Anaerobic fermentation of organic waste from juice plant in Uzbekistan

Anaerobic fermentation of organic waste from juice plant in Uzbekistan
Anaerobic fermentation of organic
waste from juice plant in Uzbekistan
INOBAT ALLOBERGENOVA
KTH Chemical Engineering
and Technology
Master of Science Thesis
Stockholm 2006
KTH Chemical Engineering
and Technology
Inobat Allobergenova
ANAEROBIC FERMENTATION OF ORGANIC WASTE FROM JUICE
PLANT IN UZBEKISTAN
Supervisor & Examiner:
Monika Olsson
Master of Science Thesis
STOCKHOLM 2006
PRESENTED AT
INDUSTRIAL ECOLOGY
ROYAL INSTITUTE OF TECHNOLOGY
TRITA-KET-IM 2006:9
ISSN 1402-7615
Industrial Ecology,
Royal Institute of Technology
www.ima.kth.se
Anaerobic fermentation of organic waste from juice plant
in Uzbekistan
Inobat Allobergenova
Master Thesis
Industrial Ecology
The Royal Institute of Technology
Supervisor: Monika Olsson
Stockholm-2006
ABSTRACT
This Master Thesis work was done at the Master’s Programme in Sustainable
Technology at the Royal Institute of Technology (KTH) in study period 2005-2006.
The aim of this Thesis work was to analyze if fermentation process is a proper method
for processing organic waste from juice production process and if so to design a fermentation
process of organic waste from juice plants in Uzbekistan taking into account the economical,
environmental and technical aspects.
In this report apple juice producing process and organic waste from juice production
in Uzbekistan were overviewed. Two juice processing plants of Uzbekistan “Bagat-Sharbat”
and “Meva” and their generated organic waste were overviewed.
Also different treatment methods of organic waste and their advantages and
disadvantages were analyzed and compared with anaerobic fermentation process. The studied
organic waste management methods are animal feeding, incineration, direct land spreading,
land filling, composting and anaerobic fermentation. Anaerobic fermentation of organic waste
generated from fruit juice production was studied.
Suggestions and recommendations were done to implement organic waste
management for fruit juice industry in Uzbekistan according to studies and calculations.
Advantages and disadvantages of different waste management methods are discussed
and compared with anaerobic fermentation. Economical and environmental calculations of
anaerobic fermentation process were done. Different biogas plant types all over the world and
their construction costs were studied and compared. According to studies and calculations
several suggestions and recommendations are made.
By studying and comparing different waste treatment methods with anaerobic digestion of
organic waste from juice plants following conclusions are made:
The benefits of the biogas plant on the fruit juice plant:
•
•
•
•
•
•
Solution of the organic waste-disposal problems
Reduction of obnoxious smells from the organic wastes
Own, stable, self-sufficient energy production (heat, steam and electricity)
Cheap energy, which yields financial savings in the longer term.
Possibility of selling energy or biogas surplus - a source of extra income for
the plant.
Production of high-volume fertiliser that carries a higher content of nitrogen
(15% or more) than artificial fertilisers, and that does not burn the crops, as
untreated slurry can do. This reduces the need for expensive artificial
fertilisers. By selling this natural fertiliser additional income for the plant can
be obtained.
Local benefits:
•
•
•
Better control of the waste from fruit juice processing organic waste means
less pollution of local environment and water sources.
Removal of chemical fertilisers from the fields and recirculation of nutrients.
Local power plants contribute to creating permanent local jobs in the area.
On a global additional, replacing fossil fuels to biogas reduces emissions of CO2. At
the same time, the emission of methane, a greenhouse gas that is 20 times more aggressive
than CO2 is reduced due to controlled anaerobic digestion.
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TABLE OF CONTENTS
ABSTRACT ................................................................................................................................... 2
ACKNOWLEDGMENT............................................................................................................... 3
TABLE OF CONTENTS.............................................................................................................. 4
List of Figures ................................................................................................................................ 6
List of Tables.................................................................................................................................. 7
Glossary and Definitions of terms................................................................................................ 8
1. INTRODUCTION............................................................................................................... 11
1.1. Aim and objectives............................................................................................................. 11
1.2. Methodology of Thesis work ............................................................................................. 11
1.3. Problem definition.............................................................................................................. 12
1.4. Structure of the Thesis........................................................................................................ 13
2. INDUSTRIAL WASTE MANAGEMENT REGULATIONS OF REPUBLIC OF
UZBEKISTAN............................................................................................................................. 14
2.1. Law of the Republic of Uzbekistan on wastes ................................................................... 14
3. STUDY FIELD .................................................................................................................... 18
3.1. “BAGAT-SHARBAT” juice producing Ltd. Co. .............................................................. 19
3.1.1. Fruit juice production process ..................................................................................... 19
3.1.2. Energy consumption and economics........................................................................... 19
3.2. “MEVA” Uzbekistan-Italy juice producing joint venture.................................................. 20
3.2.1. Fruit juice production process ..................................................................................... 20
3.2.2. Energy consumption and economics........................................................................... 20
4. FRUIT JUICE PROCESSING .......................................................................................... 21
4.1. Description of fruit juice production.................................................................................. 21
4.2. Organic waste from fruit juice processing ......................................................................... 25
4.2.1. Characteristics of Fruit juice processing organic waste .............................................. 26
5. METHODS OF PROCESSING ORGANIC WASTE ..................................................... 27
5.1. Animal feed ........................................................................................................................ 28
5.1.1. Disadvantages of using of organic waste as an animal feed ....................................... 29
5.2. Incineration......................................................................................................................... 29
5.2.1. Advantages and Disadvantages of waste incineration method ................................... 29
5.3. Direct land spreading ......................................................................................................... 30
5.3.1. Advantages and disadvantages of Land spreading method......................................... 32
5.4. Land filling......................................................................................................................... 32
5.4.1. Land filling method’s advantages and disadvantages ................................................. 33
5.5. Composting ........................................................................................................................ 33
5.5.1. Composting method benefits and disadvantages ........................................................ 35
5.6. Anaerobic Fermentation..................................................................................................... 35
5.6.1. Advantages and disadvantages of anaerobic fermentation method ............................ 37
6. BIOGAS PRODUCTION ................................................................................................... 39
6.1. Biogas................................................................................................................................. 39
6.2. Gas Production ................................................................................................................... 39
6.3. Which materials can biogas be made from?....................................................................... 40
6.4. Factor Affecting Gas Generation ....................................................................................... 41
6.5. Benefit of Biogas and Biogas Technology......................................................................... 42
6.6. Treatment of the gas........................................................................................................... 44
6.6.1. Desulphurisation of the biogas.................................................................................... 44
6.7 Gas Requirements and Storage ........................................................................................... 44
6.8. Difference between of Biogas and Natural gas.................................................................. 44
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7.
8.
BIODIGESTER................................................................................................................... 48
CALCULATIONS OF ANAEROBIC FERMENTATION PROCESS ......................... 52
8.1. Calculation of biogas yield and bio digester volume ......................................................... 53
8.2. Calculation of costs which are involved to building, operating the biogas plant............... 54
9. DISCUSSION ...................................................................................................................... 56
10.
CONCLUSION................................................................................................................ 60
11.
REFERENCES ................................................................................................................ 61
12.
APPENDICES ................................................................................................................. 64
Appendix 1. Technological line for fruit juice producing process............................................ 64
Appendix 2. Enzymes and their uses [21]................................................................................. 65
Appendix 3. Fruit juice and fruit wine manufacture bleaching agents [21].............................. 66
Appendix 4. The biogas comparison with natural gas. ............................................................. 67
Appendix 5. Flow chart of anaerobic digestion of wet organic waste ...................................... 76
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List of Figures
Figure
3.1. The map of The Republic of Uzbekistan ……………………………………………………….18
3.2. Geographic locations of fruit juice plants……………………………………………………..18
3.3. “Meva” Uzbekistan-Italy juice producing joint venture…………………………………….20
3.4. Vacuum boilers “Meva” Uzbekistan-Italy juice producing joint…………………………...20
4.1. Material flow chart in apple juice producing…………………………………………………22
4.2. Washing conveyer in “Meva” Uzbekistan-Italy juice producing joint venture………….23
4.3. Decanter …………………………………………………………………………………………..25
4.4. Separator ………………………………………………………………………………………….25
4.5. Separator illustration ……………………………………………………………………………25
5.1. Treatment options of wet organic waste ………………………………………………………28
5.2. The Composting Process…………………………………………………………………………34
5.3. The Anaerobic Process - a four stage process………………………………………………..36
5.4. Thermophilic Methane Bacteria………………………………………………………………37
6.1. Biogas yield potential from different organic materials…………………………………….41
6.2. Comparison of calorific value of different fuel gases ………………………………………45
6.3. Volumes of other fuels equivalent to 1 m3 of biogas…………………………………………46
6.4. Comparison of the calorific values of various fuels…………………………………………47
7.1. Basic layout of biogas plant……………………………………………………………………48
9.1. Treatment options of wet organic waste and their characters…………………………….58
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List of Tables
Table
3.1. Technological characteristics of fruit juice processing plant……………………………….20
4.1. Nitrogen and water contents and C:N ratios of some organic residues …………………..26
4.2. Typical proximate analysis and energy data for materials found in residential,
commercial, and industrial solid wastes……………………………………………………………27
4.3. Typical data on the ultimate analysis of the combustible materials found in residential,
commercial, and industrial solid wastes……………………………………………………………27
5.1. Recommended conditions for rapid composting …………………………………………….35
5.2. Comparison of aerobic composting and anaerobic digestion processes for organic waste
processing……………………………………………………………………………………………..38
6.1. Analysis of Biogas content …………………………………………………………………… 39
6.2. Gas production per ton of organic waste according to different temperatures…………40
6.3. Potential biogas production from fruit and tomato processing organic wastes………..41
6.4. Some biogas equivalents……………………………………………………………………… 43
8.1. Comparison of biogas plant construction cost in Germany……………………………….54
8.2. Comparison of biogas plant construction cost in India…………………………………....55
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Glossary and Definitions of terms
Aerobic process - a process requiring the presence of oxygen. See Composting.
Anaerobic Bacteria - micro organisms that live and reproduce in an environment containing
no "free" or dissolved oxygen. Used for anaerobic digestion. See Anaerobic digestion.
Anaerobic Digester - a device for optimizing the anaerobic digestion of biomass and/or
animal manure, and possibly to recover biogas for energy production. Digester types
include batch, complete mix, continuous flow (horizontal or plug-flow, multiple-tank,
and vertical tank), and covered lagoon.
Anaerobic Digestion (AD) - the complex process by which organic matter is decomposed by
anaerobic bacteria. The decomposition process produces a gaseous by product often
called "biogas" or "digester gas". See Biogas and Digester gas.
Biogas - a combustible gas created by anaerobic decomposition of organic material,
composed primarily of methane, carbon dioxide. See Digester gas.
Biogas plant – plant where the fermentation of organic waste takes place.
Biological treatment (bio treatment) – is a biological process (for example, anaerobic
digestion and composting) that changes the properties of waste using micro organisms
such as bacteria and fungi.
Bleaching - to remove the colour from, as by means of chemical agents or sunlight and make
white or colourless. See also Bleaching agent.
Bleaching agent - a chemical agent used for bleaching. See also Bleaching.
Compost - substance composed mainly of partly decayed organic material that is applied to
fertilize the soil and to increase its humus content.
Composting – is process where organic waste, including food waste, paper and yard waste, is
decomposed under aerobic conditions, resulting in compost.
C:N – Carbon to Nitrogen ratio in organic substances.
0
Brix- is used in the food industry for measuring the approximate amount of sugars in fruit
juices, wine, soft drinks and in the sugar manufacturing industry.
Digester Gas - the gas containing methane produced from anaerobic digestion of animal or
other organic wastes. See Anaerobic digestion.
DM –dry matter of organic waste
Effluent - the discharge of a pollutant in a liquid form, often from a pipe into a stream or
river.
Energy Consumption - the amount of energy consumed in the form in which it is acquired
by the user. The term excludes electrical generation and distribution losses.
Enzymes - any of numerous proteins or conjugated proteins produced by living organisms
and functioning as biochemical catalysts.
Enzymatic maceration - treatment of the mashed fruit with macerating enzymes such as
Macer8™ FJ or Pectinase 62 L further breaks down the fruit pulp resulting in
increased yields of juice, reduced viscosity and improved run-off. See also Enzymes.
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Fertilizer - organic or inorganic material containing one or more of the nutrients—mainly
nitrogen, phosphorus, and potassium, and other essential elements required for plant
growth.
Greenhouse Gas - a gas, such as carbon dioxide or methane, which contributes to potential
climate change.
Groundwater - water occurring in the subsurface zone where all spaces are filled with water
under pressure greater than that of the atmosphere.
Hazardous waste - a substance, such as nuclear waste or an industrial by-product, that is
potentially damaging to the environment and harmful to humans and other living
organisms.
Hydrogen Sulphide (H2S) - a toxic, colourless gas that has an offensive odour of rotten eggs
and is soluble in water and alcohol; freezes at –85.5ºC and boils at –60.7ºC. Hydrogen
sulphide is a dangerous fire and explosion hazard, and a strong irritant. It is used as a
reagent and as a source of hydrogen and sulphur.
Hydrolysis - a chemical decomposition process that uses water to split chemical bonds of
substances.
Incineration – the destruction of solid, liquid, or gaseous wastes by controlled burning at
high temperatures.
Landfill - a landfill is an engineered area where waste is placed into the land. Landfills
usually have liner systems and other safeguards to prevent groundwater
contamination.
Land filling - A method of solid waste disposal in which refuse is buried between layers of
dirt so as to fill in or reclaim low-lying ground. See also Landfill.
Landfill Gas (LFG) - gas generated by the natural degrading and decomposition of
municipal solid waste by anaerobic micro organisms in sanitary landfills. LFG is
comprised of 50 to 60% methane, 40 to 50% carbon dioxide, and less than one %
hydrogen, oxygen, nitrogen, and other trace gases.
Leachate - liquids that have percolated through a soil and that carry substances in solution or
suspension.
Methane (CH4) - a flammable, explosive, colourless, odourless, tasteless gas that is slightly
soluble in water and soluble in alcohol and ether; boils at –161.6ºC and freezes at –
182.5ºC.
mmho/cm - total concentration of soluble salts (salinity), usually expressed as electrical
conductivity (EC) in units of mmho/cm.
Nm3 - normal cubic meter; One Nm3 is equivalent to the amount of gas that takes up one
cubic meters volume at the pressure of 1 bar.
Organic waste – is waste such as paper, plastic, yard waste, wood, food, textiles, and other
organics.
ODM – organic dry matter of organic waste
Pay back time – time for the return on an investment equal to the amount invested.
pH - an expression of the intensity of the alkaline or acidic strength of water. Values range
from 0-14, where 0 is the most acidic, 14 is the most alkaline and 7 is neutral.
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Total solids (TS) - non-volatile ingredients of a composition after drying.
Volatile Solids (VS) - those solids in water or other liquids that are lost on ignition of the dry
solids at 550 degrees centigrade.
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1. INTRODUCTION
Organic waste is produced wherever there is human habitation. The main sources of
organic wastes are household food waste, industrial waste and agricultural waste. In
industrialised countries, the amount of organic waste produced is increasing dramatically each
year. In some countries, they already treat their organic waste in correct ways. But in some
developing countries organic waste treatment is a big problem even now.
In developing countries, there is a different approach to dealing with organic waste. In
fact, the word ‘waste’ is often an inappropriate term for organic matter, which is often put to
good use. The economies of most developing countries dictates that materials and resources
must be used to their full potential, and this has propagated a culture of reuse, repair and
recycling. In many developing countries, there exists a whole sector of recyclers, scavengers
and collectors, whose business is to salvage ‘waste’ material and reclaim it for further use.
My Master Thesis work is about taking care of organic waste from fruit juice plants in
Uzbekistan and making suitable suggestion, for treatment of organic waste from fruit juice
plants.
The waste consists of wash water, skins, rinds, pulp, and other organic waste from fruit
and vegetable cleaning, processing, cooking and canning in the juice producing industry. In
Uzbekistan, vegetable and fruit processing plants do not take care of their processing organic
waste in a proper way. There are several laws and regulations according to industrial waste
handling. But most of these regulations made are considered for processed wastes from
mining industry in Uzbekistan.
1.1. Aim and objectives
Aim:
The aim is to study if fermentation is the proper method for taking care of organic
waste from juice plants in Uzbekistan and to suggest a proper fermentation plant taking into
account the economical and technical aspects.
Objectives:
-
Describe different ways of processing organic waste from juice plants and analyse if
fermentation is the best method for Uzbekistan juice plants.
To make economical evaluations of a fermentation plant
Suggestions for how the residues (biogas and solid residues) from a fermentation plant
should be handled.
1.2. Methodology of Thesis work
Methods:
-
By study visit to get information and databases from one or more food industry plants
in Uzbekistan about their organic wastes from fruit juice processing (type, amount
content, etc.).
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-
To get information from internet and literatures (about fruit juice processing, its
organic waste, treatment methods of this kind of organic wastes, etc.).
To get information about their waste handling process by contact with food industry
plants.
Contact biogas producing plants by e-mail and phone.
1.3. Problem definition
Nowadays because of increasing human population in the world and their food
consumption, food industry sector all over the world is increasing rapidly. This is followed by
an increased amount of generated waste from this industry sector. The increasing generation
of waste can cause problems both to human health and the environment. It is therefore
important that already generated and future waste is properly cared for and that environmental
aspects are not only applied in the waste phase of a product’s life cycle but in all aspects of
society.
The more and more stringent environmental regulations and more efficiently methods
of organic waste handling are calling for action to reduce the environmental loads of food
industry.
To implement cleaner production measures and taking care of processing wastes to the
environment in each field is one of the most important issues today. Fruit juice production
industry usually generates high amount of solid wastes/by-products and high volumes of
effluents with high organic loads. As any type of industry this field also has an impact on the
environment.
In this report problems of organic waste from fruit juice production in Uzbekistan are
overviewed.
There are many fruit processing plants situated in Uzbekistan. Two juice producing
plants, which are situated near each other in Xorazm region and their organic waste problems,
are studied in this Thesis.
In the juice manufacture for human consumption a big amount of organic waste such
as peel, pulp and cores are emitted. Bruised, immature or rotten fruit and vegetables are also
removed from processing.
In the local area where the juice plants are situated many inhabitants are located. If
organic waste problems are not solved it will cause harmful emissions and odour to human
health and environment.
According to data of the Soil Science Institute about 77.2% of the irrigated area of
Xorazm region has a ground water level from 0-1.0 to 1-2.0 m [1]. This database shows that if
wastewater and organic wastes are just dumped without any treatment it may decrease
groundwater quality with their harmful emissions. Since the local population consumes the
groundwater as drinking water, pollution of it may affect human health seriously.
Industrial waste management regulations and laws are prepared for the industry sector
of Uzbekistan. But these regulations mainly consider mining industry which is a big industry
sector of Uzbekistan. There are no implementations for the food industry sector.
In Chapter 3 the fruit juice plants performances, material and energy use, producing
capacity and amount of generated organic waste are detailed.
The main problematic points of the issue are:
z Poor waste management - just dumping outside near to plants without any treatment;
z Weak legislations on waste - no or poor implementation;
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z Environmental impact - on water, air, soil, local nature and etc.
z Human health impact - by water, air, flies.
1.4. Structure of the Thesis
In Chapter 2 industrial waste management regulations of Uzbekistan are briefly described.
In Chapter 3 profiles, performances generated organic waste amount and content from fruit
juice plants in Uzbekistan are given. These databases were collected by visiting two plants in
Uzbekistan.
In Chapter 4 fruit juice processing steps and organic waste from fruit juice processing are
described. Organic waste characters from fruit juice processing are used when deciding
treatment of this kind of organic waste.
Different types of treatment methods of organic wastes are studied in Chapter 5 and there is a
discussion of each method’s benefits and disadvantages dealing with their environmental,
economical and social performances. These methods were compared according to these
studies in the discussion part of this report.
In Chapter 6 Biogas production is studied more deeply and the benefits and use are discussed.
In this chapter biogas and natural gas are analyzed and compared with each other.
Also several biogas plants and their constructions and costs are studied.
In Chapter 7 several bio digester types and construction costs of biogas plants are
investigated. Studied biogas plants are situated in Europe, India, China and Nepal.
In Chapter 8 economical and technical evaluations were done after studying and getting
information from all other upper chapters and literatures.
According to studies and evaluations, Chapter 9 describes the results and decision of this
Master Thesis research.
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2. INDUSTRIAL WASTE MANAGEMENT REGULATIONS OF
REPUBLIC OF UZBEKISTAN
Waste management and control are in the competence of the State Committee for Nature
Protection, which works out the legislative norms, controls and collects data on waste
generation, maintains state cadastre on waste dumps and collects the levies for waste storage.
Collection and analysis of the information on waste generation and disposal are the main
tasks. The present system of data collection at a regional and republican level - statistical
system - is kept, but its development is required. In the nearest future it is necessary to
introduce waste cadastre. The main way of waste disposal is the solid wastes land burial. A lot
of work should be done on disposal of hazardous wastes.
Expenses connected with waste management are mainly defined by the waste disposal
taxes, to be paid by the producers of wastes. Waste generators pay waste disposal taxes to
Government according to their waste toxicity class and amount. Resolution of the Cabinet of
Ministers of the Republic of Uzbekistan 554 of December 31, 1999 established from January
1, 2000 the waste disposal taxes [2]:
For the 1st class1 - 1500 Soums/ton (equal 1.0 EUR/ton),
2 class - 750 Soums/ton (equal 0.5 EUR/ton),
3 class - 450 Soums/ton (equal 0.3 EUR/ton),
4 class - 150 Soums/ton (equal 0.1 EUR/ton)
2.1. Law of the Republic of Uzbekistan on wastes
Below some of the articles that describe regulation according to industrial generated
wastes are shown. Because the main sector of industry of Uzbekistan is mining the
regulations mainly consider this type of waste. However from an environmental point of view
the same requirements should be applied for all industrial sectors.
Article 1. Purpose and main objectives of the Law
The purpose of the Law shall be to regulate relations in waste management. The major
objectives of this Law shall be to prevent harmful impact of waste on lives and health of
citizens, environment, to reduce generation of wastes and ensure their rational utilization in
economy.
Article 3. Legislation on waste management
The legislation on waste management consists of the present Law and other legislative
acts. The legislation on waste management shall not apply to relations linked to disposal and
discharges of pollutants into air and water sites.
Relations in waste management in the Republic of Karakalpakstan shall also be
regulated by the legislation of the Republic of Karakalpakstan.
If international agreement signed by the Republic of Uzbekistan specifies provisions
other than those specified by the legislation of the Republic of Uzbekistan on waste
management, the provisions of the international agreement shall apply.
1
Classes of industrial wastes present toxicity of generated waste; the 1st class describes high level of toxicity of
industrial wastes.
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Article 4. Waste ownership right
Waste ownership right shall belong to the owner of raw materials, semi-finished
goods, other items or products as well as goods (products), utilization of which resulted in
generation of this waste.
Ownership right to waste may be acquired by other person based on contract of
purchase, bargain, gift or any other deal on transfer of waste which is not prohibited by law.
Waste owners shall possess, utilize and manage waste within the competence
established by the legislation.
Transfer of waste ownership right and liabilities for harmful impacts in case of a
change of owner of a land plot on which waste is stored shall be decided by the legislation.
Article 14. Right of entities in waste management
Entities shall have the right to:
Obtain in the established manner information from specially authorized government bodies
for waste management about sanitary standards and rules, environmental standards in waste
management;
Waste storage at waste disposal sites under sanitary standards and rules of
maintenance of territories;
Submit proposals related to location, designs, construction and operation of waste
management sites to special authorized government bodies for waste management, local
government bodies;
Participate in elaboration of waste management government programs;
Compensation for damages inflicted to them by other entities or individuals as a result of
waste management.
Entities may have other rights in waste management under the legislation.
Article 15. Duties of entities in waste management
Entities shall be bound to:
Comply with the established sanitary standards and rules, environmental standards in waste
management;
Maintain records of waste; submit reports on them in the manner established by the
legislation;
Determine in the established manner the degree of hazard of waste to lives and health
of citizens, environment;
Work out drafts of standards of waste generation and limits of waste disposal;
Ensure collection, due storage and avoidance of destruction and deterioration of waste of
resource value and subject to utilization;
Take measures on development and introduction of technologies for recycling of
waste they own;
Not allow mixing of waste except cases specified by the production process.
Not allow storage, treatment, utilization and dumping of waste in places and sites not
allocated for this;
Maintain supervision over sanitary and environmental condition of owned waste management
sites;
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ACKNOWLEDGMENT
This Master Thesis work was done with knowledge support of Royal Institute of
Technology (KTH) and financial support of Swedish Institute foundation (SI) in Sweden.
I would like to thank some of the people that have helped and supported me in accomplishing
this study.
First of all I want to thank my supervisor Monika Olsson, for inspiring enthusiasm and
devotion. Her environmental and scientific compass has been a great help in my search for a
path through the organic waste treatment jungle.
Special thank to Royal Institute of Technology and Swedish Institute for their every
support which was very useful during my studies and writing my Master Thesis.
I would like to thank everybody at the Department of Industrial Ecology who gave
knowledge according my Master program and helped me with pleasure when I needed.
I am very grateful to my family and friends for reminding me that there is a world
outside the organic waste management matrix and believing on me that I can do all the best,
especially to my father Allaberganov Shermat and mother Zaripova Anabibi for providing me
with databases and information which I need and their encouragement during writing my
Master Thesis.
Also I am very thankful to my friends Shoira, Galya and Gulruh for their support and
advices during writing my Master Thesis.
And my endless greetings and thanks to God for His boundless gifts and blessings….
Stockholm, 2006
Inobat Allobergenova
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Carry out activity in reclamation of land damaged in waste management;
Implement complex measures on recycling of waste in maximum possible amount, sale or
transfer to other entities and individuals, engaged in collection, storage and utilization of
waste as well as ensure environmentally safe dumping of waste which is not subject to
utilization;
Submit in the established manner information to local government bodies, specially
authorized government bodies for waste management about cases of pollution of environment
with waste and actions taken to rectify the problems;
Make in the established manner payments of levies for storage of waste;
Compensate for damages inflicted on lives, health and properties of citizens,
environment, and entities as a result of waste management.
Entities may have other duties in waste management under the legislation.
Article 17. Ensuring safety in waste management
Activities of entities in waste management must ensure safety to lives and health of
citizens and environment.
Activities of entities may be restricted, suspended or stopped in the established
manner in case of violation of requirements of the legislation on waste management resulting
in damages to lives and health of citizens or environment as well in case of generation of
hazardous waste due to lack of technical or other potentials in ensuring safety to lives and
health of citizens, environment.
Article 18. Establishment of norms in waste management
In order to ensure safety to lives and health of citizens, environment, to reduce
generation of waste, norms of waste generation and limits of storage of waste shall be worked
out. Norms of waste generation shall be worked out and approved by entities upon agreement
with specially authorized government bodies for waste management.
Waste management limits shall be worked out by entities and approved by specially
authorized government bodies for waste management.
The procedure for working out and approval of norms of waste generation and limits
of disposal of waste shall be established by the legislation.
Article 19. Environmental certification of waste
Waste, which is the item of trade, export/import operations as well as hazardous
waste, which is subject to transportation, must be environmentally certified for compliance
with sanitary standards and rules, environmental norms in waste management upon
completion of which owners of waste shall be provided with environmental certificates.
The procedure for environmental certification of waste shall be established by the legislation.
Article 22. Requirements for storage and dumping of waste
Storage of waste shall be carried out under sanitary standards and rules, requirements
of environmental safety and by methods ensuring rational utilization or transfer of waste to
other entities.
Waste dumping sites (except hazardous waste) shall be determined by local
government bodies in the manner established by the legislation.
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Dumping of wastes, for recycling of which relevant technical potentials exist, shall not be
allowed.
It shall be prohibited to store and dump waste on territories of populated areas of
environment protection, health-care, recreational and historic/cultural designation, within
water protection areas, in other places where hazards may arise to the lives and health of
citizens as well as to especially protected natural territories and sites.
Dumping of waste in depth of the earth shall be allowed in exceptional cases upon admissible
results of special examinations carried out in compliance with the requirements for ensuring
safety to lives and health of citizens, environment, and natural resources.
Article 23. Levies for disposal of waste
Levies shall be charged for disposal of waste at specially allocated and equipped sites.
Amounts of levies shall be determined in the established manner based on limits for disposal
of waste depending on the degree its hazards for lives and health of citizens and environment.
Article 24. Encouraging the activities in waste utilization and reduction of waste
generation
Entities and individuals developing and introducing technologies aimed at waste
utilization and reduction of waste generation and creating enterprises and workshops,
manufacturing equipment for recycling waste, taking joint participation in financing waste
recycling and reduction of levels of their generation shall be granted privileges under the
legislation.
Local government bodies may establish within their competence additional measure to
encourage activities in waste recycling and reduction of waste generation.
Article 25. Financing of actions aimed at utilization of waste and reduction of waste
generation
Financing of actions aimed at waste utilization and reduction of waste generation shall
be paid for by owners of waste. To finance these actions environment protection funds, extra
budgetary funds, voluntary contributions for entities and individuals as well as the Public
Budget of the Republic may be involved.
Article 26. State accounting of waste
Waste brought into and taken out of the country, existing waste, waste generated on
the territory of the Republic of Uzbekistan as well as transit waste shall be subject to state
accounting.
The state waste accounting form, the procedure for its submission shall be approved
by the Ministry of Macro-economy and Statistics of the Republic of Uzbekistan.
- 17 -
3. STUDY FIELD
Two juice producing plants in Uzbekistan and their organic wastes have been studied.
In these juice plants organic waste is produced in several sub processes such as inspecting,
washing, pressing and clarification. The main part of organic waste is created in the pressing
and decanting sub processes (see Figure 4.1). Organic wastes from juice processing are
collected and dumped outside the plant.
Figure 3.1. The map of The Republic of Uzbekistan [3].
”Meva”
”BagatSharbat”
Figure 3.2. Geographic locations of fruit juice plants [4].
- 18 -
3.1. “BAGAT-SHARBAT” juice producing Ltd. Co.
3.1.1. Fruit juice production process
Uzbekistan Republic Xorazm region Bagat district, “Bagat-Sharbat” juice producing
Ltd. Co.
“BAGAT-SHARBAT” juice producing Ltd. Co. was established on October 2001 in
Xorazm region in Uzbekistan. This plant produces 100% natural fruit and vegetable juices
with pressing process. As raw material they use apple, pear, carrot, and quince.
Products: 100% natural juices
Raw material: apple, pear, carrot, quince.
Producing capacity: 600-700 litres/hour
Raw material use: 2.5-3 kg raw material will be used for producing 1 liter fruit juice and 4-5
kg raw material for producing 1 liter carrot juice.
Annually 3500 t raw material will be used in processing for juice production.
In 2005: 1700 t of raw material was processed and the amount of organic waste was 1200t.
Moisture content of fruit waste is 75%, C:N ratio (The Carbon-to-Nitrogen Ratio) 35:1 and
Nitrogen content is 1,5%.
Organic waste from juice processing: 70- 75 % (w/w) of the raw material turns up as organic
waste.
Organic wastes are dumped outside the plant.
3.1.2. Energy consumption and economics
Natural gas
”Bagat-Sharbat” uses natural gas only for heating administration and operating buildings
seasonally in cold days and the amount is 4000-5000 Nm3 per year.
Price for 1 Nm3 natural gas is 40 Sums2 in Uzbekistan.
Annually cost of natural gas is 75-85 €
Steam (for pasteurization process) and electricity consumption of the plant are shown in
following Table 3.1. The plant buys steam and electricity from the government.
2
1 Sum=0.0007 €; 1€=1427.25 Sum (March 2006)
- 19 -
Table 3.1. Technological characteristics of “Bagat-Sharbat” juice plant
Current year (2005) Possibility
Capacity: can/h(250ml)
2000
4000-6000
Capacity: kg/h
600
1200-2000
Total Power:kW
25
50
Water Consumption:t/h
3
6
Steam Consumption: kg/h(0.4MPa) 50
150
Compressed Air: m3/min
Workshop Area: m2
0.6
400
0.6
250
3.2. “MEVA” Uzbekistan-Italy juice producing joint venture.
3.2.1. Fruit juice production process
Uzbekistan Republic, Xorazm region,
Xonqa district “Meva” Uzbekistan-Italy
juice producing joint venture.
Products: 100% natural juices
Raw material: apple, apricot, peach, tomato.
Producing capacity: 500-600 liter/hour
Raw material use: 2.5-3 kg raw material
will be used for producing 1 liter fruit juice.
Annually 1000-1500 t raw material will be in
processing for juice production.
Annually 150-200t organic waste will be
produced from juice production. Waste
weight is 15.1% (w/w) of raw material.
Figure 3.3. “Meva” Uzbekistan-Italy
juice producing joint venture (photo by
Akmal Shermetov)
Organic wastes from juice processing are
dumped outside the plant.
3.2.2. Energy consumption and economics
Figure 3.4. Vacuum boilers “Meva”
Uzbekistan-Italy juice producing joint
(photo by Akmal Shermetov)
Energy consumption of the plant is similar
to the BAGAT-SHARBAT” juice plant’s
energy consumption (see Table 3.1.).
This plant also uses natural gas for heating
buildings in cold days of the year. The amount
of natural gas they use is 3500 Nm3 per year.
- 20 -
4. FRUIT JUICE PROCESSING
4.1. Description of fruit juice production
Fruit and vegetable processing increases the shelf life of fruit and vegetables. The
preservation and conservation of fruit and vegetables is achieved by canning, drying, or
freezing, and by the preparation of juices, jams and jellies. The main steps consist of the
preparation of the raw material (cleaning, trimming and peeling) and pressing, squeezing,
cooking, canning, and freezing. Fruit and vegetable processing plant operation is often
seasonal.
Fruit juices are products for direct consumption and are obtained by the extraction of
cellular juice from fruit, this operation can be done by pressing or by diffusion. The
technology of fruit juice processing will cover two finished product categories:
• Juices without pulp ("clarified" or "not clarified");
• Juices with pulp ("nectars").
Juices obtained by removal of a major part of their water content by vacuum
evaporation or fractional freezing will be defined as "concentrated juices". Fruit juice drinks
have a fruit content ranging between 6 and 30 %, and also include water, fruit aromas, sugar
and, in some cases, food acids. Food acids are organic acids and are used to give the desired
sourness to food and drinks. Examples of food acids are malic or citric acid. Ready-made
mixtures of apple juice and mineral water count as fruit juice drinks although they have a fruit
content of 50 to 60 %. [5]
The simplified manufacturing steps of apple juice producing process include
following: receipt and weighing of raw materials; storage; inspecting; washing; peeling,
grinding, chopping; crushing; extraction; filtration; heating; cooling; preservation;
concentration; packaging and storage of finished products. All steps of processing of juice are
shown in Figure 4.1 and will be described below. Technological line for fruit juice producing
process and all technological equipments which are used in juice production plants are shown
in Appendix 1.
- 21 -
Harvesting
Transportation
Inspect/Analyses
Unload
Water
Inspect/ Sort/ Dry clean
Wash/ Cool/ Store
Bleaching
agents
Solid waste (injured raw
materials, leaves, earth, etc.)
Solid waste (injured raw
materials, foreign matters)
Waste water
Inspect/ Peel/ Core/ Deseed
Solid waste (peel, core, seed)
Chopping/ Grinding/ Pulping
Enzymes
Enzymatic Maceration
Pressing or Decanting/ Juice extraction
Enzymes
Residual solids (pulp,
pomace)
Depectinization and Clarification
Deaeration
Steam (not
for using)
Concentration
Pasteurization
Organic wastes from
fruit juice processing
Stem, stalks, rotten
fruits, peels, seeds, and
pomace
Clean stable juice
Bottling
Steam
Pasteurization
Warehousing
Transportation
Consumption
Figure 4.1. Material flow chart in juice producing
- 22 -
There are a number of unit operations involved in converting whole fruit to the desired juice:
Inspect/ Analysis
Raw material for juice is inspected for visible defects and foreign matter and then
analyzed for microbial load, pathogens, pesticide residues, colour, sugar, acid, flavour, or
other important safety and quality attributes.
Unload
Handling of fruit destined for juice to operation.
Inspect/ Sort/ Dry clean; Wash/ Cool/ Store
Inspection and removal of unsound
fruit is very important, more so than in
whole fruit processing. Prior to juicing,
the fruit can be washed, thoroughly
inspected and sometimes sized (fruitdependent). Dry pre-cleaning steps and
water recycling systems may be required
depending upon the availability and
sanitary quality of water. However,
weather and delivery conditions may
require the removal of dust, mud or
transport-induced foreign matter. Cooling
depends upon heat transfer from fruit to
air (possibly water). Cooling and cleaning
can involve physical removal of surface Figure 4.2. Washing conveyer in “Meva”
debris by brushes or air jet separation Uzbekistan-Italy juice producing joint
prior to washing with water.
venture (photo by Akmal Shermetov).
Inspect/ Peel/ Core/ Deseed
Inspection can be manual, contingent upon workers observing and removing defects or
automatic, effected by computer controlled sensors to detect off colour, shape or size. This
process is usually done by human eye, hand and mind recognizing rotten and unsuitable fruits.
Fruit with inedible skin and seeds must be treated more carefully than one that can be
completely pulverized.
Chopping/ Grinding/ Pulping
With soft or comminuted fruit a cone screw expresser or paddle pulper fitted with
appropriate screens serves to separate the juice from particulate matter. Where skin or seed
shattering is a problem, brush paddles can replace metal bars.
Enzymatic Maceration
Pulping is often followed by the addition of enzymes, which break down the cell walls
of the fruit and thus increase the amount of juice extracted. The enzymes known as pectinases
have already been used for many years. Enzymes which are used in fruit juice producing are
given in Appendix 2. Pre-treatment with a macerating enzyme with or without heating to
~60ºC and holding up to ~40 minutes can greatly increase yield [6].
- 23 -
Pressing or Decanting/ Juice extraction
In this step fruit juice is pressed from pulped raw material with help of decanters or
pressor. Decanter is a horizontal, cylindrical screen lined with press cloth material, with a
large inflatable tube in the centre that inflates and presses pulp up against the loath-covered
wall [see Figure 4.3.]. The whole assemblage is rotated after it is filled and closed and as the
tube is bedding inflated. Juice is expressed into a catch trough below and collected from a
drain. Pressure on the tube reaches a maximum of 6 atmospheres or approximately 600 kPa
[6]. Usually a press aid is needed to keep the pulp from adhering to the press cloth and
stopping the free flowing of the juice. Solid waste from juice extraction process is discharged
at the end part of decanter and can be reused for getting some additional juice extraction with
help of enzymes.
Depectinization and Clarification
For more fluid juices where cloud or turbidity is not acceptable primary extracted
juice must be treated further. Rapid methods such as centrifugation and filtration can produce
a clear juice. Juices where a cloud is desired generally do not require filtration; centrifugation
is adequate. In this process the main equipment is centrifuge for clarifying fruit juices [see
Figure 4.4.-4.5.].
One litre of juice with a dry matter content of 13% can contain 2-5g of pectin. The
pectin can be associated with other plant polymers and the cell debris. The cloudiness that
these cause is difficult to remove except by enzymic depectinization. After pressing, the juice
is transferred to a stirred holding tank. Pectinases such as Macer8™ FJ, Pectinase 62 L or
Pectinase 444L can be added to the juice and incubated typically at 40°C-50°C [7].
Deaeration
Deaeration can be accomplished by either flashing the heated juice into a vacuum
chamber (Figure 2.3.) or saturating the juice with an inert gas. Nitrogen or carbon dioxide is
bubbled through the juice prior to storing under an inert atmosphere. Clearly, once air is
removed or replaced by inert gas, the juice must be protected from the atmosphere in all
subsequent processing steps. Deaeration, especially flashing off at high temperature, can also
remove some desirable volatile aroma.
Concentration
The juice is evaporated to 20 to 25°Brix at 90°C and the aroma captured by fractional
distillation. This concentrate is brought to about 40 to 45°Brix at about 100°C. In the third
stage it is heated to about 45°C and concentrated to about 50 to 60°Brix. The final heating at
45°C will bring it to 71°Brix. The concentrate is cooled to 4-5°C and standardized to 70°Brix
and then bottled and barrelled.
Pasteurization
The most important method of preserving apple juice is pasteurization, which involves
heating the juice to a given temperature for a length of time that will destroy all organisms
that can develop, if juice is put hot into containers that are filled and hermetically sealed.
Flash pasteurization is, true to its name, the rapid heating of juice to near the boiling point
(greater than 88°C) for 25 to 30 seconds. Steam or hot water passes the juice between plates
or through narrow tubes that are heated.
- 24 -
Separators and Decanters
The
main
waste
generators in juice producing
process are separators and
decanters
Separators and decanters have
been indispensable equipment
for decades in the production
of fruit and vegetable juices,
beer,
wine
and
other
beverages. In the decisive
process stages, continuously
operating centrifuges ensure
economical processing and
high quality of the end
product. Centrifuges which Figure 4.3. Decanter [8]
continuously separate solid
particles suspended in juice have now been in use for more than 35 years.
Continuous solids and liquid separation is a very important aspect at various points of making
fruit and vegetable juices. Separators have been used for separating tissue particles of the fruit
out of the press juice or fining agents during the clarification process, decanters are now also
used as a substitute for presses. Separators and decanters are systems capable of increasing
the yields during extraction and avoiding processing losses in pome, stone and berry fruits
plus grapes and vegetables [Figure 4.3-4.5]. [8]
Figure 4.5. Separator illustration [19]
Figure 4.4. Separator [ 18]
4.2. Organic waste from fruit juice processing
The fruit and vegetable industry typically generates large volumes of effluents and
solid waste. The amount of the by-product during processing is usually 30-50% depending on
- 25 -
the fruit and we can distinguish two groups of by-products, the first is originated from preprocessing including stems, stalks and rotten fruits from sorting processes, and the second
group is the processing by-products such as seeds, pulp, pomace and peels. The effluents
contain high organic loads, cleansing and blanching agents which are added in washing and
peeling processes , salt, and suspended solids such as fibers and soil particles. They may also
contain pesticide residues washed from the raw materials. The main solid wastes are organic
materials which are effluents in pressing process, including discarded fruits and vegetables.
[9]
Processing of fruits produces two types of waste
• Solid waste of peel/skin, seeds etc.,
• Liquid waste of juice and wash waters.
In some fruits the discarded portion can be very high. Therefore, there is often a
serious waste disposal problem. Odour problems can occur with poor management of solid
wastes and effluents, which can lead to problems with flies and rats around the processing
room, if not correctly dealt with.
Hazardous By-products
In fruit and vegetable processing process industry a certain %age of solid by-products
are considered hazardous. For example, residues from fertilizers or pesticides may be in
peelings, pulp after pressing or other by-products from fresh produce. Chemicals used in fruit
and vegetable processing plants for treatment, bleaching or cleaning of produce may also
generate by-products with toxic, hazardous wastes (see Appendix 3).
4.2.1. Characteristics of Organic Waste from Fruit juice processing
Organic waste from fruit juice producing process has following kind of characteristics:
•
•
•
•
Low heating value (0,004 MJ/kg (see Table 4.3))
High moisture content (62-88% (see Tabe 4.1.))
Odour
Might be hazardous (pesticides, blanching agents (see Appendix 3))
Table 4.1. Nitrogen and water contents and C:N ratios of some organic residues [10].
Organic Residue
N content
--------%--------0.9-2.6
2.5-4
13-14
6.5-14.2
Fruit waste
Vegetable waste
Slaughterhouse waste
Fish waste
Refuse
(mixed
food,
0.6-1.3
paper etc.)
2-6.9
Sewage sludge
2.0-6.0
Grass clippings
Water content
---------- % ---------62-88
30-85
10-78
50-80
C:N
10-70
34-80
72-84
30-70
5-16
9-25
- 26 -
20-49
11-13
3-3.5
2.6-5.0
In order to make decisions of designing a treatment method for organic waste there
should be done an ultimate analysis of organic waste content. The ultimate analysis of a waste
component typically involves the determination of the % C (carbon), H (Hydrogen), O
(Oxygen), N (Nitrogen), S (sulphur), and ash. The results of the ultimate analysis are used to
characterize the chemical composition of the organic waste, emissions during combustion of
organic waste and also used to define the proper mix of waste materials to achieve suitable
C:N ratios for biological conversion processes. Data on the ultimate analysis of individual
combustible materials are presented in Table 4.2. Estimation of chemical composition of fruit
waste materials using the data is given in Table 4.3.
Table 4.2. Typical proximate analysis and energy data for materials found in residential,
commercial, and industrial solid wastes [11]
Proximate analysis, % by waste
Type of
waste
Fruit
wastes
Energy content, MJ/kg
Moisture
Volatile
matter
Fixed
carbon
Noncombustible
As
collected
Dry
Dry ashfree
78.7
16.6
4.0
0.7
0,004
0,0186 0,0193
Table 4.3. Typical data on the ultimate analysis of the combustible materials found in
residential, commercial, and industrial solid wastes [11].
Type of
waste
Fruit
wastes
% by weight (dry basis)
Carbon
Hydrogen
Oxygen Nitrogen
Sulphur
Ash
48.5
6.2
39.5
0.2
4.2
- 27 -
1.4
5. METHODS OF PROCESSING ORGANIC WASTE
There are a variety of ways to treat wet organic wastes (Figure 5.1.). In this section they
are explored and compared with each other and some of the issues associated with the various
approaches are considered.
Wet organic wastes
from juice producing
plants
Animal
feed
Incineration
Direct
land
spreading
Land
filling
Composting
Anaerobic
fermentation
Figure 5.1: Treatment options of wet organic waste
5.1. Animal feed
Recovering food discards as animal feed is not new. In many countries farmers have
traditionally relied on food discards to feed their livestock. Culled fruits and vegetables, fruit
pulp after squeezing juice from raw material, sugar beet pulp, molasses, and spent brewer's
grains are also commonly used as animal feeds for beef, dairy cattle, and hogs.
The value and quality of by-products as feed are well known and, subject to market
availability, they are easily sold. Farmers may provide storage containers and free or low-cost
pick-up service.
Before applying food industry by-products for animal feed they must been carefully
analyzed for nutrient, protein content and calculated energetic value per unit. According to
analyzes by-products must be treated to good condition in order to use them efficiently in the
animal feeding process.
Characteristics of feeds vary with nutrient composition and moisture content.
Sometimes it is necessary to remove moisture from the feeds by dehydration or to store the
wet feeds in silos. Substitution of by-products for other feeds in animal diets must be done
carefully to prevent adverse effects on animal performance.
- 28 -
If there is a rich content of nutrients in organic waste it can be useful for animals’
health. Food waste typically has nutrient content composition (C:N ratio)15:1, fruit waste
35:1 (see Table 4.1).
Most feeds made from food processing by-products cannot completely replace other
animal feeds, nor can all species equally utilize the same by-product feeds. For cattle, a
typical rate of substitution for energy concentrates is 10 to 25 % in the dairy ration, and 10 to
30 % for beef in feedlots. By-product protein concentrate substitutes for 10 to 25 % of the
usual ration for dairy cows. Roughage is measured in weight fed, with acceptable substitution
from 20 to 35 pounds per cow per day for most by-product roughage feeds listed. [12]
5.1.1. Disadvantages of using of organic waste as an animal feed
Because of organic waste processed from juice producing contain cleansing and
blanching agents, salt, and suspended solids such as fibers and soil particles, also pesticide
residues washed from the raw materials, it can be harmful to animals’ health.
The possibility of toxicity from pesticides on crops or heavy metals from processing
and fruit cannery sludge is of particular concern to food processors when they redirect their
waste by-products into feed or food. Testing for chemical residues in by-products may be
necessary because of the potential for concentration of toxins. Some by-products have
naturally occurring chemicals that cause toxic results. For example, apple pomace with
nonprotein nitrogen may lead to weight loss, birth defects, and reproductive problems when
fed to cattle [12].
5.2. Incineration
The incineration of waste is a hygienic method of reducing its volume and weight
which also reduces its potential to pollute. Generating electricity or producing hot water or
steam as a by-product of the incineration process has the dual advantages of displacing energy
generated from finite fossil fuels and improving the economics of waste incineration, which is
the most capital-intensive waste disposal option. Residues from incineration processes must
still be land filled, as must the non-combustible portion of the waste stream, so incineration
alone cannot provide a disposal solution.
But not all wastes are suitable for combustion. If the moisture content is very high
(above 65-70%) it will be non efficient and not profitable.
5.2.1. Advantages and Disadvantages of waste incineration method
Advantages of waste incineration
ƒ
ƒ
ƒ
ƒ
ƒ
Can convert a large proportion of the calorific value of waste into usable energy
Reduces volumes of waste by up to 90% and the weight of waste by 70% [13]
Reduces demand for landfill and other waste management capacity
Stabilises putrescible waste, reducing the potential of leachate and landfill gas
production at landfills
More effective energy recovery than anaerobic digestion and landfill gas
- 29 -
Disadvantages of waste incineration
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
Potential for polluting gaseous and liquid (wet scrubbing systems only) emissions to
atmosphere
Produce fly ash and air pollution control residue that are special wastes
Potential for dust and odour problems during storage of waste prior to incineration
Changes in calorific value of the waste can cause changes in the operational costs
Negative public perceptions lead to planning problems
A high level of commitment to incineration may inhibit waste minimisation and
recycling
Not suitable for wastes with high water content.
5.3. Direct land spreading
High costs and capacity pressures on landfills and wastewater treatment systems have
caused many managers of these systems to seek alternatives for organic waste. Composting
has become a popular option, but it can be expensive and does not work well for processing
high-moisture waste. Increasingly, direct land application of organic waste is seen as a lowcost option that allows a waste product to be used beneficially for crop production.
Many types of organic waste products are being directly applied to land. Agricultural
waste such as manure and livestock bedding has been land applied for centuries. Land
application is the primary method of utilizing sewage sludge bio solids from wastewater
treatment systems. Today however, waste products considered for land application include
yard waste, supermarket vegetable waste, restaurant and institutional food waste, grain
handling waste, a wide variety of waste products from the food processing industry, and many
other sources [14].
Land application of organic waste materials such as sewage sludge, non-sewage
sludge, food processing, and other solid waste provides valuable nutrients that help to enrich
soils and restore the opportunity for improved plant growth. The beneficial use of these
materials not only serves to provide an effective soil amendment, but also helps divert
thousands of tons of waste from landfills and incinerators, saving cost of disposal, while
preserving valuable landfill space and eliminating the potential for harmful emissions to the
air we breathe.
Organic waste products tend to vary widely in content. It ranges from nearly dry
products to materials that are mostly water. The only thing the products have in common is
that they all contain at least some organic material, and they may contain from minute to
significant amounts of nutrients beneficial to plants. Organic waste products also may contain
components that can be detrimental to crop production and soil health, such as soluble salts,
fats, weed seeds, and pathogens, and may vary in pH (relative acidity or alkalinity). Some
may have a wide carbon-nitrogen ratio (C-N) so that microbial action may temporarily tie up
plant available nitrogen in the soil water. Wastes from processing operations could
potentially, though rarely, contain heavy metals and many other compounds, depending on
the particular process and product. Some products may result in objectionable odours or may
attract rodents, birds, or other animals [14].
Because of the wide variation in composition, it is impossible to make specific
recommendations that apply to all organic waste products. Nevertheless, there are some
general factors that should be considered in making land application decisions.
- 30 -
Laboratory analysis of organic waste content
It is very important to analyze the content of organic waste before applying it for land
spreading. Typically such analysis would include, at a minimum, the nutrients nitrogen (C:Ntotal, organic, and ammonia), phosphorus, and potassium, and pH. According these analyses
farmers can determine the appropriate application rate, which is suitable to soil content and
useful for their crop. Because if too little is applied, it will be necessary to add other fertilizer
for optimum crop production, if too much is applied, nutrients may be wasted and, in some
cases, be environmentally harmful.
Soluble salts and pH
Some organic waste products, particularly food processing waste, can contain
considerable soluble salts. Soluble salts in the soil are measured by determining the capacity
of a solution extracted from a saturated paste of a soil sample to conduct electricity.
Growth of most plants is progressively reduced as the salt level in the soil increases. Some
agricultural areas of Uzbekistan have large areas of soil naturally high in soluble salts. Both
the soil and the waste should be tested for soluble salts before application. High-salt wastes
should be applied with care to soils that are already above the 2mmho/cm level. For other
soils, regular soil tests for soluble salts should be used to ensure that salt levels do not rise to a
level that limits plant growth [14].
Most crops prefer a fairly neutral soil pH level. At normal application rates, organic waste
usually will not have a major impact on soil pH. Nevertheless, to be safe, test both the soil
and the waste for pH to ensure that the applied material will not further aggravate an existing
very high or low soil pH.
Odours, pests, and pathogens
Odours can be a problem when some organic wastes are applied to land. Some
material may have inherent unpleasant odours. Other material may become more odorous
after it is applied and begins to decay. It is helpful to immediately incorporate any applied
material into the soil [14].
Sometimes odours are difficult to avoid, but complaints can be minimized by providing
adequate buffer zones between the application area and residences or other human activity.
Transportation routes should be followed that avoid passage though concentrated residential
areas. Some organic material, especially food waste, may attract rodents, birds, and other
animals. Again, incorporation into the soil is the best practice.
Water Quality
Both surface water and groundwater must be protected in a land-application program.
Nitrogen and phosphorus are the primary water contaminates from sludge. Both nutrients are
necessary for plant growth and can be controlled in an environmentally sound manner.
Surface waters can be protected by using conservation practices that reduce erosion and
prevent the movement of sediments and accompanying nutrients from the site of application
to ponds, lakes, or streams. Groundwater contamination by nitrogen may occur if the nitrogen
applied in sludge is greater than the crop requires [14].
- 31 -
Application equipment
Frequently, application of waste material will require the use of specialized equipment
not available on many farms. Liquid materials can often be injected directly into the soil.
Injectors will need to be adjusted or specially adapted to the type of material. Very wet solids
can be difficult to spread evenly. Typical manure spreading equipment may work for this type
of material, but will often require adjustment or adaptation, especially if the material contains
large pieces, as in some food waste. [14]
5.3.1. Advantages and disadvantages of Land spreading method
Land application offers several advantages as well as some disadvantages that must be
considered before selecting this option for managing bio solids.
Advantages
Land application is an excellent way to recycle wastewater solids as long as the
material is quality controlled. It returns valuable nutrients to the soil and enhances conditions
for vegetative growth.
Land application is a relatively inexpensive option and capital investments are generally
lower than other waste management technologies.
Disadvantages
Although land application requires relatively less capital, the process can be labour
intensive.
Land application is also limited to certain times of the year, especially in colder
climates. Bio solids should not be applied to frozen or snow covered grounds, while farm
fields are sometimes not accessible during the growing season. Therefore, it is often necessary
to provide a storage capacity in conjunction with land application programs.
Weather can interfere with the application, even when the time for land application
process is right (for example, prior to crop planting in agricultural applications). Spring rains
can make it impossible to get application equipment into farm fields, making it necessary to
store bio solids until weather conditions improve.
Another disadvantage of land application is potential public opposition, which is
encountered most often when the beneficial use site is close to residential areas. One of the
primary reasons for public concern is odour [15].
By using this method organic waste also may have negative effects on both surface
and ground water due to its nutrient content. After that environmental and public health
problems may occur. If organic waste is rich in nutrient content, surplus nutrients can be
washed down from agricultural fields to ground and surface water.
5.4. Land filling
Landfill is the oldest and the most widely practised method of disposing of solid
waste. Properly constructed and operated landfill sites offer a completely safe disposal route
for municipal solid wastes, typically at the lowest cost compared to other disposal options. It
is not necessary on health or environmental grounds to invest in other disposal methods if
suitable sites are available for landfills. Uncontrolled dumping of waste, which does not
- 32 -
protect the local environment, however, should be replaced as soon as possible with
controlled sanitary land filling or other treatment and disposal methods.
Most alternative waste treatment and disposal options, such as recycling or
incineration, rely on landfill for the disposal of wastes that are unsuited to the process, as well
as for the process residues. Some landfill capacity is therefore indispensable for every region,
and will continue to be necessary in the foreseeable future, despite any technological
advances which may be made.
5.4.1. Land filling method’s advantages and disadvantages
Advantages
ƒ
ƒ
ƒ
Normally the lowest cost waste disposal method in present market conditions
Methane can be collected and used for power generation
Can be used as a restoration method for mineral extraction sites
Disadvantages of Land filling
The organic waste component of landfill is broken down by micro-organisms
(bacteria, microbes, germs) to form a liquid ‘leachate’ which contains bacteria, rotting matter
and maybe chemical contaminants from the landfill. This leachate can present a serious
hazard if it reaches a watercourse or enters the water table. Digesting organic matter in
landfills also generates methane, which is a harmful greenhouse gas, in large quantity.
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
Putrescible waste produces landfill gas and leachate
Potential dust, odour and vermin problems if site is not well managed
Stabilisation of landfill site is estimated at 50+ years
Can have detrimental effects on the landscape and local amenities
Increasing opposition to the location of sites
Low cost landfill is likely to inhibit waste minimisation and recycling
Major landfill tax liabilities
5.5. Composting
Composting is the aerobic decomposition of organic materials in the thermophilic
temperature range (40-65°C) (Figure 5.2.). Composting is simply the method of breaking
down organic materials in a large container or heap. The decomposition occurs because of the
action of naturally occurring micro organisms such as bacteria and fungi. Small invertebrates,
such as earthworms and millipedes, help to complete the process. The composted material is
odourless, fine-textured, and low-moisture and can be bagged and sold for use in gardens, or
nurseries or used as fertilizer on cropland with little odour or fly breeding potential.
Composting improves the handling characteristics of any organic residue by reducing its
volume and weight and can kill pathogens and weed seeds. Under controlled conditions,
however, the process can be speeded up.
- 33 -
Figure 5.2. The Composting Process [16].
In composting, provided the right conditions are present, the natural process of decay
is speeded up. This involves controlling the composting environment and obtaining the
following conditions:
•
•
•
•
The correct ratio of carbon to nitrogen. The correct ratio is in the range of 25 to 30
parts carbon to 1 part nitrogen (25:1 to 30:1). This is often seen as being roughly equal
amounts of "greens" and "browns". The C:N ratio can be adjusted by mixing together
organic materials with suitable contents.
The correct amount of water. Micro-organisms have a liquid rather than a solid diet
and therefore the compost pile should be kept moist at all times. On the other hand, a
wet compost pile will produce only a soggy, smelly mess.
Sufficient oxygen. A compost pile should be turned often to allow all parts of the pile
to receive oxygen.
The optimum pH level of the compost is between 5.5 and 8 [see Table 5.1.
Recommended conditions for rapid composting].
- 34 -
Table 5.1. Recommended conditions for rapid composting [16].
Condition
Carbon to nitrogen ratio
Water content
Oxygen concentration
Particle size (diameter)
Reasonable range
20:1 - 40:1
40 - 65%
5%
1/8 - 1/2 inch
pH
Temperature
5.5 - 9.0
44 - 66oC
Preferred range
25:1 - 30:1
50 - 60%
5 -15 %
Depends
on
material
6.5 - 8.0
55 - 60oC
the
In these conditions, bacteria and fungi feed and multiply, giving off a great deal of heat. In
well managed heaps, this temperature can reach as high as 600C, which is sufficient to kill
weed seeds and organisms that cause disease in plants and animals. While the temperature
remains high, invertebrates are not present in compost heaps, but when the temperature drops,
the invertebrates enter the heap from the surrounding soil and complete the process of
decomposition [17].
5.5.1. Composting method benefits and disadvantages
Composting has many benefits;
•
•
•
•
•
•
It provides a useful way of reclaiming nutrients from organic refuse
Improves the condition of soils (can be used as soil improver on farmland or in the
garden)
Reduces demand and saves valuable landfill space and possible contamination of land
and water due to landfill ‘leachate’
Recycling of nutrients usually requires less energy than the use of virgin materials
Control of pathogens from waste and wastewater
Saving of resources such as plant nutrients and water (by using it as a liquid fertilizer)
Also, this method has some disadvantages like:
•
•
•
•
•
Requirements for separation and screening
Some source materials can be unsuitable because of persistent contamination
Requires controlled conditions and careful management to produce a successful end
product
Can produce odour and leachate problems if not contained
Health, safety and amenity issues need to be addressed
5.6. Anaerobic Fermentation
During fermentation the disintegration of the organic substances is performed under
exclusion of oxygen inside of a completely capsulated digester.
- 35 -
Fermentation requires a liquid media with a dry-matter-content from 8-12%. Since
bio-wastes have a dry-matter-content of 20-25% in average, it has to be suspended in water
prior to fermentation.
The process is divided into two principal phases and four stages (Figure 5.3.):
The 1st phase is a hydrolisation process where facultative anaerobic bacteria start the
hydrolisation and disintegration of the volatile organic substances.
Complex organic compounds are split under production of organic acids, CO2, H2S and
alcohol. Dissolved oxygen is consumed by the bacteria, nitrates and sulphates are reduced.
The pH value is lowered.
In the 2nd phase, methane bacteria digest the products of the metabolism of phase 1. Final
products of the process are methane gas, CO2, and mineral salts. Due to the reducing
atmosphere inside the fermenter and the production of ammonium out of the anaerobic
degradation of proteins, the pH-value is raising continuously.
The pH-value of the fermented substrate ranges from 7.5 to 8.5.
Figure 5.3. The anaerobic process - a four stage process
Fermentation plants can be designed as single stage fermenters, where both phases of
the process are performed in one reaction chamber, or as dual-stage fermenters, where the
acidification and the methane production are done in separate tanks.
In contrary to the fast growing aerobic bacteria, methane bacteria are not present in the
initial substrate, but have to be bred inside the fermenter. Degradation rates of organic
substances are very high in between the temperature ranges where methane bacteria have their
- 36 -
maximum activity. Mesophilic methane bacteria have a temperature optimum of about 32°C
to 35°C, while thermophilic stems require substrate temperatures of 50°C to 55°C [18].
Beside the temperature, degradation rates depend mainly on volatility of the organic
substances, the specific organic load of the fermenter
(kg of organic dry matter per m3 of fermenter
volume) and the retention time of the substrate inside
the fermenter.
Gas yields are directly correlated with the
decomposition rates. Each substrate has a specific
gas yield expressed in litres of biogas produced per
kg of decomposed organic matter (see appendix 2).
The effluent of the fermenter is a homogeneous,
nearly odourless liquid with a dry matter content of
about 5-8% and a temperature of 35°C. There is only
little reduction in volume (approx. 2%). As a result of
the mineralization, plant nutrients are converted in
mineral salts, which are well available to the plants.
The substrate might be either used directly as a liquid
Figure 5.4. Thermophilic
fertilizer or composted.
Methane Bacteria [31]
So the anaerobic digestion process produces three useful products:
• Firstly, biogas, which can be used as a fuel to produce electricity.
• Secondly, a liquid which can be used as agricultural fertiliser.
• Thirdly, a solid which can be used as a soil conditioner.
5.6.1. Advantages and disadvantages of anaerobic fermentation method
Advantages
•
•
•
•
•
•
•
•
Use of a source of renewable energy
High degree of automatisation and comparatively low running costs
No odour annoyance
Little space requirements
Possibility of using remaining inert material as a fill or soil conditioner
Produces biogas for energy production
Prevents putrescible waste from being landfilled and as a result can help reduce the
production of landfill gas and leachate
Reduces demand for landfill and other waste management and capacity
Disadvantages
ƒ
ƒ
ƒ
ƒ
ƒ
Requires careful screening to remove contaminants, particularly metals
Requires controlled conditions and careful management to optimise gas production
Produces a residue that may require land filling if it contains hazardous compounds
Gas may require clean up prior to use
Solid residues may ultimately require land filling if markets are unavailable
In Table 5.2 differences between aerobic and anaerobic processes are shown.
- 37 -
Tab 5.2. Comparison of aerobic composting and anaerobic digestion processes for
organic waste processing [11, 18]
Characteristic
Aerobic processes
Anaerobic processes
Energy use
Net energy consumer
(20-100 kWh/t)
Net energy producer
(300-600 kWh/t)
End products
Humus, CO2, H2O
Sludge, CO2, CH4
Volume reduction
Up to 50%
Up to 50%
Processing time
20 to 30 days
20 to 40 days
Primary goal
Volume reduction
Energy production
Secondary goal
Compost production, waste
stabilization
Volume reduction, soil fertilizer
production, waste stabilization
Sanitation
Guaranteed under consideration
of legal standards
Guaranteed under consideration
of legal standards
Emissions
High (odours, ammonia,
methane, nitrous oxide,
hydrogen sulphate, germs)
Low (odours, ammonia)
- 38 -
6. BIOGAS PRODUCTION
6.1. Biogas
Biogas is a gas generated from the anaerobic digestion of organic waste. It consists of
Methane-CH4 (50-70%), carbon dioxide-CO2 (30-40%) with the remaining gases being: H2,
O2, H2S, N2 and water vapour. A typical analysis of biogas is shown in the following table:
Table 6.1. Analysis of Biogas content [19]
Substances
Symbol %age
Methane
CH4
55 - 70
Carbon Dioxide
CO2
30 - 40
Hydrogen
H2
5 - 10
Nitrogen
N2
1-2
Water vapour
H2O
0-3
Hydrogen Sulphide H2S
Traces
Methane is a greenhouse gas that is in fact more harmful than carbon dioxide. Carbon
dioxide, however, counts for the greatest increase of the greenhouse effect since such large
quantities are produced when fossil fuels are burned. Approximately 20 % of the increase is
made up of methane. It is therefore important to recover energy rich biogas and nutritious bio
fertilizer through anaerobic digestion instead of disposing this organic waste with other
treatment methods and thereby missing out on the benefits of biogas.
6.2. Gas Production
Biogas develops through anaerobic fermentation. During this process, organic substances are
decomposed by micro organisms. The substances added to the system produce the biogas in
an oxygen-free environment. In the first step, the organic substances are divided into
molecular components (sugar, amino acids, glycerine and fatty acids).
Micro organisms convert these intermediate products into hydrogen and carbon dioxide,
which are then transformed into methane and water according to the equation :
Organic matter(s) + H2O (l) + nutrients
new cells + resistant organic
matter(s) + CO2 (g) + CH4 (g) + NH3 (g) + H2S (g) + heat
- 39 -
To ensure optimal biogas production, the three groups of micro-organisms must work
together. In case of too much organic waste, the first and second groups of micro-organisms
will produce a lot of organic acid which will decrease the pH of the reactor, making it
unsuitable for the third group of micro-organisms. This will result in little or no gas
production. On the other hand, if too little organic waste is present, the rate of digestion by
micro-organisms will be minimal and production of biogas will decrease significantly. Mixing
could aid digestion in the reactor but, too much mixing should be avoided as this would
reduce biogas generation.
In practice, about 50% of the carbon theoretically available for gas production is
converted into gas. A metric ton of waste will normally yield about 50-70 m3 of gas per
digestion cycle, depending upon the proportion of organic matter and the carbon content of
the waste.
The digestion cycle will be shorter at high temperatures than at low temperatures, and the
daily yield per ton of material will be greater. Considerably greater digester-capacity is
required to produce a fixed amount of gas at a temperature of about 20°C than at temperature
of 30-35°C. In Table 5.2 gas producing period at different temperatures is shown:
Table 6.2. Gas production per ton of organic waste according to different temperatures
[20]
Temperature
(°C)
15
20
25
30
35
Gas production
(m3 per day)
0.150
0.300
0.600
1.000
2.000
Digestion period
(months)
12
6
3
2
1
6.3. Which materials can Biogas be made from?
Biogas is gained from organic materials. The origin of the substrates can vary, ranging from
food industry organic wastes, livestock waste, harvest surplus, vegetable oil remains, to
materials from household organic waste collection containers. The evaluation of materials for
implementation in the biogas process depends on their potential attainable yield. In figure 6.1
and table 6.3 the potential biogas yield from different organic materials are shown.
- 40 -
Figure 6.1. Biogas yield potential from different organic materials [21]
Table 6.3. Potential biogas production from fruit and tomato processing organic wastes
[21]
Feedstock
Hydraulic
retention time
Methane yield
(m3kg-1 VS)
8
16
20
24
16
16
16
Organic
loading
rate
(kg VS m-3d-1)
3.8
3.8
3.8
3.8
5.7
7.6
9.5
Fruit wastes
Tomato processing waste
24
4.3
0,420
0.030
0.250
0.320
0.190
0.110
0.040
0.420
6.4. Factor Affecting Gas Generation
The production of biogas is a natural process that functions in suited facilities. To ensure a
constant generation of gas, the following factors should be considered:
•
•
Organic substrates must be able to be biologically decomposed by micro organisms.
The substrate should contain only a minimum of microbiological restrictors.
The temperature during the decomposing process must be within a certain range (35°
to 55°C).
- 41 -
•
•
•
•
•
Organic waste should be sufficient at all time.
Daily input of waste should conform to reactor size. Too much input will reduce the
gas generation rate.
Digestion period (retention time) should be about 15-35 days. pH within reactor
should be about 7.0-8.5. Too low pH will inhibit gas production.
The fermentation must take place in an area sealed off from air and light.
The fermentation tank must be mixed at regular intervals.
6.5. Benefit of Biogas and Biogas Technology
With biogas technology the following benefits will be obtained:
• Energy
Biogas is an energy rich fuel and can be used to produce heat and power and can also be used
as a fuel alternative to wood, oil, liquefied petroleum gas (LPG) and electricity. Compared to
the use of diesel for vehicles, biogas emits 80% less hydrocarbons and 60 % less nitrogen
oxides. The concentration of particles and dust is also negligible when biogas is burned.
The part of biogas which can be used for energy production is methane. In combined heat-topower-couplings it is converted into electricity and heat. The mechanical power generated by
the processing of the biogas in the combined heat-to-power-couplings is converted into
electricity by generators. The overall efficiency of the energy is about 80 to 90 %. Generated
electricity is used for powering the facilities in the plant (for running fruit juice plant
operations) and to provide electricity in local areas. Heat is used directly for the heating of
accommodations or for warm water preparation.
Perhaps the easiest way to use biogas is directly for heating. This is because, for this purpose,
no pre-treatment other than the removal of water is required. Biogas is usually used for
heating buildings in conjunction with a biogas plant, but surplus heat can also be directed into
the district heating network.
• Agriculture use
Sludge from the biogas reactor could be used as compost. Organic nitrogen from waste will
be transformed into ammonia nitrogen, a form of nitrogen which plants can easily uptake.
• Protect environment
There are many environmental benefits. Biogas is an efficient, renewable, non-fossil fuel with
a high methane content that does not compound the greenhouse effect.
Using a hygenisation step in the organic waste treatment will reduce the risk of infection from
parasite and pathogenic bacteria inherent in the waste. Odour and flies will be significantly
reduced in the area, and water pollution created by the dumping of waste can also be
prevented.
Biogas technology never runs out
Animal and food waste and sewage sludge go through natural anaerobic digestion in an
oxygen-free environment. This means that all animal and human waste can be broken down
by a bacterial process. The rest products of the anaerobic digestion are returned to nature, so
biogas is included in the category of renewable energy sources. In short, as long as humans
and animals exist on the planet, biogas will go on being produced.
- 42 -
Biogas has a variety of applications. Table 6.4 below shows some typical applications of
biogas. Small-scale biogas digesters usually provide fuel for domestic lighting and cooking.
Table 6.4. Some biogas equivalents [22]
Application
1m3 Biogas equivalent
Lighting
Cooking
Fuel replacement
Shaft power
Electricity generation
Equal to 60-100 watt bulb for 6 hours
Can cool 3 meals for a family of 5-6
0.7 kg of petrol
Can run one horse power motor 2 hours
Can generate 1.25 kilowatt hours
electricity
of
Biogas as vehicle fuel
Relatively speaking, biogas requires considerable processing if it is to be used as vehicle fuel.
The energy value has to be raised by separating carbon dioxide in order to achieve a methane
content of between 95 and 99 %. Water, impurities and particles must be removed to avoid
mechanical as well as environmental damage. Finally, the gas has to be compressed. Although
significant work is needed to upgrade methane gas to biogas fuel, the environmental benefits
are so great that in Sweden an increasing number of filling stations are opening throughout
the country. There are at present between 40 and 50 biogas stations in Sweden and the aim is
to have 100 before the end of 2007. Approximately 4,000 vehicles now run on biogas fuel on
Swedish roads. Together with Switzerland, Sweden has come furthest as far as the use of
biogas for fuelling vehicles is concerned.
The biogas potential in Sweden amounts to 17 TWh, of which the agricultural sector accounts
for 80 %. At present, we use a total amount of energy of approximately 400 TWh per annum.
If we were to exploit the whole potential, this would correspond to a substantial proportion of
the total diesel usage in Sweden, or about 20 % of the fuel requirement for the country’s
passenger cars.
Biogas recovery can be a significant factor with regard to Sweden’s ability to fulfil the EU’s
motor fuel directive, the aim of which is for an equivalent of 5.75 % of sold motor fuel to be
biofuel by 2010.
Biogas in Sweden
Sweden is one of the leading countries in the area of biogas technology.
In 2003 the total production of biogas in Sweden was equivalent to approximately 1.5 TWh
per annum. Production was carried out at about 140 sewage works, 60 landfills and at around
ten biogas plants throughout the country. The Parliament has decreed that, by 2010 at the
latest, a minimum of 35 % of food waste from households, institutional kitchens, restaurants
and shops will be recycled biologically.
- 43 -
6.6. Treatment of the Gas
As said above the gas needs to be refined, with water being removed to different extents
depending on how the gas is to be used. There are at present four separate upgrading
technologies. The most common is water scrubbing, which is based on gases such as carbon
dioxide, hydrogen sulphide (H2S) and ammonia being soluble in water than.
6.6.1. Desulphurisation of the Biogas
Cleaning of the biogas from hydrogen sulphide is also recommended because of the very
corrosive effect of hydrogen sulphide which biogas contains. In principle, there are two basic
procedures:
•
•
Absorption of hydrogen sulphide by ferric oxide and
Microbial desulphurisation by the addition of air.
In the later process, about 4% of the surrounding air is injected into the biogas with an air
pump which bacteria use to oxidise the hydrogen sulphide to elementary sulphur. The sulphur
simply turns into precipitation.
6.7 Gas requirements and storage
The gas is produced continuously, day and night, but it is used largely during the
daytime for heating in cold days in Uzbekistan. Therefore it is necessary to provide storage
facilities so that the gas will not be wasted and will be available when needed. The storage
capacity should be estimated to meet peak demands. For small installations, storage capacity
of about one day’s requirement of gas should be provided. The volume of the gas-holder
should not be less than about 2 m3, even for very small installations.
The gas-holder may be circular or square and should be provided with a water seal to
prevent the escape of gas or admission of air. The weight of the floating cover of the gasholder provides the gas pressure.
6.8. Difference between of Biogas and Natural gas
Natural gas was formed 150 million years ago in pockets of the earth crust and in porous rock.
It is a non-renewable, fossil fuel recovered from deep gas wells. Biogas is the product of the
natural biological breakdown of crop and animal waste when the supply of oxygen is
restricted. This is a continuous, ongoing process in nature and it also takes place under
controlled conditions in our sewage plants and landfills.
Natural gas and biogas both contain methane. If biogas is refined, with everything except
methane being removed, its properties are then similar to those of natural gas (See Appendix
4). This means that the technology that has been developed for the distribution and use of
natural gas can also be used for biogas.
- 44 -
Because of the aim to replace used natural gas in juice plant to biogas different fuels are
compared with biogas by their calorific value In following diagrams (6.2-6.4):
Calorific value of different fuel gases
140
107,3-125,8
calorific value MJ/m3
120
81,4-96,2
100
38,9-81,4
80
60
33,2-39,6
40
20-26
20
0
Methane
Biogas
Natural gas
Propan
Butane
fuel
Methane
Biogas
Natural gas
Propan
Butane
Figure 6.2. Comparison of calorific value of different fuel gases [22].
- 45 -
Volumes of other fuels equivalent to 1 m3 (1000 L) of
biogas (5500 kcal)
1
Biogas
0,57
Natural gas
0,87
Liquid butane
0,7
Petrol (gasoline)
0,62
Diesel
0
0,2
0,4
0,6
0,8
1
1,2
Figure 6.3. Volumes of other fuels equivalent to 1 m3 (1000 L) of biogas (5500 kcal) [22]
Natural Gas kcal/m3
Comparison of the calorific values of various fuels (Approximate)
Liquefied petroleum gas
kcal/kg
12000
10 800
10 300
Kerosene kcal/kg
10 700
Diesel kcal/kg
10000
8600
Biogas kcal/m3
8000
5000
6000
4000
2000
0
Figure 6.4. Comparison of the calorific values of various fuels (Approximate) [23].
From these diagrams one can calculate that:
1 m3 biogas equal to 0,57 m3 of Natural gas by their calorific value. This data is used in
calculations in Chapter 8.
- 47 -
7. BIODIGESTER
The biodigester is a physical construction, commonly known as the biogas plant. Since
different chemical and microbiological reactions take place in the biodigester, it is also known
as bio-reactor or anaerobic reactor. Basically, all biogas plants consist from the similar
standard components: a digester, a gas holder, a gas engine, tubes, mixers, etc. the rough
layout is shown in Figure 7.1.
Figure 7.1. Basic layout of biogas plant [24].
The main function of this structure is to provide anaerobic condition within it. As a
chamber, it should be air and water tight. It can be made of various construction materials and
in different shape and size. The scale of simple biogas plants can vary from a small household
system o large commercial plants of several thousand cubic metres. Depending on several
factors, which have to be known before engineering of the biogas plant has begun, an
experienced engineer chooses the most suitable process technology. Construction of this
structure forms a major part of the investment cost. Some of the commonly used designs are
discussed below.
In Europe currently in general, three different kinds of digester types are in use for
anaerobically treating organic wastes: small horizontal digesters, medium sized upright
concrete ones and large upright steel digesters:
Horizontal Digesters
The smallest biogas plants are often constructed with horizontal digesters, Appendix
5. The material used is steel. Ordinally, old used tanks were taken to avoid unnecessarily,
high costs. These tanks were cleaned, reconstructed with central shafts, equipped with mixer
arms, insulation gas dome, etc., and re-used as a digester.
Today, the digester tanks are normally fabricated for use as a digester. Generally, the
standard volume is between 50 and 150 m3.
This type of tank is well-suited for treatment of organic waste from juice plants as there is
very good mixing conditions even for solids. Grid removal is unproblematic.
- 48 -
The hydraulic retention time is usually between 30 and 50 days, depending on the
input substrate. The input is first heated by the heating arms, see Appendix 5. When
mezophilic temperatures are reached, the necessary mixing is done by standard mixing arms.
This digester type is comparatively cheap but cannot be manufactured and transported in large
sizes. This makes it most suitable for small farms [24].
Upright Standard Agricultural Digester
The standard digester is an upright, concrete digester, Appendix 6. The standard size is
between 500 and 1500 m 3. The height is often between 5 and 6 m; the diameter varies
between 10 and 20 m.
The tanks are equipped with a heating system which delivers hot water into tubes fixed along
the walls. The mixer is either completely immersed or equipped with an engine located
outside the tank as shown in Appendix 6. Large tanks are equipped with two or more mixers.
On top of the tank is a double-membrane, gas holder roof. The inner membrane is the gasholding buffer; the outer membrane is the weather cover. The inner membrane is flexible in
height; whereas the outer one is always ball shaped, as there is a blower which delivers air
pressure between the two membranes in a manner similar to that used to support an air hall.
The hydraulic retention time is generally between 30 and 80 days depending on the input
substrate.
This type of tank is well-suited for every kind of substrate as long as the flow rate is low
enough. Grid removal is not a problem if there is a special device for mechanically removing
this grid. For this reason some tanks are equipped with a concrete roof.
This type of digester is used for treatment of up to 10,000 m3 input per year [24].
Upright Large Digester
For large quantities of input substrate, for example 30,000 m3 per year, large upright steel
digesters are in use. The steel in general is coated in order to avoid corrosion. In most cases
glass-coated prefabricated steel plates are used. The standard size is between 1,500 and 5,00
m3. The height is often between 15 and 20 m, the diameter varies between 10 and 18 m.
The mixing is done by a centrally located mixer on the roof, which is in operation
continuously. The input substrate is pre-heated before entering the digester. The hydraulic
retention time is generally 20 days. This short retention time can be chosen because of the
advantages of continuously mixing and pre-heating.
This type of digester is used for the treatment of up to 90,000 m3 input per year per single unit
[24].
Those digester types above are used in most areas in Europe. Costs for construction of this
kind of biogas plant in Germany are given in Appendix 15.
There are several types of digesters which are commonly used in low income countries such
as Chine, India and Nepal:
Floating Drum Digester
Experiment on biogas technology in India began in 1937. In 1956 a floating drum biogas
plant popularly known as Gobar Gas plant was constructed. This design soon became popular
in India and around the world. The design of the plant is shown in Appendix 8 [25, 19].
In this design, the digester chamber is made of brick masonry in cement mortar. A mild steel
drum is placed on top of the digester to collect the biogas produced from the digester. Thus,
there are two separate structures for gas production and collection. With the introduction of
fixed dome Chinese model plant, the floating drum plants became obsolete because of
comparatively high investment and maintenance cost along with other design weaknesses [25]
- 49 -
Fixed Dome Digester
Fixed dome Chinese model biogas plant (also called drumless digester) was built in
China as early as 1936. It consists of an underground brick masonry compartment
(fermentation chamber) with a dome on the top for gas storage. In this design, the
fermentation chamber and gas holder are combined as one unit. This design eliminates the use
of costlier mild steel gas holder which is susceptible to corrosion. The life of fixed dome type
plant is longer (from 20 to 50 years) compared to floating drum digester. This plant’s sketch
is given in Appendix 9 [25, 19].
Deenbandhu Model
In an effort to further bring down the investment cost, the Deenbandhu model was put
forth in 1984 by the Action for Food Production (AFPRO), New Delhi. In India, this model
proved 30 % cheaper than Janata Model (also developed in India) which is the first fixed
dome plant based on Chinese technology. Deenbandhu plants are made entirely of brick
masonry work with a spherical shaped gas holder at the top and a concave bottom. A typical
design of Deenbandhu plant is shown in Appendix 10 [25].
In addition to above designs developed particularly for household use in developing
countries, there are other designs suitable for adoption in other specific conditions. These
designs are briefly described below for reference.
Bag Digester
This design was developed in 1960s in Taiwan. It consists of a long cylinder made of
PVC (thermoplastic resin) or red mud plastic (Appendix 11). The bag digester was developed
to solve the problems experienced with brick and metal digesters [1].
Plug Flow Digester
The plug flow digester is similar to the bag digester. It consists of a trench (trench
length has to be considerably greater than the width and depth) lined with, concrete or an
impermeable membrane.
The reactor is covered with either a flexible cover gas holder anchored to the ground, concrete
or galvanized iron (GI) top. The first documented use of this type of design was in South
Africa in 1957. Appendix 12 shows a sketch of such a reactor [1].
Anaerobic Filter
This type of digester was developed in the 1950's to use relatively dilute and soluble
waste water with low level of suspended solids. It is one of the earliest and simplest types of
design developed to reduce the reactor volume. It consists of a column filled with a packing
medium. A great variety of non-biodegradable materials have been used as packing media for
anaerobic filter reactors such as stones, plastic, coral, mussel shells, reeds, and bamboo rings.
The methane forming bacteria form a film on the large surface of the packing medium and are
not earned out of the digester with the effluent. Appendix 13 presents a sketch of the
anaerobic filter. This design is best suited for treating industrial, chemical and brewery wastes
[19].
Upflow Anaerobic Sludge Blanket (UASB)
This UASB design was developed in 1980 in the Netherlands. It is similar to the anaerobic
filter in that it involves a high concentration of immobilized bacteria in the reactor. However,
the UASB reactors contain no packing medium, instead, the methane forming bacteria are
- 50 -
concentrated in the dense granules of sludge blanket which covers the lower part of the
reactor [19].
The feed liquid enters from the bottom of the reactor and biogas is produced while liquid
flows up through the sludge blanket (Appendix 14). Many full-scale UASB plants are in
operation in Europe using waste water from sugar beet processing and other dilute wastes that
contain mainly soluble carbohydrates [1].
The main factors that influence the selection of a particular design or model of a
biogas plant are as follows:
•
Economic. An ideal plant should be as low-cost as possible (in terms of the
production cost per unit volume of biogas) both to the user as well as to the society.
•
Simple design. The design should be simple not only for construction but also for
operation and maintenance. This is an important consideration especially in a country
like Uzbekistan where the rate of literacy and knowledge are low and the availability
of skilled human resource is scarce. This because until now biogas plants were not
designed or constructed in Uzbekistan.
•
Durability. Construction of a biogas plant requires certain degree of specialized skill
which may not be easily available. A plant of short life could also be cost effective but
such a plant may not be reconstructed once its useful life ends. Especially in situation
where people are yet to be motivated for the adoption of this technology and the
necessary skill and materials are not readily available, it is necessary to construct
plants that are more durable although this may require a higher initial investment.
•
Suitable for the type of inputs. The design should be compatible with the type of
inputs that would be used. If plant materials such as rice straw, maize straw or similar
agricultural wastes are to be used, then the batch feeding design or discontinuous
system should be used instead of a design for continuous or semi-continuous feeding.
•
Using local materials in construction of biogas plant. This is an important
consideration, particularly in the context of Uzbekistan as this country is economically
developing. Buying construction material from abroad may make biogas plant
building costs higher. There are a lot of local construction materials which are
produced in Uzbekistan. By using local building materials the biogas plant
construction costs can be decreased.
•
Frequency of using inputs and outputs. Selection of a particular design and size of
its various components also depend on how frequently the user can feed the system
and utilize the gas.
- 51 -
8. CALCULATIONS
PROCESSES
OF
ANAEROBIC
FERMENTATION
The most important issues of the plant are economical cost and benefits for running the
biogas plant. An ideal plant should have as low costs as possible (in terms of the production
cost per unit volume of biogas) both to the user as well as to the society.
In this part economical cost and benefits of anaerobic fermentation plant are evaluated and
analysed from a cost-beneficial point of view.
The following costs need to be considered:
• Equipment costs- costs for building biogas plant.
• Labour costs- costs for operating and maintenance biogas plant
• Material costs-costs for input material (because of input material generates from fruit juice
processing in fruit juice plant itself this cost is equal to 0).
And weighed against the benefits:
• Selling of surplus biogas
• Lower disposal costs
• Reduced costs for using of natural gas by replacing it with biogas.
• Reduced environmental impact and higher social benefits
• Selling of residues as soil improver.
Also fermentation has benefits for agriculture sector of Uzbekistan such as:
• Lower mulch, soil and fertiliser needs
• Reduced need for pesticides and herbicides
In order to calculate economical cost and benefits we should need to calculate:
™ Annually generated organic waste
™ Organic waste content:
• Dry matter of organic waste (DM)
• Organic dry matter of organic waste (ODM)
™ Biogas yield per kg of DM and ODM
™ Daily input of organic waste into the digester
™ Daily yield of biogas
™ Annually yield of biogas
™ Annually yield of biogas converted to amount of natural gas
™ Biogas digester volume
™ Costs for building and operation of the biogas plant
™ Income and outcome per year or per day
™ Pay back time
- 52 -
8.1. Calculation of biogas yield and bio digester volume
In case of pre-sorted bio-wastes, average gas yields can be calculated as follows:
•
Daily input of organic waste into the digester
In “Bagat-Sharbat” juice plant annually amount of organic waste from juice processing is
1190-1200 t (see Chapter 3)
The juice plant works seasonally, when raw material is ready for processing, which will be in
July-October. So total of juice producing days is approximately 125 days a year.
Organic waste generated per day is average (1200t/125 days) =9.6 t
•
Dry matter of organic waste (DM)
Fruit juice waste has a moisture content of 62-88% (average 75%) (Table 3.2) and 25% dry
matter.
The amount of DM per day is therefore 9.6*0.25=2.4 t:
•
Organic dry matter of organic waste (ODM)
Usually in fruit and vegetable wastes the ODM is 75 % of DM [26].
Then the amount of ODM per day is 2.4*0.75=1.8 t
• Retention time inside the digester
To estimate the range of possible sizes for most high solids digesters, I use the retention
time (average residence time in the digester) of 15 days with a limit of +7 days for wide
range of materials. So the time for digestion period will be approximately 15-22 days
•
Calculation of average biogas yield
Retention time inside the digester
20 days
Max 4,5 kg ODM/ m3 [26]
Specific load of the digester per day
Expected decomposition rate of ODM
70%
Specific gas yield per kg of decomposed ODM
Average gas yield from 1 kg of fruit waste (fresh material)
=0,25x0,75x0,7x0.9
0.9 Nm3/kg ODM
0.118 Nm3
Average gas yield per annum (1200t fruit waste with 25%DM)
=1200000x0,25x0,75x0,7x0.9
142000 Nm3/per annum
Average biogas yield per annum is 142000 Nm3
- 53 -
•
Calculation of the digester volume of
For a retention time of 20 days
Since daily loading rate is 4,5 kg ODM/ m3 [26]
The total volume of digester should be
1800/4,5=400 m3
8.2. Costs which are involved to building, operating the biogas plant
In Chapter 7 several bio digesters types in Europe and Asia and their costs are described (see
Appendices 15-16). On the following tables costs for various biogas plants with different
construction materials and different volumes are shown for comparison.
Table 8.1. Comparison of biogas plant construction cost in Germany
Biogas plant
Fermenter
Costs
Concrete Tank, 600 m³
Ca. € 350.000,-
Concrete Tank, 1.000 m³
Ca. € 400.000,-
Biogas Plant HAUS
RISWICK
Concrete Tank, 570 m³
Ca. € 600.000,-
Biogas Plant
OBERNJESA
Concrete Tank, 680 m³
about. € 680.000,-
Concrete tank, 445 m³
about € 380.000,-
Concrete Tank, 450 m³
ca. € 200.000,-
Steel Tank, 2,400 m³
About € 1.000.000,-
Concrete Tank, 1.100m³
€ 600.000,-
Steel Tank, 4.250 m³
About € 2.000.000,-
Steel Tank, 2 x 3,200 m³
-
Steel Tanks, glass coated,
4 x 2.500m³
ca. € 200.000.000,-
Biogas Plant EICHHOF
Biogas Plant FABEL
Biogas Plant SCHMITZ
Biogas Plant STANGE
Biogas Plant
TODENDORF
Biogas Plant UELZEN
Biogas Plant VAN
GENNIP
Biogas Plant WERLTE
Biogas Plant
WIETZENDORF
- 54 -
Table 8.2. Comparison of biogas plant construction cost in India.
Biogas plant
Plant type
Cost of the unit
Tnau Sakthi Model fixed dome model
Biogas Plant
€ 132 (2 m3 plant)
Cost
of
operation
€ 0.08 per day
fixed dome model
€ 188 (2 m3 plant)
€ 0.1 per day
€ 226 (3 m3 plant)
€ 1881,5(35 m3 plant )
€ 1.88 per day
Janata Plant
Community Biogas ________________
Plant
As shown in these tables above the cost of biogas plant varies a lot. A part of the cost
depends on what kind of construction materials are used for biogas plant and local costs of
these materials.
For example, concrete tank biogas plants are cheaper than steel tank biogas plants. By
increasing the biogas digester volume costs per 1 m3 of biogas plant and pay back time will
decrease. Even if biodigester volume increases, other equipment’s size and quantity will not
change that much, the costs of these equipments will not increase proportional to the increase
in volume.
Calculation of annual income for the biogas plant
In order to calculate pay back time of biogas plant one should know it’s annually
income.
From Diagrams 6.2-6.4 in Chapter 6 we know how much volume of natural gas is
equal to 1 m3 biogas by their calorific value:
1 m3 biogas=0.57 m3 natural gas
Seasonally 142000 Nm3 biogas is expected to be produced, this is equivalent to
(142000x0,57=) 80940 Nm3 Natural gas. The “Bagat-Sharbat” juice plant buys 5000 Nm3
Natural gas for heating buildings. The annually surplus volume of biogas is then equivalent to
(80940-5000=) 75940 Nm3 natural gas.
Since 1m3 Natural gas costs 0,028 €, the savings of 5000 m3 natural gas will be 75-85
€ per year. In additional, if the plant can sell the surplus biogas (corresponding to 75940 m3
natural gas) the additional income will be € 2126 per year.
- 55 -
9. DISCUSSION
Problem solution for organic wastes from Uzbekistan juice processing is discussed from
an economical and environmental point of view.
During the study visit it was identified that organic waste from juice plants after
processing juice is dumped outside the plants. Juice plants do not treat their organic waste in
order to get economical and environmental benefits. There are several cases of the juice plants
in Xorazm that do not take care of their organic waste. This because of
•
•
•
Lack of knowledge about what prolems organic waste can cause to environment
and human health by air and water with its harmful effluents and possibility of
containing hazardous chemical such as pesticides, cleansing and bleaching agents;
Lack of knowledge about organic waste treatment;
Lack of capital for designing sustainable organic waste treatment methods;
The main aims of this Master Thesis were to study if fermentation is the proper
method for treating organic waste from fruit juice plants in Uzbekistan and comparing this
method with other alternative waste treatment methods such as incineration, animal feeding,
land spreading, landfilling and composing.
The following parameters were discussed for evaluating the anaerobic fermentation waste
management options: cost and benefits, consumption of energy resources, emissions of
greenhouse gases, emissions of acidifying substances, local environmental conditions and
organic waste content.
Animal feeding
To dispose organic waste fruit juice process as animal feeding is the cheapest treatment
way for juice plant. However it is not beneficial for fruit juice plant, because organic wastes
from fruit juice manufacturing have hazardous contents such as bleaching and cleansing
agents from fruit juice processing. The possibility of consisting pesticides and herbicides in
raw material might cause harm to animal health and animal reproductive possibilities.
Incineration
By incineration of organic wastes heat can be produced, and additionally a decrease in
waste volume will be achieved. Produced bottom ash can be used as soil improver for
phosphorus and calcium. But this method is not suitable for organic wastes with high
moisture content. Because organic waste from fruit juice manufacturing has 75-80 % moisture
content incineration of this kind of wet organic waste is not energy efficient. Also incineration
plant costs would be high and non beneficial for the fruit juice plant.
Direct land spreading
In this type of waste processing it is helpful to immediately incorporate any applied
material into the soil.
Direct land spreading requires special transport equipments such as land spreading trucks.
Because of agricultural jobs are not purposed in the juice plants’ function, this type of
organic waste processing is not beneficial for the plant, however they can make a benefit by
selling it to farmers.
The main problem of this method is odour problem. This problem may occur when non
treated organic waste is applied to agricultural lands and may cause discomfort and health
- 56 -
problems of inhabitants in the local area. Also non treated organic materials may attract
rodents, birds and other animals which may cause decreasing of crops.
Also because groundwater level is high in the Xorazm region, direct land spreading may
cause negative effects to the groundwater which local people use as drinking water.
After studying this method I can not recommend it for disposing organic wastes from
juice plant.
Landfilling
The most obvious conclusion is that landfilling should be avoided. Wastes that can be
incinerated (combusted), material recycled, anaerobically digested or composted should not
be landfilled. This is motivated from both environmental and economic reasons. This is valid
even if landfill gas is extracted and utilised, and the leachate is collected and treated. This is
due to that the resources in the waste are inefficiently utilised when landfilled, making it
necessary to produce materials, fuels and nutrients from virgin resources.
Although landfilling is the cheapest way of disposing organic wastes from juice plants,
this method has environmental and social problems such as eutrophication of surface and
ground water, decreasing of agricultural areas and odour problems. In Xorazm region ground
water levels is high and people in local area use groundwater for drinking water from by hand
pump, bucket-well or tube-well without any treatment.
As a result, since the juice plant’s organic waste is nutrient rich, organic waste should not
be landfilled in the Xorazm region in Uzbekistan.
Composting and Anaerobic Fermentation
By comparing composting with anaerobic digestion we can see that anaerobic digestion
has more environmental and economic advantages than composting. In Table 5.2 a
comparison between composting and anaerobic digestion methods is described.
The anaerobic digestion of bio-waste from juice manufacturing industry has a high
energy potential compared to the aerobic treatment in a composting plant. In anaerobic
process several advantages will be achieved. For example, biogas and fertilizer production,
reducing emissions to air and to water as operations will take place in close system, inside the
biogas plant.
According to economical calculations for the biogas plant, following results were obtained:
•
•
•
•
Average biogas yield per season – 142000 Nm3 (equivalent to 80940 Nm3 Natural
gas)
Average volume of biogas plant – 400 m3
Annual saving (for heating) - 75-85 €
Annual income - € 2126,32 (This benefit will be obtained if surplus biogas can be
sold)
From an environmental point of view using anaerobic fermentation for processing organic
waste from fruit juice plants is very useful to surrounding neighbourhoods’ health and the
local ecosystem.
According to the comparisons in the study of different waste management types the
following results were achieved:
- 57 -
Wet organic wastes
from juice producing
plants
Animal
feed
Non
profitable
Incineration
-Pollution
-Energy loss
Direct
land
spreading
-Pollution
-Odour
problems
Land
filling
-Pollution
-Shortage
of land
filling site
Composting
-Shortage of
demand
-Long
treatment
time
Anaerobic
digestion
-Energy
recovery
-Long
treatment
time
Figure 9.1: Treatment options of wet organic waste and their characters
The contamination of hazardous chemicals such as pesticides and cleansing, bleaching
agents in organic waste may shut down the anaerobic fermentation process, because
pesticides and other chemicals will kill the methane bacteria in the biogas digester. Also by
using residue from anaerobic fermentation as soil fertilizer, pesticides might be circulated
again to agricultural products. Additionally using pesticides against pests and insects will
raise the concentration of pesticides in crops. Therefore, before anaerobic treatment, organic
waste should be analyzed by its chemical content. If the concentration of chemicals is high
some measures should be taken in order to decrease and dilute the chemicals.
For solving this problem the concentration of pesticide in organic wastes can be
decreased by mixing with organic wastes which do not contain pesticides. For example,
organic waste from juice processing plant can be mixed with animal manure generated from
nearby farms. With this method, additionally to decreasing concentration of pesticides, the
biogas plant could also achieve a high volume of biogas production per unit of organic waste
as biogas production rate from animal manure is high.
Waste water from juice plant is led from drainage system to water channels which are
located outside the juice plant. Because there is no waste water treatment plant this also is a
cause for problems with the environment and people’s health. By treating waste water
together with the organic solid wastes for biogas production this wastewater problems can be
reduced.
Wastewater from juice plant can be used for moistening the dry matter content of organic
waste after mixing with animal manure.
- 58 -
Nowadays prices on natural fuels are rising year by year. It could therefore be much
more beneficial to keep surplus biogas some years and sell it in the fuel market with a high
price than selling it immediately after producing.
Annual income from selling surplus biogas will reach € 2126 per year and the saving
for natural gas for heating is 75-85 € (see Chapter 3 and Chapter 8).
In order to get the income from surplus biogas a market for biogas should be found by
advertising and marketing. If there is no interest for buying biogas then the payback time for
the biogas plant will increase and count only on savings.
Since the biogas plant uses natural gas only for heating, saving from biogas plant will
not be so high. If biogas is used for producing steam and electricity for juice processing, juice
plant’s annual savings will be increased.
Also benefit can be obtained by selling digestate after fermentation process. It
contains nutrients (ammonia, nitrates, phosphorus, sulphates, potassium, and more than a
dozen trace elements) which will enhance agricultural productivity and it is an excellent soil
conditioner that can be replaced with artificial expensive fertilisers.
- 59 -
10. CONCLUSION
By studying and comparing different waste treatment methods with anaerobic digestion of
organic waste from juice plants following conclusions are made:
The benefits of the biogas plant on the fruit juice plant:
•
•
•
•
•
•
Solution of the organic waste-disposal problems
Reduction of obnoxious smells from the organic wastes
Own, stable, self-sufficient energy production (heat, steam and electricity)
Cheap energy, which yields financial savings in the longer term.
Possibility of selling energy or biogas surplus - a source of extra income for
the plant.
Production of high-volume fertiliser that carries a higher content of nitrogen
(15% or more) than artificial fertilisers, and that does not burn the crops, as
untreated slurry can do. This reduces the need for expensive artificial
fertilisers. By selling this natural fertiliser additional income for the plant can
be obtained.
Local benefits:
•
•
•
Better control of the waste from fruit juice processing organic waste means
less pollution of local environment and water sources.
Removal of chemical fertilisers from the fields and recirculation of nutrients.
Local power plants contribute to creating permanent local jobs in the area.
On a global additional, replacing fossil fuels to biogas reduces, emissions of CO2. At
the same time, the emission of methane, a greenhouse gas that is 20 times more aggressive
than CO2 is reduced due to controlled anaerobic digestion.
Suggestions and recommendations
By researching and analyzing the problems in the study area some suggestions and
recommendations are made:
For fruit juice plants:
z Make more accurate economic calculation with valuable costs in Uzbekistan for
construction materials of biogas plant.
z Find market for digestate.
For the government:
z Reform current industry waste management law and regulations
z Reform current tax system; develop taxes for land filling
z Reform tax system for food industry sector and implement fees for plants, which do
not take care of their wastes in a good way.
z Creating local authorities which implement regulations and check local industry waste
management behaviour
z Investigate capital for biogas production technology
- 60 -
11. REFERENCES
1. Dr. Umid Abdullaev, Director, Institute Uzgipromeliovodkhoz, Tashkent, Uzbekista,
last updated: 18 April 2002.
http://www.fao.org/ag/agl/swlwpnr/reports/y_nr/z_uz/uz.htm (visited in February
2. ECOINFORM, an ecological Internet project of Uzbekistan Republic, Law of the
Republic of Uzbekistan on wastes, http://ecoinform.freenet.uz/zacon_oth_en.html#1
(visited on February 2006)
3. http://www.worldpress.org (visited in Februaty 2006)
4. http://www.mapzones.com (visited in Februaty 2006)
5. Importance and use of apple juice
http://www.foodstudents.com/pdf/apple_juice/background_apple_juice.pdf (visited
in September 2005)
6. Principles and practices of small - and medium - scale fruit juice processing by
R.P.Bates, J.R.Morris and P.G.Crandall Food Science and Human Nutrition
7. Biocatalysts Limited, Cefn Coed, Parc Nantgarw, CF15 7QQ, Wales, UK.
www.biocatalysts.com (visited in January 2006)
8. Homepage of Westfalia Separator company http://www.wsus.com/ (visited in
December 2005)
9. Pollution Prevention and Abatement Handbook, World Bank Group Effective July
1998 Fruit and Vegetable Processing
10. Source is On Farm Composting, by R. Rynk, M. van de Kamp, G.B. Wilson,
M.E. Singley, T.L. Richard, J.J. Kolega, F.R. Gouin, L. Laliberty, Jr., D. Kay,
D.W. Murphy, H.A. J. Hoitink, and W.F. Brinton, 1992, Northeast Regional
Agricultural Engineering Service, Ithaca, N.Y.
11. George Tchobanoglous, Hilary Theisen, Samuel Vigil, Integrated Solid Waste
Management, Engineering Pronciples and Menegment Issues, International Edition
1993, pages 79, 80, 684
12. Managing solid by-products of industrial food processing - turning solid by-products
into useful products instead of waste. Food Review, 4/1/91 by Luanne Lohr
13. Homepage of North West region waste management group, Waste Management Plan
http://www.northwestwasteplan.org.uk/ (visited in December 2005)
14. Land Application of Municipal Sludge-advantages and Concerns, Published by:
North Carolina Cooperative Extension Service, Publication Number: AG 439-3 Last
Electronic Revision: March 1996 (JWM),
http://www.bae.ncsu.edu/bae/programs/extension/publicat/wqwm/ag439_3.html
(visited in December 2005)
15. United States Environmental Protection Agency, Office of Water Washington, D.C.
EPA 832-F-00-064 September 2000. Bio solids. Technology Fact Sheet. Land
Application of Bio solids.
http://www.epa.gov/owm/mtb/land_application.pdf
(Visited in January 206)
16. Leslie Cooperband University of Wisconsin-Madison, The Art and Science of
Composting, A resource for farmers and compost producers, Center for Integrated
Agricultural Systems March 29, 2002
17. Recycling organic waste. Website of ITDG – the Intermediate Technology
Development Group http://www.itdg.org (visited in November 2005)
18. Considerations for Direct Land Application of Organic Waste Products. Author:
Eberle, William M.Publication Date: August 1997
19. Biogas technology: A training manual for extension; Food and Agriculture
Organization/Consolidated Management Services, Kathmandu, 1996
- 61 -
20. Dr. Suporn Koottatep, Mr. Manit Ompont, Biogas: GP Option for Community
Development Prepared for Asian Productivity Organization http://www.apotokyo.org/gp/e_publi/biogas/BiogasGP1.pdf (visited in November 2005)
21. Industrial ecology in food industry , 480370S Industrial Ecology and Recycling
course, Lecture on November 4th 2004 by Nora Pap Department University of
Florida United States, ISBN 92-5-104661-1 © FAO 2001
22. Francisco X. Aguilar, Agronomic Engineer.Polyethylene biodigesters (PBD),
Production of biogas and organic fertilizer from animal manure, Integrated Biosystem Network, International Organisation of Biotechnology and Bioengineering, T.
1999 (visited December 2005).
23. Energy Techonologies - Biogas Plant. http://www.techno-preneur.net/newtimeis/New-technologies/Energy/biogas.htm (visited in February 2006)
24. Krieg & Fischer Ingenieure GmbH, Planning & Construction of
Biogas Plantshttp://www.kriegfischer.de/ (visited in February 2006)
25. Homepage of The Energy and Resources Institute; Biogas plant models,
http://new.teriin.org (visited in January 2006)
26. Biogas and Liquid Biofuels, Practicl guide. Fruit and vegetables processing in
developing countries http://www.unido.org/userfiles/cracknej/fvtp2.pdf (visited in
November 2005)
27. http://ifcln1.ifc.org/ifcext/enviro.nsf/AttachmentsByTitle/gui_fruitveg_WB/$FILE/fr
uitandvg_PPAH.pdf (visited in November 2005)
28. Recommendations for the Production and Distribution of Juice in Canada
http://www.cfis.agr.ca/english/regcode/hrt/juchap-e.pdf (Visited in November 2005)
29. Pollution prevention and abatement guidelines for fruit and vegetable processing
industry.
http://www.cleantechindia.com/eicimage/210602_30/fruit-guideline.htm
(visited in November 2005)
30. Fruit and Vegetable Processing, Pollution Prevention and Abatement Handbook,
WORLD BANK GROUP, Effective July 1998.
31. Fruit waste utilization
http://www.itdg.org/docs/technical_information_service/fruit_waste_utilisation.pdf
(visited September 2005)
32. Recycling organic waste
http://www.itdg.org/docs/technical_information_service/recycling_organic_waste.pd
f (visited September 2005)
33. Bahman Eghball, Assistant Professor of Agronomy, Composting Manure and Other
Organic
Residues,
Electronic
version
issued
January
1998,
http://ianrpubs.unl.edu/wastemgt/g1315.htm (visited in December 2005)
34. Homepage of Hutchison Hayes, The development of liquid/solids separation
technology http://hutchisonhayes.com/index.html (visited in January 2006)
35. ARTICLE. Future Fuels via Microbial Digestion of Waste, Dr. V.C. Kalia, Scientist,
Centre for Biochemical Technology,
http://www.undp.org.in/programme/GEF/june/page21-23.htm (visited in November
2005)
36. B. Nagamani and K. Ramasamy, Biogas production technology: An Indian
perspective Fermentation Laboratory, Department of Environmental Sciences, Tamil
Nadu Agricultural University, Coimbatore 641 003, India
37. PRACTICALLY GREEN, Environmental Services, Solar House, Magherafelt ,Co.
Londonderrry, BT45 6HW, Northern Ireland, http://www.practicallygreen.com
(visited in January 2006)
- 62 -
38. M. Köttner, Biogas in agriculture and industry potentials, present use and
perspectives, International Biogas and Bio energy Centre of Competence
39. Kajima technical research institute website, Cost-effective and highly-efficient
treatment systems for organic liquid/solid wastes,
http://www.kajima.co.jp/welcome.html (visited in February 2006)
40. http://www.itdg.org/docs/technical_information_service/biogas_liquid_fuels.pdf
(visited November 2005)
- 63 -
Filter
Sandwich pot
Seamer
Homogenizator
Crasher
Marks sprayer
Mixing pot
Air remover
Steam sterilizing pot
Fruit selector
Fruit washer
Appendix 1. Technological line for fruit juice producing process [7]
12. APPENDICES
Filler
Vacuum boiler
Decanter
Can washer
Centrifuge
Appendix 2. Enzymes and their uses [7].
ENZYME
APPLICATION
Cellulose 13L
Fruit liquefaction
Depol 40L
General maceration
Depol 220L
Removal of starch from juice
Depol 670L
Cell wall digestion
Macer8TM FJ
Fruit maceration/ depectinisation
Pectinase 62L
Fruit maceration/ depectinisation
Pectinase 444L
General depectinisation
Glucose oxidase G 168L
Removal of oxygen
Appendix 3. Fruit juice and fruit wine manufacture bleaching agents [7]
Code
Food Additive Items
04001
Potassium Sulfite
04002
Sodium Sulfite
04003
Sodium Sulfite (Anhydrous)
04004
Sodium Bisulfite
04005
Sodium Hydrosulfite
04006
Potassium Metabisulfite
04007
Potassium Bisulfite
04008
Sodium Metabisulfite
04009
Benzoyl Peroxide
04008
Sodium Metabisulfite
04009
Benzoyl Peroxide
Scope and Application Standards
Fruit juice manufacturing, syrup-preserved
fruits, shrimps, shellfish: not more than 0.10
g/kg calculated as residual SO2.
Fruit wine manufacturing: not more than
0.25 g/kg calculated as residual SO2.
Appendix 4. The biogas comparison with natural gas [25].
Substances
Simbol
Methane
CH4
[vol%]
55-70
Natural
gas
91,0
Ethane
C2H6
[vol%]
0
5,1
Propane
C3H8
[vol%]
0
1,8
Butane
C4H10
[vol%]
0
0,9
Pentane
C5H12
[vol%]
0
0,3
Carbon dioxide
CO2
[vol%]
30-40
0,61
Nitrogen
N2
[vol%]
0-2
0,32
Water vapour
Hydrogen
sulphide
H2O
H2S
[vol%]
ppm
0-3
~500
~1
[MJ/nm3]
23.3
39,2
[kWh/
nm3]
6-8
10,89
20.2
48,4
[MJ/kg]
[kg/ nm3]
1.16
0,809
[MJ/nm3]
27.3
54,8
[nm3/ nm3 6.22
gas]
10,4
[0C]
2040
Net
value
calorific
Density
Wobbe
index W
(Heating value)
Air requirement
Flame
temperature*
Biogas
*) Adiabatic flame temperature
- 67 -
1911
Appendix 5. Horizontal Digester [24]
- 68 -
- 69 -
Appendix 6. Standard digester in Agriculture [24]
Appendix 7. Upright Large Digester [24]
- 70 -
Appendix 8. Floating Drum Digester [1]
- 71 -
Appendix 9. Fixed Dome Digester [1]
- 72 -
Appendix 10. Deenbandhu Model [1]
- 73 -
Appendix 11. Bag Digester [1]
Appendix 12. Plug Flow Digester [1]
- 74 -
Appendix 13. Anaerobic Filter [1]
Appendix 14. Upflow Anaerobic Sludge Blanket (UASB) [1]
2002
2002/2003 Energy
Crops
2002/2003 Manure,
Vegetable
Fats and Oils
1999 Chicken
2000
Manure, Pig
East of
Uelzen, North
Germany
Kleve,
Germany
Germany
Germany
Bischhausen,
Germany
Biogas Plant
FABEL
Biogas Plant
HAUS
RISWICK
Biogas Plant
OBERNJESA
Biogas Plant
SCHMITZ
Biogas Plant
STANGE
Pig Manure,
Corn, Potato
Starch
Residues,
Cabbage
Residues,
Agricultural
Residues
Manure,
Agricultural
Organic
Waste
2001
Bad Hersfeld,
Germany
Biogas Plant
EICHHOF
Construct Input
ion
Period
2001 Manure,
2002
other
Organic
Waste
Location
Biogas plant
Ca. €
600.000,-
Concrete
Tank, 570
m³
ca. € 200.000,-
about
€ 380.000,-
about.
€ 680.000,-
Ca. €
400.000,-
Concrete
Tank,
1.000 m³
Concrete
Tank, 680
m³
Concrete
tank, 445
m³
Concrete
Tank, 450
Ca. €
350.000,-
Costs
Concrete
Tank, 600
m³
Fermenter
Appendix 15. Profiles of several biogas plants in Germany [24]
Replacement of old Biogas
Plant, Gas Holder above
Manure Storage Tank,
Demonstration Biogas Plant
for Education of
Gas holder above Fermenter
2.250m³-Manure Storage
Tank
Solids Input Device
Special Features
Dual Fuel
Special Features: External
Co-generator, Heat Exchanger, Gas Holder
65 kW
above Fermenter,
Demonstration Biogas Plant
for Education of Farmers
Dual Fuel
Co-generator,
160 kW
Gas Engines,
100 kW, 70
kW
Gas Engine,
Gas Holder above 1.000m³45 kW
Manure Storage Tank
Dual fuel Cogenerator, 30
kW, Gas
Engine, 15
kW
Dual fuel Cogenerator,
110 kW,
containerised
CoGenerator
2001/2002 Potato Pulp,
Waste Water
of a Potato
Starch
Factory
Uelzen, 80
km SE
Hamburg,
North
Germany
Germany
Germany
Wietzendorf,
Lower
Saxony,
North
Germany
Biogas Plant
UELZEN
Biogas Plant
VAN GENNIP
Biogas Plant
WERLTE
Biogas Plant
WIETZENDOR
F
- 77 -
2001/2002 Pig Manure,
Corn,
Onions,
Potatoes,
Agricultural
Residues
2003
Pig Manure,
Turkey
Dung,
Energy
Crops
2002/2003 Manure, Fats
Germany
Biogas Plant
TODENDORF
Manure,
Turkey Dung
2002/2003 Manure and
Grass Silage
-
Steel Tank,
2 x 3,200
m³
Steel
Tanks,
glass
coated, 4 x
2.500m³
ca.
€
200.000.000,-
About
€ 2.000.000,-
€ 600.000,-
Concrete
Tank,
1.100m³
Steel Tank,
4.250 m³
About €
1.000.000,-
Steel Tank,
2,400 m³
m³
Gas Engines,
2 x 1,262
MW
Gas Engines,
4 x 2,1 MWel
Gas Engines,
1 x 167 kW,
1 x 344 kW
Protein Recovery
3 Tanks for Hydrolyses
Stage
pH-Value Regulation
Gas Holder, 5.000m³
Liquid-/Solid Separation
Membrane Technique for
total Treatment of Effluents
General Contractor: Hese
Umwelt GmbH
Dual Fuel
Co-generator,
2 x 180 kW
Dual fuel Co- Biogas Plant of 4 Farmers
Generator, 2 Gas Holder above
x 100 kW
Fermenter and Post
Digestion Tank
Solid input device
General
Information
Cost of the
unit
Cost of
operation
Salient
features
Function
This is a semi-continuous flow plant for producing
biogas from cattle waste in domestic level. This is
a fixed dome model. Main feature of janata design
is that the digester and gas holder are part of a
composite unit made of bricks and cement masonry.
It requires centering for making the dome shaped
roof and skilled and trained mason is a must for the
construction. Based on the requirement and
availability of feed material the size of the plant
may be fixed suitably.
TNAU sakthi model plant is made of
brick, cement, sand and jelly. The only
skill required is arch (dome)
construction which can be done by
masonry work. The new model not only
eliminates the centering, false roof and
false pillar for the dome construction but
also separates outlet tank. Hence the
cost of construction of this digester is
lesser than other types of biogas plants.
- 78 -
20-30% costs saving than KVIC floating drum
type plant
15 to 20 % cost saving when
compared to deenbhandu biogas
model.
€ 0.08 per day
€ 188 (2 m3 plant)
€ 226 (3 m3 plant)
€ 0.1 per day
Household cooking, lighting and running
engines
Components: Digester, and inlet and outlet
tanks
Feed material: Cow dung, pig manure, poultry
droppings etc.
Shape of the plant: Cylindrical
Janata Plant
€ 132 (2 m3 plant)
Cooking, lighting and engine
running
Specification Components: Digester, inlet pipes
and effluent collector
Feed material: Cow dung, pig
manure, poultry droppings etc.
Shape of the plant: Spherical
Tnau Sakthi Model Biogas Plant
Appendix 16. Indian Biogas Plants profiles [1]
The community level biogas plant will be
constructed in a common place, the feed
material will be collected from a group of
households and the produced biogas will be
distributed to all the beneficiaries. The size
and cost of the plant may vary based on the
availability of feed material, requirement of
biogas and initial investment.
Rate of biogas production : 1.5 m3/h
No. of hours 5 hp dual fuel engine can
run: 14 h
Electricity production potential:50 kWh
No. of beneficiaries for Cooking gas: 40
- 50 families
€ 1.88 per day
Gas volume: 35 m3
Gas holder height: 1.0 m
Inlet/outlet opening: 2.0 x 1.2 m Initial
dung required: 35 to 40 tonnes of cow
dung
Daily loading rate: 600 to 700 kg
No. of cattle required: 60 to 70 animals
€ 1881.5
Cooking, lighting and running engines
Community Biogas Plant
Appendix 17. Flow chart of anaerobic digestion of wet organic waste
Wet Organic
Waste
Juice plant
Anaerobic
digestion
Heat
Exchanger
BIOGAS
BOILER
Gas
Cleaning
Gas
Storage
Liquid
fertilizer
TRITA-KET-IM 2006:9
ISSN 1402-7615
Industrial Ecology,
Royal Institute of Technology
www.ima.kth.se
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