Clean with coir

Biofilter for domestic wastewater

By R K Srinivasan
Published: Saturday 04 July 2015

The biofilter (right) can repl the humble coir may soon help treat domestic wastewater.

Arakkal Praveen, a lecturer at the Government Engineering College, Thrissur, Kerala, has developed a biofilter made of coir, which can be attached to a septic tank. Called 'coir-geotextile', the rectangular biofilter can remove 97-99 per cent of organic waste from wastewater, according to a study conducted by the college. It can replace soak pits (which can lead to ground-water contamination) that are usually attached to septic tanks.

But the filter should be used only for wastewater retained for at least 24 hours in the septic tank (to allow the sludge to settle down). Otherwise the filter can get clogged. As the wastewater passes through the filter, microorganisms present in it get attached to the coir and grow on it. Subsequently, these microorganisms help break down organic waste.

"Domestic wastewater is rich in microorganisms and does not need inoculation with bacterial culture. However, in case of weak domestic wastewater, where organic load is low, cow dung is sprayed over the coir-filter to act as a catalyst (which acts as a starter) by creating a bacterial population ready for decomposition treatment," says Arakkal.

A four-member family would require a coir-filter one metre long, 0.15 m thick and 0.20 m wide. Such a filter can treat wastewater with high organic load -- 250-450 milligramme per litre.

Arakkal says large 'bio-blankets' can also be prepared using these coir-geotextiles to improve performance of centralised wastewater treatment systems such as sewage treatment plants. "For larger treatment units such as lagoons, coir-geotextiles can be used to create an attached growth system without compromising the volume of water being treated in them," he adds.

Moreover, the biofilter consumes 3-4 kg of coir fibre per house and thus may give a push to the dwindling coir industry in the country.

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