26 Vermicomposting

Dr. Yogalakshmi K. N

 

Objectives:

1.      To familiarize the definition of vermicomposting

2.      To gain knowledge on the benefits and types of Earthworms used for vermicomposting of solid waste

3.      To understand the process and essential requirements of vermicomposting process

4.      To gain knowledge about the nutritive value of vermicompost

Vermicomposting

It is the process of composting biodegradable wastes into worm castings using selected species of worms such as earthworm, red wrigglers and white worms. It is the nature’s way of recycling organic nutrients from dead tissues back to living organisms. The organic waste is broken down or decomposed into vermicompost or humus or worm manure. The worm castings are highly beneficial to the soil. The vermicomposting process takes place in long troughs where the temperature is maintained below 35ºC. The vermicompost produced contains water soluble nutrients and serves as an excellent nutrient rich organic fertilizer and soil conditioner. They contain reduced levels of contaminants and a higher saturation of nutrients than the organic waste before vermicomposting. The vermicomposting process relies on the earthworms to mix, aerate and fragment the waste combined with the biodegradation process of the microorganisms.

Since composting is a biodegradation process it not only leads to compost formation but also other products that require control and treatment like the leachate which is formed when there is high moisture content. Leachate generated is allowed to collect in channels and is discharged into sewers. They have the composition and properties of leachate from landfills. Gaseous emissions consisting of highly volatile organic compounds that are malodourous and potentially toxic are also generated by the composting process.

Vermicomposting is practised in small-scale or home systems for wastes from kitchen and garden such as vegetable and fruit peels, coffee grounds and filters, tea bags, grains such as moldy and stale bread, cracker and cereal, eggshells, leaves and grass clippings etc. In large-scale or commercial, vermicomposting is practised for wastes that include cattle wastes, sewage sludge, brewery waste, cotton mill waste, agricultural waste, food processing and grocery waste, cafeteria waste, grass clippings and wood chips.

Phase of vermicomposting

Vermicomposting is carried out in several phases as described below

Collection and separation

This phase involves the collection of wastes from various sources. Before taking it to vermicomposting, a minimum preprocessing is required. It includes mechanical separation of the metal, glass and ceramics, segregation, storage of organic wastes. The separated organic wastes can be used as such or shredded. Shredding increases the surface area and fasten up the decomposition process.

Digestion of organic wastes

The organic wastes must be pre-digested for a period of twenty days by heaping the waste along with cattle dung slurry. Digestion partially digests the wastes, making it suitable for earthworm consumption. Dried cattle dung and biogas slurry can also be used. Wet dung is usually avoided in vermicomposting process as they generate too much heat during decomposition.

Preparation of earthworm bed

Earthworm bed is very essential as they act as nesting and breeding grounds of the worms. Loose soil is a suitable bed for the earthworms. The earthworm drags the waste to the bed and consumes them in its burrow built in the bedding material. Also, while watering, all the dissolvable nutrients go into the soil along with water.

Collection of the vermicompost

The completely composted material is separated by sieving. The uncomposted or partially composted material will be once again put into vermicomposting pit bed for further composting.

Storage of the compost

The vermicompost obtained after sieving are stored in proper cool and shady place to maintain moisture and allow the growth of beneficial microorganisms.

Essential conditions for survival of the compost worms

Bedding

The worm requires a suitable environment for its survival. Bedding is any material that provides a relatively stable habitat for the worms. The bedding environment should have the following characteristics such as a good food source, adequate moisture and aeration, protection from temperatures. Based on these characteristics the bedding materials are chosen for effective vermicomposting. The mentioned characteristics are discussed in detail below.

High absorbency (Moisture)

Worms breathe through their skin and therefore require a moist environment for their survival.

If a worm’s skin dries out, it dies. Therefore, the bedding should possess good water retention and absorption capacity so that worms can thrive well in the bedding material.

Good bulking potential (Aeration)

Worms require oxygen to live, just as we do. So the bedding material should be packed in such a way that there is an adequate supply of air to support the life of the worms. Tight packing or if the material is too dense, then the air flow is restricted resulting in death of worms. The overall porosity of the materials used for bedding is determined by factors such as the particle size and shape, texture, strength and rigidity. The overall effect is referred to as the material’s bulking potential.

Low protein and/or nitrogen content (Food source)

During the process of vermicomposting, the bedding material is consumed by the worms. It should be ensured that the material breaks down at slow pace. Low protein/Nitrogen source is suitable for the worms because high protein/nitrogen levels can result in rapid degradation and its associated heating. It also creates inhospitable atmosphere for the worms. Often, high protein/nitrogen levels become fatal to worms. Moreover, heating can occur safely in the waste layers of the vermicomposting system, but not in the bedding.

Methodology for the production of vermicompost

Selection of suitable earthworm

Epigeic or surface dwelling earthworm are suitable for vermicomposting process. Of about 350 species of earth worms found in India with varied food and burrowing habits, the Red worms (Eisenia fetida), African earthworm (Eudrilus eugeniae) and composting worm (Perionyx excavates) are some of the species that are reared to convert organic wastes into manure. The African worms (Eudrillus eugenial) are much preferred over the other two types, because it produces higher production of vermicompost in short period of time and produces more young ones in the composting period.

Selection of suitable location

The earthworms should be cultured in an sheltered environment to protect the worms from excessive sunlight and rain. Vermicomposting process requires shaded place with high humidity and a cool environment. Abandoned cattle shed, poultry shed, basements, back yards or unused buildings are used. If composting is to be carried out in an open area, shady place is selected and provided with thatched roof to protect the process from direct sunlight and rain. The waste layered or heaped in vermicomposting pit can be covered with moist gunny bags to avoid dryness and maintain moisture.

Selection of Containers

Cement tanks of dimensions 2½ x 3 feet height and breadth, respectively are used for vermicomposting process. However, the length of the tank depends upon the size of the room. The tank should be well drained with a sloppy bottom to drain the excess water from vermicomposting unit. The drained water is collected in a small sump built next to vermicomposting tank. Vermicomposting can also be performed in wooden boxes, plastic buckets or in any containers at a smaller scale. Care should be taken to provide drain hole at the bottom of the wooden containers.

Vermiculture bed

As mentioned earlier bedding material is very essential for earthworms to live in the vermicomposting pit. The bedding material can be prepared by placing saw dust / husk / coir waste / sugarcane trash at the bottom of the container with a layer of fine sand and garden soil spread over the culture bed. The layers should be moistened with water.

Bedding materials

The selection of bedding materials is a key to successful vermiculture or vermicomposting. Shredded paper or cardboard combined with typical on-farm organic resources such as straw and hay makes an excellent bedding. Paper-mill sludge with high absorbency and small particle size can also be used as bedding material. It has high C:N ratios and good bulking properties of straw, bark, or wood shavings.

Worm Food

Compost worms are big eaters, they eat almost anything organic. Under ideal conditions, they are able to consume in excess of their body weight each day. On an average they can consume ½ of their body weight of food per day. Manures are the most commonly used worm feedstock. Dairy and beef manures can also be used as worm food.

Vermicompost production Process

Biodegradable wastes such as cattle dung, farm wastes, crop residues, vegetable market waste, flower market waste, agro industrial waste, fruit market waste etc are suitable for vermicompost production. Before vermicomposting, cattle dung should be dried in open sunlight and all other wastes should be pre-digested with cow dung for twenty days.

The predigested waste material is mixed with 30% cattle dung and then placed into the container. Moisture level is maintained at 60%.

Selected earthworms are placed uniformly over the material that has to be composted. There is no need to put the earthworms inside the waste as they move inside on their own. Roughly for one-meter length, one-meter breadth and 0.5-meter height of the vermibed, 1 kg of worm (1000 Nos.) is needed.

Moisture  should  be  maintained  to  60%  throughout  the  composting  process.  Hence,  daily watering of the vermibed is not required but water should be sprinkled over the bed if necessary.

Harvesting of the castings formed on the top layer are done periodically i.e., may be once in a week. Watering should be stopped before the harvest of vermicompost. The casting are scooped out with hand and placed as heap in a shady place. Periodical harvesting is necessary to retain the quality of compost or else the finished compost get compacted when watering is done to maintain moisture.

After the vermicompost production, the earthworm present in the bed should be harvested. Simple trapping method can be used wherein small, fresh cow dung balls are made and inserted inside the bed in five or six places. After 24 hours, the cow dung balls are removed. The balls with the worms are put in a bucket of water to separate the worms. The collected worms are used in next batch of composting.

Worm harvesting methods

Worm harvesting is usually carried out to either use them for further composting or for selling purpose. There are three basic methods that are popularly used by growers to harvest worms. They include manual, migration, and mechanical harvesting methods. Each of these is described in detail below.

Manual Methods

Manual harvesting involves hand-sorting, or picking the worms directly from the compost by hand. It is practiced in small scale composting. They are also practiced at times when worms are to be sold to the home-vermicomposting or bait market. This method is labour-intensive and make sense if the operation is small and the value of the worms is high.

Self-Harvesting (Migration) Methods

These methods, are based on the worm’s tendency to migrate to new regions, either to find new food or to avoid undesirable conditions, such as dryness or light. These methods often make use of simple mechanisms, such as screens or onion bags. The screen method is very common and easy to use. A box is constructed with a screen bottom. There are two different approaches. The downward-migration system the worms are forced downward by strong light. The worms go down through the screen into a prepared, pre-weighed container of moist peat moss. Once the worms have all gone through, the compost in the box is removed and a new batch of worm-rich compost is put in. The process is repeated until the box with the peat moss has reached the desired weight. Likewise in the upward-migration system, the box with the mesh bottom is placed directly on the worm bed, filled with a few centimeters of damp peat moss and then sprinkled with a food attractive to worms, such as chicken mash, coffee grounds, or fresh cattle manure. The worms collected through the migration technique are separated, weighed, and then transported in a relatively sterile medium, such as peat moss.

Storing and packing

The harvested vermicompost should be stored in cool, dark place with a minimum 40% moisture. It should not be exposed to sunlight as this will lead to loss of moisture and nutrient content. It is recommended that the harvested composted material be openly stored with periodical sprinkling of water to maintain moisture level and also to maintain beneficial microbial population. If needed, the material can be stored in laminated over sac as this will minimize the moisture evaporation loss. Vermicompost can be stored for a year without loss of its quality, if the moisture is maintained at 40% level. Packing is done at the time of selling.

Nutritive value of vermicompost

The nutrients content of the vermicompost depends on the waste materials used for compost preparation. If the waste materials are heterogeneous one, there will be wide range of nutrients available in the compost. If the waste materials are homogenous one, there will be only certain nutrients are available. The common available nutrients in vermicompost are as follows organic Carbon (9.5-17.98%), Nitrogen (0.5-1.5%), Phosphorus (0.1-0.3%), Potassium (0.15-0.56%), sodium (0.06-.3%), Calcium and Magnesium (22.67-47.6 meq/100g), Copper(2-9.5 mg/kg),Iron(2-9.3 mg/kg),Zinc(5.7-11.50 mg/kg) and Sulphur (128-548 mg/kg).

Benefits of vermicomposting

Soil

Vermicompost due to its rich nutrient content serves as an excellent fertilizer to improve soil fertility. The worm castings contain 5 times the available nitrogen, 7 times the available potassium, 1 ½ times more calcium, phosphorus, and magnesium than found in good topsoil. It has excellent porosity, structure, drainage, aeration, water holding capacity and prevents soil erosion. Microbial activity in vermicompost is higher than the soil and organic matter from which the compost was formed. It is rich in beneficial micro flora such as a fixers, P- solubilizers, cellulose decomposing micro-flora etc and the enzymes such as phosphatase and cellulose released enrich the soil microbes. Vermicompost contains earthworm cocoons and increases the population and activity of earthworm in the soil. Attracts deep-burrowing earthworms already present in the soil. It enhances the decomposition of organic matter in soil. It is free from pathogens, toxic elements, weed seeds etc. It prevents nutrient losses and increases the use efficiency of chemical fertilizers.

Plant growth

Vermicompost is rich in all essential plant nutrients. The nutrient rich property of the compost formed by worms enhances germination, plant growth, and crop yield. It also improves root growth and structure.it improves quality and shelf life of produce. It contains valuable vitamins, enzymes and hormones like auxins, gibberellins etc. Vermicompost minimizes the incidence of pest and diseases.

Economic

Bio-wastes conversion by vermicomposting reduces waste flow to landfills. It creates low-skill jobs at local level with low capital investment and relatively simple technologies for less-developed agricultural regions

Environmental

Through the use of vermicomposting the generation of greenhouse gas emissions such as methane and nitric oxide produced in landfills or incinerators are reduced. Vermicompost is free flowing, easy to apply, handle and store and does not have bad odour.

Summary

To Summarize, at the end of the this module, we have

• Studied the concept of vermicomposting
• Understood the benefits of vermicomposting
• Types of Earthworms used for vermicomposting
• Gained knowledge about the process and essential requirements of vermicomposting Understood the nutritive value and uses of vermicompost

References

• Williams, Paul T. (2013) Waste treatment and disposal, John Wiley Publishers.