Drenner hopes the revamped system will provide a cheap means by which village and farming communities can clean up their sewage, especially in tropical climates where the temperatures better suit the fish. He says it will take two years to find out whether it is practical.
The fish might also be a safe source of food, provided the original sewage is free of contaminants such as pesticides and heavy metals. "They taste excellent," he says. If the water does contain heavy metals, however, the fish would have to be treated as toxic waste and disposed of by burning or burial in landfills.
Specialists in water treatment say space and the low rate of removal are the main obstacles to the system being widely used. "It's fun and provocative, but I wouldn't regard it as practical in most cases, the demand for space being the key point," says Rod Palfrey of the process technology group at Britain's Water Research Centre in Swindon, Wiltshire.
Palfrey says that the most practical and efficient way to remove phosphorus is to precipitate it out with iron or aluminium salts. Another method, being developed in Australia (New Scientist, 15 January, p 16), uses a clay spray to lock up phosphorus in clay particles where algae cannot feed on it.
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-0-207-331-2751
New Scientist
22-Feb-2000