mechanical composting..its problems

Almost all the large cities of the developing countries in the region in the past installed imported mechanical composting plants (for instance, built six). Most are now defunct and the remaining ones are not operating at full capacity (e.g., Bangkok, Hanoi, Shanghai, and Tokyo). The reasons why centralized mechanical MSW composting plants are not functioning effectively, are underutilized, or are closed down include: (a) high operating and maintenance costs compared to open landfilling (including foreign exchange costs for replacement parts of imported plants); (b) the cost of compost is higher than commercial fertilizers (both cost to purchase, and labor cost to apply to the fields); (c) incomplete separation of materials such as plastic and glass, making the compost poor for agriculture application; and (d) poor operation and maintenance of the facilities.

There are many technical and aesthetic problems to be solved in the composting of MSW. As one small example, an important, privately run vermiculture experiment in Indonesia failed when toxics in the MSW killed the earthworms.

 

Composting can be viable, especially for smaller cities with intensive agricultural areas near cities. Many international agencies and environmental consulting firms are offering Asian cities technology for composting as the process is increasingly gaining importance in all parts of the world. An issue here is whether the equipment offered is appropriate for the wastes of that particular place

 

Although one of New Delhi's plants has been closed, another is still operating. The compost is absorbed by the city's parks department, an example of how city procurement policies can help the marketing problem. In Kathmandu, the compost from a municipal plant was in high demand by local farmers in the late 1980s and early 1990s, and the plant continued with a simple windrow system after the machinery broke down. It was forced to close recently when residents of new housing estates protested.

Recently, however, private firms, alone or in public-private partnership, have revived centralized composting in a few places. Bangalore's windrow compost plant is reported to be cost-effective since privatization, although there are now NIMBY ("Not In My Back Yard") pressures at the site. There are experiments with new techniques for producing compost by processing partly decomposed wastes at dump sites (being done by a private company subsidized by the Bombay and Ahmedabad municipal corporations).

The subcontinent has wide experience with anaerobic digestion of cattle dung, and it was assumed that similar digesters could be adapted to ferment MSW, but producing animal-dung-like slurries from urban organic waste proved energy-intensive and the product was poor. A major problem with anaerobic digestion is that MSW used as feedstock tends to float. A number of design changes have to be achieved to produce small-scale digesters. Research is being done in Bangalore at the Indian Institute of Science, but there are no reports of successful large-scale anaerobic digestion.