This document discusses various waste disposal and processing technologies including landfills, thermal conversion, biological and chemical conversion, and recycling. Landfills are engineered facilities for waste disposal that must consider site characteristics and manage landfill gas and leachate. Thermal conversion includes combustion, pyrolysis, and gasification to convert waste into energy. Biological processes like aerobic composting and anaerobic digestion stabilize organic waste. Recycling and various unit operations can recover materials from waste streams. Proper waste management requires an integrated approach considering environmental and public health impacts.

1. Waste disposal and
processing

2. Contents
1. Landfills
Landfill site consideration
Landfill gas
Leachate
2. Unit operations for processing
3. Thermal conversion technologies
combustion
dioxin
pyrolysis
gasification
4. Biological and chemical conversion technologies
aerobic composting
anaerobic digestion
5. Recycling at a glance

3. Landfills
 These are the physical facilities for the disposal of residual solid waste in the
surface soils of the earth
 Sanitary landfill refers to an engineered facility for the disposal of MSW
designed and operated to minimize public health and environmental impacts
 Landfills for the disposal of hazardous waste are called secured landfills
 The term cell is used to describe the volume of material placed in a landfill
during one operating period, usually one day
 A lift is a complete layer of cells over the active area of landfill
 Daily cover usually consists of 6-12 inches of native soil or alternative
materials

4. Landfill site consideration
1. Haul Distance
2. Location restrictions
3. Available land area
4. Site access
5. Soil conditions and topography
6. Climatologic conditions
7. Surface water hydrology
8. Geologic and hydro geologic conditions
9. Local environment conditions
10. Ultimate use for completed landfills

5. Landfill Gas
 "Landfill gas" is not the same thing as "natural gas" or "methane." They are
three separate terms which mean different things. They should not be used
interchangeably. The term "landfill methane" is deceiving as it's usually used
to imply that landfill gas is simply methane.
 Natural gas is approximately 80-99% methane, with the remainder being
mostly other hydrocarbons (ethane, propane, butane, etc.) as well as some
nitrogen, oxygen, water, CO2, sulfur and various contaminants.

7. Leachate
 The liquid that collects at the bottom of the landfill is known as leachate. In
deep landfills leachate s often collected at intermediate points. In general
leachate is a result of percolation of precipitation, uncontrolled runoff and
irrigation water into the landfill
 Leachate can also include water initially constituted in the waste. It is a
source of ground water pollution
 Leachate contains a variety of chemical constituents derived from
solubilisation of the materials present in the landfill
 Clay layer and geomembrane serves as a barrier for the movement of
leachate

9. Unit operations used for processing
1. Size reduction
It is the unit operation used to reduce the size of the materials in MSW. It is
done to use the process material directly for composting.
Types of equipments used – hammermill shredders, shear shredders, tub
grinders
2. Size separation
In this process screens are used to separate waste on the basis of size
3. Density separation
typical applications include air, classifiers for the preparation of RDF; inertial
separation for the processing of commingled waste; floatation for processing
of construction debris

10. Contd..
4. Electric and magnetic field separation
Typical applications include, separation of plastics or paper; the separation of
ferrous from non ferrous materials
5. Densification (compaction)
These are the unit operations that are used to increase the density of recovered
materials to reduce transportation costs and simplify storage. Typical
applications include baling for cardboard, paper, plastics, and aluminium cans;
and the use of cubing and pelletizing for the production of densified RDF.
6. Materials handling
Typical applications include conveyors for transport of MSW and recovered
materials, storage bins; rolling stock such as forklifts, front-end loaders,etc,

11. Thermal conversion technologies
It is the conversion of waste into gaseous, liquid and solid conversion products.
On the basis of air requirement it is of three types

12. Combustion (Incinerators)
 It is a process of chemical oxidation with excess air
 End products include nitrogen, carbon dioxide and flue gas
 Energy can be recovered by heat exchange from the hot combustion gases
 Solid waste combustion systems are designed to operate with two types of
solid waste fuel
1. commingled solid waste(mass fired)
2. processed solid waste refuse-derived fuel (RDF-fired)

14. Dioxins
"Dioxins" refers to a group of toxic chemical compounds that share certain
chemical structures and biological characteristics. Dioxins can be released into
the environment through forest fires, backyard burning of trash, certain
industrial activities, and residue from past commercial burning of
waste(incinerators). Dioxins break down very slowly and past releases of dioxins
from both man-made and natural sources still exist in the environment.
Almost every living creature has been exposed to dioxins. Studies have shown
that exposure to dioxins at high enough levels may cause a number of adverse
health effects, including cancer. The health effects associated with dioxins
depend on a variety of factors including: the level of exposure, when someone
was exposed, and for how long and how often someone is exposed.

15. Pyrolysis
 Thermal processing of waste in complete absence of oxygen
 pyrolysis use an external source of heat
 Gasification on the other hand is self sustaining
 It is an endothermic process
 Three major components resulting from pyrolysis process are:-
1. a gas steam(hydrogen, methane, carbon monoxide, carbon dioxide)
2. a liquid fraction( tar, oil stream of complex hydrocarbons)
3. a char(pure carbon)

17. Gasification
 Process of partial combustion
 Efficient technique for volume reduction and energy recovery
 Generation of a combustible fuel gas rich in CO, hydrogen and some saturated
hydrocarbons
 This gas can be used in IC engines, gas turbine, or boiler under excess-air
conditions
 It is an exothermic process

19. Biological and chemical conversion
technologies

20. Aerobic composting
 This is most commonly used for the conversion of organic portion of the MSW
to a stable humus like material known as compost
 volume reduction is up to 50%
 Processing time is 20 to 30 days
 Applications of aerobic composting include
1. yard waste
2. separated MSW
3. commingled MSW
4. co-composting with waste water sludge

21. Anaerobic digestion
 It is used to produce methane from organic fraction of MSW
 The first step involves hydrolysis of higher-molecular mass compounds
 The second step involves conversion to low-molecular mass compounds
 The third step involves intermediate compounds to simpler end products,
principally, methane and carbon dioxide.
 The process is net energy producer
 Time required is 20-40 days
 Volume reduction is up to 50%

22. Recycling at a glance

23. References
 http://www.syngastechnology.com/
 http://www.pyrolysisplant.net
 http://Yokogava.com
 Wikipedia.org
 George Tchobanoglous Integrated solid waste management
 http://www.environmentalchoice.co.za

24. Thanks..