Main stories from 6 October 1997 Adelaidean

Monday, 6 October 1997

Toxic sludge research accentuates the positive

So-called 'toxic' sludge which is filtered out of Adelaide's drinking water might not be that dangerous after all, and could actually have some beneficial uses (such as improving the quality of soil and preventing blue-green algae) according to University of Adelaide researchers. Filtration, designed to remove organic matter, clay and harmful microbes from the water, produces about 15,000 tonnes of sludge every year in South Australia. This sludge is produced at filtration plants using alum (aluminium sulphate) and is considered by the Environmental Protection Authority as a 'metal hydroxide waste'. Its disposal is heavily regulated and costly. But researcher Dr Cameron Grant (Department of Soil Science) says because the aluminium in the sludge is insoluble, it poses no risk to the environment or to human health. "The justification for this cautious approach to the disposal of alum sludge is therefore questionable," Dr Grant says. When applied to soil, alum sludge has been found to have a number of benefits. This includes improving the structural stability and water-holding capacity of soil, improving plant performance and yield, and 'soaking up' phosphorus, which is a major cause of toxic blue-green algae in waterways. "There is no evidence to suggest that land application of alum sludge poses any environmental hazard with respect to aluminium pollution. We need to further explore ways in which we can better understand the potential benefits and applications of this sludge, rather than simply dumping it at great cost to the taxpayer and leaving its beneficial properties untapped," Dr Grant says.

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