Solid waste, often called the third pollution after air and water pollution, as that material which arises from various human activities and which is normally discarded as useless or unwanted. It consists of the highly
heterogeneous mass of discarded materials from the urban community as well as the more homogeneous accumulation of agricultural, industrial and mining wastes.
Solid wastes may be classified based partly on content and partly on value. A typical classification is as follows :
(a) Garbage : Refers to non-putrescible solid waste constituents produced during the preparation or storage of meat, fruit, vegetables, etc. These wastes have a moisture content of about 70% .
(b) Rubbish: Refers to non-putrescible solid waste constituents either
combustible or non-combustible. Combustible waste would include paper,
wood, scrap, rubber, leather etc. Non-combustible wastes are metals, glass , ceramics etc. These wastes contain a moisture content of about 25% and the heating value of the waste is around 15 x 106 J/kg.
(c) Pathological Wastes: Dead animals, human waste, etc. The moisture content is 85% and there are 5% non-combustible solids.
(d) Industrial wastes: Chemicals, paints, sand, fly ash etc.
(e) Agricultural wastes: Farm animal manure, crop residues, etc.
In India authentic information regarding the composition of the urban wastes is not generally available as regular analysis of the refuse is not carried out by the municipalities. In fact, refuse is very heterogeneous in composition and the geographical, temporal and seasonal variations in its composition make it difficult to define a “typical refuse”. The solid refuse generated in urban areas contains articles of various sizes and types and consists of dust, vegetable leaves, waste paper, large paper-board cartons, glass bottles, worn out tyres, carcasses of animals and night soil.
Potential Methods of Disposal
In recent years new and better methods for solid waste management have been suggested and / or developed. Some of the ideas are discussed in this section.
(a) Utilization: Many solid wastes generated by industry can be utilized directly. Fly and bottom ash from power plants can be used commercially, largely as cement substitute. New uses are being developed for fly ash, e.g.,. to make bricks, do dewater industrial wastewater sludge, as a land cover etc. India produces about 6 x 10 tones of bagasse from sugar cane annually. This bagasse can be utilized for the manufacture of paper pulp which can displace hardwood pulp of similar quality and cost. There are some novel uses of sugar cane bagasse. One sugar cane company in South Africa has integrated its operation with the production of eggs and dairy products.
(b) Recovery and Recycling : Solid wastes contain significant amounts of valuable materials like steel, aluminum, copper and other metals which, if they are recovered and reused, would reduce the volume of the wastes to be collected and at the same time would yield significant salvage and resale income. In addition, better reclamation techniques will help to save valuable natural resources and turn wastes, which could be dangerous, into useful products. Some important solid wastes that have been successfully reclaimed are paper, glass, metals and plastics.