All solid and semi-solid waste arising from human and animal activities, except human- excrete and sullage (liquid wastes from bathroom and kitchen etc.) those are discarded as useless or unwanted, are included in the term solid wastes.
The term solid wastes encompasses the highly heterogeneous mass of discarded materials or throwaways from urban community as well as the more homogeneous accumulation of waste generated by agricultural, industrial and mining activities. Solid waste (waste other than liquid or gaseous) can be classified as municipal, industrial, agricultural, medical, mining waste and sewage sludge.
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Solid waste may be classified based partly on content and partly on moisture and heating value. A typical classification is as follows:
1. Municipal Solid Waste:
Municipal solid waste consists of household waste, construction and demolition debris, sanitation residue, and waste from streets. This garbage is generated mainly from residential and commercial complexes. They may be categories as:
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Garbage:
Refers to the putrescible solid waste constituents produced during the preparation or storage of meat, fruit, vegetable etc. these waste have a moisture content of about 70% and a heating value of around 6106 J/kg.
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Rubbish:
Refers to non-putrescible solid waste constitute, either combustible or non- combustible. Combustible wastes would include paper, wood, scrap, rubber, leather etc., while non-combustible waste are metals, glass, ceramics etc. these waste contain a moisture content of about 25% and the heating value of the waste is around 15106 J/kg.
2. Hospital Waste:
Hospital waste is generated during the diagnosis, treatment or immunization of human beings or animals or in research activities in these fields or in the production or testing of biologicals. It may include wastes like sharps, soiled waste, disposables, anatomical waste, cultures, discarded medicines, chemical wastes, etc.
These are in the form of disposable syringes, swabs, bandages, body fluids, human excreta, etc. The moisture content is 85% and there are 5% non-combustible solids. The heating value is around 2.5106J/kg. This waste is highly infectious and can be a serious threat to human health if not managed in a scientific and discriminate manner.
3. Industrial Waste:
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They include chemicals, paints, sand, metal ore processing, fly ash, sewage treatment sludge etc. Manufacturing industries produce wastes which are solid or semi-solid. This waste can be self-igniting, explosive, toxic or radioactive. Chemical process industries generate a variety of waste, both organic and inorganic, which are mixtures with wide range of component concentration.
4. Agricultural Waste:
These include farm animal manure, crop residue etc. Animal and vegetable waste contain valuable minerals and nutrients. Humus from agricultural wastes contains nitrogen, phosphorus, potash and trace elements which are vital to the fertility of the soil and optimum plant growth.
Burning of these wastes as fuel in the conventional manner makes poor use of the leaf content of the fuel burnt and further, leads to loss of valuable nutrients. In India, agricultural wastes content is around 2 kg/person day.
