Organic Gardening

From Down Under

Worm Farm

by Kay Heaton

Not only has the Redland Shire Council and an organic waste management company called Vermitech solved the problem of what to do with 10,000 tonnes of sewage sludge a year, but they are also removing old sludge from land fill.
At the Cleveland Sewage Treatment Plant, the sludge, the residual material after household effluent has been through the sewage plant, is carted to the adjacent worm farm where it is turned into a saleable soil conditioner marketed as BioVerm. Sewage from the other four major shire plants and retrievals from land fill are also trucked in to this farm.
The worm farm covers one hectare and there are 4000 square metres of raised beds containing 160 tonnes of worms. It is the largest worm farm to treat sewage in the world.
The worms are not our garden worms. The types used are African Night Crawler, Red and Tiger. They require specialised care and a carefully managed environment to transpose of the waste quickly and correctly.
The whole area is covered by shade cloth to reduce wind, protect against seed and the dreaded Ibis and of course, the sun. The beds are protected from rain by plastic sheeting. Worms retreat from light. The temperature (20°C –28°C) and moisture content of the sludge must be correct to keep them well and active.
Before the sludge is given to the worms it is mixed with zealite.
Zealite is an amazing odour absorbing material. Each molecule has a huge surface area and ‘grabs’ gases from the material. Material with odour present is detrimental to the worms.
Other additives, including green waste, are mixed with the sludge. Green waste is mulched vegetation and adds oxygen to the mixture, an essential for the worms.
This mixture is spread an inch deep on top of the beds 3-5 times a week. This uses around 300 tonnes of sludge. As well as the worms environmental requirements their food must always be just a little more than enough to keep the beds viable.
The worm castings are collected from underneath the raised beds. (Garden worms deposit their castings on top of the soil). There are between 150-200 cubic metres harvested per week.
The primary sludge, as is the case with ‘manures’ contains many unpleasant substances; pathogens including salmonella, ecoli and the rest. These are reduced harmless by the enzymes in the worm’s digestive system. (In a compost heap pathogens are killed by the heap exceeding 70°C and/or the addition of lime).
Vermitech closely monitors the final product, the worm castings.
Any run off from the beds is collected and put through the plant again.
The plant has been in operation this year and has proved very successful. Not only does it eliminate the necessity for land fill but it will reduce the costs of sewage treatment by 50% It is also producing a valuable and very saleable soil conditioner in the worm castings from which the Redland Shire will benefit by a percentage of the profits.
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