You say ozone; I say filtration – either way, the water’s safe | TahoeDailyTribune.com
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You say ozone; I say filtration – either way, the water’s safe

Patrick McCartney

Across the country, water suppliers who draw drinking water from rivers and lakes have scrambled during the past 10 years to meet stringent new safety standards.

As outlined in 1986 amendments to the federal Safe Drinking Water Act, drinking water from surface sources must be filtered to protect the public from such common microorganisms as giardia and cryptosporidium, which can cause intestinal disorders.

Since the water in Lake Tahoe is relatively pristine, water suppliers in the basin have won the right to disinfect lake water with ozone instead.

So far, two basin districts have built ozone disinfection plants, and two have completed filtration plants. The most recent is the microfiltration facility built by the Skyland General Improvement District.

Also under construction in the basin are three more ozone plants and a filtration plant, all expected to open this summer.

So, which treatment facility is better, filtration or ozone disinfection?

Joseph D. Rufo, an engineer and chairman of the Skyland General Improvement District, is certain that filtration plants are the technology of the future.

“Everything on this planet should be filtered,” Rufo said. “No (disinfecting) system can give you 100-percent eradication of two things – cryptosporidium and giardia – and there are a hundred other things out there.”

By comparison, Rufo said, filtration plants, especially the type of microfiltration plant operated by the Skyland district, are more effective at removing microscopic critters that can cause maladies.

“We’re not perfect; but we’re damn close,” the voluble Rufo claimed.

Taking exception to Rufo’s claim of superiority for filtration is Daniel St. John, the director of engineering for the Incline Village General Improvement District. Incline Village completed construction last year of a $3.5 million ozone disinfection plant that treats 8.5 million gallons of water a day – 10 times the amount that the Skyland plant treats.

“Every system is different,” said St. John. “With differences in the size, location and operations, there’s a whole myriad of issues that come into play when you decide what type of treatment system you want.”

St. John said a microfiltration plant might have been prohibitively expensive for the Incline District. Although it treats just a tenth as much water as Incline’s facility, the Skyland plant, at $4.9 million, costs more.

Another negative, St. John said, is that if Incline opted for a filtration plant it would discharge more than 10 times as much tainted “backwash” into the sewer system than Skyland does.

The bottom line, according to a Nevada public health engineer, is that both ozone and filtration kill more than 99.9 percent of any dangerous organisms in the water.

“You can’t say which is best, because both meet federal requirements for cryptosporidium and giardia inactivation and removal,” said Rick Reighley of the Nevada Bureau of Health Protective Services.


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