7.6 Vermicomposting

Earthworms are among the most ancient of terrestrial animal groups. Originally they were marine animals. Fossils of Polychaete worms have been found in South Australia in Precambrian sediments 630-570 million years old. Today's earthworms belong to the Oligochaetes. The limits of evolutionary and ecological diversity must be defined by inherent limitations of their mechanical "design" and behavioral and physiological adaptability.

Earthworms are traditionally used in domestic compost heaps and earth toilets. People are now looking for ways to dispose of domestic and industrial wastes without polluting the environment. This has sparked interest in using earthworms for large-scale waste disposal. Worms are thus seen as a biological resource for rural development. Maintaining the diversity of resources such as worms will help ensure a resource base for future technologies such as vermicomposting.

Vermicomposting

The practice of using earthworms for composting is known as vermicomposting. Not all earthworms are useful for vermicomposting. Earthworms are classified into two groups:

· Humus-formers (detritivores) - useful for vermicomposting

· Humus-feeders (geophagous) - useful for soil turnover and tillage. Worms used for vermicomposting should have following characteristics:

· Able to live in active compost.

· Tolerate extreme changes in temperature.

· Multiply fast, undergo rapid incubation, and mature quickly.

· Digest well and have such enzymes as cellulase and chitinase in their gut.

Aristotle described earthworms as "intestines" of the earth. Charles Darwin wrote about earthworms, "it may be doubted where there are many other animals which have played so important a part in the history of the world as have these lowly organized creatures."

Humus former

· Surface dwelling
· Red color
· Feed on nearly 90% fresh organic matter and 10% soil
· Harnessed for vermicomposting

Humus feeder

· Deep burrowing
· Pale color
· Feed on nearly 90% soil and 10% nearly degraded or humified organic matter
· Useful in making the soil porous and mixing and distributing humus through soil

Humus former and feeder

Species useful for vermicomposting are:

Effects of vermicomposting on indigenous species

It is not possible to use both exotic and endemic humus-forming species for vermicomposting. Exotic species multiply very rapidly and outgrow the endemic species.

However, using humus-forming exotic species for vermicomposting can be useful. Fast turnover of organic matter by these humus-formers produces food rich in bacteria and humus for the indigenous humus-feeders. The humus-feeders can then multiply very fast under vermicompost heaps and after the compost is added to the field, stimulating their soil processing activities such as aeration, tunneling and soil turnover.

Vermicomposting for rural sanitation

Earthworms can be used to process human faeces. Vermiculture may be particularly useful for treating sewage in rural areas. Research has shown that some types of bacteria found in faeces, Serratia marcessens and Escherichia coli, are killed when they are ingested by the earthworm L. terrestris. The worms reduced numbers of the pathogen Salmonella erteriditis to a level of 2000-fold less, possibly because of competition from the endemic microflora of the worm gut.

Earthworms aerate sewage sludge and speed its drying, thereby favouring aerobic bacteria. Since most human enteric pathogens are anaerobes, sludge condtioning by earthworms can be beneficial from the public health standpoint. More research is needed on the effect of vermicomposting on other enteric bacteria, pathogenic viruses and parasites.

In villages in India, vermicomposting of latrine waste mixed with other agricultural waste can help dispose of sewage and produce valuable compost that can increase soil fertility and agricultural production.

Vermicomposting for rural sanitation

Vermicomposting of sewage sludge

· Aerobic sludge ingested by E. fetida is decomposed and stabilized about three times as fast as non-ingested sludge.

· Objectionable odors disappear more quickly.

· Marked reduction in populations of Salmonella enteriditis and other Enterobacteriaceae.

· Anaerobic sludge and sun-dried sludge is toxic to E. fetida.

· Sewage sludge can be, mixed with cellulosic and lignin-rich wastes.

· Earthworms, which accumulate heavy metals and agrochemicals from sewage, may be environmentally hazardous if used as protein source.

Practical applications of biodiversity

Symbiotic relationship between detritivorous worms and micro-organisms

Vermicomposting potential

· Population of India is 8,000,000.

· The average person produces an average of 1/2 kg of excrete every day.

· 4,000,000 kg of night soil, if vermicomposted, would yield 2,000,000 kg of humus-rich organic compost a day.

· Considering the night soil of the 70% of the population living in villages, nearly 1,400,000 kg vermicompost could be prepared every day.

Prepared by Dr. Jambbekar