Sound method...

...of cleansing the membranes used in filtration of polluted water

Published: Saturday 15 June 2002

membrane technology is today considered the best option for treating effluent. Yet it has its own problems. The membranes used as filters have limited life and frequently get clogged with the residue and have to be 'backwashed' using acids (see 'Sifting success', Down To Earth, Vol 11, No 1). Now ultrasound could be used to clean the backwashing process.

Ultrasound can make bubbles in water that could clean ceramic filters quickly and cheaply, say Linda Weavers and colleagues of Ohio State University, Columbus. When the bubbles burst, they release energy that makes tiny, but fiercely powerful, jets of water that scour the filter's surface and flush away the residue.

Membrane filters have minuscule pores that they sieve out particles and microorganisms as small as viruses; but they get clogged easily. Fouled filters must be removed and either scrubbed or replaced, leading to further pollution.

Ultrasound cleansing could make membrane filtration the rule rather than the exception, hopes the Ohio team. "If you use ultrasound continuously you could clean the filter while in use and keep it from ever getting clogged in the first place," says Weavers (, May 15) .

Philip Brandhuber of McGuire Environmental Consultants in Denver, Colorado, who specialises in membrane filtration, agrees, saying he is pleased to see this "completely new approach to the fouling problem".

One potential problem is that the bursting bubbles could damage the filters and degrade the cheaper polymer membranes that are more widely used.

Others think that the benefits of a switch to ceramic filters would justify the costs. But the technology must undergo much more rigorous investigation. Weavers' group intends to do just that in the near future.

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