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11 Aug 08
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When you flush in Santa Ana, the waste makes its way to the sewage-treatment plant nearby in Fountain Valley, then sluices not to the ocean but to a plant that superfilters the liquid until it is cleaner than rainwater. The “new” water is then pumped 13 miles north and discharged into a small lake, where it percolates into the earth. Local utilities pump water from this aquifer and deliver it to the sinks and showers of 2.3 million customers. It is now drinking water. If you like the idea, you call it indirect potable reuse. If the idea revolts you, you call it toilet to tap.
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inside each of 16 concrete bays hangs a rack of vertical tubes stuffed with 15,000 polypropylene fibers the thickness of dental floss. The fibers are stippled with holes 1/300th the size of a human hair. Pumps pull water into the fibers, leaving behind anything larger than 0.2 microns, stuff like bacteria, protozoa and the dread “suspended solids.”
The excitement and the bubbles were backwash: every 21 minutes, air is injected into the microfibers to blast them clean. The schmutz goes back to the sewage-treatment plant, and the cleaner water, now the color of chamomile tea, is pumped toward reverse-osmosis filters in another building.
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The stuff that’s removed is washed back to a pipe that discharges into the ocean. The filtered water, now known as permeate, moves one building over, where it’s spiked with hydrogen peroxide, a disinfectant, and then circulated past 144 lamps emitting ultraviolet light. “Destruction of compounds through photolysis,”
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it still needed to be decarbonized and dosed with lime, to raise its pH. Finally it would enter a massive purple pipe, which dives into the ground inside a nearby pump house and reappears 13 miles to the north, in Anaheim. There, the water would pour into Kraemer Basin, a man-made reservoir, where it would mix with the lake water and filter for six months through layers of sand and gravel hundreds of feet deep before utilities throughout the county pumped it into taps.
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The process isn’t risk-free. Some scientists are concerned that dangerous compounds or undetectable viruses will escape the multiple physical and chemical filters at the plant. And others suggest that the potential for human error or mechanical failure — clogged filters or torn membranes that let pathogens through, for example — is too great to risk something as basic to public health as drinking water.
Recycled water should be used only as nondrinking water, says Philip Singer, the Daniel Okun Distinguished Professor of Environmental Engineering at the University of North Carolina. “It may contain trace amounts of contaminants. Reverse osmosis and UV disinfection are very good, but there are still uncertainties.”
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If everything in the Fountain Valley plant is in perfect working order, its finished water will contain no detectable levels of bacteria, pharmaceuticals or agricultural and industrial chemicals. The same can be said of very few water sources in this country. But once the Fountain Valley water mingles with the county’s other sources, its purity goes downhill. Filtering it through sand and gravel removes some contaminants, but it also adds bacteria (not necessarily harmful, and local utilities will eventually knock them out them with chlorine) and possibly pharmaceuticals.
In other words, nature messes up the expensively reclaimed water. So why stick it back into the ground? “We do it for psychological reasons,” says Adam Hutchinson, director of recharge operations for the water district. “In the future, people will laugh at us for putting it back in, instead of just drinking it.”
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You could argue that in coming to terms with wastewater as a resource, we’ll take better care of our water. At long last, the “everything is connected” message, the bedrock of the environmental movement, will hit home. In this view, once a community is forced to process and drink its toilet water, those who must drink it will rise up and change their ways. Floor moppers will switch to biodegradable cleaning products. Industry will use nontoxic material. Factory farms will cut their use of antibiotics. Maybe we’ll even stop building homes in the desert.
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