VERMICOMPOSTING: BASIC PROCESS
The preparation of vermicompost involves five stages as shown inTable.5.The process takes place in the mesophilic temperature range (35–40◦C). The different phases during the process are as follows:
Initial pre-composting phase: The organic waste is pre-composted for about 15days before being fed to earthworms. During this phase, readily decomposable compounds are degraded and the potential volatile substances are eliminated which may be toxic to earthworms. Pre-composting the feedstock decreases the amount of energy contained within the material, so that heating doesn't take occur within the worm system. Feedstock which are pre-composted for 10-14 days retain sufficient nutrition for the worms, but not so much energy that they are able to generate heat (Nair, et al, 2006)
Mesophilic phase: The predigested waste material should be mixed with 30% cattle dung either by weight or volume. The mixed waste is placed into the tub / container up to brim. The moisture level should be maintained at 60%. If necessity arises, water should be sprinkled over the bed rather than pouring the water. Over this material, the selected earthworm is placed uniformly. For one-meter length, one-meter breadth and 0.5-meter height, 1 kg of worm (1000 Nos.) is required. During this phase, earthworms, through their characteristic functions of breaking up organic matter, combine it with the soil particles and enhance microbial activities and condition organic waste materials for the formation of organic manures.
Maturing and stabilization phase: In the vermicomposting process, the action of the earthworms is both physical/mechanical and biochemical. Physical participation in degrading the organic substances results in fragmentation, thereby increasing the surface area for further microbial colonization. Biochemical changes in organic matter decomposition are carried out through enzymatic digestion, enrichment by nitrogen excrement and transport of organic and inorganic material. The passage of material through the earthworm intestine rapidly converts the locked up minerals of nitrogen, potassium, phosphorus, calcium etc. into the forms that are much more soluble and available to plants than the parent material. This is made possible by various enzymes present in their gut as well as enzymes of certain type of ingested microorganisms, viz., proteases, lipases, amylases, cellulases, chitinases, etc which degrade the cellulosic and proteinaceous materials in organic waste. The earthworms seem to have developed mutualistic relationship with microorganisms ingested for decomposition of organic matter present in their food. Thus, the final quality of the vermicompost is the result of combined efforts taken by earthworms and the microorganisms.
Table.5: The steps involved in the process of vermicomposting
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Step 1 |
Collection of wastes, shredding, mechanical separation of the metal, glass and ceramics and storage of organic wastes. |
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Step 2 |
Pre-digestion of organic wastes by heaping the material along with cattle dung slurry. This process partially digests the material and fit for earthworm consumption. Cattle dung and biogas slurry may be used after drying. Wet dung should not be used for vermicompost production. |
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Step 3 |
Preparation of vermibed. A concrete base is required to put the waste for vermicompost preparation. Loose soil will allow the earthworms to go into soil and also while watering; all the dissolvable nutrients go into the soil along with water. |
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Step 4 |
Collection of earthworm after vermicompost collection. Sieving the composted material to separate fully composted material. The partially composted material will be again put into vermicompost bed. |
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Step 5 |
Storing the vermicompost in proper place or room to maintain moisture and allow the beneficial microorganisms to grow. |
Mechanism of Earthworm action
Earthworms promote the growth of ‘beneficial decomposer aerobic bacteria’ in waste biomass and also act as an aerator, grinder, crusher, chemical degrader and a biological stimulator. Earthworms host millions of decomposer (biodegrader) microbes in their gut. Edwards (1988) showed that the number of bacteria and ‘actinomycetes’ contained in the ingested material increased up to 1000 fold while passing through the gut. A population of worms numbering about 15,000 will in turn foster a microbial population in billions in short time. Under favourable conditions, earthworms and microorganisms act ‘symbiotically and synergistically’ to accelerate and enhance the decomposition of the organic matter in the waste.
It is the microorganisms which breaks down the cellulose in the food waste, grass clippings and the leaves from garden wastes.The waste feed materials ingested is finely ground (with the aid of stones in their muscular gizzard) into small particles to a size of 2-4 microns and passed on to the intestine for enzymatic actions. The gizzard and the intestine work as a ‘bioreactor’; The worms secrete enzymes proteases, lipases, amylases, cellulases and chitinases in their gizzard and intestine which bring about rapid biochemical conversion of the cellulosic and the proteinaceous materials in the waste organics.The final process in vermiprocessing and degradation of organic matter is the ‘humification’ in which the large organic particles are converted into a complex amorphous colloid containing ‘phenolic’ materials. Only about one-fourth of the organic matter is converted into humus.