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Report 5 of 5: Worm's Eye
- Ireland
Introduction
Approximately ten per cent of homes in the Irish countryside still use underground septic tanks to deal with their household sewage. The biggest drawback to the tanks is that they have to be emptied two or three times each year. It is also important to site the tanks carefully to ensure that the contents cannot leak into the ground water supply.
As a solution for storing human faeces and urine, the Irish Earthworm Company has developed a household wormery for composting domestic waste. The prototype sewage tank is made of recycled plastic and can be adapted to any size. Once harvested, the vermicompost can be used in the garden or pot plants. It has a high nutrient content and a granular structure which is beneficial to plants, soil and crops. Worms eggs will also be present in the vermicompost and, once hatched, these worms will continue their good work around the garden.
Waste management using earthworms
Earthworms have been recycling waste for thousands of years. They are vital for the health of the soil and the plants growing on it. They will eat almost any organic matter from kitchen scraps to grass cuttings and agricultural residues, and so they are ideal for domestic composting. Through the simple process of eating, earthworms enhance soil structure, quicken the decomposition of organic matter and promote bacterial growth.
The earthworm feeds on organic material, breaks it down and then excretes it as small pellets of finely ground soil, called casts, which are coated with a gel. Earthworms are constantly tunnelling which aerates the soil, improves drainage and enables water, nutrients and oxygen to filter down to the roots of plants. This also speeds up the decomposition of vegetable matter and generates conditions that are conducive for all kinds of small animal and plant life to flourish in the soil.
After the earthworm eats vegetable matter and soil etc., the ingested material undergoes chemical changes. During this process, the nutrients become more readily accessible to plant roots but in a form that is slowly released when required by the plants. The vermicompost acts like a buffer for plants. Where soil pH levels are too high or low, it allows soil nutrients to become available to the plant once again. Vermicomposting has the same affect on toxins, such as heavy metals found in sewage sludge. By "fixing" the toxins, the plants are prevented from absorbing more than they need.
Nutritional importance of vermicompost
The castings, or vermicompost, are much richer in bacteria, organic matter and available nitrogen, potassium, phosphorus, calcium and magnesium than the soil itself. These nutrients are essential for plants to grow. The vermicomposting process also reduces waste volume by up to 50% and compacts the original substances. This gives the material higher nutritional intensity and improved water holding capacity. Earthworms are also known to help in maintaining water balance and other chemical levels in the soil.
Vermicomposting containers
Creating a home for composting worms is easy but necessary to contain the worm colony and ensure efficient recycling. In some countries, however, it may be necessary to build a moat or ditch with water in it to prevent ants from getting to the worms. Suitable pits can be constructed either above or below the surface but any reasonably sized bin or box can be adapted for vermicomposting. If conditions in the container are correct, the worms will thrive. Vermicompost units need some ground area and a simple roof structure for shade.
Pit construction, using brick masonry, stone slabs or plastic, is relatively inexpensive but the pits should be large enough to protect the worms from temperature extremes. The optimum moisture level is between 40 and 50% and the temperature needs to be maintained between 20 and 30°C. Higher moisture levels cause acidic conditions which are fatal for earthworms, as are high temperatures.
When other types of container are used, they should be positioned out of direct sunlight on blocks or bricks to allow free drainage, either through holes or a tap where appropriate. A large plastic bin, well-cleaned oil drum or wooden box (preservatives should not be used on the wood as they are toxic to the worms) will make a fine home for worms. However, as composting with worms is an aerobic process, it is important that the container allows in lots of oxygen. A number of small vents should be drilled in the container and these should be covered with mesh to deter flies. A tap fitted near the base of the container will allow any liquid produced to be collected and used as a plant feed. If a tap is not being fitted, some holes should be made in the base of the container for drainage purposes. A secure fitting lid should be found for the container to keep flies and vermin out. It is essential that the container is protected from predators. A wire mesh will keep away cats, dogs or birds.
Composition of the container
A layer of gravel (about 10 centimetres in depth) should be put into the base of the container and then covered with a layer of sand on top. This acts as the drainage system for the tank.
The bedding mix contains the worms. There are many materials suitable for worm bedding but the most common types available in, or around, the home are shredded or torn newspaper, cardboard (preferably corrugated), leaves or manure. About 40 centimetres of material should be used for the bedding layer. If this fills up the container, it does not matter because it will reduce down quite rapidly once the worms get to work. If only paper or cardboard are being used in this layer, a shovel full of soil should be added as this will introduce many beneficial composting creatures to the bin to work with the worms.
Composting worms can be found feeding on rotting debris or in the outer layers of compost heaps or manure piles. The worms should be placed on top of the bedding and then they will burrow down into it away from the light. As there is plenty of feed for the worms in their bedding, it is better to feed them lightly at first. Worms will eat almost anything but be careful not to add too much acidic, salty or spicy foods.
Making vermicompost
The containers manufactured by the Irish Earthworm Company use the existing connections for the transportation of sewage from the houses and therefore require only minimal installation. The solid waste enters the holding tank while the liquid waste flows through to the filter level of sand and gravel. The bacteria building up here will feed off and clean the pollutants in the liquid. The liquid is drained off through the valves, into either a small wetland system or into land nearby. Meanwhile, the worms feed on the solid parts of the waste, excreting about 90% in the form of nutrient rich casts. Once the organic matter consists mainly of casts, it can be removed from the holding tank. A five cubic metre pit will process up to 40 kilograms of organic waste per day.
Using alternative holding tanks, one kilogram of earthworms (about 600 to 1000 worms) can convert 45 kilograms of wet biomass in a week, which will yield about 25 kilograms of vermicompost. Once the casts have been formed in the organic matter, it can be dumped in a conical heap and left for a few hours. The worms collect at the base and can then be easily retrieved for reuse. The remaining dried material is passed through a 3mm sieve to collect the casts as vermicompost.
Benefits of vermicomposting
- Earthworms produce no toxins and carry no diseases.
- Earthworms are hermaphrodites therefore all worms can lay eggs. Although worms mate enthusiastically, once the optimum population for a pit size is reached it will stay at this level.
- Earthworms help neutralise soil acidity.
- Earthworms can reduce waste volume by up to 50%.
- Earthworms convert organic waste into vermicompost or worm castings.
- Waste materials, like food scraps or animal manure and human waste are packed with primary nutrients such as energy, proteins and minerals. Vermicomposting this waste converts it into a valuable end product and returns these nutrients to the soil, making it an important feed for plants, lawns and crops.
- Vermicomposting also improves soil conditions because it aids soil aeration and drainage.
- Vermicomposting waste produces no pollution or unusable residue which makes it a very effective form of recycling. The by-products of this process are water vapour and carbon dioxide which occur at the natural rate of organic matter decomposition.
- Once the vermicompost has been processed by the worms, it requires no further maturing and is ready to use.
- The turnover of vermicomposting is much higher than regular composting and takes place once a month instead of once every six months.
It should be noted that it takes two to three years of regular use of vermicompost for all benefits to become apparent.
The future of vermicomposting
Vermicomposting is set to become increasingly popular in the 21st Century because it yields rich organic fertiliser, recovers energy rich resources, safely disposes of organic waste and helps tackle environmental problems such as landfill and the expense of collecting and transporting this waste.
For further information, please contact:
Intermediate Technology Development Group would like to thank the Irish Earthworm Company for providing the original material on vermicomposting.
This document is an output from a project funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.
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