Introduction: Solid wastes are all the wastes arising from human and animal activities that are normally solid and that are discarded as useless or unwanted. It also encompasses the heterogeneous mass of throwaway from residences and commercial activities as well as the more homogenous accumulators of a single industrial activity.

Types of solid wastes: The types and sources of solid wastes and the physical and chemical composition of solid wastes are to be considered. Three general categories are considered

(1). Municipal wastes: The classification of materials comprising of municipal solid waste is as follows.

·          Food waste

·          Rubber

·          Ashes and Residues

·          Demolition and construction wastes

·          Special wastes

·          Treatment plant wastes

(2). Industrial wastes: Those wastes arising from industrial activities and typically include rubbish, ashes, demolition and construction wastes, special wastes and hazardous wastes.

(3). Hazardous wastes: Wastes that pose a substantial danger immediately or over a period of time to human, plants or animal life are classified as hazardous wastes. A waste is classifies as hazardous if it exhibits any of the following characteristics. (a) Ignitability (b) Corrosivity (c) reactivity (d) toxicity.

                Hazardous wastes were often grouped into the four categories. (i) Radioactive substances (ii) Chemicals (iii) Biological waste (iv) Flammable wastes and (v) Explosives. The chemical category includes wastes that are corrosive, reactive or toxic. The principal sources of hazardous biological wastes are hospitals and biological research facilities.

Functional Elements:

The activities involved with the management of solid wastes from the point of generation to final disposal have been grouped into six functional elements.

(i)                   Waste generation

(ii)                 On site handling, storage and processing

(iii)                Collection

(iv)                Transfer and transport

(v)                  Processing and recovery

(vi)                Disposal 

Solid waste generation:

Solid wastes include all solid or semisolid material that is no longer considered of sufficient value to retain in a given setting. It should be noted that the wastes that are discharged may be of significant value in another setting.

Factors that affect generation rates:

• Season of the year

• Frequency of collection

• Characteristics of the population

• Public attitude

• Geographical location

Disposal of solid waste:

·          Mechanical volume reduction or Compaction - Mechanical compactors are used to compress the waste materials so as to form bales that can be placed in big containers.

·          Incineration or thermal volume reduction - Combustible waste such as plastics, cardboard and rubber are subjected to burning at high temperature in hearth furnaces. If not carried out properly incineration results in air pollution.

·          Open dumping - It is done in low lying areas and outskirts of city. This method has various disadvantages as it causes foul smell due to release of obnoxious gases. Moreover it becomes breeding ground for flies, mosquitoes which causes various health hazards.

·          Destructive distillation or pyrolysis – Heating the solid waste under anaerobic conditions is referred to as pyrolysis. The organic waste spilt up in fractions of CO, CO₂, CH₄ and tar.

·          Landfilling- Solid waste is dumped into low lying areas in the upper layers of the earth’s surface and spread in thin layers. With course of time decomposition of the organic matter occurs and there is conversion to stabilized end products. It is a simple and economical method.

·          Landfarming – In this method the organic waste is either applied on top of the land or injected below the soil surface where it undergoes bacterial decomposition.

·          Composting - There is bacterial decomposition of the organic matter and converted into humus. The volume is considerably reduced and is made free of pathogenic organisms. In this process compost pile is made by alternate layers of organic matter and soil which acts as a source of micro-organisms. It is a hygienic method which converts solid waste into manure by anaerobic bacterial action.