San Diego Learns How to Recycle Water
Thursday, June 25, 2009
Credit: City of San Diego Water Department
The ultimate solution to California's water dilemma will draw on many sources. And one of them will be the supply of water we currently throw away. The water that goes down the drain, and down the toilet, can be reused. But finding the best way for San Diego to recycle is a technical and political question.
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SAN DIEGO The ultimate solution to California's water dilemma will draw on many sources. And one of them will be the supply of water we currently throw away. The water that goes down the drain, and down the toilet, can be reused. But finding the best way for San Diego to recycle is a technical and political question.
Recycling wastewater is nothing new. It's common and often unavoidable. Alan Rimer is a water reuse specialist with the firm Black and Veatch. He says wastewater reuse has taken many forms.
"I grew up in Pittsburgh Pennsylvania," he says. "And when I flushed my toilet, it went into the Ohio River with some treatment, and Cincinnati drank that water after taking it out of riverbank wells and treating it. And that's what we call indirect potable reuse."
To water reuse experts, San Diego is famous for the expression "toilet to tap." It arose about ten years ago when the city's first effort to reuse wastewater as potable water did a political crash and burn. But the reality of today's water shortage has put wastewater recycling back on the table. That's why San Diego is embarking on a plan to test a system for "reservoir augmentation." Wastewater will be purified to an advanced level so it could be piped to the San Vicente Resevoir, where it would become part of San Diego's supply of drinking water.
Marsi Steirer, with the San Diego Public Utilities Department, says, for now, the goal is test some new equipment at the North City Water Reclamation Plant.
"Basically what we're constructing as a temporary plant is a one million gallon a day advanced water treatment facility," she says.
The north city plant currently treats about nine million gallons of wastewater every day that's reused, mainly for irrigation. This kind of reuse requires a dual delivery system, since the North City plant doesn't currently treat its recycled water to the level of drinking water. The non-potable water flows through purple pipes to golf courses, parks and freeway medians. But the North City plant recycles less than half of what it could, due to a very limited distribution system.
Mixing highly treated wastewater with a city's drinking water supply, reservoir augmentation, is what they already do in part of Northern Virginia. Chuck Boepple is executive director of the Upper Occoquan service authority. He says his plant's wastewater is treated and discharged into the historic creek called Bull Run. That leads to a reservoir that provides drinking water for a million people in suburban Washington D.C. Boepple adds the water he puts in Bull Run is very clean.
"Our effluent, as a matter of fact, meets drinking water standards. Every parameter that EPA has on maximum contaminant levels for drinking water… we're beneath those levels," he says.
So why does Occoquan put safe drinking water in the reservoir where it'll just get dirty and need to be treated again? Beopple says doing a system where water really goes straight from toilet and tub to treatment to tap is still unacceptable to the public. Maybe so. But the water San Diego draws from the Colorado River contains lightly treated wastewater Las Vegas dumps into Lake Mead. Some say that the water people in New Orleans drink, that comes from the Mississippi River, has already been through about nine sets of human intestines.
Rick Gersberg is a public health professor at San Diego state, and he's on an advisory task force for the San Diego water recycling project. He says scientists can talk all they want to about actual health risks of recycled, drinking water. But what the public perceives as sanitary, is just as meaningful.
"Maybe a scientist would say 'Well, you know, risk is just the numbers we calculate.' But if you're dealing with risk and you're expecting to communicate and inform and have acceptance of a certain project, then that strictly science opinion is not the way it happens," says Gersberg.
Reusing wastewater has a political price and it has a monetary price. If the San Diego water recycling project becomes reservoir augmentation, it'll require a permanent treatment facility and a pipeline. The total cost would be at least $237 million.
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