ADVERTISEMENTS:
In some countries (particularly in third world) wastes (solid as well as liquid) are the major source of pollution due to generation in large quantities, and pose environmental problems.
Wastes generated after biogas production in the form of slurry, used as compost for agricultural fields. The human and animal excreta are used for biogas production. The ‘Integrated Health and Energy System Project’ for poor countries used for growing Spirulina, an alga rich in protein. The sewage is also used for the growth of Spirulina.
The liquid effluents are added in artificially constructed ponds meant for cultivation of algae. In such system, NaNO3 and NaHCO3 are mixed so as to induce growth of Spirulina.
ADVERTISEMENTS:
The liquid coming out from factories and sewage, after treatment proved beneficial for irrigation purposes. Large quantities of organic wastes are used for cultivation of mycelial forms and other fungal forms. Such waste, if enriched in cellulose (agricultural waste) proved as a potential source for production of enzymes (cellulases and xylanases), proteins, biogas, ethanol, glucose, fructose syrup, etc..
Urban (city) garbage is a problem in Indian cities. It is estimated that production of city garbage in India is about 41,000 tonnes per day; the annual production is about 15 million tonnes.
Nonetheless, city garbage produced in Bombay, Chennai and Kolkata is comparable to that of developed countries. In India, garbage is dumped in the outer skirt of the cities. In some big cities, municipal solid waste composting plants are in operation.
ADVERTISEMENTS:
The Bombay and Delhi, Municipal Corporations have already established treatment plants. The Central Mechanical Engineering and Research Institute, Durgapur has established a first pilot plant to produce electricity by using city garbage.
The plant has a capacity to use about 500 kg garbage/ha, as a result of which about 5 KW electricity can be generated. Process of electricity production is the conversion of garbage anaerobically into biogas and in turn into electricity. Now-a-days, municipal, agricultural and light industrial wastes are used for conversion into energy by direct burning in refuse fired energy system.
The mixture of wood and bark waste burnt directly is collectively called “hog fuel”. The hog fuel combustion technology has been developed in the USA. This fuel is produced in large sized boilers made up of steel. A cogeneration technology has been developed to generate electricity from hog fuel, and to use the exhaust heat in the form of process steam for manufacturing operations.
