1. Solid Waste Disposal
Lecture - 3

2. Incineration
Incineration is a thermal treatment process by which the waste is burnt to ashes, in the presence of excess oxygen, to reduce the hazardous nature and / or toxicity of the wastes. Volume /mass reduction of the wastes is also achieved by incineration.
Incineration can also be defined as a controlled combustion process for reducing solids, liquids, sludge’s and gaseous combustible wastes primarily to carbon dioxide, other gases and relatively non-combustible, though occasionally hazardous, residue. Overall, incineration is becoming very attractive as an alternative hazardous waste disposal method.

3. Land filling
Land filling is not strictly a disposal method, but really one of containment or indefinite waste storage. Many landfills are used for the disposal of municipal and hazardous waste. The latter are “co-disposed” with the municipal waste utilizing the absorptive properties of the bulky municipal waste and the microbial degradation reactions with occur wherever putrescible material is buried.
There is now a move towards exploiting the microbial methanogenic processes in landfills and using them as bioreactors to both dispose of waste and also produce methane which can be recovered and used as source of energy.
The advantages of Landfilling are that it is relatively inexpensive; methane production can be exploited from municipal wastes and the wastes can be recycled or treated at a later date.
The disadvantages are that there is a danger of leakage and pollution of groundwater, a danger of explosions from methane and the problem that there are fewer and fewer suitable sites available.
Modern landfills sites need to be located in impermeable strata or sealed with an appropriate membrane before the wastes are deposited and should have a system for managing the leachate.

4. Composting
Involves shredding and separating the putrescible fraction of municipal waste, often mixing it with other organic materials (including sewage sludge) and allowing microbiological decomposition reactions to take place. This involves regular turning of the compost in order to promote aerobic decomposition processes and allowing the compost temperature to rise sufficiently to kill off pathogenic organisms and weed seeds and other undesirable constituents.
The finished compost is intended for use as a growing medium for plants. Especially for substitute for peat which is a scarce resource from an ecosystem at risk of destruction with the accompanying problems of extinction of species.