Treating sewage by aquaculture

India continues research into finding a use for one of its least coveted resources: the 15 million cubic metres of sewage it generates every day.

Acting on the principle that sewage is not just waste water but also a source of nutrients, an experimental plant in operation since 1994 treats sewage with aquatic weeds and fish. One million litres of primary treated sewage a day sits first in ponds containing duckweed, then in ponds stocked with carp and prawns. After five days, water quality has improved to the point where it may be used for agriculture, although not for drinking.

A river of raw sewage (left) runs out of the city of Cuttack. One million litres a day are pumped into an experimental Aquaculture Sewage Treatment Plant (right), where it is treated with aquatic weeds and fish.

Although faecal coliforms were found to be present in the system and in the guts and gills of fish fed on sewage, none were found in fish muscle. The sale of fish fattened in the sewage ponds for 8 to 12 months almost offsets the operating cost of the plant, leaving a net cost of 15 000 rupees a year, about US$385. The plant, which covers half a hectare, is run by two men.

The Aquaculture Sewage Treatment Plant (ASTP) cost 1.5 million rupees (US$38 000) to build, compared with 5 million to 6 million rupees (US$128 000 to US$154 000) for a standard Indian sewage treatment plant and 10 million rupees (US$256 000) for a comparable Western plant.

The plant, located in Cuttack, Orissa, eastern India, is the brainchild of the Central Institute of Freshwater Aquaculture (CIFA), founded in 1986 with FAO's assistance.

Cuttack, a city of 700 000, would need a plant with 60 times the capacity of the experimental station to treat its daily sewage output, currently untreated.

A National Workshop on Sewage Treatment through Aquaculture, held in 1997 at CIFA, recommended that research continue into the method, endorsed the plant design and recommended that more state governments adopt it.

For more information on the science behind ASTP, contact CIFA Director Dr S. Ayyappan at [email protected]; or c/o CIFA, Kausalyaganga, Bhubaneswar, 751002, Orissa, India.

20 August 1998

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