Wealth in waste

irradiated sewage sludge would be used to make the deserts bloom and increase food production. Radiation will be used to convert sewage into fertiliser in a commercial plant that would be the first of its kind in the world. The International Atomic Energy Agency ( iaea ), Vienna, and the Atomic Energy Commission of Argentina ( cnea ) are jointly developing the plant in San Miguel de Tucuman, Argentina. It is expected to start operations by the end of this year ( New Scientist , Vol 154, No 2087).

Gamma radiation from cobalt-60 will be used to kill micro-organisms in the sludge to produce a fertiliser for local crops. cnea makes the sources for cobalt-60 itself. Filipa Zapata, a soil scientist with the iaea , says that if the technology is successful, it could be used to fertilise deserts and restore eroded topsoil in Africa and Asia. Turning sludge into fertiliser would help increase world food production. However the risks, costs and effectiveness of the project have not been fully assessed.

According to iaea , the population of 400,000 in San Miguel de Tucuman dumps nearly 90,000 tonnes of sewage sludge into the Sali River every year. Once the irradiation plant becomes operational, it will treat upto 180 cu m of sludge a day. Cecilia Magnavacca of cnea says that efforts are on to find out the effect of irradiated sludge on sugar cane yields in farms near the city. "When we are sure it works, we will transfer the technology to other Latin American countries,' he says.

However, the technology has its limits. Radiation kills micro-organisms but it will be ineffective on the sewage that contains elements like heavy metals. Effluent discharge into a sewer from factories may pollute the sludge, making its treatment difficult.

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