works that serve whole towns. To serve the city of Waco, which has a population of about 100 000, would require almost 100 hectares of tanks of fish, Drenner says. To improve on this, he will try out a new system this summer that uses taller tanks, about 3 metres deep. The idea is to reduce the land area needed by increasing the number of fish in each tank. "It's analogous to saving land by building high-rise flats," he says.
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.
Page: 1 2 Related biology news :1
Contact: Claire Bowles
. Endometriosis: Could angiostatic therapy be the new treatment of the future?2
. Could mice hold the secret to longer life?3
. Could vitamins raise levels of bad cholesterol? Animal study suggests they might4
. Could memory performance and spatial learning be genetically based?5
. Could a specific protein contribute to erectile dysfunction for the diabetic and obese?6
. Could diabetes treatments fight cancer?7
. Could rice be the source for a natural herbicide?8
. Could hibernators hold the key to improving organ preservation?9
. Could Bt transgenic crops have nutritionally favourable effects on insects?10
. Could one less cookie a day help the fight against fat?11
. Could an anti-marijuana compound hold the key to body weight and appetite control?