Municipal Solid Wastes Handling and Management

1. Prof. M.R.Ezhilkumar
Assistant Professor
Department of Civil Engineering
Sri Krishna College of Engineering and Technology
Coimbatore
ezhilkumar@skcet.ac.in
I only feel angry when I see waste.
When I see people throwing away
things we could use. – Mother
Teresa
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17CE413
SOLID AND HAZARDOUS
WASTE MANAGEMENT
2.12 – Principles of aerobic and
anaerobic composting

2. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar 2
Learning Outcomes
☼ Biological conversion
☼ Aerobic Conversion
☼ Anaerobic Conversion
☼ Anaerobic Fermentation
☼ Anaerobic Digestion
2.12 – Principles of aerobic and anaerobic composting

3. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar 3
Video Session
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4. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
 Biological conversion of municipal solid wastes is becoming more and more popular
these days.
 End products that can be derived from biological conversion of solid wastes include
compost, methane, various proteins, alcohols, and a variety of other intermediate
organic compounds.
 Principal processes that are used for biological conversion are Aerobic Conversion
(Composting), Anaerobic Conversion, and Anaerobic Fermentation and
Digestion.
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Biological Processing

5. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Aerobic Conversion
 Composting is the most commonly used process for the decomposition of the organic
components of MSW.
 In this system the non-biodegradable components e.g. plastics, rubber, paper, leather
are separated out from MSW and the biodegradable fraction is allowed to decompose
in an aerobic environment.
 This produces a humus like material known as compost.
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Composting

6. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Aerobic Conversion
 The biological and chemical changes that take place during composting can be
described as,
 Organic fraction of MSW includes nutrients and several kinds of microorganisms.
 Microorganisms are mainly responsible for the conversion of MSW into compost.
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Composting

7. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Critical Design Parameters in
Composting
 Critical design parameters which
affect the composting process are
Particle Size, Moisture content,
Carbon to Nitrogen (C/N) ratio, pH,
Temperature, Blending and
Seeding, Air circulation by mixing
and turning, and Control of
pathogens and Odor.
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Composting

8. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Particle Size
 Organic fraction of solid wastes are generally irregular in shape.
 Smaller size of particle increases the biochemical conversion rate during composting.
 Size of particles to be composted should preferably be less than 50mm. For optimum
results, 25mm and 75mm is preferred.
 Shredding can be carried out for reducing the size of waste particles.
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Composting

9. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Moisture content
 An important parameter in the design of a composting system.
 MC to be maintained between 50 – 60 % (Optimum: 55%).
 If MC is less than 40%, the process biological conversion slows.
 MC can be controlled by addition of water to the wastes or by blending of the wastes
with sludge from treatment plant
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Composting

10. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
C/N ratio
 It is a critical parameter in the desing of composting system.
 Ratio for composting should be ideally between 25 and 50 (Optimum:- 25:1).
 In general, the nitrogen present in the organic fraction of waste will be available for
biodegradation, but all the carbon available may not be biodegradable.
 C/N ratio can be adjusted by blending of wastes of high C/N ratio (e.g. saw dust,
paper) with the wastes of low C/N ratio (e.g. yard wastes, raw activated sludge)
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Composting

11. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
C/N ratio
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Composting

12. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
pH Control
 pH during the composting process varies with time.
 Initially when organic components of wastes are broken down biologically they
convert into organic acids and bring down the pH level to less than 5.
 The desirable value of pH for composting is between 7 & 7.5.
 If pH value decreases to less than 4.5 it reduces the rate of biological conversion.
 If it rises to more than 8.5, some nitrogen is lost as ammonia.
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Composting

13. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Temperature
 Temperature control is required in the composting process as it affects the growth of
cells and rate of composting.
 Initially the temperature is maintained between 50 and 55OC.
 After a day or two, it is increased to between 55 and 60OC, the microorganisms die
out and biological activities reduce significantly.
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Composting

14. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Blending and seeding
 Blending is carried out to achieve the required moisture content and C/N ratio.
 Laboratory tests are carried out in order to determine the proportions of wastes for
blending.
 Seeding is the process of adding microorganisms culture to the wastes to be
composted.
 This is required to accelerate the biological decomposition of wastes.
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Composting

15. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Air requirement
 Aeration is an important requirement for aerobic composting.
 Air is supplied to the composting system through frequent turning of wastes or
through air nozzles.
 In a highly controlled composting system, pure oxygen is supplied for oxidizing the
biological fraction of solid wastes.
 The quantity of oxygen or air is required for composting depends upon the
composition of solid waste.
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Composting

16. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Mixing and turning
 Mixing and turning are two important operations of composting process.
 Mixing is carried out to obtain a homogeneous mixture of biodegradable components.
 It also helps in uniform distribution of nutrients and micro organisms in the wastes, so
as to accelerate the biological transformation of wastes.
 Turning of slid wastes is carried out at regular interval.
 This provides sufficient amount of air required for aerobic conversion of solid waste.
 Carried out to maintain the moisture content uniform through the mass of composting
material.
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Composting

17. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Pathogens control
 The control of pathogens is important in the design of any composting system as their
presence is a health hazard.
 The most important parameter in pathogen control is the ambient temperature in the
composting system.
 Most of the pathogens die off at a temp of 55OC, though some may survive even at
temperature more than 60OC.
 Pathogens can be completely removed from the composting material by maintaining
its temperature at about 70OC for 1 to 2 hrs.
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Composting

18. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Odor control
 Odor control in the composting is necessary, as otherwise it will create nuisance in
the neighborhood.
 Odor is produced due to insufficient supply of oxygen to the wastes during their
biodegradation.
 Lack of oxygen in the wastes results in anaerobic conditions generating various
malodorous organic acids and gases such as ammonia, and hydrogen sulfide.
 Large size particles present in the wastes also prevent flow of air.
 Shredding and conversion of wastes to smaller size is to be done before composting.
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Composting

19. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Types of Composting Systems
 Depending upon the status of wastes during the process, composting systems can be
broadly classified as agitated and static.
 In an agitated system, the waste to be composted is agitated to supply oxygen.
Turning is usually carried out for this purpose.
 In a static system, wastes are kept static while the air is supplied by mechanical
means such as blowers.
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Composting

20. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Types of Composting Systems
Three main methods are
 Windrow method
 Static pile method
 In-vessel method
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Composting

21. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Windrow method
 Windrows of wastes of about 1.5 to 2m height and 4 to 5 m width are prepared.
 Waste materials are shredded before making windrows.
 The size of windrows also depend upon the size of equipment available for turning.
 Turning is carried out at regular intervals.
 The moisture content is maintained between 50 to 60 percent.
 This system takes about four to six weeks to convert the waste materials into
compost.
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Composting

22. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Windrow method
 The composted material obtained ist hen cured (i.e. allowed to stand without turning)
for a period of two to three weeks for complete stabilization.
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Composting

23. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Static Pile method
 In static pile method the waste is kept in static piles.
 These piles are provided with a grid of perforated pipes, which are used to supply the
air.
 The air may be heated to the desired temperature.
 This method is faster and provide better control than the windrow method.
 The waste materials are composted in a period of two to four weeks.
 It is then cured for a further period of two to three weeks.
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Composting

24. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
In-Vessel method
 As the name suggest “in-vessel composting” is carried out in a closed container.
 Various types of vessels or containers e.g. vertical cylinder, horizontal cylinders,
rectangular or circular tanks can be used for composting.
 Mechanical agitators are used for mixing of composting materials.
 Air can be supplied through nozzles connected with blowers.
 The merit of this system is a high degree of control over temperature, air, pH, odor
etc.
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Composting

25. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
In-Vessel method
 This system is therefore popular, especially in developed countries.
 The system takes about one or two weeks for converting waste into compost but a
longer curing period, about four to ten weeks, for complete stabilization.
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Composting

26. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Properties of Compost
 Compost, the final end product of composting, is better than a chemical fertilizer for
agriculture purposes.
 It is also ecofriendly and economically attractive.
 Good quality compost should be blackish brown in color with an earthy odor.
 It should be slightly moist with pH range between 6.5 and 7.5.
 It should also not contain excessive amount of heavy metals.
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Composting

27. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Properties of Compost
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Composting

28. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Neighborhood Composting
 Can be a viable option for disposal of biodegradable wastes especially in residential
areas.
 The location and capacity of compost plants is best determined according to the
amount of biodegradable component generated in the area.
 Residents welfare societies and other voluntary organizations may participate in this
tasks.
 The entire biodegradable wastes from households can be collected and transferred to
the nearby composting unit.
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Composting

29. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Neighborhood Composting
 This will minimize the transportation cost also.
 The final compost can be utilized for development of parks, gardens and for
plantation of trees in that neighborhood.
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Composting

30. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Anaerobic Conversion
 In this process organic waste materials are fermented in the absence of air.
 Depending upon the concentration of solids in the wastes, this system can be
categorized as low-solid digestion and high-solid digestion systems.
 This system is suitable for the production of biogas from wastes such as cow-
manure, agricultural wastes.
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Composting

31. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Anaerobic Conversion
 Anaerobic fermentation of SW is carried out in three basic steps,
1. Preparation of the organic fraction of solid wastes for anaerobic digestion. Usually
includes receiving, sorting, separation, and size reduction.
2. Addition of moisture and nutrients, blending, pH adjustment (6.7), heating of slurry
(55 – 60 deg Cel), and finally anaerobic digestion in a reactor. A continuous flow of
solid waste is maintained keeping the contents well mixed for about 5 to 10 days.
3. Collection, storage, and if necessary separation of the gas components evolved
during the digestion process.
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Composting

32. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Vermiculture
 It is a simple, low cost and appropriate biotechnology used for the stabilization of
organic municipal solid wastes using earthworms or other mircoorganisms.
 Earthworms, particularly, burrowing type consume biodegradable organic matter and
produce material termed as vermicomposting which mainly consists of earthworm
excreta.
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Composting

33. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar
Vermiculture
 This process includes,
a) Separation of biodegradable fraction of MSW
b) Maintenance of proper moisture and temperature
c) Addition of minerals and selected burrowing type of earth worms
d) Sieving the vermicasting. The vermicasting production is formed at the rate of 75 kg per 1000 kg of
MSW.
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Composting

34. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar 34
Assessment Time
Review
Question
Justify the significant control parameters in composting.
Give their optimum values and the methods for controlling the
same.

35. SHWM – Module 2 – MUNICIPAL OF SOLID WASTES HANDLING AND MANAGEMENT  Mr.M.R.Ezhilkumar 35
End of this topic