CHEMICAL CHARACTERISTICS

Information of chemical characteristics is important in evaluating alternative processing and recovery options. Typically waste is considered as combination of combustible and noncombustible components. If solid waste is to be used as a fuel or for any other use we should know its chemical components.

Lipids

These are included in the class of fats, oils and grease. The principal sources of lipids in the garbage are cooking oil and fats. Lipids have high heating values about 38,000 Kj/Kg (kilojoules/kilograms), which makes the waste with high lipid content suitable for energy recovery. Since lipids become liquids at temperature slightly above ambient they add to the liquid content during waste decomposition. They are biodegradable, but they have low solubility in water and hence the rate of biodegradation is slow.

Carbohydrates

These are primarily originated from the food sources rich in starch and celluloses. These readily biodegrade into carbon dioxide, water and methane. Decomposition of carbohydrates attracts the flies and rats and hence should not be left exposed for long duration.

Proteins

These are the compounds containing carbon, hydrogen, nitrogen and oxygen and organic acid with amino groups. They are primarily found in food and garden wastes, but their partial decomposition result in the production of amines, which impart unpleasant odors.

Natural Fibers

These are the natural products contain cellulose and lignins that are relatively resistant to biodegradation. These are found in paper products, food and yard wastes. Paper is almost100% cellulose, cotton over 95% and wood products over 40-50%. These are highly combustible products most suitable for incineration. The calorific value of oven dried paper products are in the range 12000-18000 kj/kg.

Synthetic Organic Materials

In the recent years plastics have become a significant components of solid waste, accounting for 1-10%. They are highly resistant to the biodegradation; hence their presence in the waste is objectionable. Currently much attention is given to reduce this component at disposal sites. Plastics have a high heating value, about 32000 kj/kg, which makes them very suitable for incineration. However, among the plastics Polyvinyl chloride (PVC) when burnt produces dioxin and acid gas. The trace gases produced during the burning of plastic are proved to be carcinogenic.