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Wastewater reuse

By Kim Robson:

Water recycling, reuse and reclamation are not new concepts. Non-potable (not for drinking) water systems have been around for decades. The state of California is a leader in this worldwide trend: treating, disinfecting, and reusing municipal wastewater near its source for a variety of uses that don’t involve human contact, like agricultural irrigation, landscaping, decorative fountains, and golf course watering.

water-recycle-symbol-Header-640x360Because of worsening drought conditions and groundwater depletion, non-potable uses are expanding in scope. In addition to the more common uses mentioned above, recycled water is being used also for street cleaning, firefighting, geothermal energy production, prevention of seawater intrusion into freshwater aquifers, industrial processing, commercial laundering, restoration of natural wetlands, and creation of constructed wetlands.

Only seven out of every 100 gallons of U.S. wastewater gets recycled near its source, but that number is growing by about 5% per year. While the EPA updates its guidelines for reuse every decade or so, water recycling is regulated at the state level. More than half the states have some kind of regulation in place for water reuse.

The San Antonio River Walk, billed as Texas’ No. 1 tourist attraction, uses recycled water. Greg Flores, vice president of public affairs for the San Antonio Water System, says, “Everything that goes down the drain here is treated and reused.” University campuses, the San Antonio River Walk, and the Toyota and Microsoft facilities are examples.

Water reuse reduces the amount of fresh water diverted from sensitive ecosystems, as well as the amount of wastewater and pollution discharged to waterways. Non-potable reuse avoids using precious potable water where that level of quality is not required. In many cases, it’s even better: water not treated to drinking water standards retains nutrients like nitrates and phosphates, and irrigating with recycled water means less need for chemical fertilizers.

Wastewater reuse is energy intensive but still yields an energy savings because pumping imported water from waste water recycling outside sources requires so much energy itself. In California’s Orange County, recycling water for their groundwater replenishment system uses half the energy of importing water.

Cities have found that as public understanding of water reuse grows, so does public acceptance. “Almost one in five Californians are already connected to a utility that uses, or has [as] part of its water supply portfolio potable reuse,” says Dave Smith, managing director of the WateReuse Association‘s California chapter.

More notably, however, a growing number of municipalities are considering “potable reuse” — recycling wastewater back into drinking water, either directly or indirectly. In 2008, Orange County started operating its Groundwater Replenishment System, which reintroduces treated wastewater into the water table serving nearly 600,000 residents. The project, says Orange County Water District president Shawn Dewane, is “taking water reuse to the next level. Instead of pouring it on the ground, in terms of landscape irrigation, [we are] turning it into drinking water.”

Most potable reuse projects today practice “indirect” reuse, which means there’s an environmental buffer zone such as a groundwater basin, reservoir, or water table between treatment and water supply intake.

OC wastewaterWith a capacity of 70 million gallons per day, Orange County’s indirect system is the world’s largest for water purification and potable reuse. It’s projected to reach 100 million gallons per day by 2015. The system has attracted both national and international interest. They’ve met with officials from Japan, the United Arab Emirates, England and Singapore (which already has about 30 percent of its drinking water supplied by a potable reuse system). Reuse is also established and growing in Australia and some European countries.

With “direct” potable reuse, there’s no environmental buffer in place. Instead, water is treated and sent directly back to the municipal water supply. More places, primarily in arid areas, are starting to consider direct reuse as a way to maximize their increasingly scarce water resources.

The biggest problem with direct reuse lies in gaining public acceptance. The now familiar term “toilet to tap” is inaccurate and sounds as though toilet water is being piped right to your faucet. This term, in my opinion, is responsible for negative feelings toward and rejection of wastewater reuse. When municipalities consider wastewater reuse, the hardest part isn’t figuring out the right technology or engineering the system: it’s educating the public.

Reuse technologies have been proven safe, and treatment plants can get wastewater as clean as distilled water. The three-step process used in Orange County — microfiltration, reverse osmosis and ultraviolet treatment with hydrogen peroxide — is becoming the standard for indirect potable reuse.

Direct potable reuse is practiced in areas with increasing drought, notably in Big Spring, Texas, and in the southern African nation of Namibia, which boasts the world’s first large-scale direct potable reuse system. Cloudcroft, New Mexico, expects to have a new direct potable reuse system up and running by the summer of 2014, and projects the system will provide 40,000 of the approximately 70,000 gallons used daily by the town. Brownwood, Texas, has plans to start direct potable reuse and is just waiting for city council approval. And San Diego is considering it as an alternative to upsizing its existing million-gallon-a-day indirect reuse project to 15 million gallons daily.

Ellen Gilinsky, senior policy advisor for the EPA’s Office of Water, says the success of non-potable reuse projects lays a foundation for expanded potable reuse in the future. “I think you’re seeing sort of that progression. People dip their toe in and then they see — oh, this is not so bad.”

About Kim Robson

Kim Robson lives and works with her husband in the Cuyamaca Mountains an hour east of San Diego. She enjoys reading, writing, hiking, cooking, and animals. She has written a blog since 2006 at kimkiminy.wordpress.com. Her interests include the environment, dark skies, astronomy and physics, geology and rock collecting, living simply and cleanly, wilderness and wildlife conservation, and eating locally.

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