THESIS REPORT National Institute of Technology Rourkela ANUBHAV ABHINAV

THESIS REPORT National Institute of Technology Rourkela ANUBHAV ABHINAV
THESIS REPORT
National Institute of Technology Rourkela
ANUBHAV ABHINAV
111CE0026
Civil Engineering Department
SINGLE STAGE ANAEROBIC DIGESTION FOR
SEWAGE SLUDGE TREATMENT
A Thesis submitted in partial fulfilment
for the requirement of the degree of
Bachelor of Technology in Civil Engineering
By
Anubhav Abhinav
111CE0026
Under the supervision of
Prof. Kakoli K. Paul
Department of Civil Engineering
National Institute of Technology, Rourkela
ii
Certificate of Approval
This is to certify that the thesis entitled ‘SINGLE STAGE ANAEROBIC
DIGESTION FOR SEWAGE SLUDGE TREATMENT’ submitted by Anubhav
Abhinav (111CE0026) has been carried out under my supervision in
partial fulfillment of the requirements for the Degree of Bachelor of
Technology in Department of Civil Engineering at National Institute of
Technology Rourkela, and this work has not been submitted elsewhere
before for any other academic degree/diploma.
Prof. Kakoli K. Paul
Department of Civil Engineering
National Institute of Technology, Rourkela
iii
Acknowledgement
It is a great pleasure to acknowledge all those individuals who have
directly or indirectly helped me through the course of this project. This
project would have never been completed without the contribution of
those people.
First and foremost I wish to express my deep sense of gratitude to Prof.
K.K.Paul, Department of Civil Engineering - N.I.T, Rourkela for
assigning me the project and for her inspiring guidance, constructive
criticism and valuable suggestion throughout this project.
I want to express my gratitude to Mr. Nagachaitanya Kavuri, Mr.
Deepayan Priyadarshi and Mr. Parmanand Pandit for their important and
valuable input in my project.
Also I want to thank my friends and seniors for their constant support
and encouragement for which I am able to complete my project in time.
Anubhav Abhinav (111CE0026)
Department of Civil Engineering
National Institute of Technology
Rourkela – 769008
iv
Contents
Sl.no Chapters
List of Tables and Figures
Abstract
1
1.1
1.2
1.3
1.4
INTRODUCTION
Sludge
Sludge stabilization
Objectives of the Study
Literature Review
Page. No.
vi
vii
1
2
3
4
5
2 MONITORING PROTOCOLS
2.1 Study Area
2.2 Sampling Techniques
7
8
8
3
3.1
3.2
3.3
3.4
3.5
9
10
11
12
13
14
ANALYSIS TECHNIQUES
Pre-Requisite Work
Methodology for process of Digestion
Methodology for measurement of pH
Methodology for determination of metals
Methodology for determination of
chemical characteristics
4 RESULTS AND DISCUSSION
4.1 Tabulations
17
18
5 CONCLUSION
26
6 REFERENCES
28
v
List of Tables
Page No.
1. Concentration of metals in the three
samples
2. Chemical Characteristics of the three
samples
3. Chemical characteristics of the samples at
different time of sampling
18
4. Concentration of metals in the sample at
different time of sampling
5. Concentration of nonmetals in the three
samples in %
6. Weight volume of all three samples
7. Concentration of nonmetals in the three
samples in mg/g
8. N: P: K ratios of all the three samples
9. N: P: K ratios of various synthetic fertilizers
10.N: P: K ratios of various mined fertilizers
11.N: P: K ratios of various bio solids
20
List of Figures
19
19
21
21
22
22
23
24
24
Page No.
1. Schematic Diagram of AAS
14
2. An Atomic Absorption Spectrometer
15
3. A colorimeter (DRB 200) Schematic
Diagram of AAS
16
vi
ABSTRACT
National Institute of Technology Rourkela is one of the largest academic
institutions in India with lots of people residing in its campus. Such large number
of people will lead to large amount of sewage from hostels and academic areas. A
sewage treatment plant has setup near V.S. Hall of Residence for the treatment of
all municipal wastes from the hostels and academic areas. As a result a
considerable amount of municipal sewage sludge is generated in the plant which
has no use.
Chemical characterization has been performed on the municipal sewage sludge so
that it can be used as a domestic fertilizer. The present study involves the analysis
of heavy metals such as mercury, arsenic, iron, nickel, copper, zinc, calcium, lead,
chromium, magnesium, aluminum, sodium, potassium, phosphorus, silicon by
using the Atomic Absorption Spectrometer. The physical and chemical parameters
like TOC, hardness, colour, pH, total nitrogen, fluoride has also been determined
for the sewage sludge sample.
Six number of samples are collected from the Sewage Treatment Plant at different
times of the day to have an average data of the measured parameters. The average
values of all the parameters are found out. The samplings are also dried in different
methods to have a comparative study.
Keywords: characterization, sewage, municipal waste
vii
INTRODUCTION
INTRODUCTION
1.1 SLUDGE
The solid byproducts left out after the purification and filtration process of waste water is called
sludge. Sludge is composed of pollutants that have been removed by sedimentation and filtration.
It comprises of solid waste, heavy metals, pathogens and disease causing organisms. Since
sludge is a biodegradable element and is rich in organic content it has various uses in the field of
environmental engineering.
Sludge is the end product of the waste water treatment process. There are many physical and
chemical processes involved in the treatment process which results in the concentration of heavy
metals and many pathogens present in the waste water. But sludge contains valuable nutrients
like phosphorus and nitrogen and also abundant organic matter that is very useful when the soil
is subjected to erosion. The nutrients and organic matter are the two main reasons why sludge
being a waste is used as a fertilizer on lands.
Advantages of using sludge






Land filling: It is the simplest solution for the dumping of sewage sludge. It prevents the
spreading of pathogens/pollutants by concentrating the sludge into a single location.
Incineration: In this method sludge is dried and then burned to recover the energy from
the sludge. Heat from sludge incineration can also be used for heating buildings. Heat
produced can also be used to produce steam and electricity generation. This method
destroys pathogens and decomposes organic chemicals.
Biofuels production: municipal sewage sludge can be used for production of methane
gas which is rich in energy. It is produced by anaerobic digestion in sludge digesters.
Methane gas is used to generate power via turbines. The gas can also be used for
household utilization instead of conventional CNG gas.
Mine reclamation/landscaping/forestry: Extensive heat dried sewage sludge can be
used on landscapes where organic matter has been depleted through continuous irrigation
and cropping/ mining. Here sewage sludge are put in layer in places where soil has no
organic value. This result in the increase in the organic content in soil resulting in
increase in vegetation cover.
Use in Agriculture: In many developed countries this process has been used for
obtaining the nutrients from sludge for plant growth. Sludge is a valuable source of
organic matter and are nutrient rich fertilizers. It can contain even more nutrients present
in inorganic fertilizers.
Other Potential uses include: Use in cement production, as herbicides, as fish food and
also production of bricks.
2
1.2 Sludge Stabilization
For uses in the above processes sludge has to be properly stabilized and must be free from the
toxic organics, heavy metals and disease causing pathogens. It is needed to reduce the harmful
content of the sludge so that it can be used in above said processes. Stabilization helps in
reducing pathogens, eliminating odors and inhibit the potential for putrefaction. Sludge
stabilization is done in following processes.





Alkaline stabilization: In this method alkaline materials are used to make the sludge
unsuitable for survival of pathogens. A commonly used alkaline material is lime.it
increase the pH value to 12 or more. The high pH environment doesn’t destroy the
microorganisms but inhibit their growth.
Anaerobic Digestion: In this method the organic matter is converted into methane and
carbon dioxide by the process of fermentation. Fermentation occurs in the absence of
oxygen. Methane gas can be used for the generation of heat and electricity. The left out
bio solids may be suitable for land application. This process can be done in single stage
or in two stages.
Aerobic Digestion: this process is similar to anaerobic digestion but with the presence of
oxygen. Here no usable gas is produced instead this process is energy intensive. As the
supply of available substrate is depleted the microorganisms try to eat themselves which
lead to their removal.
Auto thermal Thermophilic Digestion: This process of digestion is equivalent to the
aerobic digestion except that huge amount of oxygen is processed to increase the
conversion of organic substances present in sludge. This method is operated at a
temperature of 400C – 800C auto thermally in an insulated tank. There are many
advantages of this method like degradation of the mass of sludge, inactivation of
pathogens and short retention time of sludge.
Composting: It is the process of biological conversion of solid organic matter in an
enclosed reactor or in piles. Composting requires addition of a bulking agent to provide
an environment suitable for biological activity. Volume of compost is always more than
the volume of sludge being composted. This process is very odorous.
In this project work single stage anaerobic digestion has been performed to get the desired
stabilization so that characterization of the sample could be performed.
Sewage Treatment Plant is a facility designed to receive the waste from domestic, commercial
and industrial sources and to remove materials that damage water quality and compromise public
health and safety when discharged into water systems. It includes physical, chemical, and
biological processes to remove various contaminants depending on its constituents.
3
1.3 Objectives of the Study
The principal objective of the study is to use the unused sludge generated from the sewage
treatment plant as a domestic fertilizer. The sludge includes household waste solids from toilets,
baths, showers, kitchens, sinks and so forth that is disposed of via sewers. Sludge contains a lot
of organic matter which if stabilized can be used as manuring agent which can restore the
fertility of the soil.
The objectives of the study are:
1. Physical and chemical characterization of the sewage sludge from the Sewage Treatment
Plant behind V.S. Hall of Residence, NIT Rourkela.
2. Comparison of the N: P: K ratio of the municipal sludge samples with other synthetic
fertilizers and bio solids.
4
1.4 Literature Review
There is always sludge to be disposed of after the waste water treatment. Secondary sludge
treatment plants generate a primary sludge which is generated in the primary
filtration/sedimentation process and a secondary sludge after the final filtration/sedimentation
process. At the time of disposing the secondary sludge is mixed with primary sludge. The
treatment and disposal of sewage sludge cost around half of the original cost. Use of sewage
sludge in land applications can reduce significantly the cost as well as the volume of the sludge
to be disposed of. Also the plant can get necessary nutrients like potassium and nitrogen from the
application of sewage sludge. [1]
In addition to the municipal waste industrial effluents, water from excess rainfall are all
transported to the sewage treatment plant via the sewers. Thus the sewage sludge contains many
toxic materials with the organic materials. Some of those toxic substances can be harmful to the
human/animals so therefore it is necessary to remove or at least control the concentrations of the
toxic materials before their application to the soil. [1]
Sewage sludge also contain many pathogenic viruses and bacteria which can provide a potential
health hazard to the animals, animals or humans whichever tries to be in contact with it. The
pathogenic content in the sewage sludge can be significantly decreased by the application of
sewage sludge treatment before it is used in any land application. The risk is further reduced by
factors like climate, and time which have a very positive effect on the reduction or control of the
pathogenic bacterias. [1]
[2] studied that electrochemical technique is an effective technology that has been applied widely
in the wastewater treatment field for its effective degradation of the refractory pollutants.
Electro-oxidation of pollutants can take place directly on anodes by generating physically
adsorbed active oxygen. The introduction of chloride as supporting mediators for electrolysis
will generate some active chlorine species (Cl2, HClO, and ClO), and these powerful oxidants
could efficiently convert high biopolymer substances to low-molecular weight products in the
region close to the anode surface.
If the mobilization of the anaerobic microorganisms is prevented in the fixed bed digesters, then
it is a very good alternative to reduce the hydraulic retention time of the anaerobic digestion. It
can be done so that the hydraulic retention time of the conventional method is very lengthy. 7080 % of the volatile solids have been removed by the process studied by [3]. By using a fixed
bed reactor the hydraulic retention time was reduced from 20 days in a conventional reactor into
3-7 days.
Hygienization treatment method was adopted by [4] for better production of sludge yields to
fulfill the legislation of American and European nations for the use of land application.
Hygienization treatment is performed after a mesophilic or an anaerobic digestion in a constant
temperature of 60 0C to 80 0C.
5
Effect of Co-digestion of sewage sludge with various biodegradable wastes
Various types of enzymes has been used to speed up the process of anaerobic digestion. This has
been studied by [5]. The enzymes application can improve the anaerobic degradation of lipids,
since it catalyzes the hydrolysis of long chain fatty acids. Enzymes are biodegradable and
harmless for the anaerobic treatment processes and aquatic ecosystems; in addition, their
contribution to the BOD in the waste stream is negligible. Lipases have been used in anaerobic
treatment of fat-wastewater. However, there is a lack of literature regarding the enzyme lipase
application in anaerobic co-degradation of solid-lipid waste.
[6] studied that the suitability of mechanically biologically treated material for the anaerobic
digestion treatment and the effect of these waste products when co digested with sewage sludge.
The results suggested that mechanically biologically treated materials are amenable to anaerobic
digestion with sewage sludge. The material contamination of the mechanically biologically
treated materials provide a major setback in the recycling of MBT materials as well as in codigestion.
Anaerobic co-digestion of fruit and vegetable waste and activated sludge was studied by [7]
using anaerobic sequencing batch reactors. The effects of activated sludge: fruit vegetable waste
ratio and the organic loading rate on digesters performances were examined. Increasing the fruit
and vegetable waste proportions in the digestion process significantly increased the biogas
production yield.
A great number of experiments have been performed on the co-digestion techniques of sewage
sludge with various biodegradable wastes. Some are co-digestion with agro-industrial waste [8],
co-digestion with meat processing by products [9], co-digestion with shredded grass [10], codigestion with rice straw [11] and various other biodegradable waste products. The co digestion
process of sludge with different biodegradable wastes and enzymes increases the efficiency of
the sludge, increase the volume of sludge produced and also increase in production of methane
and hydrogen gas.
6
MONITORING PROTOCOLS
7
2.1 Study Area
National Institute of Technology Rourkela is one of the largest academic institutions in India
with lots of people residing in its campus. Such large number of people will lead to large amount
of sewage from hostels and academic areas. A sewage treatment plant having a capacity of 0.18
MLD has been setup near V.S. Hall of Residence for the treatment of all municipal wastes from
the hostels and academic areas. As a result a considerable amount of municipal sewage sludge is
generated in the plant which has no use.
The sludge used for the research work is primarily obtained from the Sewage Treatment Plant of
capacity 0.18 MLD behind V.S. Hall of Residence and the chemical characterization is done in
the environmental engineering lab.
2.2 Sampling Techniques
Six sewage sludge samples have been collected in contamination free sampling bottles of
1000ml. Samples were collected at different times (8 a.m., 12 p.m., and 2 p.m.) and also with
different consistencies. Two sampling bottles are then kept in a pre-heated oven at 55 0C for 48
hours. Oven temperature was maintained at 550C so that the organic matter of the sample are
intact. In two sampling bottles MgSO4•H2O was added and stirred until lumps of sludge have
been formed. The last two samples were dried in the sun for almost 5-6 days.
8
ANALYSIS TECHNIQUES
9
3.1 Pre-requisite Work

Collection of wet sludge sample from the newly installed Sewage Treatment Plant.

Pre Heating of Sludge sample
This was done by keeping the sludge sample in oven at 55 0C for 48 hours. Oven temperature
was maintained at 550C so that the nutrients of the sample are intact. For Digestion the
moisture content of the sample should be less than 1%, so the sample was heated in oven.
[12]
Other methods were adopted for the removal of moisture from the sludge sample. They were:
o Quick Drying method for a fresh sludge sample
The fresh sludge sample was in liquid state which was difficult to dry in oven in the
period of 24-48 hours. So, MgSO4 was used for its quick drying. MgSO4•H2O is
reducing moisture in a quick time interval 25 to 30 min.
Sample was taken in a beaker and same amount of MgSO4 was taken in that beaker
and stirred. (MgSO4 is to be preheated in the oven at any temperature above 500 0C).
The solution is stirred continuously for 15 minutes. After some time lumps of sludge
sample is formed with a white residue as MgSO4 absorbs all water and only leaves
the sludge which are formed as lumps.[12]
o Sun dried sample
This sample was obtained when it has been already dried by sun for several days. The
same procedure was repeated for this sample also.

Determination of the moisture content
After 48 hours in oven the sludge sample was kept in a desiccator and its moisture content
was determined. This was done by taking a small amount of sample, weighing it and again
heating in oven at 1100C for 24 hours. After 24 hours the sample was taken out and weighed.
Then the moisture content of the sample was determined. [13]
Weight of sample before heating: 10g
Weight of sample after heating : 9.953g
Moisture Content of sample
: Initial weight – Final weight
`
Initial weight
: (10-9.953)/10 *1000/0
: 0.470/0
* 1000/0
10
The moisture content of the sludge sample was 0.47%.
The moisture content of the fresh sludge sample with quick dring technique was found to
be 1.24%
The moisture content of the sun dried sludge sample was found to be 2.67%.

Grinding and sieving of sludge sample
After determining the moisture content the dry sludge is grinded in a small mixer up to 2-3
minutes. Then the whole sample is sieved through a sieve of 75 micron. The particles which
passed and also which did not pass are kept separately in the desiccator so that no moisture is
absorbed by the sludge.

Digestion of Sludge Sample
The moisture content was optimum for the digestion process. Digestion was done in a
microwave digester as it is very fast, efficient and accurate in the process. 0.2g of the sieved
sample is taken in the pressure vessel with 4ml of HNO3, 2ml of HF and 2ml of H2O2. The
vessel is kept inside the digester and the temperature rod is inserted inside the vessel.
Suitable programming is done and left for 2-3 hours. After getting the digested sample, it is
taken in a beaker and diluted to 50 ml with distilled water. The sample is now ready for the
characterization process. [14]
11
3.2 Methodology for the process of Digestion
Digestion means breaking down of complex particles into simpler particles. In case of sludge the
municipal sewage is also broken down into simpler particles like methane, digestate. There are
many methods of digestion but anaerobic digestion the most effective of them all. It reduces the
quantity of sludge to be disposed of and also it provides energy in the form of methane gas. This
increase the effectiveness of anaerobic digestion. Since the disposed sludge is treated, it poses a
minimal threat to the surrounding environment.
Before the digestion process, sewage sludge is properly treated and processed. Some preliminary
operations are..:
Grinding: Large particles present in the sludge are cut and shredded into small particles.
Screening: Here the coarse particles are removed.
Grit Removal: Grits which are not useful are removed.
Blending: The sludge is then mixed with chemicals and stored.
Thickening: water is removed from the sludge to make it thicker.
After performing these processes the sewage sludge is ready to be put inside the anaerobic
digesters so that the anaerobic digestion can take place.
Principle
In this project work the digestion is done in a microwave digester. A microwave digester is a
very fast way to digest and get the results. It is very effective against the normal digestion
techniques. The principle behind the microwave digestion is when a sample is exposed to strong
acids in an enclosed vessel and increasing its temperature by microwave irradiation then it
increase the rate of thermal decomposition of the samples. When the samples are completely
decomposed it becomes easy to detect the heavy metals in the solution through characterization
techniques. [14]
Procedure
The moisture content was optimum for the digestion process. Digestion was done in a
microwave digester as it is very fast, efficient and accurate in the process. 0.2g of the sieved
sample is taken in the pressure vessel with 4ml of HNO3, 2ml of HF and 2ml of H2O2. The vessel
is kept inside the digester and the temperature rod is inserted inside the vessel. Suitable
programming is done and left for 2-3 hours. After getting the digested sample, it is taken in a
beaker and diluted to 50 ml with distilled water. The sample is now ready for the characterization
process. [14]
12
3.3 Methodology for the measurement of pH
pH is the negative logarithm of concentration of hydrogen ions in a sample. pH varies from 6-8
for waste water sample but varies in case of sludge sample. In a sludge sample there can be many
organic and mineral components which may increase or decrease the pH value of the sample. pH
value of a sample can be more than 10 or even less than 5 depending on its content. There is no
specific range within which pH value of a sludge sample can be obtained. Municipal as well as
Industrial wastes affect the pH of a sludge sample. The pH in laboratory may differ than in the
field conditions due to various reasons like reaction with sampling bottles, loss of gases, reaction
with sediments in sampling bottles. Therefore pH value should be determined at the time of
collection of sample. The pH of a sample can be obtained electrometrically as well as
calorimetrically. Electrometrically pH analysis is more accurate than the latter as special
apparatus is required for pH determination. Calorimetrical analysis can be used in case of general
work.
Principle
The pH value is found out by measuring the electromotive force generated in a sample. It is
made up of electrodes that are reactive to hydrogen ions. When is immersed in a test solution, by
the reaction between the reference electrode and test solution a electromotive force is generated.
That force measured in the instrument is pH. Usually pH measuring devices are high impedance
voltmeters. Hydrogen gas electrode is the primary standard. Glass electrode with calomel
electrode is generally used as reference potential provided by the saturated calomel electrode.
The glass electrode system is based on a theory that an electrical change of 59.1 mV occurs when
pH changes by 1 unit at 25 0C. The glass member forms a partition between the two liquids with
varying hydrogen ion concentration and thus a potential is developed between the two sides of
the membrane which is proportional to the difference in pH between the liquids. [15]
The apparatus are:
o pH meter: with reference or glass electrode
o thermometer: with a least count of 0.5 0C
Procedure
The instrument is normalized after its warm tip period. A buffer solution is used to determine the
pH. The electrodes are checked in at least one other buffer solution of different pH value. The
electrodes are taken out gently and wiped to be used in the solution. The electrodes are then
dipped in the digested solution of the sewage sludge sample. After taking out the electrodes they
are washed with normal water and then with distilled water. Then the experiment is repeated for
two other samples.[15]
13
3.3 Methodology for determination of metals
To determine the metals in the digested sludge sample Atomic Absorption spectrometer is used.
The underlying principle of this instrument is that a light beam is passed through a flame
containing atomized particles into a monochromator which then leads to a detector which detects
the presence of those atomized particles by measuring the light absorbed by the atomized
elements in the flame. For determination of each metal a different source lamp is used with the
wavelength identical to the wavelength of the metal which is to be found. This makes it free from
spectral interference. The concentration of the element in the sample is directly proportional to
the amount of energy of characteristic wavelength absorbed in the flame.
The presence of metals in the sludge can be beneficial or troublesome or toxic to the soil or to
the plants or to animals which eat those plants depending upon the concentration. Flame and
electro-thermal methods are generally applicable at low as well as moderate concentrations. The
concentrations of all the metals are determined using Atomic Absorption spectrometer. [16]
Atomic Absorption Spectrometer consists of





A light emitting source
Burner : To atomize the digested sample
A display unit
Hollow Cathode ray lamps
Pressure reducing valves
Fig 2 showing the schematic diagram of an AAS
14
The Atomic Absorption Spectrometer consists of an atomizer which converts the sample in to
atoms. Many atomizers convert sample into atoms through flames. Some example of atomizers
are flame atomizers, electro thermal atomizers, etc. radiation source of most of the AAS is
hollow cathode lamps. These lamps are available in different wavelengths as per the
requirement of the element. The hollow cathode lamps provide a constant supply of radiation
so that the atomized elements can absorb the wavelength of the source and get detected.
When the atoms absorbs the particular wavelength then it is passed through a monochromator
which passes only the element of required wavelength through it. After the element is passed
through the monochromator it gets detected on a detector and gets amplified. Then by signal
processing the concentration of the required element is determined.
Procedure
The sample is prepared according to the metal to which we are measuring. Manufacture’s
operation manual is studied and instrument is operated accordingly. Hollow cathode lamp of the
required metal is installed in the instrument. As per manual is slit width is set for the metal. The
instrument is ran for 20 minutes so that the energy source is stabilized. Then the instrument is
calibrated with a blank solution and three standard solutions of required concentrations. The
absorbance is recorded in the display unit. A graph of absorbance vs concentration is recorded in
the display unit and it came out to be a straight line. Then the sample was analyzed and
concentration of the required metal is recorded. [16]
Fig 1 showing the AAS at Environmental Engineering Lab
15
3.4 Methodology
characteristics
for
determination
of
chemical
All the chemical characteristics of the digested sewage sludge sample was found with the help of
a colorimeter (DRB 200 model) thermostat.
The following chemical characteristics were studied:
 pH
 Total Nitrogen
 Sulphates
 Total organic carbon
 Flourides
Fig 3. A colorimeter (DRB 200 model)
Procedure
The instrument is switched on. Manufacture’s manual is read and the program is set for
determination of TOC. Two samples are created. One blank for calibration of the instrument
and other one with the desired sample. First the blank is inserted and the instrument is
calibrated and then the vial containing the sample is inserted into the instrument. The required
program is selected and the concentration of TOC is obtained. The same steps are repeated for
sulphates, total nitrogen and fluorides.[17]
16
Results and Discussion
17
4.1 Tabulations
The samples are tested in the AAS and the concentrations of various metals and chemical
characteristics are tabulated in Table 1 and Table 2.
Metals
Sample 1 oven dried
Sundried sample
(ppm)
Sample dried with
magnesium sulphate
(ppm)
Mercury
0.001
0.001
0.001
Copper
0.341
0.325
0.320
Zinc
3.733
3.210
2.986
Calcium
15.839
15.102
14.863
Lead
0.129
0.121
0.102
Chromium
0.479
0.423
0.399
Iron
16.308
15.962
14.214
Nickel
0.208
0.196
0.152
Magnesium
4.551
4.217
3.986
Aluminum
70.266
65.244
68.378
Silicon
105.54
50.201
109.245
Potassium
9.868
9.547
9.154
Phosphorus
5.324
5.109
4.214
Sodium
4.424
4.271
3.841
(ppm)
Table 1 showing the concentrations of metals in the three samples.
18
Chemical
characteristics
Sample 1 oven dried
Sample dried with
magnesium sulphate
Sun dried sample
pH
5.9
6.6
6.9
Fluoride (mg/g)
0.07
0.07
0.07
Total Nitrogen
(mg/g)
11.00
10.21
9.24
Sulphate (mg/g)
0.40
0.68
0.32
TOC (mg/g)
6.24
5.21
8.20
Table 2 showing the chemical characteristics of all the three digested sludge sample.
The concentrations of metals and the chemical characteristics of the digested samples collected
at different times are determined and tabulated in Table 3 and Table 4.
Chemical
characteristics
8-11 am
12-3 pm
3-5 pm
Permissible
value
pH
5.9
6.6
6.9
6.5-8.5
Fluoride (mg/g)
0.07
0.07
0.07
1.00
Total Nitrogen
(mg/g)
11.00
10.21
9.24
12.5
Sulphate (mg/g)
0.40
0.68
0.32
1.20
TOC (mg/g)
6.24
5.21
8.20
10.0
Table 3 showing chemical characteristics of the digested sludge sample with time
19
Metals
8-11 am
(ppm)
12-3 pm
(ppm)
3-5 pm
(ppm)
Permissible
value (ppm)
Mercury
0.001
0.001
0.001
2.500
Copper
0.341
0.325
0.320
1.250
Zinc
3.733
3.210
2.986
5.000
Calcium
15.839
15.102
14.863
50.00
Lead
0.129
0.121
0.102
1.500
Chromium
0.479
0.423
0.399
2.500
Iron
16.308
15.962
14.214
30.254
Nickel
0.208
0.196
0.152
1.500
Magnesium
4.551
4.217
3.986
6.500
Aluminum
70.266
65.244
68.378
90.00
Silicon
105.54
50.201
109.245
150.0
Potassium
9.868
9.547
9.154
20.00
Phosphorus
5.324
5.109
4.214
10.00
Sodium
4.424
4.271
3.841
10.00
Table 4 showing metal concentration at different times
20
The concentrations of the nonmetals were found in the C.H.N.S laboratory of NIT Rourkela and
their values are tabulated in Table 5. The values were given in terms of percentage of total
weight volume of the sample. The weight volume of all the three samples are given in Table
6.The concentrations of nonmetals are then converted in mg/g in Table 7.
Nonmetals
Sample1 oven dried
(%)
Sample dried with
magnesium sulphate
(%)
Sun dried sample
(%)
Nitrogen
10.48
7.72
5.24
Carbon
4.36
3.78
3.21
Hydrogen
1.29
1.06
0.86
Sulphur
0.23
0.19
0.14
Table 5 showing the concentration of nonmetals in %
Weightvolume
Sample1 oven dried
Sample dried with
magnesium sulphate
Sun dried sample
8.32
7.48
6.96
Table 6 showing weight volume of the samples.
21
Nonmetals
Sample1 (mg/g)
Sun dried sample
(mg/g)
2.62
Sample dried with
magnesium sulphate
(mg/g)
1.93
Nitrogen
Carbon
1.09
0.94
0.80
Hydrogen
0.32
0.26
0.21
Sulphur
0.05
0.04
0.03
1.31
Table 7 showing concentrations of nonmetals in mg/g
The N: P: K ratios of all three digested sewage sludge samples are calculated. It is calculated by
dividing ppm concentration of the specific element. N: P: K ratio is the percentage of Nitrogen,
Phosphorus and Potassium to the total weight. A fertilizer with an N: P: K ratio of 1:5:7 will
have 1% of the total weight of the fertilizer as nitrogen and 5% as phosphorus and 7% as
potassium.
Sample1 oven dried
(%)
Sample dried with
magnesium sulphate
(%)
Sun dried sample
(%)
Nitrogen
1
1
1
Phosphorus
2.45
3.18
3.87
Potassium
8.63
11.33
11.91
Table 8 showing the N: P: K ratios of all the three samples.
22
The N: P: K ratios calculated for the sludge sample is then compared with the N: P: K ratios of
various synthetic fertilizers and bio solids. The N: P: K ratios of several synthetic fertilizers are
tabulated in Table 9 and various mined fertilizers and bio solids in Table 10 and 11 respectively.
Syntheic Fertilizers
N (%)
P (%)
K (%)
Calcium Nitrate
15
00
00
Ammonium Sulphate
21
00
00
Sulphur coated urea
30-40
00
00
Isobutylidene Diurea
31
00
00
Ammonium Nitrate
33
00
00
Ureaform
35
00
00
Methylene ureas
40
00
00
Urea
46
00
00
Anhydrous Ammonia
82
00
00
Ammonium
Polyphosphate
10-11
34-37
00
Monoammonium
Phosphate
11
48-55
00
Diammonium
Phosphate
18-21
46-54
00
Potassium Nitrate
13
00
44
Super Phosphate
00
17-22
00
Triple
Superphosphate
00
44-52
00
Table 9 showing N: P: K ratios of other fertilizers. [18]
23
Mined fertilizers
N (%)
P (%)
K (%)
Bird guano
11-16
8-12
2-3
3-8
00
Raw phosphate rock 00
Potassium
Magnesium
sulphate
Potassium Chloride
00
00
22
00
00
60
Biosolids
N (%)
P (%)
K (%)
Daily manure
01
00
00
Horse manure
01
00
01
Poultry manure
03
02
02
Bone meal
04
12
00
Fish bone
05
05
06
Milorganite
06
02
00
Table 10 and 11 showing N: P: K ratios of mined minerals and bio solids. [18]
24
Table 1 shows the concentration of metals in the three samples obtained from the Sewage
Treatment Plant behind the V.S. Hall of Residence, NIT Rourkela. It is observed that the
concentration of all the metals vary very little with the method of drying. The sun dried sample
has the least concentrations of metals among all three. Therefore the sun dried method should be
adopted if the sludge is to be used as a fertilizer. The same is true for Table 4 where the
concentration of metals is low around 12 noon to 3 p.m. All the metals in Table 1 and 4 are in
within prescribed limits of the IS codes and are therefore safe to be used as a fertilizer.
Table 2 shows the concentration of fluorides, sulphates, etc of all the three samples. All the
values are very less for the sundried sample. As it is stable and dried in sun all the harmful
characteristics of the sludge is destroyed in the heating process. In Table 3 the concentration of
various chemical characteristics is displayed with respect of the time. Again in the time between
12 noon to 3 p.m. the values are at all-time low and is therefore can be used as a fertilizer.
Table 5 shows the concentration of nonmetals namely Carbon, Nitrogen, Hydrogen, Sulphur are
determined as a percentage to the total weight volume of the sample. The nitrogen content of the
oven dried sample is better than the other counterparts. All the concentrations of the non-metals
are found in the C.H.N.S laboratory of NIT Rourkela. The concentration of nonmetals are
converted from percentage to mg/g in Table 7.
In Table 8 the N: P: K ratios of all three digested sewage sludge samples are calculated. It is
calculated by dividing ppm concentration of the specific element. N: P: K ratio is the percentage
of Nitrogen, Phosphorus and Potassium to the total weight. A fertilizer with a N: P: K ratio of
1:5:7 will have 1% of the total weight of the fertilizer as nitrogen and 5% as phosphorus and 7%
as potassium.
Potassium and phosphorus are present as K2O5 and P2O5. So to find the percentages of N P K we
have to find the total solution weight. The empirical formulas are:
Percentage of Nitrogen = ((concentration of Nitrogen in ppm) / Total solution weight) * 100
Percentage of K as K2O5 = (((conc. of Potassium in ppm) / Total solution weight)*1.2046) *100
Where 1.2046 is the K to K2O conversion factor.
Percentage of P as P2O5 = (((conc. of Phosphorus in ppm) / Total solution weight)*2.2914) *100
Where 2.2914 is the P to P2O conversion factor.
After tabulating the N: P: K ratios of the digested sludge sample, the N: P: K ratios of other
various synthetic fertilizers as well as bio solids are compared with the digested sludge sample
and are tabulated in Tables 9, 10, 11.
25
CONCLUSION
26
Conclusion
Chemical characterization of all the sludge samples were performed. The pH value was found to
be slightly acidic, ranging from 5-7. Concentrations of all the metals are found to be within the
permissible limit prescribed by WHO.
The concentrations of fluoride, TOC, sulphates, total nitrogen are within the permissible value
according to the guidelines of WHO. The concentrations of Mercury (0.001 mg/l), Iron (15.962
mg/l), Lead (0.129 mg/l) was found to be within the permissible value suggested by WHO.
The average N: P: K ratio of the sludge sample taken from Sewage Treatment Plant was found
out to be 1: 3.2: 10.6. The N: P: K ratios of the sludge sample is compared with other synthetic
fertilizers and bio solids. The sludge of the Sewage Treatment Plant has all the characteristics to
be a good domestic fertilizer but its strong and pungent odor creates a problem in its land
application.
27
REFERENCES
28
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29
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30
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