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Water cleaning technologies present challenges - some work better than others

Posted by: Aqua Blog Maven on May 3, 2008 at 7:19 am

From the San Francisco Examiner, a story that discusses in-depth wastewater treatment, and the use of reverse-osmosis systems to remove trace pharmaceuticals from drinking water supplies:

A large-scale reverse osmosis system is expensive. It costs Orange County about one-eighth of a penny per gallon - or $15 month for the 12,000 gallons used by a typical family of four, a price that doesn’t include overhead charges, such as construction, salaries and maintenance.

Officials at the Greater Cincinnati Water Works say their granular activated carbon filtering system costs 93.6 cents per month for the typical family of four.

Following a parasitic outbreak, the Southern Nevada Water Authority in Las Vegas - which processes up to 900 million gallons daily at two treatment plants - invested millions of dollars in a different advanced system that dissolves ozone gas into water to destroy micro-organisms. Ozonation costs less than one-thousandth of a penny per gallon there - just 9 cents per month for the typical family.

The extra cost of reverse osmosis is nearly impossible to justify because at this point there are no confirmed human health risks posed by pharmaceuticals, according to David Rexing, water quality research and development manager at the Southern Nevada utility. “How do we strap the customer with that cost?” asks Rexing.

Unlike the other treatments, reverse osmosis requires several gallons for every gallon it produces, with the excess an undrinkable brine - and that creates “a bigger environmental issue” than the presence of trace pharmaceuticals, according to Paul Westerhoff, an engineering professor at Arizona State University.

The cheaper ozonation process isn’t designed to remove pharmaceuticals, though it does take care of many compounds. Still, tests at the Nevada authority have shown that tiny concentrations of the tranquilizer meprobamate and an anti-epileptic drug regularly resist the treatment, as on occasion has carbamazepine, another anti-convulsant. At the Metropolitan Water District of Southern California, which serves 18.5 million people, tests at one of its five plants show that ozonation failed to remove a tranquilizer and an anti-epileptic drug from the finished drinking water, according to an ongoing study.

That district and the Southern Nevada Water Authority both draw from the Colorado River, which, tests show, can contain several hundred parts per trillion of pharmaceuticals including the active ingredients in medicines to treat depression and anxiety. The drugs get there because wastewater plants that drain into the river use basic treatments designed to remove microbes and industrial contaminants, not pharmaceuticals - the same scenario in many rivers nationwide.

Even in Europe, where governments have gone much further in addressing trace levels of pharmaceuticals in the environment, there’s scant political will to invest broadly in advanced wastewater treatment. “The cost isn’t acceptable right now,” Yves Levi, a pharmacist and professor of public health at Paris-South 11 University, said in an interview in French. “No one knows if the risk is considerable or not.”

Read the full text of this article from the San Francisco Examiner by clicking here.

May 3, 2008 · Filed Under Recycled Water