Vermicompost


Vermicompost is the product of the decomposition process using various species of worms, usually red wigglers, white worms, and other earthworms, to create a mixture of decomposing vegetable or food waste, bedding materials, and vermicast. This process is called vermicomposting, with the rearing of worms for this purpose is called vermiculture.
Vermicast is the end-product of the breakdown of organic matter by earthworms. These excreta have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than the organic materials before vermicomposting.
Vermicompost contains water-soluble nutrients which may be extracted as vermiwash and is an excellent, nutrient-rich organic fertilizer and soil conditioner. It is used in gardening and sustainable, organic farming.
Vermicomposting can also be applied for treatment of sewage. A variation of the process is vermifiltration which is used to remove organic matter, pathogens, and oxygen demand from wastewater or directly from blackwater of flush toilets.

Overview

Vermicomposting has gained popularity in both industrial and domestic settings because, as compared with conventional composting, it provides a way to treat organic wastes more quickly. In manure composing, the use of vermicomposting generates products that have lower salinity levels, as well as a more neutral pH.
The earthworm species most often used are red wigglers, though European nightcrawlers and red earthworm could also be used. Red wigglers are recommended by most vermicomposting experts, as they have some of the best appetites and breed very quickly. Users refer to European nightcrawlers by a variety of other names, including dendrobaenas, dendras, Dutch nightcrawlers, and Belgian nightcrawlers.
Containing water-soluble nutrients, vermicompost is a nutrient-rich organic fertilizer and soil conditioner in a form that is relatively easy for plants to absorb. Worm castings are sometimes used as an organic fertilizer. Because the earthworms grind and uniformly mix minerals in simple forms, plants need only minimal effort to obtain them. The worms' digestive systems create environments that allow certain species of microbes to thrive to help create a "living" soil environment for plants. The fraction of soil which has gone through the digestive tract of earthworms is called the drilosphere.
Vermicomposting is a common practice in permaculture.
Vermiwash can also be obtained from the liquid potion of vermicompost. Vermiwash is found to contain enzyme cocktail of proteases, amylases, urease and phosphatase. Microbiological study of vermiwash reveals that it contains nitrogen-fixing bacteria like Azotobactrer sp., Agrobacterium sp. and Rhizobium sp. and some phosphate solublizing bacteria. Laboratory scale trial shows effectiveness of vermiwash on plant growth.

Design considerations

Suitable worm species

All worms make compost but some species are not suitable for this purpose. Vermicompost worms are generally epigean. Species most often used for composting include:
  • Eisenia fetida, the red wiggler or tiger worm. Closely related to Eisenia andrei, which is also usable.
  • Eisenia hortensis , European nightcrawlers, prefers high C:N material.
  • Eudrilus eugeniae, African Nightcrawlers. Useful in the tropics.
  • Perionyx excavatus, blueworms. May be used in the tropics and subtropics.
  • Lampito mauritii, used locally.
These species commonly are found in organic-rich soils throughout Europe and North America and live in rotting vegetation, compost, and manure piles. As they are shallow-dwelling and feed on decomposing plant matter in the soil, they adapt easily to live on food or plant waste in the confines of a worm bin. Some species are considered invasive in some areas, so they should be avoided.
Composting worms are available to order online, from nursery mail-order suppliers or angling shops where they are sold as bait. They can also be collected from compost and manure piles. These species are not the same worms that are found in ordinary soil or on pavement when the soil is flooded by water.
The following species are not recommended:
  • Lumbricus rubellus and Lumbricus terrestris. The two closely related species are anecic: they like to burrow underground and come up for food. As a result, they adapt poorly to shallow compost bins and should be avoided. They are also invasive in North America.

    Large scale

Large-scale vermicomposting is practiced in New Zealand, Canada, Italy, Japan, India, Malaysia, the Philippines, and the United States. The vermicompost may be used for farming, horticulture, market gardening, landscaping, to create compost tea, or for sale. Some of these operations produce worms for bait and/or home vermicomposting.
There are two main methods of large-scale vermicomposting, windrow composting and raised bed. Some systems use a windrow, which consists of organic feedstock for the earthworms to feed on. Earthworms will move into the windrows and remain within them as long as conditions are favourable; typically involving a balanced mix of feedstock, appropriate moisture content and a comfortable temperature. Often windrows are used on a concrete surface to control and manage leachate.
The world's largest vermicomposting operation by volume is MyNoke, a New Zealand-based operation that's processed over 1.4 million tonnes of organic waste since establishment in 2007.
Windrow turners were developed by Fletcher Sims Jr. of the Compost Corporation in Canyon, Texas. The Windrow Composting system is noted as a sustainable, cost-efficient way for farmers to manage dairy waste.
The second type of large-scale vermicomposting system is the raised bed or flow-through system. Here the worms are fed an inch of "worm chow" across the top of the bed, and an inch of castings are harvested from below by pulling a breaker bar across the large mesh screen which forms the base of the bed.
Because red worms are surface dwellers constantly moving towards the new food source, the flow-through system eliminates the need to separate worms from the castings before packaging. Flow-through systems are well suited to indoor facilities, making them the preferred choice for operations in colder climates.

Small scale

For vermicomposting at home, a large variety of bins are commercially available, or a variety of adapted containers may be used. They may be made of old plastic containers, wood, Styrofoam, or metal containers. The design of a small bin usually depends on where an individual wishes to store the bin and how they wish to feed the worms.
Some materials are less desirable than others in worm bin construction. Metal containers often conduct heat too readily, are prone to rusting, and may release heavy metals into the vermicompost. Styrofoam containers may release chemicals into the organic material. Some cedars, yellow cedar, and redwood contain resinous oils that may harm worms, although western red cedar has excellent longevity in composting conditions. Hemlock is another inexpensive and fairly rot-resistant wood species that may be used to build worm bins.
Bins need holes or mesh for aeration. Some people add a spout or holes in the bottom for excess liquid to drain into a tray for collection. The most common materials used are plastic: recycled polyethylene and polypropylene and wood. Worm compost bins made from plastic are ideal, but require more drainage than wooden ones because they are non-absorbent. However, wooden bins will eventually decay and need to be replaced.
Small-scale vermicomposting is well-suited to turn kitchen waste into high-quality soil amendments, where space is limited. Worms can decompose organic matter without the additional human physical effort that bin composting requires.
Composting worms which are detritivorous, such as the red wiggler Eisenia fetida, are epigeic and together with symbiotic associated microbes are the ideal vectors for decomposing food waste. Common earthworms such as Lumbricus terrestris are anecic species and hence unsuitable for use in a closed system. Other soil species that contribute include insects, other worms and molds.

Climate and temperature

There may be differences in vermicomposting method depending on the climate. It is necessary to monitor the temperatures of large-scale bin systems, as the raw materials or feedstocks used can compost, heating up the worm bins as they decay and killing the worms.
The most common worms used in composting systems, redworms feed most rapidly at temperatures of. They can survive at. Temperatures above may harm them. This temperature range means that indoor vermicomposting with redworms is possible in all but tropical climates. Other worms like Perionyx excavatus are suitable for warmer climates. If a worm bin is kept outside, it should be placed in a sheltered position away from direct sunlight and insulated against frost in winter.

Feedstock

There are few food wastes that vermicomposting cannot compost, although meat waste and dairy products are likely to putrefy, and in outdoor bins can attract vermin. Green waste should be added in moderation to avoid heating the bin.

Small-scale or home systems

Such systems usually use kitchen and garden waste, using "earthworms and other microorganisms to digest organic wastes, such as kitchen scraps".
This includes:
  • All fruits and vegetables
  • Vegetable and fruit peels and ends
  • Coffee grounds and filters
  • Tea bags
  • Grains such as bread, cracker and cereal
  • Eggshells
  • Leaves and grass clippings
  • Newspapers
  • Paper toweling

    Large-scale or commercial

Such vermicomposting systems need reliable sources of large quantities of food.
Systems presently operating use:
  • Dairy cow or pig manure
  • Sewage sludge
  • Brewery waste
  • Cotton mill waste
  • Agricultural waste
  • Food processing and grocery waste
  • Cafeteria waste
  • Grass clippings and wood chips