play an important role by feeding on and
reducing the number of bacteria degradating target contaminants. A rise in bacterial
numbers in soil undergoing active biodegradation is often accompanied by a rise in
number of protozoa /10/. Protozoa can help control bacterial growth near injection
wells in in-situ bioremediation processes, where excessive bacterial growth may
cause clogging of porous media and thus decrease hydraulic conductivity /10/.
4.3.
Community of organisms
The soil consists of various consortia of micro-organisms and larger organisms up
to the level of animals. All have their specific role in the cycles of organic and
inorganic constituents that make up the soil system. A consortium can consist of
two or more organisms living in close proximity to other ecosystems which are
interacting with each other. A consortium generally implies a positive interaction
where one group benefits from the actions of the other /10/.
The surface soil, generally entitled the rhizosphere is the richest in microbial
activity due to the good environmental conditions and the positive influence of the
plant roots which excrete organic and inorganic nutrients for the micro-organisms.
Still, life is not limited to the top one meter layer of soil, as micro-organisms have
been detected at depths up to 600 meters in soil /10/ mainly the amount of microorganisms depends on the availability of organic and inorganic nutrients to support
life.
In biodegradation, several groups of bacteria may be necessary to completely
mineralize one compound. Individual species isolated in pure culture and given the
target compound as a sole carbon source may be found to be incapable of
mineralizing it. Generally, a consortium of micro-organisms is able to carry out the
degradation faster and more efficiently compared to a pure culture. Several
organisms may be involved in each step and compete for the target compound or
breakdown products during mineralization. The species suited to the particular
environment will predominate. However a change in the environmental conditions
will result in a different species rising to dominance /10/.
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MICROBIAL METABOLISM
All organisms require energy, carbon and other molecules to grow and divide. The
assimilation of these materials through chemical transformations into new cell
material is called metabolism /10, 15/.
There are different ways that organisms carry out their metabolism, and not all use
carbon in its organic forms as some, like plants take the required carbon for cell
construction from inorganic atmospheric CO2 and energy from photosynthesis.
There are four generally differentiated methods for obtaining energy and carbon for
cell construction; Photoautothropy, photoheterotrophy, chemoautothropy and
chemoheterothopy. The basis on how the classification is conducted is quite
straightforward, but the categorization cannot achieve full accuracy due to the
metabolic diversity within microbes in reality. Basically, when carbon is derived
from inorganic CO2 the metabolism is termed as autotrophic, when from organic
compounds it is termed heterotrophic. Similarly, when energy is derived from
chemical compounds, the metabolism is termed chemotropic, and when light is
used, phototrophic. By combining the classifications, it is possible to classify most
organisms by carbon and energy source (see table 2) /10/.
Table 2. Classification of organisms on basis of carbon and energy sources /10/
Classification
Based on carbon source
Autotrophs
Heterotrophs
Based on energy source
Chemotroph
Chemolithotroph
Chemoorganotroph
Phototroph
Combined terms
Chemoautotroph
Photoautotroph
Chemoheterotroph
Photoheterotroph
Carbon source
Energy source
CO2
Organic compounds
Chemical compounds
Inorganic compounds
Organic compounds
Light
CO2
CO2
Organic compounds
Organic compounds
Chemical compounds
Light
Chemical compounds
Light
The largest classes are photoautotrophs and chemoheterotrophs, and they also have
the largest impact on bioremediation. The former use light as energy source and
obtain their carbon from inorganic CO2 as the latter use organic compounds for
both energy and carbon source. Main phototrophic species are plants and algae, but
also some prokaryotes and photosynthetic bacteria fall into this category. The
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chemoheterotrpohic category is the largest, including the majority of bacteria and
many eukaryotes /10/. The main focus in this paper is on the heterotrophic microorganisms, which will be discussed further in the following. The use of autotrophs
in in-situ remediation will also be discussed shortly.
5.1.
Metabolism of organic material
Metabolism is the biochemical modification of various chemical compounds by
synthesis and breakdown, called anabolism and catabolism /15/. It includes the
uptake and assimilation of these compounds, their distribution, biosynthesis and
biotransformations and the elimination of the remaining compounds and
metabolites /43, 15/. Metabolism usually consists of sequences of enzymatic steps,
also referred to as metabolic pathways /43/. Without metabolism no living
organisms could survive as it is the fundamental process that supports life.
Anabolic processes are involved with building of new cell material, not only the
proteins, carbohydrates and lipids, but also the intermediary products as amino
acids, pyruvate, fatty acids, sugars and sugar phosphates /15/. Cells are not able to
synthesise all compounds required in metabolism, therefore they require various
trace elements for construction which also have to be readily available to complete
enzymatic steps. The anabolic ‘biosynthesis’ is basically and endothermic process,
as it requires energy for building processes. The energy required for these internal
building processes is provided by catabolic processes, which oppositely are
exothermic, meaning they are energy producing. In simple, carbohydrates are
degraded to ultimately give out CO2, water and generate energy /15, 10, 9/. The
energy generated in the exothermic catabolic metabolism is usually chemical
energy in the form of ATP (adenosine triphosphate) but other forms exist as NAD
(nicotinamide ademine dinucleaotide), PEP (phosphoenolpyruvate) and acetyl-CoA
(acetyl coenzyme A) /19/.
Anabolism and catabolism are required to function with each other but not
simultaneously as it is counterproductive. There are many signals that switch on
anabolic processes while switching off catabolic processes and vice versa. Most of
the known signals are hormones and the molecules involved in metabolism itself.
/43/.
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Cometabolism
Cometabolism is a biodegradation process during which an organic compound is
transformed by the micro-organism but no energy or carbon is derived from the
process /1/. As such these organisms would require another substrate as a carbon
and energy source on which to grow, thus in cometabolism micro-organisms use
other compounds as primary energy and carbon source while metabolizing another
compound to utilize the enzymes gained from metabolism to enhance
mineralization of the primary substrate /10/. The environmental benefit of
cometabolism is that hazardous and recalcitrant chemicals may be altered to
structurally less harmful compounds that can be metabolized by other microorganisms; similarly there is hazard that the compounds may be transformed to
more toxic or bounding forms.
The term cometabolism is often debated, since the ‘philosophical’ reasons for the
process are somewhat unclear. Cometabolism occurs not only in the presence of
primary substrate, but also when one is not available, therefore it is sometimes
called as fortuitous metabolism /10/.
5.3.
General metabolic pathways
Chemoheterotrophic micro-organisms metabolize organic material using two
different pathways, namely fermentation and respiration. Fermentations are
reactions where the final electron acceptor is a product of metabolism and not
exogenous as in respiration, thereby they could be described as internally balanced
oxidation-reduction reactions /10/. Fermentation does not yield as much energy as
aerobic respiration, as the compounds cannot be fully oxidized /19/. Fermentation
has significant economical importance in food and brewing industry and in futures
in bio-energy production.
5.3.1.
Respiration
Respiration involves usage of exogenous (extracellular) electron acceptors, and is
commonly divided into aerobic- and anaerobic respiration, carried out mainly by
aerobic, facultative or anaerobic bacteria. The metabolic processes involved in both
are essentially the same, but differ at the final steps /10/. The main differences arise
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from the compounds used as terminal electron acceptors; as in aerobic respiration
the terminal electron acceptor is always oxygen, in anaerobic it is other than
oxygen as NO3–, SO42–, CO2, S–, Fe–. In aerobic respiration, O2 is the terminal
electron acceptor preferred by the organisms due to its high energy yield in
complete reactions. The aerobic respiration of glucose can be summarized as
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
It is worth noting that this is exactly the reverse of photosynthesis, another
important biological reaction that occurs in many photoautotrophs and is necessary
to support most life on Earth.
When oxygen is not available, the organisms will concentrate on the next available
electron acceptor. Aerobic respiration is commonly the preferred method of
metabolism, as anaerobic metabolism yields only about 8% of the energy that can
be produced under aerobic conditions /15/.
Aerobic cellular respiration has three main stages: glycolysis, the citric acid cycle,
and electron transport when anaerobic includes only glycolysis and the anaerobic
pathway, generally fermentation.
Glycolysis
Glucose, a six carbon sugar, is split into two molecules of a three carbon sugar. In
the process, two molecules of ATP and two NADH electron carrying molecules are
produced. Glycolysis can occur with or without oxygen. In the presence of oxygen,
glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis
allows cells to make small amounts of ATP. This process is called fermentation
/15, 19, 9/.
TCA
The citric acid cycle or ‘Krebs cycle’ begins after the two molecules of the three
carbon sugar produced in glycolysis are converted to a slightly different compound
(acetyl CoA). Through a series of intermediate steps, several compounds capable of
storing high energy electrons as NADH and FADH2 (nicotinamide adenine
dinucleotide and flavin adenine dinucleotide) are produced along with two ATP
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molecules. These reduced forms carry the high energy electrons to the next stage.
The citric acid cycle occurs only when oxygen is present but it doesn't use oxygen
directly /15, 19, 9/.
Electron transport chain
The electron transport chain is a series of electron carriers in the membrane of the
mitochondria. Through a series of reactions, the high energy electron carriers pass
the hydrogen from NADH to electron acceptor that becomes reduced. In the
process, a gradient is formed, and from this ultimately ATP is produced /15, 19, 9/.
5.3.2.
Oxidation-reduction reactions
Chemical energy is utilized through oxidation-reduction (redox) reactions. A redox
reaction is a coupled reaction that involves transfer of electrons from one molecule
to another; oxidation describes the loss of an electron when reduction describes the
gain of an electron. An electron donor becomes oxidized after releasing electrons
while electron acceptor is reduced after receiving electrons, the two molecules
involved in this process are generally called redox pair /10/.
The amount of energy release in a redox reaction can be calculated from the
standard reduction potentials that are commonly published as electron tower (see
table 3, for common redox potentials), where the most likely oxidized compounds
are a top and most likely reduced at the bottom. The redox potentials are commonly
measured in Volts. The released energy will be higher, the further the two
compounds are in the tower. /10/
Table 3. Typical redox potentials measured in bioremediation sites /43/
Process
aerobic:
anaerobic:
denitrification
manganese IV reduction
iron III reduction
sulfate reduction
fermentation
Reaction
-
+
O2 + 4e + 4H → 2H2O
-
-
+
2NO3 + 10e + 12H → N2 + 6H2O
+
+
MnO2 + 2e + 4H → Mn2 + 2H2O
+
2+
Fe(OH)3 + e + 3H → Fe + 3H2O
+
SO42 +8e +10H → H2S + 4H2O
2CH2O → CO2 + CH4
Redox potential
(Eh in mV)
600 — 400
500 — 200
400 — 200
300 — 100
0 — -150
-150 — -220
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In micro-organisms, the energy is generated from the flow of electrons during
redox reactions. The process of electron transfer is mediated by electron carriers,
which are of two distinct types; freely diffusible and ones attached to enzymes. The
most common electron transporters are NAD+ and NADP+ (NAD-phosphate),
which are hydrogen atom transporters /10/. Energy released during redox reactions
is stored in the cell in the form of high energy phosphate bonds in phosphate
containing compounds, of which most important is ATP. The energy from ATP is
released in hydrolysis and the amount of energy released in hydrolysis of one
phosphoanhydridic bond is -30.5 kJ/mol. /10/
5.3.3.
Fermentation
Fermentation is fundamentally an anaerobic metabolism. When the oxygen levels
are low, the consortia of anaerobic and facultative aerobic micro-organisms are the
dominant species. Fermentation begins with an organic substrate, continues to
glycolysis and finally fermentation of the end product, which can vary from
methane gas to lactic acid which is used commonly in food industry. /19/ During
fermentation only 2 ATP are generated in the glycolysis phase as in the anaerobic
conditions the Krebs cycle is not available /15/.
5.4.
Development of new metabolic pathways
Micro-organisms, mainly bacteria and archaea are a diverse, old in evolutionary
terms and possess the capability for rapid evolution during binary fission. They
have survived in the worlds most harsh conditions, mainly due to their capabilities
to adapt to new environmental conditions. Generally micro-organisms live in
mixed communities rather than groups of cloned organisms. The synergetic
benefits from consortia are obvious; it can increase the habitat range, the overall
tolerance to stress and metabolic diversity of individual members of the group /19/.
The cometabolic features in micro-organisms make possible that a consortia of
organisms can more easily degrade a wider spectrum and more recalcitrant
compounds than monocultures.
Another consequence of this close proximity is the increased likelihood of bacterial
transformation by absorption of extracellular free DNA released e.g. in death of
another organism. This process is dependant on the competence of a cell to take up
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DNA and is referred to as horizontal transfer. In addition to transformation, genes
are readily transferred on plasmids. Plasmids are parts of bacterial cells which carry
DNA and are also circular and self replicating, and most importantly, often carry
the genes that hold the information of metabolic pathways. Plasmids may move
between bacteria and by replicating make their DNA transferable /19/.
Often micro-organisms carry within their DNA the information for many metabolic
pathways, but only a few are at use at one time. When the organisms encounter
new energy and carbon sources, they can attempt to activate an ‘old’ metabolic
pathway that would develop required enzymes or try develop a new pathway from
the basis of old pathways that is able to utilise similar carbon sources.
6.
CONDITIONS FOR GROWTH
The microbial growth as growth of any living organisms is dominated by
environmental factors. The possibility to utilize bioremediation requires specific
control over the subterranean environmental conditions to increase the control over
the size and composition of the microbial community.
Microbes have been discovered in the extremely hostile environments around the
world; from the arctic permafrost to the volcanic oceanic deeps. These bacteria
(mainly archaea) are those with the capabilities to degrade the most hazardous and
recalcitrant chemicals in our environment and provide the array of vast microbial
metabolic pathways /19/ that can be utilized e.g. in developing new enzyme
processes or bioaugmentation.
6.1.
Environmental parameters
The density and composition of microbial community and the growth rate are a
direct function of the environment and available nutrients. Primary environmental
factors include temperature, pH, moisture, oxygen- and nutrient availability /10, 9/.
Biochemical
factors
influencing
growth
include
contaminant
toxicity,
concentration, solubility and volatility, and most importantly, the existence of
microbial community with the metabolic pathways to mineralize the contaminant
/10/.
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Temperature
Temperature influences the growth of micro-organisms as they generally live well
in narrow temperature ranges and majority have the optimum growth range from
30-37 ˚C /19, 10/. In bioremediation the majority of the bacteria utilized is from the
groups entitled psychrophilic and mesophilic (see figure 2 for classifications),
depending on the used remediation technology.
In general, at temperatures above +40 ˚C the activity decreases due to enzyme and
protein denaturation and at temperatures closing 0 ˚C the activity essentially stops
/10/. The bacteria are generally more tolerant to low temperature extremes, since
they can capsulate and recover, but at high temperatures the population is at
increased risk to die. As a rule of thumb, for every 10 ˚C increase in temperature
(within the limits presented) the microbial activity increases twofold. /10/
Figure 3. Classification based on temperature range /27/
6.1.2.
pH
Micro-organisms usually live in conditions where the pH is close to neutral,
namely the optimal growth range of most micro-organisms is within the pH range
of 6-8 /10, 19/. As is the case with temperature, thought most micro-organisms
favour the near neutral pH range, there are bacteria that can survive in very harsh
conditions, but generally, highly acidic or alkalic conditions inhibit growth; for
classifying bacteria on basis of optimal pH, see figure 4.
The pH does not only affect the bacterial growth directly, but also by affecting the
solubility of nutrients and metals. An important nutrient for microbial growth is
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phosphorous, which solubility is maximized at pH 6,5. Similarly metal transport is
minimized at pH above 6.
Figure 4. Classification based on pH range /27/
6.1.3.
Oxygen availability
Micro-organisms are usually divided into groups depending on their response to
oxygen; the division is simply aerobic and anaerobic. Aerobic organisms are those
that require oxygen for growth and for anaerobes oxygen is lethal. In reality, the
division is not as straightforward, and within a microbial community different
groups with different relation to oxygen availability can exist, for various
definitions on microbial groups and their relation to oxygen see table 4.
Table 4. Bacterial classification and response based on O2 /27/
Group
Aerobic
Environment
Anaerobic
O2 Effect
Obligate Aerobe
Growth
No growth
Required (utilized for
aerobic respiration)
Microaerophile
Growth if not
too high
No growth
Required but at levels
below 0.2 atm
Obligate Anaerobe
No growth
Growth
Toxic
Facultative Anaerobe
(Facultative Aerobe)
Growth
Growth
Not required for growth but
utilized when available
Growth
Not required and not
utilized
Aerotolerant Anaerobe
Growth
The largest microbial group is definitely the obligate aerobes that utilize oxygen for
aerobic respiration. In the same group with obligate aerobes can grow facultative
aerobes, that are microbes which utilize oxygen when available, otherwise use
secondary metabolic route with different final electron acceptor. Another common
group are the obligate anaerobes, which live only in anaerobic conditions and do
not utilize oxygen. There are also different microbial groups that live in the very
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28
low oxygen environments, but their metabolism is restricted and focused usability
in bioremediation nonexistent.
6.1.4.
Nutrient availability
Micro-organisms are constructed, besides from water, mainly from carbon, oxygen,
nitrogen, hydrogen and phosphorus (for full reference on microbial composition,
see table 5). All these compounds and other trace elements have to be readily
available and obtainable by the micro-organisms from their environment or they
have to be able to synthesize them to thrive. The lack of one of the components
required will restrict the growth /19/, as is often found in the natural and engineered
environments.
6.1.5.
Moisture
Micro-organisms consist of 80-90 % water and therefore will only grow in
conditions where there is enough free water /19/. Water also serves as the transport
medium through which organic compounds and nutrients are moved into the cell
and through which metabolic waste products are moved away from the cell /10/.
The water content also affects the aeration of the soil and the potential for
contaminant solubility.
The availability of water in a solution is called water activity. Water activity is
defined so that de-ionized water has the reference value of 1.0 and most bacteria
require a water activity level of 0.9 /19/ (see figure 5). Water activities in
agricultural soils range between 0.9 and 1.0. /27/. In saline environments, salt has a
natural decreasing effect on water activity; most marine organisms can tolerate salt
levels up to 3 % /19/, but there are some that require salt for growth and grow in
salt concentrations above 15%, these organisms are called halophiles. The term
osmophiles is usually reserved for organisms that are able to live in environments
high in sugar /19, 27/.
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Figure 5. Classification based on Aw. /27/
6.2.
Phases of growth
Bacterial growth is controlled by environmental factors as represented previously.
Most bacteria cells tend to divide in a process known as binary fission when they
reach their correct size /10, 19, 27/. The cycle of life for bacterial population
consists of a sudden, exponential growth, followed by a short stationary phase and
finally after environmental conditions can no longer support the community, the
decline in population.
As said, most bacteria tend to increase their population by dividing their cells. At
the start of the division, a cross wall forms, DNA doubles and separates into the
new cells and at the end the cell separates into two genetically similar cells. In
some cases like the chain-forming streptococci, the cell fails to separate, forming
chains. Besides, not all micro-organisms divide by binary fission, some form buds
which pinch off from the mother cell, others, like fungi, form elongating hyphaes.
Most eukaryotic micro-organisms as yeast, algae and protozoa divide asexually
after mitosis /19/.
The bacterial growth rate is defined by the environmental conditions. As long as
the bacteria have optimal living conditions, sufficient carbon source and nutrients,
the population will continue to grow. After all the food and nutrients have been
used, the population will stabilise for a while, but very soon, the population will
die.
In enhanced remediation systems, the duration of phases might differ highly from
the natural or laboratory scale. The lag (or ‘acclimation’) period, is the time the
bacteria require to get used to the new environment and during the lag phase, the
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growth is nearly zero /19/. The lag phase can last for hundreds of days /10/
depending on the previous growth history, biodegradability of contaminant,
microbial metabolic capabilities and existence of preferential carbon sources /10,
19/. The microbes might require a lengthy exposure to the chemical to induce
enzymes or even genetic mutations might be required /10/.
The growth phase is usually exponential; microbes grow faster than they tend to die
off, therefore the population doubles at regular intervals. Only when carbon source
or a nutrient becomes limiting, the growth slows down but the living cells may stay
viable for a long period /19/. When the bacteria reach the upper limit of their
environmental sustainability the growth rate decreases to zero and metabolic
activity decreases. When the bacteria stop growing, they either physically die or
just inactivate metabolic activity and wait for the next growth phase. /10/
In engineered systems, environment and nutrients are controlled at a predefined
level to ‘host’ required microbial population and maintain the ongoing remediation.
Usually there is no need to grow the microbial mass very high, because if the
system flow is not sufficient, the metabolic wastes may change the environment or
the increased bacterial mass may cause clogging in the piping or in decrease the
subterranean hydraulic conductivity. It is important to control that the microbial
population is not allowed to enter the decline phase as the re-activation of their
metabolic activity and re-growth might take a long time.
Cell count
Stationary
Exponential
growth
Death
Lag / acclimation
Time
Figure 6. Bacterial growth curve (Data from: /27/)
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Table 5. Bacterial composition and elemental functions in cellular
metabolism /10, 27/
Element
% of dry
weight
Source
Function
50
organic compounds
or CO2
Main constituent of cellular material
Oxygen
20
H2O, organic
compounds, CO2,
and O2
Nitrogen
14
NH3, NO3, organic Constituent of amino acids, nucleic acids
compounds, N2
nucleotides, and coenzymes
Hydrogen
8
H2O, organic
compounds, H2
Main constituent of organic compounds
and cell water
Phosphorus
3
inorganic
phosphates (PO4)
Constituent of nucleic acids, nucleotides,
phospholipids, LPS, teichoic acids
Sulfur
1
SO4, H2S, So,
organic sulfur
compounds
Constituent of cysteine, methionine,
glutathione, several coenzymes
Potassium
1
Potassium salts
Main cellular inorganic cation and
cofactor for certain enzymes
Sodium
1
Sodium
Major cellural inorganic cation
Magnesium salts
Inorganic cellular cation, cofactor for
certain enzymatic reactions
Carbon
Magnesium
0.5
Constituent of cell material and cell
water; O2 is electron acceptor in aerobic
respiration
Calcium
0.5
Calcium salts
Inorganic cellular cation, cofactor for
certain enzymes and a component of
endospores
Chlorine
0.5
Chlorine
Major cellural inorganin anion
Iron salts
Component of cytochromes and certain
nonheme iron-proteins and a cofactor for
some enzymatic reactions
Varies
Confactors in electron transport in
specific enzyme catalyzed reactions
Iron
0.2
Trace
elements:
manganese,
cobalt,
copper, zinc,
0.3
etc ..
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PART III
Bioremediation
“The contamination of soil and water with organic and inorganic pollutants is of
increasing concern and a subject of legislation. These pollutants include complex
organic compounds, heavy metals, and natural products such as oils and are
derived from industrial processing, deliberate releases, and accidental releases”
/19/.
7.
POLLUTION CONTROL AND ROLE OF BIOREMEDIATION
As noted in the previous chapter on environmental biotechnology when the scope
for use was discussed, waste is one of the most frequently discussed topics in the
field of environmental sciences. Even thought there are an ever increasing amount
of xenobiotics released to the environment, not all manufactured chemicals are
harmful in nature and some naturally occurring substances may contribute to the
pollution or be extremely dangerous when concentrations increase above suitable
values.
7.1.
Classifying pollution
Classifying pollution is a difficult task and no single classification can exist due to
the diverse nature of contaminants. Most commonly contaminants are classified on
basis of nature, composition, properties, sources or uses, mainly depending on the
topic to be analyzed. In our case the pollution will be classified more in the
perspective of a required risk assessment. The classification outline suggested here
is based on the is based on Swedish EPA Quality criteria on contaminated sites,
Finnish
Research
institutes
(VTT)
publication
“Pilaantuneiden
maiden
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kunnostushankkeiden hallinta – Managing remediation on contaminated sites” and
on the comments of Evans (2003) from the university of Durham, representing the
current views of the UK. The Finnish legislation is in the course of transformation,
and due to the fact that there will be a proposal on the new recommendations on
contaminated sites which will be published in 2006, which is still in the draft
phase, the legislative renewals from Finland will not be considered here.
Mainly pollution classification in the case of contaminated soil and groundwater is
conducted though a risk assessment based procedure, where the actual
contamination levels are estimated through holistic analysis including site
investigations and laboratory analysis. The potential for risk is estimated on the
basis of extensive research and using tools and software developed for modelling.
In the case of contaminated soil and groundwater the risk assessment procedure
should be done according to well established procedures. There are many national
guidelines for conducting risk assessment of contaminated sites, and one should
use the national, legally recommended methods. The following subtopics give
implication on the issues that are to be considered when classifying sites.
7.1.1.
Chemistry and concentration of contaminant
The chemistry and concentration are one the most basic defining factors of
contamination. Even moderately harmful substances can cause serious damage if
they are present in high concentrations or large amounts /31/. The issue is even
more complicated as the initial contamination does not always fully define the
whole nature of pollution. Due to chemical or biochemical reactions the
contaminant may be transformed into other more hazardous substances that can
cause increased risk. Some contaminants also possess synergetic properties, that
when found together they may cause an increased risk that is higher than the sum
of the two individually /19, 31/.
7.1.2.
Toxicity
Toxicity refers to the potential of the contaminant to cause hazard or risk to
humans or other living organisms. Toxicity of a substance can be affected by many
different factors, such as the contact media; skin, inhalation, injection, the time of
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exposure, the number of exposures and the physical form of the toxin; solid, liquid,
gas.
Most commonly in environmental remediation cases the contact with the
contaminant is not acute, but rather chronic, as the contact with the toxin can last
for years, e.g. in the case of contaminated water that is drank or volatile emissions
that enter e.g. through the foundation of apartment buildings to the respiratory
system of occupants. Cases where there is a risk for acute toxic effect are usually
noted early as the volume of the concentration is either high or otherwise obvious.
Toxicity is usually measured in LC50 or LD50, ‘lethal concentration’ or ‘lethal
dose’, notably values that when reached cause and lethal effect in 50% of certain
population when consumed in a specific manner. The toxicity test are usually
conducted on Vibrio fischeri, Eisenia fetida, etc., but the tests are under criticism
from animal rights movement and other institutions. More advanced and accurate
methods are developed for testing toxicity directly on humans cells. For example
the Tampere University Dept. of Medical Science has studied the possibilities to
use human tissue cultures for rapid toxicity testing /46/.
7.1.3.
Mobility and persistence
Perhaps the most effecting factor in overall risk analysis is the mobility of
pollutant. If the pollutant has tendency to disperse and dilute, this has effect on the
remediation possibilities and pollution control as the dispersion is rarely uniform. If
the pollutant is not mobile, it has a tendency to remain in ‘hot-spots’ near the origin
of contamination /9/. Non-mobile contaminants are easier to control thought their
concentrations may be inhibitory to biological remediation methods.
Persistence of a compound is the duration effect. Highly toxic chemicals which are
environmentally unstable and break rapidly are less harmful then persistent
substances, even thought they may be intrinsically less toxic /9/.
The mobility of a substance depends highly on its chemical stability, polarity,
solubility and Kow ratio. Larger compounds are usually more stabile and are
biodegraded more slowly, hence their persistence will be higher. Non-polar
compounds tend to be hydrophobic and tend to partition to soil surface or form
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NAPLs, therefore their mobility is decreased as persistence is increased due to
lower solubility /10/. Solubility is the single most affecting parameter for
biodegradation as microbes use nutrients from aqueous phase /10, 19/, solubility is
usually linked with Kow, which is the octanol-water partition coefficient; the ratio
of the concentration of a chemical in octanol and in water at equilibrium /6/.
7.1.4.
Bioaccumulation / magnification
Some compounds are not readily biodegradable but instead are accumulated in the
tissues of living organisms and concentrated over time. /9/ Examples of such
chemicals are DDTs and PCBs which are recalcitrant chemicals that do not only
bioaccummulate, but are increased in concentration in the food chain in a process
called biomanification /19/.
These recalcitrant xenobiotics do degrade in nature, but their half time is on
average 5-10 years /19/. This combined with the slow biodegradation and
accumulation effect makes these compounds very dangerous in the environment.
7.1.5.
Risk to humans / nature.
What is degree of risk this contamination causes to the surrounding nature, and
more importantly to humans? The decision on risk is nearly always qualitative,
even thought it might be based on quantitative data. It is impossible to accurately
know the subterranean conditions and the behaviour of the chemical contaminant
in-situ or ex-situ.
In modern legislature the MCLs (maximum concentration limits) for contaminants
in soils and groundwater are defined. Also the latest versions include classification
of different contaminants to different ‘risk groups’ that can have differing exposure
limits and management restrictions /31/.
Assessing the potential hazard should be fundamentally conducted for the whole
ecosystem as the contamination is likely to effect the whole biota, not only humans.
It is possible that some contamination is so ‘insignificant’ that it can be left
untreated, but when this is not the case, the contamination should be remediated
and the threat removed.
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36
Role of bioremediation
Contaminated soils and groundwater are a common harm and an increasing risk in
today’s urban societies. They are, according to Netherlands environmental agencies
study in 2001, the most important environmental issue in Netherlands /26/. The
contaminants are mainly rising from the old industrial sites that have historically
been located close to urban habitation centres. The contaminants that are spread in
the environment are mainly organics, originating from the chemical and
petrochemical industries and inorganics from the metal and mineral extraction and
various mixtures from agroindustries. Another thought separate category is the
MSW and MWW organic wastes.
7.2.1.
Novel remediation strategies
In the past the most common soil remediation method has been excavation and off
site disposal. Today the method is not favoured in most environmentally conscious
nations, as the basic operating principle and ecological effect is very poor. In this
classic technique the contaminated soil is excavated and taken elsewhere for
disposal. The void that has naturally remained on-site is then filled with virgin
material to replace the contaminated soils and make the site again usable. When the
remediation or disposal off-situ costs are calculated, summed with the virgin
material costs and the environmental effects of the transportation, the technology
does not seem feasible anymore. The technology is in fact not remediation or
purification, but instead removal and replacement, with no real treatment. As
stated, this is fundamentally false, and many nations, as USA, GB and NL are
encouraging to use other real remediation techniques, if not clearly forbidding the
use of excavation and disposal.
Other traditional technique for soil remediation is containment and in the case of
groundwater, pump-and-treat. Neither of these technologies offers cost effective
solution for soil and groundwater treatment, as containment again is no remediation
and pump-and-treat is a very time consuming process that can not guarantee the
full remediation of the groundwater and the saturated zone as it is dependent on
contaminant solubility and Kow.
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Today most of the environmental protection agencies recommend the use and
research of other, more advanced remediation techniques that can be used for
complete mineralization of the contaminants or for collecting the contaminant in a
re-usable form or otherwise minimizing the environmental effect.
The US EPA and Department of Defence have been working together with national
agencies in a project called Federal Remediation Technology Roundtable, available
online, which describes clearly most novel technologies by principle and
capabilities. Also US Air Force Centre for Environmental Excellence and other
sections working under department of defense have developed programs for testing
and working with novel technologies for soil remediation. The probable reason for
the high degree of military involvement is the fact that in most nations military is
responsible for military sites and their remediation.
Figure 6 is a mind map of novel soil and groundwater remediation techniques that
have been tested and recommended by numerous governmental and research
institutes. A lot of research is also conducted on the economical benefits of novel
technologies, but they are not covered here. For examples of other novel techniques
and their expenditures see Scragg (2005), Evans (2003), Eweis (1998) or Penttinen
(2001).
As one can note, the remediation techniques presented are categorized as in-, on-,
and ex-situ techniques. No generalization has been made on the basis of technology
methodology to categorize into biological, chemical, physical or thermal and
classical techniques that have been proven functional as excavation and disposal or
pump-and-treat are not covered here. Instead, in the following chapters a more
thorough view on especially biological remediation techniques is given.
By looking at figure 6 it can be noted that most novel techniques that have been
developed can be operated in-situ. It is clear that there are both environmental and
economical benefits from not excavating the site and dealing with the problem
elsewhere. The in-situ techniques are from numerous categories, including all
biological, chemical, physical and thermal methods.
By using these novel techniques, most contamination should be able to be
remediated, including radionuclides, explosives and heavy metals. It has to be still
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38
noted, that in some cases the contamination cannot be degraded or detoxified to
levels where it would not impose risk, and in these cases the contamination has to
be either excavated or isolated from the surrounding nature.
Figure 6. Many modern remediation technologies are incorrectly classified as
bioremediation. The following mind map is a generalized overview of
the novel remediation techniques used today with highlight on
technologies accepted as bioremediation.
7.2.2.
Role of bioremediation
Bioremediation is term that is applied to any systems or process in which biological
methods are used for transforming or immobilising contaminants in soil or
groundwater /10/. It is a set of techniques that uses micro-organisms to remove
pollutants from the environment. The principal organisms in bioremediation are
bacteria and fungi that have the ability to degrade hydrocarbons such as oil, coal
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39
tar, and various xenobiotics such as pesticides. Although heavy metals can not be
degraded they can be accumulated by micro-organisms and therefore removed from
the environment /19/.
The role of bioremediation is defined by the environmental factors influencing
natural biodegradation capability and the chemical properties of the contaminant.
Bioremediation is not a universal answer to soil and groundwater remediation, as it
required specific conditions to fulfil and later high tech process optimization and
control throughout the process.
As noted, bioremediation is mainly used for removing organic contaminants,
thought it has been found to be able to remediate a wider range of contaminants,
including inorganic substances as nitrates that are classified as toxic when
exceeding certain limits.
7.2.3.
Separation of ex-, on- and in-situ bioremediation
The classification of techniques is done here on the basis of the location where the
treatment takes place. It is by no doubt an artificial classification, but as the
techniques share certain fundamental operational similarities and the classification
is widely accepted in industry and literature /10/ the same classification will be
used here.
Basically the division means where the treatment is conducted, weather it is done at
site of pollution, when the classification is either in-situ, as the soil and
groundwater are not removed from origin, or on-site, when the soil and
groundwater are excavated or pumped for external treatment above ground usually
on the same site. The ex-situ techniques are operated by excavating the polluted
soil or extracting the groundwater for external treatment elsewhere, in this case by
using biological treatment trains.
7.2.4.
Why in-situ?
In-situ is usually selected on sites where the treatment by using traditional methods
would lead to extensive costs. In-situ is often the only solution on sites where
excavation is technically difficult or even impossible. Such areas may be found
under or near buildings, under hard surface materials, around sewers, cables or
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pipelines, at great depths and in areas of widespread contamination /45, 9/. In-situ
remediation is mainly suitable for soils with sufficient hydraulic conductivity, and
low to medium contamination concentration /10, 9/.
The techniques are not however without disadvantages and problems. The most
chronic is the requirement for thorough preliminary site survey which requires high
level of resources. Process optimization of the remediation requires constant
monitoring and because the reaction conditions cannot be maintained constant, the
end point may be difficult to determine. Finally the methods require extensive
monitoring and the process may last for very long time periods.
If in-situ is selected as the feasible remediation technique, there should be a
decision process on which technology to use on the specific site. In table 7 most
common and proven in-situ bioremediation techniques are listed, with applicability
to different soil and contaminant conditions.
Table 7. Representative biological in-situ methodologies and their applicability for
various contaminants and soil textures
Technology name
Natural attenuation
Enhanced soil mixing
Land Farming
Bioventing / Biosparging
Enhanced bioremediation
Groundwater circulation well
Cometabolism
Percolation
Phytoremediation
Bioslurping
Permeable reactive Barrier
Contaminants
Groundwater
Bedrock
Morein
Sand
Silt
Clay
Soil
TPH
PAH
VOC
VOC Cl
SVOC
SVOC Cl
Pesticides
Metals
Inorganics
Radionuclides
Explosives
Feasibility
+
+
+
+
+
+
+
+
-
+
+
o
+
+
+
+
o
+
+
o
+
+
+
+
+
+
+
+
+
+
o
+
+
+
+
+
+
+
+
+
+
o
-
+
+
+
+
+
+
+
+
+
+
+
+
o
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
o
+
+
+
+
+
+
+
+
o
+
o
+
+
+
+
o
+
+
+
o
o
+
o
+
+
+
o
o
+
o
o
o
o
+
+
+
o
o
+
o
+
o
+
o
+
-
+
-
+
+
-
o
-
o
+
-
Time
Many years
Years
Years
mm -> yy
Years
Years
mm -> yy
mm -> yy
Many years
mm -> yy
Depends
+) Positive effect, field testing done
o) Effect varies, laboratory and pilot scale results
-) Negliciable effect, havent been able to prove positive results
7.3.
Bioremedeable contaminants
As the table 7 shows, most techniques are not applicable on bedrock and clay, and
only half can be used in conjunction without existing GW. The technologies are
mainly functional with organic contaminants, not with metals, or other inorganic
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contaminants, radionuclides or explosives. The typical time span for a
bioremediation process is rather years than months.
As the basic principle laying within bioremediation is to accelerate the microbial
growth and promote their accessibility to carbon in organic contaminants for
nutrition, hence the main pollutants to be removed are organic. The currently
acknowledged list of the potential contaminants for bioremediation is listed below
in table 8, the table has been quoted from Evans (2003). The list is continuously
changing as extensive research is conducted on the field, hence for reference of
latest achievements and laboratory scale results one should reference to online
sources.
Table 8. Bioremediation potential of selected contaminants /9/
Readily possible
Acids
Alcohols
Aldehydes and ketones
Ammonia
Creosote
Chlorophenols
Crude oil
Petroleum hydrocarbons
Glycols
Phenols
Surfactants
7.4.
Possible under certain
circumstances
Chlorinated solvents
Cyanides
Explosives
PCBs
PAHs
Pesticides
Herbicides
Fungicides
Tars
Timber treatments
Currently impossible
Asbestos
Asphalt
Bitumen
Inorganic acids
Bioavailability
Bioavailability is defined as the degree to which toxic substances or other
pollutants present in the environment are available to potentially biodegradative
microorganisms. The rate and extent to which a compound can be mineralized
defines the possible benefits of bioremediation, hence knowing the bioavailability
is a key factor /20/. Bioavailability is not a function of the microbial metabolism,
the environment or the contaminant alone, but it defines the interaction capability
of them, the ‘availability’ to which the contaminant can be mineralized by the
micro-organisms. There is no exact parameter used for measuring bioavailability, it
is only a set of factors to be considered when considering bioremediation
Bioavailability of a contaminant is affected by numerous factors, as environmental
parameters, molecular structure, hydrophobicity, desorption, diffusion, dissolution,
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solubility, bacteria characteristics and aging. The pre-mentioned are by far not in
any order of importance but some do affect the bioavailability more than others.
/20, 21/.
The environmental factors influencing bioavailability from the micro-organisms
perspective have been dealt in the previous chapters, but not the effects it has in the
context of the contaminant. Environmental factors are mainly the environmental
pH and temperature; acidic or alkaline conditions can cause the contaminant to
precipitate and coagulate or otherwise decrease the possibility to be absorbed inside
the micro-organism and temperature can affect the contaminant volatility and
mobility. The contaminant chemical structure also has its effect, as for example
non-polar compounds tend partition to soil surfaces /19/.
Bioavailability may also be limited due to physical entrapment of the contaminant
inside the soil pore structures or due to chemical bonding on surfaces. The
chemical bonds are weak and easily broken by micro-organisms, and electrokinetic
techniques can aid in this, however the physical entrapment can be more of a
problem /21/. According to Valdes (2000) there is a debate in the scientific
community concerning the physical state of biodegradable contaminants, while
some research states that only dissolved substrates are bioavailable, some say that
also solid phase substrates can be degraded directly off surfaces.
Hydrophobicity affects the dissolution of a contaminant. Some compounds are
hydrophobic by nature which decreases their bioavailability. In cases where the
contaminant is hydrophobic, surfactants may be used to increase the solubility of
the substance /21, 20/. Diffusion through natural organic matter can be the most
important mechanism contributing to the slow release of hydrophobic contaminants
/21/.
The topic under most research today in the field of bioavailability is aging, or
weathering as it is sometimes called. It has been noted in numerous remediation
projects and proven in laboratory experiments that the duration of bioremediation
increases as the time that the contaminant is in contact with the soil increases. This
means that ‘old pollution’ is more difficult to remediate than fresh pollution. The
reasons are mainly due to the previously explained physico-chemical reactions of
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absorption and adsorption into soil pores and entrapment into organic material, not
only soil but also inside dead micro-organisms /21, 20/.
8.
DATA REQUIREMENTS
The data required in designing bioremediation projects is mainly from the fields of
geology, hydrology, biology, chemistry and naturally engineering. The interlinked
nature of the technology requires understanding on all of the fields to build a
holistic view of the site and its properties and possibilities. The requirement for
multidisciplinary knowledge causes the working group to have a widespread
knowledge.
Geology and hydrology are not often separated but instead dealt as one major field
entailing the whole spectrum of properties required in understanding subterranean
soil properties and their effect to groundwater flow. Hydrogeology is the part of
hydrology that deals with the distribution and movement of groundwater in the soil
and rocks, commonly in aquifers.
Biology and chemistry are often similarly interlinked to biochemistry, where the
principle focus is not on chemicals, nor ecosystems, but moreover on the chemistry
of living organisms, especially focusing on metabolism, which dictates the
degradation of various compounds.
8.1.
Hydrogeology
Site geology provides important information that has to be established prior to
analysing the hydrological conditions. The geological surveys can be conducted
during the preliminary investigations or separately. At some sites the geological
data already exists and it only has to be linked with the other available data to form
e.g. groundwater flow models.
The layout of the site vertical layout is to be defined as accurately as possible as
well as the composition of soil texture in the saturated and unsaturated zones.
Important geological information on soil matrix includes particle size distribution,
soil homogeneity, permeability, porosity, hydraulic conductivity, humus content
and soil moisture.
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Geological characterization is needed to assess the uniformity of the subsurface
hydrostratigraphy. The average rate of ground water flow can be estimated from
the hydraulic conductivity, hydraulic gradient, and porosity. Hydraulic gradient is
calculated from ground water elevations measured in monitor wells. Effective
porosity and hydraulic conductivity are usually assumed based on ranges of values
cited in scientific literature or estimated from pumping tests.
Besides the basic geological parameters on the soil structure and bedrock layout,
the hydrological data on groundwater flow paths and speed, other physico-chemical
information is to be addressed, as pH, redox and electron acceptors.
It is very important to know the site geology and hydrogeology well to determine
and model the possible plume distribution of the contamination and to be able to
better design the preferred remediation technology setup in-situ.
8.2.
Biochemistry
The contamination source, type and concentration are required information in
designing the bioremediation system. Not all contaminants are readily metabolized
by micro-organisms and not all sites have rich naturally occurring micro-organism
populations; hence pre-feasibility studies have to be conducted prior to system
design.
Biochemistry helps selecting the most appropriate strategy to treat a specific site by
considering three basic principles: the amenability of the pollutant to biological
transformation to less toxic products, the accessibility of the contaminant to
microorganisms and the possibilities for optimization of biological activity.
The basic data required for biochemical site characterization include the soil
properties; pH, BOD, COD, Redox, electron acceptors, nutrients and most
importantly the composition and size of the microbial population. Commonly,
when designing bioremediation a biochemical study is made to analyze the rate and
requirements for optimizing contaminant mineralization in gathered soil samples.
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IN-SITU BIOREMEDIATION TECHNIQUES
The fundamental basis of in-situ bioremediation involves introducing nutrients and
electron acceptors to the contaminated area by various methods. The main goal of
the methods is to induce the natural biological activity to increase contaminant
biodegradation. The major benefits from of in situ technologies arise from their low
intrusion level as noted earlier.
The following chapters will explain the basic technologies underlying
bioremediation in detail and provide information on different system designs. All
technologies share common attributes as they are fundamentally one and same
technology, based on natural biogeochemical process.
9.1.
Monitored natural attenuation
Description
In nature various processes, such as dilution, volatilization, biodegradation,
adsorption, and chemical reactions reduce contaminant concentrations /24/. The
subterranean soil matrix behaves as a natural bioreactor that even without any
augmentation is able to biodegrade most organic compounds in a long timeframe.
Even if natural processes are left to degrade the contaminants, it is necessary to
constantly monitor the development; hence the name, monitored natural
attenuation.
Applicability and operational principles
The applicability of MNA is dependant on sufficient knowledge on the site’s
biogeohydrochemical properties, the contaminant properties and modelling of the
concentrations on the down gradient, especially when the plume is still expanding
/24/. MNA is usually not considered as an option for remediation due to the basic
passive properties of the technique and the unpredictability of the process. In
general, neither US EPA or SYKE encourage the use of natural attenuation, except
on case to case basis when by risk analysis it can be shown that there are no
possibilities for spreading of the pollution or risk for living organisms, now or in
the future /39, 14/.
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Target contaminants for natural attenuation are VOCs, SVOCs and fuel
hydrocarbons. Pesticides also can be allowed to naturally attenuate, but the process
may be less effective and may be applicable to only some compounds within the
group. Additionally, natural attenuation may be appropriate for some metals when
process results in a change in the valence state of the metal that results in
immobilization (e.g., chromium). /24/
The operation of MNA is based on natural processes that dilute, adsorb, volatize
and biodegrade the contaminant. Depending on the immobilization level of the
pollutant, it is possible that further adsorption or volatilization will not happen,
thought if the pollutant is immobilized in the saturated zone, the pollutant can
leach, hence diluting the concentration thought spreading the plume. In case of
highly mobile pollutants, the spreading of the pollution is an urgent risk but usually
more mobile pollutants are also simpler in chemical form and more readily
biodegradable /39, 14/.
System design
UST
Monit or ing
well
network
GROUNDWATER
BEDROCK
Figure 7. Characteristic system design for MNA
When considering MNA for remediation method, most important phase of the
process is the preliminary studies, gathering of data to quantify and qualify the
contamination size and spread. Geohydrological data needs to be acquired to
sufficiently model the geological matrix and permeability of the area. Biochemical
studies on the soil/water samples need to be conducted to measure the
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bioavailability. Chemical analysis on the contaminant composition needs to be
made to assess toxicity and migration potential should be compared against
biodegradation potential to quantify the potential for spreading.
If MNA is selected as the preferred remediation method, extensive monitoring
should be arranged to verify that natural attenuation is happening and the pollution
does not continue spreading. The results gained from monitoring should correlate
with the results from pre-made modelling otherwise re-evaluation is necessary.
As an aim, one should be able to show based on modeling and supported by actual
field measurements that natural attenuation is taking place as estimated and
remediation to acceptable level can be achieved in a reasonable timeframe.
Limitations and concerns
Natural attenuation has not gained public acceptance as an “active” remediation
technology. The timeframe in MNA is very long and results can not be guaranteed
only based on laboratory experiments, the failure risk is very high. The costs of
MNA can also increase to exceed other more active methods due to intensive
monitoring required and if potential risks realize, the costs can increase
dramatically.
9.2.
Land farming
Description
Land farming is a bioremediation technology, where contaminated soils are mixed
with amendments such as soil bulking agents and nutrients, then tilled into earth.
Contaminants are biodegraded, transformed and immobilized by microbiological
processes and oxidation. /44/ The process is controlled to optimize the contaminant
degradation by addition of nutrients and aeration. Land farming can be conducted
in-situ for contaminations not deeper than 1,5 meter /10/ and for deeper
contaminations the polluted soil needs to be excavated and spread ex-situ, to make
the layer depth tillable.
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Applicability and operation principles
LF is applicable on sites where the contamination source is close to surface and the
on- and off-site leaching problems can be controlled. The soil matrix plays a
significant part in LF, all soil types are feasible for processing but there should
exist and impermeable layer, weather clay or bedrock, to prevent the leaching of
the pollution /24, 37/.
This technology is best used on sites where the contaminants are petroleum
hydrocarbons, SVOCs, pesticides, inorganics or explosives. LF should not be used
on sites where the contaminants are easily volatized, due to possible vapor phase
pollution excretion /14, 37/. The operation of LF is based on natural mechanisms,
and when the contaminants are non- or semi-volatile, most of the contaminant
degradation is due to biodegradation, not volatilization.
System Design
Figure 8. Characteristic system design for LF
In-situ LF systems should be designed to minimize the risk for contamination of
groundwater or surrounding soil matrix /10/. If the technology is applied in-situ, it
should be made sure that there is no possibility for leaching either by knowing the
ground formation or installation of horizontal drainage piping, that can also assist
in aeration. Usually the depth of the LF should not exceed 0,5 meters to allow
sufficient tilling and aeration.
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The systems operation depends on maintaining sufficient environmental conditions
for the microbial population to grow. The main parameters to be controlled are:
temperature, moisture content, aeration, pH and nutrients /37, 14, 24/. Moisture
content is usually controlled by irrigation, aeration by tilling the soil and pH and
nutrient with addition of agricultural amendments.
Limitations and concerns
In-situ LF is limited to sites where an impermeable layer exists below the
contaminated layer and prevents leaching to groundwater. The system requires
large ‘open’ system to be monitored and controlled. Temperature is difficult to
control due to daily variations, as is moisture due to rainfall. These variables can
effect the time required for remediation and cause risks for surrounding
environment due system distortion.
If the contaminant concentrations are high enough, they can inhibit the microbial
activity. LF is not suitable for soils with concentrations above 100 g/kg of
hydrocarbons /10/ or 2,5 g/kg of metals /37/, hence the technology is not useful e.g.
for oilfields or large accidents.
9.3.
Phytoremediation
Description
Phytoremediation is a set of processes that uses plants to remove, transfer, stabilize
and destroy organic and inorganic contamination from ground water and surface
water /44/ Phytotechnologies have been used with good results as protective
barriers or in remediation of contaminated zones. The use of the technology is
more widely encourages today as there is more information on the applicability and
data on positive results. Phytoremediation offers an aesthetic and low-cost
remediation technique to sites with low to moderate contaminant concentrations
where the pollutants are not located very deep. /19, 37/
Applicability and operational principles
PR is an applicable technology on sites where the pollution is located close to the
surface. The technology is able to remediate both soil and groundwater from low-
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to midlevel contamination. The technology takes a very long time to sufficiently
remediate contaminated sites futures usage, and this can hinder the usage of the
sites. Sufficient risk analysis should be conducted on all sites prior to beginning
operation.
There are over 400 different species considered suitable for use as
phytoremediators /9/. There are different mechanisms for PR to remove the
contaminants; some are applicable in-situ and some only ex-situ, like artificially
constructed wetlands providing on-site rhizofiltration for effluent or wastewater
treatment. In the following a short survey on the possible in-situ PR techniques is
given.
1. Phyto-accumulation / Phyto-extraction are names for basically one and
same process where plants roots absorb the contaminants along nutrients
and water. Mainly metals and inorganic substances that are water soluble
are taken up by this process. Commonly the contaminant is not degraded,
but stored in the plant roots, leaves and stems. /44, 19/
“As a general rule, readily bioavailable metals for plant uptake include
cadmium, nickel, zinc, arsenic, selenium, and copper. Moderately
bioavailable metals are cobalt, manganese, and iron. Lead, chromium, and
uranium are not very bioavailable. Lead can be made much more
bioavailable by the addition of chelating agents to soils. Similarly, the
availability of uranium and radio-cesium 137 can be enhanced using citric
acid and ammonium nitrate, respectively.” /32/
Thought some plants can accumulate heavy metals in their tissues, some,
called hyperaccumulators, are able to accumulate as much as 1,5% of dry
biomass concentration /9/. These are the plants that are the focus of current
technological genetic investigations. The benefits of using plants in
accumulating close surface metal concentrations is obvious; they could be
used for roadsides, industries, ‘green’ city centers, etc.
2. Phyto-stabilization. In this process, chemical compounds produced by the
plant immobilize contaminants, rather than degrade them. Green plants
have been used for ages for prevention of erosion and stabilization of soil.
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Basically, green plants are able to excrete chemical compounds that
immobilize the contaminants in the rhizosphere, either on- or in- the roots.
Plants do not have the capability to biodegrade metals, but studies have
shown that the rhizosphere bacteria can convert heavy metals into less
toxic forms, e.g. Cr(VI) to Cr(III) /19/.
3. Hydraulic Control is a process where plants act as hydraulic pumps and lift
the water from the groundwater table with their roots to bring up water and
nutrients. The drawing of water upwards through the soil into the roots and
through the plant to atmosphere decreases the movement of soluble
contaminants down- or forward. Plants have the capability to affect
groundwater flow; especially trees have large root biomass and
transpiration pull. Evans (2003) among others quotes that poplars for
example have very deep roots extending to even 15 meters of depth and
transpire up to 1100 litres per day. In an EPA study /37/ a riparian corridor
‘a buffer strip’ engineered from poplars showed to decrease the nitrate
concentration in ground water at the edge of a corn field from 150 mg/L to
3 mg/L after the buffer zone, while also retaining toxic herbicides and
pesticides.
4. Phyto-degradation which is sometimes alternatively known as phytotransformation involves the biological breakdown of contaminants, either
internally or externally, using enzymes /9/. In this process, plants actually
metabolize and destroy contaminants within plant tissues or biodegrade
them to simpler substances that are then incorporated in the plant vacuoles
/9, 19/.
Plant degradation of herbicides and pesticides has been studied in
agriculture for a long time. In the 1990’s the focus has transferred to plant
metabolism of TCE, TNT, PAHs, PCBs and other chlorinated substances
and recently some plant cell structures have been shown capable of
degrading nitro-glycerin /19/. This suggests that plants have the potential to
degrade various environmental pollutants and through biotechnology these
properties could possibly be isolated.
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The phyto-degradation capabilities of TCE by poplars has been studied
extensively /19, 2/, it has been shown that poplars are able to absorb TCE
in water and biodegrade it almost fully, only respirating less than 5%.
5. Rhizosphere biodegradation is a process where the plant releases nutrients
through its roots as a product of photosynthesis that enhance natural
microbial biodegradation in the rhizosphere. The biodegradation is mainly
applicable for organic contaminants at low concentrations. This is a form
of enhanced natural bioremediation.
6. Phyto-volatilization is property of some plants to convert metal ions and
organic contaminants to more volatile forms and release them through the
stomata /19, 44/. Commonly known phyto-technological pairs (besides
poplars) are MTBE and eucalyptus, selenium by Indian mustard, methyl
mercury and tobacco and the list continues. /19/
System Design
Figure 9. Characteristic system design for PR
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The phyto-technological remediation systems are usually designed for specific
contaminants and environmental conditions. The major criteria for plant selection
are the desired remediation method and the nature of the contaminants /19/
On some sites planting grass varieties with trees to protect the soil, maybe the best
route since they generate a tremendous amount of fine root near surface. This
particularly suits the transformation of BTEX and PAH compounds /9/. Similarly,
on some sites selecting deep rooting plants that grow fast and are easy to maintain
and are capable to degrade e.g. chlorinated compounds planting trees or willows
might be the choice.
Phytoremediation is considered as a ‘novel and innovative’ technology that has not
yet established its status /9/. Many pilot scale studies has been conducted and some
full scale successful remediation projects have also been carried out, there still is
not enough data gathered to exactly predict the performance prior to actual
remediation.
Limitations and concerns
Phytoremediation has not gained public acceptance as a active remediation
technology, but is has a very ‘green’ image and could be very well used e.g. in last
phase treatment in a treatment train combined from biological and non-biological
remediation technologies.
It is still unknown what ecological effects hyperaccumulator plants may have if
ingested by animals. If these contaminants start bioaccumulating in the foodweb,
what is their effect to the ecosystem. Also fallout of plant tissues in autumn may reenter the food chain or contaminate the soil again, depending on site. There are
open questions on phyto-volatilization, as do volatilized contaminants remain at
‘safe’ levels in the atmosphere or are they possibly at toxic levels already when
volatized. Most importantly, sufficient risk assessment has to be made prior to
selecting phytoremediation as favored method, as due to the timeframe required by
the technology, the exposure of the ecosystem to contaminants is prolonged.
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Bioventing and biosparging
Description
Bioventing and biosparging are techniques where oxygen is pumped to the
unsaturated or saturated zone, respectively. The principles are similar to widely
used soil vapor extraction (SVE) as all aim at stimulating the underground airflow.
However, when SVE is designed to maximize contaminant volatilization, BV and
BS are designed to maximize contaminant oxygen contact to increase microbial
enhanced mineralization /2/.
Applicability and operational principles
BV and BS are applicable on sites where the contamination is located deeper in the
subsurface. Bioventing is used for treatment of contaminants in the unsaturated
zone and biosparging for contaminants in the saturated zone. The main geological
factor affecting their usage is the soil matrix, mainly the hydraulic conductivity
which affects the aeration potential.
The benefits of BV and BS are that the systems can be installed inside buildings at
already constructed areas and they do not cause distortion to the current activities
on site. When designing the same precautions as with SVE should be considered so
the operation does not cause volatized contaminants to spread around. e.g. in
basements, which can be controlled by combining the method with SVE wells.
These technologies are best suited for contaminants that are not easily volatized, as
the aim is to biodegrade the contaminants. The technology has been effectively
used for treatment of petroleum hydrocarbons, PAHs and semi-volatile compounds.
/2, 10, 37, 24/. Bioventing and biosparging are the most used bioremediation
technologies worldwide and the US AFCEE has studied them widely and
determined them as the most feasible technologies for the treatment of UST
leakages. /24, 34/.
The main principle of the technology is to lead air underground through an aeration
pipe network through the contaminated zone to provide sufficient oxygen delivery
for mineralization. Biodegradation capability is also affected by moisture and
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nutrient content, thereby both are often added in both bioventing and to a degree
also in biosparging, thought moisture is hardly a factor with the latter.
System Design
Figure 9. Characteristic system design for BV and BS
Bioventing
Bioventing systems are used on soils with hydraulic conductivity more than 10e-5
cm s-1 /10/. The principal design factor is to verify that oxygen, moisture and
nutrients are provided throughout the contaminated zone /10/. Oxygen is forced
with a high pressure blower into the soil matrix on low injection rates to prevent
possible volatilization but to maintain sufficient aeration. If the contamination is
located on shallow sites and the site typography is compatible, percolation can be
used for nutrient and moisture controlling, if not nutrients can be added.
The required oxygen flow rate can be calculated mathematically on the basis of
preliminary studies on microbial community structure, namely maximum microbial
oxygen demand has to be prior analyzed. Second important factor in the design
layout of BV system is the design of well layout. Well layout is usually determined
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by dividing the horizontal area of contaminated zone by the influence area of a
single venting well. The radius of influence (ROI) for a single bioventing well can
also be determined either quantitatively by measuring airflow at surrounding wells,
or mathematically. Usually the well spacing on field are 1 to 1,5 times the ROI and
the radius can vary from 1,5 to 30 meters /2/.
BV vent wells are constructed by either installing them horizontally or vertically,
depending on depth of polluted zone and site geology and above ground
constructions. The wells are installed as standard procedure groundwater (GW)
well installations. The installation piping used is usually 10,2 cm-diameter slotted
PVC pipe used in landfill applications /2/ in Finland the normal piping is 52/60 mm
HDPE piping used in GW monitoring wells. The sloth size of the piping varies
based on soil texture, but most commonly used is 0,3 mm slots. The installation
holes are drilled to desired depth and slotted piping is installed to the whole length
of the contaminated zone and extended a meter deeper when applicable. The
interstice is filled with installation sand (silica) and near the ground level bentonite
is used to seal the hole to prevent blow-by in the operation phase. The above
ground installed piping manifolds are usually hided into shallow covered trenches
or connections are drawn so that normal site operation can continue undisturbed.
US EPA has developed accurate instructions for BV and BS well designs and
installation procedures, which can be found e.g. from Atlas (2005).
BV is a technology that lends itself to combination with other soil remediation
technologies. The complexity of the subsurface sometimes dictates that no single
technology is suitable on its own /2/. As BV increases the subterranean airflow it
increases the possibility that contaminants are volatized.
Biosparging
Biosparging systems are similar on construction and operational principles to
Bioventing. The main difference is the operation zone; when bioventing is used
above GW-level in the unsaturated zone, biosparging is oppositely used in the
saturated, below GW-level zone. The airflow rate should be higher in BV systems
to increase the oxygen saturation in water, but not as high as in normal air sparging
systems where the aim is to volatilize the contaminant compounds. There has been
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evidence showing that increasing the airflow in biosparging systems from the
moderate required for sustaining microbial activity to doubled flow increased the
cumulative mass removal by a factor of two to three /2/. Atlas (2005) references a
study where air had been supplied with high flow in pulsed injections for a short
while and then shut off, but the air had still continued to be supplied to the aquifer
for a day. This method delivers both the high flow advantages of air sparging and
satisfies the lower airflow requirements of bioremediation.
Biosparging is a new technology and before air sparging has been the dominant
method of removing volatile contaminants from the subsoil saturated zone /10/.
Biosparging is able to mineralize more contaminants than air sparging as the
technology is not only confined to volatile compounds, but also petroleum
hydrocarbons, PAHs and SVOCs can be remediated.
BS wells are installed similarly to previously explained BV wells. The installation
can be conducted either horizontally or more commonly vertically, as usually is
due to installation depths. The installation depths are often deeper and the existence
of groundwater causes the pumping pressures to be increased due to increase in
hydrostatic pressure. Also due to more variable subterranean conditions than in
BV, the individual injection wells can be equipped with pressure gauges and valves
to individually control the spread of oxygen. Well spacing is similar to BV, namely
from 1,5 to 30 metres, depending on hydraulic conductivity and pollution
concentration /2/.
BS is often used in conjunction with other techniques as SVE and enhanced
bioremediation techniques as pump, treat and re-inject. Alternatively, methane can
be used as an amendment to the sparged air to enhance cometabolism of
chlorinated organics /24/. Nitrate is often used as an injection gas to produce
anaerobic conditions instead of oxygen. That has been evaluated benefits of
anaerobic conditions in the degradation of certain compounds, especially
chlorinated solvents. /24, 45/
Limitations and concerns
When conducting BV or BS based remediation on sites with nearby basements or
similar constructions the possibility of vapor phase contaminants spreading should
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be analyzed and minimized. A common technique is to install SVE extraction wells
close to the constructed areas or surrounding the contaminated and remediated
zone. The extraction of air underground increases the borderline airflow and
catches the non bioremediated contaminant vapors to above ground treatment,
either by biofiltration or more commonly GAC.
BS should not be used on sites where there is a free phase contaminant as the risk
of spreading the contaminant in the whole water body increases.
The most limiting factor for both BV and BS technologies is the soil matrix and
heterogeneity. Neither can function on soils where the hydraulic conductivity is
less than 10e-5 cm s-1 /2/, hence the technologies are constrained to sandy soils. If
impermeable soil layers exist in the treatment area it can be that those cannot be
treated, and depending on the estimated pollution and risk assessment, it might be
necessary to excavate them which would lead to re-consideration of the
technological feasibilities of BV and BS.
9.5.
Bioslurping
Description
Bioslurping is a remediation process that combines elements from bioventing and
vacuum enhanced pumping of LNAPLs. Bioslurping lifts LNAPLs off the water
table and from the capillary fringe without lowering the oil-laden water table into
clean soil /36/. Bioventing is achieved in the unsaturated soils as air replaces the
soil gas that is removed via the recovery well and stimulates aerobic
bioremediation /44/. When LNAPL removal is finished the system is easily
transformed to a regular bioventing system to complete the remediation.
Applicability and operational principles
Bioslurping systems are applicable on all sites where the contamination is found as
a LNAPL on top of the groundwater, which can be collected individually. Usually
the removal of LNAPLs is done by oil skimmers, but bioslurpers generally result
more then two times the LNAPL removal volume /33/. Bioslurping is used to
remediate soils, as well as groundwater. It can also help to remediate soils
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contaminated with VOCs and SVOCs. It is applicable at sites with water tables
deeper than 10 meters /32/.
System Design
Figure 10. Characteristic system design for bioslurping
There are different techniques for the Bioslurping system, mainly with the
difference being the collection method of LNAPLs, water and soil gas. The older
system are constructed on basis of a single ‘slurp’ tube that collects all three into a
single influent pipe which leads to the aboveground treatment facility. There first
the air and liquid are separated after which the water and oil are separated. Next
step in the process is to clean both air and water to reach dischargeable
contamination levels. /24/
More modern implications of the bioslurping technology have been developed in
the last years to increase the simplicity and operational certainty of the system.
Emulsion usually forms in the vacuum piping of the old ‘single drop-tube system’
as the oil and groundwater are subject to the mixing. The potential for the
production of these solids and emulsions should be significantly reduced if LNAPL
and groundwater can be separated in the well prior to vacuum extraction. The inwell ‘dual drop-tube system’ provides an effective means to achieve this goal. A
single aboveground vacuum pump is used to enhance the subsurface migration of
LNAPL to the extraction well, which is similar to the conventional single drop tube
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design. However, with the dual drop tube design, LNAPL and groundwater are
extracted from the well in separate streams through two separate drop tubes. /2,
29/.
The benefits of bioslurping system compared to normal pump-and-treat or oil
skimming are the increased recovery rate, hence decreased treatment time /29/.
Bioslurping system also separates the oil and water already in-well, so there is not
need for as effective treatment of water as in pump-and-treat. The decreased
amounts of lifted liquids also contribute to decreased expenses. The effectiveness
of bioslurping can be increased by addition of normal bioventing or biofiltration
techniques in the process.
Limitations and concerns
In bioslurping, as in all remediation techniques, the preliminary data gathering is
important. The geohydrological conditions on site affect the effectiveness of the
bioslurping as the bioventing and SVE effect are not as effective in low hydraulic
conductive soils. The biochemical properties of soil, as pH, moisture and nutrient
concentration effect the biodegradation, and aerobic biodegradation of many
chlorinated compounds may be limited unless there is a co-metabolite present /2,
24/.
Bioslurping systems have a difficulty establishing a vacuum on deep, high
permeability sites /32/ and in reference to all previous concerns, the accurate
placement of extraction point is a key to the success of bioslurping.
9.6.
Enhanced saturated zone bioremediation
Description
Enhanced bioremediation is technique which aims at enhancing the natural
conditions to optimize the contaminant degradation in-situ. The method utilizes the
naturally occurring microbial populations, but bioaugmentation can also be applied
when necessary /14/. The principal aim of the technology is to make the
subterranean soil matrix function as a bioreactor. In typical enhanced groundwater
bioremediation systems, groundwater is extracted using one or more wells and if
necessary, treated to remove residual dissolved constituents. The treated
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groundwater is then mixed with an electron acceptor, nutrients and other
constituents if required, and re-injected upgradient of or within the contaminant
source /37/. In an ideal system, the EB would operate as a closed-loop where no
external microbes or water is required and everything that is extracted, is also reinjected.
Applicability and operational principles
ESB can be applied to sites where the hydraulic conductivity of the aquifer is high
and homogenous enough to enable the even distribution of electron acceptors and
nutrients in the subsurface. If the soil matrix is not homogenous, it is difficult to
estimate the flow paths of the GW. The contaminant has to also be dissolved in
groundwater or adsorbed to onto saturated soil matrix within the aquifer to be
readily available for microbial degradation.
The technology is feasible for contaminations at any depth within the aquifer, and
mainly for organic compounds, including petroleum hydrocarbons, PAHs, Cl and
non Cl-VOCs and SVOCs.
The basic operational principle of EB includes extraction of groundwater and reinfiltration after the water has been treated and enriched with nutrients and electron
acceptor. The method can be applied in a number of treatment modes, including:
Aerobic (oxygen respiration); anoxic (nitrate respiration); anaerobic (non-oxygen
respiration); and co-metabolic /37/. The aerobic method is usually most efficient
with petroleum hydrocarbons and PAHs, when anoxic, anaerobic and co-metabolic
are used in remediation of other compounds, such as chlorinated solvents /37/.
The groundwater oxygenation is usually done by direct sparging as in BS or the
water is aerated prior to re-infiltration by bubble saturation or addition of hydrogen
peroxide H2O2 /37, 10/. The nutrients are also added prior to re-infiltration, mainly
nitrogen and phosphate. A key design factor is to verify the even distribution of
nutrients and oxygenated water to the remediated zone.
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System Design
Figure 8. Characteristic system design for ESB
EB systems should be designed very carefully to confirm the applicability of the
remediation method to the site in question. Prior to considering EB as remediation
method, extensive geo-, hydro- and microbiological testing has to be made. The
site has to be geologically evaluated and the groundwater flow mapped. Water and
soil samples should be taken for biological testing of biodegradation capability of
the naturally occurring microbial population.
The system layout is constructed on the basis of the preliminary data gained from
the pre-feasibility studies. The system should be dimensioned to accommodate the
GW volume, the contaminant concentration and location and spread. Operational
principle requires in the minimum system a setup of extraction and infiltration
wells installed at designed locations and aboveground system that facilitates
pumping and nutrient and electron acceptor addition. The system can be modified
to facilitate various conditions and increased to treat larger areas if necessary, due
to modular design. The technology can be combined with in-situ biosparging to
inject the oxygen in-situ instead of aerating it aground.
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The extraction and injection of water affects the subterranean groundwater flow. To
make sure that the contamination plume is not spread due to the changed hydraulic
conditions, it is necessary to maintain sufficient control over the system flow.
Without adequate hydraulic control, this situation can lead to worsening of the
original condition and complicate the cleanup or extend it /37/.
The system should be designed so that the extraction wells are located downstream
from the contamination and injection wells upstream. The location of the wells
should be designed so that the injected, enriched water is able to freely flow to all
sections of the contaminated site, similarly, the extraction wells should be located
so that the natural flow direction will not change. The pumping and infiltration
volumes should be minimized to prevent changing the natural system.
Limitations and concerns
The location, distribution, and disposition of petroleum contamination in the
subsurface can significantly influence the likelihood of success for bioremediation.
This technology generally works well for dissolved contaminants and
contamination adsorbed onto higher permeability sediments. If the concentration is
located in the unsaturated zone, in clay or other low hydraulic conductivity
fractions of the soil or outside the ‘enriched’ zone, the technology will not function
properly and other solutions should be considered /37, 10/.
A current field of research is in system functioning under excessive concentrations
of calcium, magnesium, or iron in groundwater. These metals can react with
injected nutrients, namely phosphate or oxygen and form precipitate. The
precipitate has been noted to cause scaling that clogs the infiltration pipes and can
damage pump systems which causes distortion and extra costs for the operation
/37/.
9.7.
Permeable reactive biobarrier
Description
Permeable reactive biobarriers have been successfully used for containment and
remediation of pollutant plumes. The aim of these technologies is to constrain the
pollution at source to protect surrounding areas or groundwater from effects of
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other remediation techniques /2, 37/. Novel technologies have been developed for
cases where there are large, widely distributed plumes that are not easily
accessible. Enhanced bioremediation systems may be configured as permeable
reactive biobarriers that intercept and treat contaminant plume Biobarriers typically
consist of substrate injection wells or a solid substrate injection trench located
perpendicular to the direction of groundwater /35/.
Biobarrier technology has been applied only on few sites and is not commonly
documented technology. Usually these reactive barriers have been constructed by
using zero valent iron or other inorganic reactive material /28/ that has been dug
underground and through which polluted GW is then diverted. Biological barriers
give possibility to protect and manage larger plumes with less costs and can be
more easily built and operated on areas otherwise unacceptable.
A more detailed description is offered in the case study enclosed as part four of this
thesis.
10.
MONITORING AND QUALITY CONTROL
For bioremediation to be successful there has to be sufficient proof of the
detoxification of the contaminants, preferably proven by complete mineralization
/20/. Rigorous, well documented and successful remediation projects lay the
foundations in building societal confidence and practitioner competence. Until the
technology is tested and proven, careful emphasis on monitoring the functioning of
bioremediation systems is required as they are, in some situations, inappropriate or
unreliable /21/.
As Valdes (2000) notes “The fundamental paradigm for verifying bioremediation
technology begins by modestly admitting that both micro-organisms and their
habitats are incomplete puzzles”.
10.1.
Verifying bioremediation
As stated above, the expected endpoint of bioremediation is the de-contaminated
site. This we can be verified only at the end of the process, and only indirectly by
measuring the contaminant concentrations. Still, we cannot be sure how it is
remediated or has it just disappeared (e.g. volatized or by abiotic means). How do
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we know something is happening in the soil matrix, how do we verify that
bioremediation is in action?
The NRC (national research council) released in 1993 “In Situ Bioremediation:
When Does it Work?” where it recommended a three issues for verifying
bioremediation, which are as follows:
1. documented loss of contaminants from the site,
2. laboratory assays showing that micro-organisms in site samples have the
potential to transform the contaminants under the expected site conditions,
and
3. one or more pieces of evidence showing that the biodegradation potential is
actually realized in the field.
The principles recommended coincide well with the commonly recognized and
applied methodologies and conceptions on bioremediation verification, and no
doubt that the report has had significant impact on the development of monitoring
and quality control of bioremediation. Generally, the process has to make sense;
there needs to be consistency, redundancy and convergence of all types of evidence
from many scientific disciplines /21/.
Documented loss of contaminants
The site has to be continuously and vigorously sampled to establish an empirical
track record of the development of the remediation process. The samples are
usually analyzed in analytical laboratories according to proper international,
national or internal standards.
Very often this is the only issue in bioremediation that is considered as important,
but as mentioned, this only provides information on the current contaminant
concentration, not on the process itself nor can it be used to measure the
effectiveness of bioremediation. It is understandable that the main concern in the
context of legislation is the decrease of contaminant concentrations to legally
acceptable levels, but it does not verify that the compound is mineralized /20/.
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Laboratory assays on the contaminant bioavailability
As a part of preliminary feasibility studies on site considered for bioremediation,
laboratory scale bioavailability studies should be conducted. This means sampling
the site soil and groundwater to replicate with fidelity the in-situ conditions in
laboratory, because if the research is done with optimal conditions, the results will
not apply to the site as conditions which will significantly differentiate from the
laboratory setup.
General methodology for the experiments is quite simple. A known weight or
volume of the sample is measured in similar containers, the container are equipped
with measuring apparatus to monitor the respiration rate (O2/CO2 ratio) and
incubated in laboratory conditions /20/. Samples can be provided with differing
concentrations of nutrients and electron acceptors to quantify and qualify their
effectiveness in the engineering measures on remediation. For a good listing of
available estimation methods for biodegradation potential, please refer to 20, 2003.
When the bioavailability and microbial potential for bioremediation has been
shown, the samples should still be imposed to chemical and biochemical test assays
to verify that required level of mineralization and full detoxification has occurred.
10.1.1.
Realization of biodegradation process in-situ
The final step in verification of bioremediation is to show based on
multidisciplinary evidence that the estimated biodegradation potential is actually
realized. In gathering data to ultimately proof and intermediately to optimize the
bioremediation process, various techniques can be used, some more resource
intensive than others. Commonly the measuring techniques are based either on (i)
detailed knowledge on specific microbiological processes, (ii) computer modeling
or (iii) mass balancing the contaminants, reactants and products.
Analyses based on specific microbial processes
The measurements based on microbial processes include methods from simple
evaluation of the size of bacterial population (MPN, Plating, BIOLOG, etc.) to
adding isotopic tracers for evaluation in respiration products. The methods offers
generally a very good picture of the extent of the in situ biodegradation, but are
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very laborious to conduct. Modern biotechnology is developing constantly new
tools for simplified measurement of bacterial capabilities without extensive sample
pre-treatment. One of the upcoming techniques is ‘bacterial sensors’ /20/ which are
based on using reporter genes for characterization.
Modelling
Modelling can be used both as a design tool as well as a verification tool in
bioremediation. Models consider quantitative aspects of fluid flow, dilution,
sorption, volatilization, mixing, microbial growth and metabolic action rates /21/ to
predict the development of remediation in the subterranean. It should be
remembered that a model is never a true image of reality as it is a generated on the
basis of measured data. The main usage of a model in bioremediation verification
is that when the model is generated and the process development is inputted to the
model, real-life measurements can be compared against the model and recognized
weather the bioremediation is proceeding as designed.
Mass balancing
Under well defined hydrogeologic regimes, fluxes of water, contaminants and
electron donors and acceptor can be quantified between sampling stations /21/. Site
specific gradients of electron acceptors and metabolic end products can be
observed inside the remediated site. Thought, the stoichiometric amounts should be
high within the zone of increased microbial activity and smaller outside the
contaminated area /21, 20/.
10.1.2.
Simple field measurements for analysis
As most of the previously mentioned methodologies for verifying bioremediation
require laborious analytical measurements and preparations, there are some field
measurement methods that can be used to analyze the biodegradation potential insitu.
Commonly taken measurements in-situ include redox, O2, pH and temperature. The
most important results from these are gained from the redox and oxygen
concentration, which tell very straightforward weather there is on-going
remediation. The redox potential shows indirectly the remediation activity
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(depending on method, naturally). In aerobic respiration the redox values are
always positive, and the higher the redox, the more microbial activity is present. As
the redox value decreases, it indicates that the biodegradation is also slowing down
and the microbial population is decreasing in size. When there redox values are
negative, commonly the micro-organisms are utilizing fermentation as metabolism.
Oxygen concentration verifies weather there is, or isn’t, sufficient oxygen levels for
aerobic or anaerobic metabolism. The oxygen concentration can be also used as an
indicator for microbial activity, similarly to BOD method. In aerobic systems,
either samples are collected or the air sparging is stopped and the probe is inserted
to the sample or ground water wells to measure the rate of oxygen consumption. To
distinguish oxygen used by contaminant-degrading microbes from oxygen used by
ordinary microbial activity, background oxygen uptake rates should be measured in
adjacent uncontaminated wells. Relatively rapid oxygen loss in the contaminated
area compared to the uncontaminated area, coupled with a drop in the contaminant
concentration, suggests successful bioremediation. /40/
10.2.
Quality control
The general aim of quality control is to control the remediation so that everything
is done according to plans. Proper quality control realizes the possible faults in
plans or lapses in realization and provides a possibility to tackle these issues if
necessary. The quality control makes sure that the set goals are met and the result is
sustainable. Also the possible harms to humans and nature during the process are
controlled and eliminated. /13/
The tools for quality control are standardising, planning, trained and professional
employees, high quality supply chain and external supervision.
Before remediation project is engaged, a quality control document should be
established and agreed upon amongst all parties. The document should contain
information on the materials used, their handling and protection during
construction. The key components of the equipment have to be tested and quality
control log recorded. All employees have to be informed on the content of the
quality control document and the issues have to be taken in consideration during all
phases of installation and operation phase work /17/.
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Sampling has to be designed and a detailed document on the procedures and
locations to be sampled is to be produced. The plan has to include detailed
information on sampling times, locations, used methods, sample handling, analysis
methods, quality control and reporting. Detailed guidelines for sampling are
provided in various literatures, thought generally the sampling should only be
conducted by a certified person. /13/
The final chain in the series of quality control tools is the independent, external
supervision. The process should supervised from planning to sampling, with
special emphasis on the construction period, as this is the time when most critical
flaws are made. The supervisor should not be economically interconnected with the
companies conducting the remediation nor to the owner of the site.
Quality control is an important part of the everyday operations for most large
companies today. Especially in the environmental field, when working with novel
technologies, special emphasis should be given for these issues.
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PART IV
Case study: Biowall -pilot
11.
PROJECT INFORMATION
11.1.
Introduction
In year 2004, Ratahallintokeskus and Kapiteeli Oyj with Ramboll Finland Oyj as
consultant, begun discussions with selected Finnish high-tech soil and groundwater
remediation companies to develop and test new methodologies for soil and
groundwater remediation; the selected companies were Doranova Oy, Nordic
Envicon and Envitop Oy with Niska & Nyyssönen Oy. The aim of the discussions
was to develop a cost effective strategy (BATNEEC) for remediation of a creosote
contaminated site located in the same groundwater region that is extracted by
Pursiala municipal water plant in the city of Mikkeli, Finland.
The contaminated site had been sold by RHK (Ratahallintokeskus) to Kapiteeli Oyj
(both government owned institutions) in 2000, and with the sales all rights and
liabilities were transferred. All involved parties, including Kapiteeli, City of
Mikkeli and Road Administration hold as their opinion that the legal and
economical liabilities concerning the remediation of the site fall under the
respective responsibilities of VR who had been the owner during the time polluting
occurred. The approximated amount of costs for the full scale remediation (that
were already taken in notice when the property was sold in 2000) are
approximately 3,2 M€.
During the years 2003-2004 a preliminary survey on the type and extent of the
pollution on the site was conducted. The survey focused on locating and
quantifying the amounts of PAHs in the soil and groundwater in the area. The
survey was conducted by Ramboll Finland Oy (previously known as SCC Viatek
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Oy). During this period also a biodegradation study on the soil and groundwater
samples acquired from the site was conducted by the VTT Technical Research
Centre of Finland.
After the preliminary surveys were conducted, the aim was to test and analyze
novel remediation methods in a pilot field trial during year 2005, before selecting
the best technologies (BATNEEC) for the full scale remediation. Three different
methodologies were selected for pilot scale operations, of which Doranova tested a
“Biowall” technique, Nordic Envicon “In-situ bioremediation enhanced with
electric-osmosis” and Envitop Oy tested “pump and treat” with various reactive
filter materials.
In the selection of the remediation technologies used for the full scale remediation
planned for 2007-, emphasis is on the end results, feasibility, risks, environmental
effects, duration and costs of the technologies. A special focus is on protecting the
water quality, as the city of Mikkeli has a legitimate fear on the security of their
municipal water supply.
11.1.1.
Historical information
An old wood preservation facility has been operated in Pursiala, in the city of
Mikkeli (site n:o’s. 491402134, 49140251M602 and 49140251M603) during the
years 1905…1920-1982. The facility has been owned and operated by RHK and
has mainly processed railway sleepers with creosote. Today the old site is located
in an important area for Mikkeli, as it is in the groundwater flow path to their
municipal raw water pumping station (see map 1). The operations that have been
conducted on site for decades have caused widespread pollution of soil and
groundwater. The pollutants are mainly derivates of creosote; mineral oils and
PAH compounds.
During the final years of operation, the factory impregnated wood approximately
14-15000 m3/a, and the amount of creosote used was about 1300 m3/a. In year
1959, phenol pollution was found on the site, which alarmed the owners to modify
the site by covering the sleeper trickle plane and storage facilities with asphalt
which had previously been gravel surfaced. During the following years of 1960-
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1961 tens of thousands of cubic meters of polluted soil was removed. Later in 2002
more soil was removed by excavation from the opposite side of V5.
11.2.
Site background
As presented in map 1 the site is located near the central are of city of Mikkeli and
the property is currently zoned for industrial use. In the location of the old
impregnation facility area today is located highway 5 an important connection road
and the eastern railroad. The ‘hot-‘spot’ has not been constructed yet but there is
pressure toward utilizing this property due to its central location.
The area which has not been remediated (north side of highway 5) has elevated
contaminant concentrations in the top layers to the depths of 1-3 meters, but also as
deep as 25 meters, bound to the soil matrix and as DNAPL on top of the bedrock.
Highest amounts of contaminants have been found from the swamp located close to
the old impregnation facility (see map 1, black box). It has been suggested that
during the operating period of the facility, waste creosote has been lead to the
swamp.
Due to the difficult location of the contamination, it is not possible to excavate the
creosote contaminated soils. Railroad, roads, plumbing and buildings inhibit this
and therefore other technical solutions are necessary for successful remediation.
11.2.1.
Geohydrological data
The contaminated site is located in the pathway of groundwater flow which ends up
in the Pursiala water utility extraction site approximately 1,5 kilometres south-east
of the old impregnation plant. The groundwater flows through the so called
‘northern route’ by first heading east and then turning south toward the
Kaijunharjun-Kaijanniemi eskers through which it continues straight to the water
utility. By modelling, it has also been estimated, that it might be possible that there
is another route, the ‘southern route’, which would basically be direct south-eastern
pathway to the utility.
The site geology is not uniform and there are ruptures in the bedrock which can
divert and collect the creosote DNAPL flow. The soil in the area is mainly sand
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and moraine, and it can be expected to continue similarly in the esker formations
leading to the water utility. The ground water level is expected to follow the
Saimaa lake water levels with small delay.
Map 1. The project site and more general location in the city of Mikkeli. The
detailed map shows the site of the impregnation facility, previously remediated
area and the estimated groundwater flow path ‘northern route’ and pollution
dispersion route.
11.3.
Application process
Due to the nature of the project being a pilot scale operation instead of a full scale
remediation, no environmental permit was acquired. Instead a notice of
experimental action was given for the environmental office of Etelä-Savo, which
gave a positive decision for all parties to go through with the planned pilot
experiments (Doranova Oy permit Dnro ESA-2005-Y-101-18).
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OPERATIONAL PRINCIPLES AND CONSTRUCTION
12.1.
Aim
74
The Biowall method piloted by Doranova was designed to prevent the flow of
pollutants dissolved in water from the contaminated area. As the polluted water is
flowing from the hot-spot towards the raw water pumping station in south-east, the
‘biowall’ forms a biologically reactive barrier perpendicular to the groundwater
flow which induces a full mineralization of organic pollutants by aerobic bacteria.
The pilot phase aim of the Biowall construction was to find out the effectiveness of
the method in practise by measuring the changes in pollutant concentrations in the
upstream and downstream monitoring wells and learn to produce an optimum
process status in the biowall operation with minimal site disturbance.
12.2.
Principle
Figure 9. Characteristic system design for biowall
The biowall is an underground in-situ aerobic bioreactor, which is operated by
infiltrating nutrients and air at different levels of groundwater. The specific
amounts of nutrients and air is generally dependant on the amount of pollutants and
the time wanted for total mineralization of the pollutants, which in this case it was
basically a function of the groundwater flow rate and the biowall length.
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The construction does not aim in functioning as a ‘bio-barrier’ which would
prevent or divert the groundwater flow by changing the underground hydraulic
conductivity by maintaining a high density microbial culture, instead it aims at
minimizing the disturbances to the natural groundwater flow and nutrient balance
outside the active zone.
In the pilot phase the aim of the Biowall was not to treat the whole amount of
polluted water. The designed construction width was 25 m and length 5-10 m.
according to notice of experimental action.
Biowall’s have been constructed earlier e.g. in Netherlands with good experiences
on the functioning and results. Doranova Oy has a collaboration agreement with a
Dutch expert organisation, namely Biosoil B.V. who’s experiences and knowledge
was also used in the design and operation phase.
12.3.
Construction work
Doranova Oy begun site operations by installing monitoring wells on southern and
western sides of the contract area in the beginning of July ’05 (11.-15.7.2005),
titled M1, M2, M3 and M4 (see appendix 2 installation locations, appendix 3 for
installation data and appendix 1 for pictures 2). The monitoring wells were
installed perpendicular to the Biowall so that at both sides of the Biowall there
would be monitoring wells dedicated for shallow and deep water sampling. During
the installation of the monitoring wells information on the geohydrological
parameters was acquired; as soil texture, bedrock type and depth and level of water
table.
The installation work begun with the removal of the top (~1m) of the soil layer
from an area sized 25 x 15 m (Appendix 1, pic. 3). The removed soil was piled next
to the excavation and sampled for contamination by Ramboll Finland Oy to resolve
possibilities for locating.
The final design planning for the Biowall construction was made at this phase prior
to installation of the required infiltration and pumping wells, and air sparing points.
The design was made on-site by visualizing and measuring correct installation
locations (Appendix 1, pic. 3).
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The well installation was done during weeks 30-31. The procedure was to drill to
the bedrock level and simultaneously install protective iron casings for the wells.
Inside these casing, HDPE pipes were later installed with different configurations
on the locations of the slotted sections to enable nutrient infiltrations at different
levels underground. After the HDPE pipes were installed the iron casings were
removed by welding a hole in their upper part and lifting them with a crane. Prior
to removal the interstice of the iron casings and HDPE pipes was filled with sand to
prevent later vertical cross flow. Pictures of the installation procedure are found
from the appendix 1, pic. 4, 5, 6, 7 & 8. Specific locations of the wells can be
found from appendix 1 and information on the installation depths from appendix 2.
During week 32 all the infiltration- and extraction wells, with aeration points were
linked. All installed plumbing were individually insulated and equipped with
electric heating cable. Underneath and above the installations, sand was provided to
further protect the connections (see appendix 1, pic 9, 10, 11 & 12). The extraction
wells were equipped with a curb and a covering to make later maintenance possible
(see appendix 1, pic 13 & 14). After all installation work was finished the site was
re-filled with the same soil material which was removed during start-up (appendix
1, pic 15 & 16). The material had been analyzed during the operations and no
pollution exceeding base or limit values was found.
The container providing the technology for the circulation of water and air
injection arrived in the week 33 when the final connections between the plumbing
that was now underneath the soil and the container were made (appendix 1, pic 17,
18, 20 & 21). During the on-site earthwork, the container containing process
instrumentations was pre-built ex-situ (appendix 1, pic 19).
The final installations were made to the container in-situ including electric
connections, checking all plumbing and installing a remote on-line monitoring
system. Also an additional monitoring well M5 was installed based on the
hydrogeological data acquired during installation procedure (location in appendix
2, details in appendix 3).
The biowall was in process preparedness in the change of August-September 2005,
and the pilot remediation was initiated accordingly.
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On-site measurements and modelling
Before installation, the site geology was analyzed by using ground penetrating
radar technology. The system uses high frequency electromagnetic pulses to
analyse the soil and bedrock structure by mathematically estimating the reflection
effect of different density materials. The analysis was done on east-north axis in
between the monitoring wells M1, M2 & M3, M4 to establish ground formations in
the site of the designed biowall.
During the installation of process wells constant monitoring of the soil structure,
bedrock depth and fractures were recorded. Similarly sensory observation on the
location and degree of pollution were conducted.
Similarly, during the installation the groundwater flow within the designed biowall
was measured by using a Phrealog method. The technology is based on observation
and optical recording of the movement of omnipresent suspended particles in
water, and therefore does not require introduction of any artificial tracers. Based on
the recorded movement of particles, the system mathematically calculates the
direction based on point of compass and the horizontal flow velocities.
12.5.
Process instrumentation and parts lists
See appendix 4.
13.
MONITORING
As the remediation was operated as a pilot scale field trial, the process
measurements were done often to gather sufficient data on the forming of the
subterranean in-situ bioreactor and the changes in pollutant concentrations to
quantify and qualify the necessary process adjustments to optimize the functioning
of the system and incrementally aim toward the system equilibrium.
In the environmental permit, the agreed minimum monitoring scheme suggested for
the pilot was to analyse every two weeks PAHs, phenols, mineral oils (TPH) and
nickel from the established monitoring wells M1 - M5. The results were to be
reported periodically (after each consecutive measurement period) to the
environmental officials and the customer.
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Monitoring program
Doranova Oy carried out an extensive monitoring scheme including sampling from
the border areas of the biowall (points M1 – M5) and within it (E20, E22, E10) (see
appendix 2 & 3). Besides the required parameters, also BTEX, TAME, MTBE,
total phosphate, nitrite, nitrate, total Kjheldhal nitrogen, TOC and occasionally iron
were analyzed. Besides the analytically analysed results, the process was measured
on-site by using field measurement device (WTW Multi 350i) to measure pH,
redox, conductivity and oxygen content.
13.2.
Methodologies
Sampling was carried out according to internal guideline for groundwater sampling
(DN-i001-2005) which is designed in reference to Doranova Oy’s quality
management system and in accordance with ISO 9000:2000.
The samples were analysed in an accredited environmental laboratory Analytico
Milieu B.V. located in Netherlands. Samples were delivered by global express (24 h
delivery) via UPS and were stored throughout the delivery chain in airtight, dark
and cooled containers.
13.3.
Results
See appendix 5.
13.4.
Budget
See appendix 6.
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REFERENCES
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APPENDICES 1, 2, 3, 4, 5 & 6
ARE NOT INCLUDED IN
THIS VERSION DUE TO
LIABILITY ISSUES.
For further information, please contact the author
jarno.laitinen AT gmail.com
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