VERMITECHNOLOGY IN WASTE MANAGEMENT
Open dumping is the prevailing method of solid waste disposal in many of the developing countries. It has become increasingly expensive and hazardous to the natural environment. Therefore, presently there is an urgent need to explore the potential of earthworms in waste management. For millennia, earthworms have been preparing soil for the colonization and evolution of plants. They have played a commendable role in agriculture. Their value in supporting the waste disposal and management systems is being realized by the day. Earthworms, in dense culture and in large quantities, can physically handle virtually any biological waste.
Vermitechnology, based on this inherent ability of earthworms has the capacity to handle large quantities of organic wastes and is seen as a viable industrial process capable of sustained commercial operation (Sharma, S., et al, 2005).The core of the system is the process bed in which millions of worms are regularly fed with organic waste and from which worm stabilized organic matter, referred to as vermicompost, is harvested.
Feeds for Vermitech systems
1. Animal manures
Use of animal manure as primary feed for earthworms is very common in vermitech systems. Cattle solids are the most suitable of all animal wastes for earthworm biomass increase. They usually do not have materials that deter the growth of earthworms. Cowdung slurry is a suitable substrate for vermicomposting, both when mixed with solid materials or on applying to the surface of bedding materials containing earthworms. Horse manure is also suitable for the growth of earthworms. (Manaf, L.A., et al, 2009) Horse manure contains 0.7 % of nitrogen, 4.38 % of protein and 60 % of organic matter, trace amounts of phosphoric acid and potassium oxide (Ronald and Donald, 1977) and can therefore be applied directly as feed. Waste from the piggeries is probably regarded as the most productive refuse for growing the earthworms. Poultry wastes are higher in protein content, nitrogen and in terms of phosphoric acid than any other animal manure. The fresh waste generated from the poultry farms contains significant amount of inorganic salts, and if used directly might threatened the survival of the worms (Edwards, 1988).These wastes have to be pretreated by composting, washing or simply by aging process to reduce the inorganic salt content and the heating potential.
2. Kitchen Waste and Urban waste
The residential and the commercial portion make up to about 50 to 70 percent of the total Municipal solid wastes (MSW) generated in a community. The solid waste so generated can be of two types:
A. Biodegradable or organic- kitchen waste, straw, hay, paper and animal excreta.
B. Non-biodegradable- ash, stone, cinders, plastics, rubber and metals.
The food waste from domestic households and restaurants and other yard waste are good for growth of earthworms (Gandhi M, et al,1997;Bharadwaj, A., 2010). Vegetable scraps from kitchen and other yard wastes provide ideal feed bed for growing earthworms. Earthworms digest municipal biosolids along with green mulch. About two thirds of this volume becomes vermicompost. (Giraddi, R.S., et al, 2008; Singha, R.P, 2011)
3. Paper pulp and card board solids
Paper and cardboard are excellent materials, both for feeding and for the bedding of earthworms due to their cellulose content. Earthworms convert cellulose into its food value faster than the proteins and other carbohydrates .These wastes do not need any special pretreatment and can be applied directly as a feed. In a recent work, Basheer, M and Agrawal,O.P.(2013) successfully utilized epigeic earthworm, Eudrilus eugeniae for the conversion of paper waste into vermicompost.
4. Compost and waste products
Spent mushroom compost is also a good medium to grow earthworms. It is low in plant nutrients. Brewery waste needs no modification, in terms of moisture and the worms can process it quickly.
5. Industrial Wastes
Wastes from the canning plant and potato chip or corn chip manufacturing unit are excellent food for worms. Wastes generated from vegetable oil factory are also suitable as feed (Kale, 1998). Wastes from logging and carpentry industries and sugar factories are also used as substrate to feed earthworms. When the earthworms are reared in the ratio of 1:1 sawdust and press mud, the cast generated shows 1.2 times more CFU (Colony Forming Units) than saw dust and 1.6 times more than the press mud (Parthasarathi,et al., 1999).Earthworms can partially detoxify wastes. The fly ash waste generated from the thermal power plants creates a major disposal problem due to its heavy metal content although it is supposed to be very rich in microbial biomass. It was found out that the organic waste, sisal green pulp, Parthenium and green grass cuttings admixed with 25% of fly-ash proved to be a potential valuable material for E.fetida biomass. The vermicompost so produced contains higher NPK content than the other available commercial manures. In some cases, earthworms are also used in the management of distillery waste containing wastes of malt, spent grain wash, yeast and molasses settled at the bottom of the lagoon. Seenappa, et al., (1995) observed that the total volume of cow dung leaf litter should be proportional to the total volume of distillery waste and press mud to have positive impact on the growth and production of worm biomass. Lakshmi and Vijayalakshmi (2000) reported that the filter press mud from the sugar factory could be used as a feed in the vermicomposting units. It is seen that after worms have worked on it, the press-mud is converted to nutrient rich manure and its physico-chemical features improved after vermicomposting. In 2011, Murali,M.,et al reported that coir wastes could be converted into vermicompost by utilizing Eudrilus Eugeniae. Studies by this author reported that chip wash residue, a kind of wood waste from wet-process hardboard factory could be converted into vermicompost by utilizing E. eugeniae (E.Sreenivasan, 2013a).
Other applications
1. In aquaculture
In aquaculture, the most common method of solid waste disposal is land spreading, which causes pollution of soil, surface and ground water bodies resulting in untimely death of aquatic organisms. Vermicomposting of such waste controls water and soil pollution, thereby ensuring better survivability and growth offish, prawn and other aquatic organisms within its natural habitat. The application of vermi-castings, which is a high-grade organic fertilizer to the aquaculture ponds, reduces the input cost and makes the aquaculture process more profitable. It also helps in combating the harmful effects against chemical fertilizer if so ever present in the receiving water.
Large-scale vermiculture has the potential of supplying earthworm meal as a substitute for fishmeal. (Pucher J, et al, 2014) Earthworm meal contains all the essential amino acids required in fish feed. The methionine and lysine availability is higher than that of the normal fishmeal. There is also an increasing demand for protein-rich raw materials in other animal-feed industry.
2. Vermifilter
Ground Water Recharge
Earthworm increases the hydraulic conductivity and natural aeration by granulating the clay particles. They also grind the silt and sand particles, increasing the total specific surface area, which enhances the ability to adsorb the organics and inorganics from the wastewater. This is ideal for dilute wastewater (such as sewage). Figure shows the vermifilter that could be used to recharge groundwater. The loading rate of wastewater is calculated as 2m2/m3 of sewage. Earthworms ensure bio-sanitation and prevent sewage sickness through effective regeneration of adsorption ability with their bacterial farming along with their grazing act on surplus bacterial biomass (Bhawalkar, 1995).
Water recovery
It is possible to have single or multiple stage vermifilter depending on the strength of the wastewater and desired quality of renovated water. In principle, a single unit can produce any given purity of water by increasing the recyclable ratio, which reduces the organic loading. The first stage achieves roughing filtration and the second stage achieves polishing (Bhawalkar, 1995).