Environmental Engineering

Vermicompost

Content Cover Image

By Red58bill (Own work) [CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

caption Vermicompost/vermicast

Vermicomposting, which is composting using worms, can be a faster alternative for organic waste treatment, with the added advantage of better quality fertilizer with nutrients in the slow-release form. Vermicomposting also adds valuable soil microbes into compost and digestive fluids of worms can also be beneficial. Vermicomposting is the breakdown of organic material that, in contrast to microbial composting, involves the joint action of different species of earthworms (not all earthworms are composting worms) and microorganisms and does not involve a thermophilic (i.e., high heat) stage. Because the matrix contains many different organisms, this can be considered as an anthropogenic ecosystem. As the agents of turning, fragmentation and aeration, the worms consume organic wastes such as food waste, animal wastes and sewage sludge to produce a soil conditioner. Vermicomposting may only process organic waste of a suitable structure for worms and the optimum waste streams include some food wastes, sewage sludge, garden waste (leaves and grass) and manure. Studies have shown that vermiculture is an effective method of treating pathogen-rich waste materials and domestic solid and liquid wastes. Charles Darwin was the first to write that worms could be used in converting organic waste into a fertilizer.

In the absence of high temperatures reached (as in microbial composting), pathogen inactivation takes place by the actions of worms (digestive fluids, competition for available nutrients, consumption). The waste material treated in normal microbial composting is mostly dry, as higher moisture content can reduce the interstitial space thus reducing air passage. This can lead to process failure, as aerobic microbes cannot survive in the absence of oxygen. In vermicomposting, higher humidity is tolerated/required as worms can survive humid environments and the burrows created by worms act as channels for air passage. Thus vermicomposting is less labor-intensive in this regard. A varied substrate mass can be treated by wet vermicomposting. A good carbon to nitrogen ratio is required (C:N = 20-35) as high nitrogen content can cause ammonia which is toxic to worms. Unlike microbial composting, aeration demand for heat removal is avoided because high temperature are never met in vermicomposting - making the process easier and cheaper. In vermicomposting, lack of adequate air can cause worm fatality or worm migration and thus the cause of process failure is evident.

caption Red worm
caption European nightcrawler

The worm castings (worm excreta) from vermicomposting contain plant nutrients encased in mucus membranes secreted by the worms. These dissolve slowly rather than allowing immediate nutrient leaching. Vermicompost includes worm castings, some earthworm cocoons, inert materials such as sand and rocks, fibrous and woody material and some undigested waste material that will continue to be decomposed by the indigenous bacteria in the soil. Some species of composting worms are native to temperate climate, such as Eisenia foetida (tiger worm or red wiggler), Dendrobaena veneta (European nightcrawler) and Lumbicus rubellus (red worm), while some come from the tropics such as Eudrilus eugeniae (African nightcrawler) and Perionyx excavatus (Indian blueworm). So accordingly, it could be expected the favorite diet of worms will show locally adapted variations. Vermicomposting is sometimes known as vermiculture because the worms can be harvested from the mass and used in aquaculture.

Glossary

Citation

Panikkar, A. (2014). Vermicompost. Retrieved from http://www.eoearth.org/view/article/51cbef257896bb431f69cb1c

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