1. PB389 Integrated Solid Waste Management
Numfon Eaktasang, Ph.D.
Thammasat University

2. Solid Waste Management
generation
Waste reduction
and separation at the source
Collection
Transportation
Separation, processing & transformation
Disposal

3. Disposal Technology Dumping on land Burial Hog feeding Incineration
Sanitary landfill
Composting
Biogas

4. Processing compost for market
Compost must be of a consistent size
Free from contaminants: glass, plastic, metals
Free of objectionable odors

5. Processing compost for market
Shredding and screening

6. Processing compost for market
Additives may be added to enhance the value of the final product.
Design and packaging

7. Aerobic composting

8. Aerobic composting

9. Anaerobic digestion Low-solid anaerobic digestion
High-solid anaerobic digestion

10. Low-solids anaerobic digestion
solids concentration equal to or less than 4 to 8 %.
used in many parts of the world to generate methane gas
from human, animal, agricultural wastes, and organic fraction of MSW
disadvantage in the application to solid waste
requirement of water addition to achieve 4 to 8 % of solids concentration
diluted digested sludge, which must be dewatered prior to disposal

11. Low-solids anaerobic digestion
Process description
First step: preparation of input materials (sorting, separating, size reduction)
Second step:
addition of moisture and nutrients, blending, pH adjustment to about 6.8, and heating of the slurry to between 55 and 60 degree-C
anaerobic digestion in a continuous-flow reactor (completely mixed) or a series of batch reactors
adequate mixing is important to avoid foaming and the formation of surface crusts
Third step:
capture, storage and, if necessary, separation of the gas components
dewatering and disposal of the digested sludge

12. Low-solids anaerobic digestion

13. Low-solids anaerobic digestion
Process design considerations
Size of material: shredded to a size that will not interfere with the efficient functioning of pumping and mixing operations
Mixing equipment: to achieve optimum result and to avoid scum buildup
Percentage of solid wastes mixed with sludge: amounts of waste varying from 50 to 90 %, typically 60%
Hydraulic and mean cell-residence time: washout time is in the range of 3 to 4 day. Use 10 to 20 day for design
Loading rate: 0.04 to 0.10 lb/ft3/d (0.6 to 1.6 kg/m3/d)
Solids concentration: equal to or less than 8 to 10%
Temperature: Between 30 to 38 degree C for mesophilic, and between 55 and 60 for thermophilic reactor

14. Low-solids anaerobic digestion
Process design considerations, contd.
Destruction of volatile solid wastes: depends on the nature of the waste characteristics. varies from 60 to 80 percent. 70% can be used for estimating purpose.
Total solids destroyed: varies from 40 to 60 %, depending on amount of inert material present originally.
Gas production: 8 to 12 ft3/lb (0.5 to 0.75 m3/kg) of volatile solids destroyed (CH4=55%, CO2=45%)
Selection of equipment and facilities
type of mixing equipment: internal mixers, internal gas mixing, and external pump mixing
General shape of the digester: circular, egg-shaped
Control systems
dewatering system of digested sludge

15. Low-solids anaerobic digestion
Conventional circular type and egg-shaped type

16. High-solids anaerobic digestion
a total solids content of about 22 % or higher
relatively new technology, and its application for energy recovery from MSW is not fully developed
Advantages are
lower water requirements
higher gas production per unit volume of the reactor size
Process description
Almost same as the low-solids process
less effort is required to dewater and dispose of the digested sludge

17. High-solids anaerobic digestion
Process microbiology
the effects of many environmental parameters on microbial population are more severe, because of high solids concentration
Process design considerations
size of material: shredded to a size that will not interfere with the efficient functioning of feeding and discharging mechanisms
mixing equipment: depend on the type of reactor
percentage of solid wastes mixed with sludge: depend on the characteristics of the sludge
Mass retention time: Use 20 to 30 day for design
Loading rate based on biodegradable volatile solids: to 0.4 lb/ft3/d (6 to 7 kg/m3/d), but not well defined
Solids concentration: between 20 and 35 % (22 and 28% is typical)

18. High-solids anaerobic digestion
Process design considerations, contd.
Temperature: Between 30 to 38 degree C for mesophilic, and between 55 and 60 for thermophilic reactor
Destruction of biodegradable volatile solid wastes: varies from 90 to 98 percent, depending on the mass retention time and the BVS loading rate.
Total solids destroyed: varies depending on the lignin content of the feedstocks.
Gas production: 10 to 16 ft3/lb (0.625 to 1.0 m3/kg) of biodegradable volatile solids destroyed, (CH4=50%, CO2=50%)

19. Example:
Estimate the amount of methane that can be recovered form ton of waste, consisting of the organic fraction of MSW, and its dollar value. Assume that the following conditions and data apply.
Moisture content of organic fraction of MSW = 20%
Mass retention time = 30 days
Volatile solids, VS = 0.93 x TS (total solids)
Biodegradable volatile solids, BVS = 0.7 x VS
Expected BVS conversion efficiency = 95%
Gas production = 8 ft3/Ib BVS destroyed
Energy content of biogas = 500 Btu/ft3
One therm of power = 105 Btu/therm
The value of one therm of power = $0.60/therm

20. Solution
Determine the mass of volatile solids in one ton of organic waste.
Mass VS = 1 ton x 2000 Ib/ton x 0.8 (moisture content) x 0.93 = 1488 Ib
Determine the mass of BVS destroyed based on one ton of organic waste.
Mass of BVS destroyed = 1488 Ib x 0.7 x 0.95% = Ib
Determine total volume of gas produced from one ton of organic waste.
Gas produced = Ib x 8 ft3/Ib BVS destroyed = 7916 ft3
Determine total Btu content of the gas.
Btu = 7916 ft3 x 500 Btu/ft3 = 3.96 x 106 Btu
Determine total value of the gas produced from one ton of organic waste.
Value, $/ton = [(3.96 x 106 Btu)/ (105 Btu/therm)] x $0.60/therm = 23.76

21. High-solids vs. Low-solids anaerobic digestion
Comparative analysis of the low-solids and high-solids anaerobic digestion process consideration for the organic fraction of MSW
Design and/or operational parameter
Comment
Low-solids
High-solids
Reactor design
Complete-mix reactors have been used in large-scale systems for MSW. Plug-flow reactors are used widely for other materials.
Complete-mix, plug-flow, and batch reactors have been studied experimentally.
Solids content
4 to 8 %
22 to 32 %
Reactor volume
Large volume is required
A much smaller volume is required
Water addition
large volume is required
much less
Organic loading rate
Relatively low rate per unit of reactor volume
relatively high rate per unit of reactor volume
Gas production rate
Maximum rate of up to 2 volumes per active reactor volume have been reported
Maximum rate of up to 6 volumes per active reactor volume have been reported
Mass removal rate
low due to higher water content
significantly higher rate in the same retention time period

22. High-solids vs. Low-solids anaerobic digestion
Comparative analysis of the low-solids and high-solids anaerobic digestion process consideration for the organic fraction of MSW, contd.
Design and/or operational parameter
Comment
Low-solids
High-solids
Mechanisms for feeding and discharging
Pumps of all types have been used
not well defined due to new technology. High-solids pumps and screw conveyors have been used
Toxicity problems
less severe
Salts and heavy metals are more common. Ammonia toxicity is a major problem with low C/N ratios
Leachate problem
Stabilized effluent can generate leachate problem
effluent normally contains 25 to 30 % solids, which minimize the leachate generation potential
Effluent dewatering
Large and expensive facilities to separate solids. separated water should also be treated.
Inexpensive equipment is adequate
Technology status
Not commercialized for energy recovery from MSW. The commercial use for agricultural waste is worldwide.
Not commercialized for MSW.

23. Application of anaerobic digestion
Great interest in applying anaerobic digestion
opportunity to recover methane
fact that the digested material is similar to compost produced aerobically.
Many investigation has been done for application to the organic fraction of MSW.

24. Anaerobic digestion (Biogas) plant in Rayon Municipality

25. Anaerobic digestion (Biogas) plant in Rayon Municipality
- Receiving area
- Manual removal of contaminants (plastics)
- conveyor and shredder for preprocessing

26. Anaerobic digestion (Biogas) plant in Rayon Municipality
Gasholder
Digester
Dewatered sludge

27. Anaerobic digestion (Biogas) plant in Rayon Municipality

28. Anaerobic digestion in household scale
Biogas

29. Combined high-solid anaerobic digestion/Aerobic composting
Organic fraction of MSW
High-solids anaerobic digester
Aerobic composter
Complete-mix or plug-flow reactor
Complete-mix reactor
Fuel for power plants
Humus

30. Combined high-solid anaerobic digestion/Aerobic composting

31. Combined high-solid anaerobic digestion/Aerobic composting
Organic fraction of MSW
Digested sludge
Blend tank
Mixer
High-solids anaerobic digester
Aerobic composter
Plug-flow reactor
Sludge
(optional)
Biogas
Thermal energy
Aerobic
reactor
Dryer
Humus
Soil amendment
Fuel for power plants

32. Other biological transformation processes
Biological processes for the recovery of conversion products from the organic fraction of MSW
Process
Conversion product
Preprocessing
Aerobic conversion
Compost (soil conditioner)
Separation of organic fraction, particle size reduction
Anaerobic digestion (landfill)
Methane and carbon dioxide
None
Anaerobic digestion (low-solids)
Methane and carbon dioxide, digested solids
Anaerobic digestion (high-solids)
Enzymatic hydrolysis
Glucose from cellulose
Separation of cellulose-containing materials
Fermentation (following acid or enzymatic hydrolysis)
Ethanol, single-cell protein
Separation of organic fraction, particle size reduction, acid or enzymatic hydrolysis to produce glucose

33. Thank YOU