Sewers to sinks
A drought-stricken California county has found a new source of water: its toilets.
Wed, Apr 08, 2009 at 02:23 PM
PURIFIED WASTEWATER: In the wake of water shortages, cities begin to purify wastewater for drinking.
“Here, try this," says Gina DePinto, a spokesperson for the Orange County Water District [OCWD] as she offers me a bottle of NEWater from a cooler. It looks like it could be any other brand, but there’s one slight difference: this water came from a sewer in Singapore. I unscrew the cap and go bottoms up. Although it has been down a toilet, water-purity tests have shown the water to be some of Earth’s cleanest — and a possible solution to a global problem.
Water is so commonplace in countries like the US we sometimes take it for granted; it's safe, fresh and available at the flick of the wrist. But as drought in arid regions like northern China, eastern Australia, and the American Southwest intensifies and global warming alters weather patterns, clean water will grow more scarce for many; already, according to the UN, a billion people worldwide lack access to clean drinking water. The UN estimates that by 2025, two-thirds of the world’s population could face water shortage. Here in the US, the parched Southwest is already struggling: nearly eight years of drought have left reservoirs in the Colorado River basin almost half-empty, and in Northern California, 2008’s spring was the driest on record — with some researchers predicting still worse to come.
To meet the challenge, a growing number of cities are purifying wastewater to recharge groundwater or reservoirs, a process engineers call “indirect potable reuse” and skeptics refer to as “toilet-to-tap.” Among the early adopters are El Paso, Texas; Singapore; Windhoek, Namibia; and Fairfax County in Virginia. Other US cities considering or launching similar projects include Los Angeles, San Diego, and Miami-Dade County, which is scheduled to begin an operation in 2013 at an estimated cost of $350 million (that’s still cheaper and more energy-efficient than seawater desalination). Leading the way is Orange County, California.
Known more for its wealth than its filth, the county has a new state-of-the-art plant that opened in January. OCWD engineer Mehul Patel boasts of an 80-to-85 percent recovery rate; the plant produces some 70 million gallons of potable water a day — enough to meet the needs of nearly half a million thirsty Southern Californians.
Our tour of the filtration plant starts next to a row of concrete basins where Coca-Cola colored wastewater churns in the depths; solids have been removed, but this water is thick with muck. In a technique called microfiltration, pumps draw the wastewater through bundles of fibers shaped like ultra-slim drinking straws, with holes 1/300 the size of a human hair, trapping bacteria and dirt. Every fifteen minutes a blast of air flushes the dirt from the microfilter while the water passes to the next stage.
In a separate, supermarket-sized building crowded with PVC tubes, water is forced at high pressure through thousands of plastic membranes in a process called reverse osmosis, which is also used by bottled water companies like Aquafina, Singapore’s indirect potable reuse program, and desalination plants. Contaminants like viruses, salts, chemicals, and trace pharmaceuticals are trapped by each membrane's microscopic pores as the water filters through. According to Shivaji Deshmukh, the program manager at OCWD, some things make it past reverse osmosis at appreciable levels: dissolved CO2, some 15-20 parts per million of dissolved salt (levels similar to those found in most brand-name bottled water), and a couple of other compounds. The potential problem is a carcinogen called NDMA, which can pass through reverse osmosis membranes at levels measured in parts per trillion. NDMA is believed to form as a result of chlorination of wastewater (ironically enough), and can come from certain industrial pollutants; even though it’s very difficult to filter or remove from water, NDMA rapidly disintegrates under strong ultraviolet light.
Hence the next step in OCWD’s process: OCWD adds hydrogen peroxide to the water and blasts it with UV rays to destroy organic compounds. The purified water is monitored extensively for quality, and finally pumped into the groundwater or piped to percolation ponds where it slowly trickles into the soil. Ultimately 20-to-25 percent of Orange County tap water is recycled, and the output is so pure “it actually improves groundwater quality,” says DePinto.
This last step is actually unnecessary from a purity standpoint; it’s only undertaken, essentially, for PR reasons. People just seem to feel better about recycled wastewater coming from the ground like the rest of their water, rather than going directly into the water district’s pipes.
Yet OCWD’s meticulous means of ensuring purity don’t satisfy everyone; critics contend that water from waste is too much to swallow. Though no one has been shown to have fallen ill in Orange County or in Singapore from drinking the recycled water, a lot of people and politicians just find the whole idea gross. (A San Diego Union-Tribune editorial about a similar proposal a few years ago began, “Your golden retriever may drink out of the toilet with no ill effects. But that doesn’t mean that humans should do the same.”) Most expert opposition has revolved around concern that there might be something dangerous that OCWD isn't testing for, or that the system could break down somehow, leading to a public health outbreak that's simply not worth the risk.
What some may not realize is that Westerners are already drinking sewage water: Las Vegas alone flushes 64 million gallons of treated sewage a day into the Colorado River, which feeds faucets throughout the Southwest; time, exposure to sunlight and banging against rocks does the OCWD’s job naturally.
Still, like most other counties or districts considering sewage recycling, Orange County had to overcome widespread skepticism before they could convince the public. How would the system work? Was it safe?
“We spent seven years out there talking to anyone and everyone who would listen,” explains OCWD’s DePinto. “I think it was really important that we were being very transparent and open about what we were doing and how it works.”
Past experience was key in persuading OC residents to accept the new plant. Back in 1975, seawater was threatening to creep into the groundwater and ruin it completely. To stave off the threat, Orange County adopted the then-novel idea of using recycled sewage to replenish their groundwater supply, employing a similar if less advanced filtration process on a limited scale. The plan was so successful Orange County upgraded to the full scale plant that opened earlier this year. Even so, convincing customers wasn’t always easy. “A lot of people don’t think about where their water comes from,” says DePinto. “That’s why it was so important to go out and explain the technology and how it works.”
In a larger sense, as Zachary Dorsey of the WateReuse Association (a nonprofit that advocates for better management of water resources) points out, “All water is recycled.” Whether it be waste-, fresh-, or salt-, H2O worldwide shares one thing in common: every drop eventually evaporates and falls back to earth as rain or snow. Then the cycle repeats. “There is no new water,” Dorsey says.
Story by Jonathan Parkinson. This article originally appeared in "Plenty" in December 2008.