As with the backyard compost pile, the micro-organisms, which effect the decomposition, are ingredients to the wastes themselves, but when there is a variety of domestic wastes, granulation of the dry waste is necessary along with a thorough mixing to ensure homogeneity and definite control of moisture content as well as complete aeration of the material being treated. Under these conditions, the wastes decompose rapidly at decomposition temperatures which are lethal to pathogenic organisms.
A completely automatic system involves several steps. The crude refuse is dumped into a container on to a belt conveyor, and then iron or metallic particles are removed by a magnetic separator. There is also a means for extracting magnetic metal materials which will not decompose. The degradation of the material actually occurs in a rotating cylinder similar to a rotatory drier.
This cylinder contains as much as 5 day’s supply of refuse, depending upon the degree of treatment required, and these wastes are delivered to the cylinder in a moistures condition. This cylinder rotates slowly on large ‘tyres’, much like a cement kiln, and the wastes move from one end towards the other. They are thoroughly mixed and granulated by abrasion. Air is added at low pressure and in controlled amounts throughout the length of the cylinder. In this manner, an environment is created where the action of aerobic micro-organisms ensures a rapid decomposition of the wastes under inoffensive conditions.
Normal operating temperatures up to 140° F are spontaneously developed. The final process material is, then, delivered on to a conveyor belt and through a screen where the compost is separated from more durable matter, and delivered into a storage container, where splinters of glass from bottles, etc. are extracted. From 100 tonnes of crude refuse, it is possible to extract between 60 and 70 tonnes of compost. India has made remarkable and speedy progress in organizing many compost plants. Four plants have already gone into production, while 21 other plants are at various stages of completion/implementation.
The Ahmadabad plant was commissioned in 1975, the Baroda plant in 1977, while the Bangalore and Calcutta plants were recently commissioned. The plant at Bombay has the largest capacity, viz., 300 TPD. The minimum plant capacity is 100 TPD.
In India, mechanical compost plants were encouraged by the Government of India as a national programme. Under this scheme, substantial incentives are also offered to municipal corporations for generating infra-structure facilities to ensure supplies of refuse to compost plants. The know-how and equipment required for the establishing of compost plant is indigenously available. In fact, Indian Engineering firms are coming out with many innovative and practical suggestions and are offering equipments with know-how at competitive prices.
Indian know-how is now offered to other needy countries by the National Research Development Corporation-a Government Company. There is another interesting and useful area where compost is used-the Indian Agricultural Research Institute, Pusa, New Delhi, has developed strains of blue green algae for use in rich fields for direct nitrogen fixation. An appropriate technology is being developed in India to produce blue green algae coated granulated compost. The importance attached to and the momentum that composting has attained is clearly reflected by studying the list of installed and proposed units as given important design consideration for anerobic composting processes and for anaerobic digestion.