Domestic wastewater as fish food

treated domestic wastewater helps production of carp fish. The nutrients in the sewage are used to develop fish food organisms. Fish food is generally grown in fresh water and the joint research by scientists from Bhubaneswar and Kolkata says that using sewage will help save freshwater.

The treated sewage makes the water productive by 64 per cent higher than fertilizers. The study was published online on September 18 in the Bioresource Technology. "In India, every individual produces about 100 litre sewage per day. This method will help clean up the mess," says Subrata Dasgupta at the Regional Research Centre of Central Institute of Freshwater Aquaculture, Kolkata.

Scientists say the practice is cost-effective and will yield good returns. "The net return in sewage-fed carp production system at lower stocking density is Rs 1.61 per cubic metre water and Rs 0.98 per cubic metre water over six months excluding the cost spent on pond lease," says Dasgupta. The net return will be 10,000 times per hectare water area.

There is also concern of contamination. Dasgupta says the levels of heavy metals were not found beyond critical limits. Accumulation, even if it occurs, could be in kidney and liver which are not consumed by people, he adds.

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