From Wastewater to Drinking Water

Across the globe, 2 out of 10 people practise not have access to safe drinking h2o, and in the U.S., many states face h2o shortages and droughts. Meanwhile, reports Robert Glennon in Unquenchable: America's Water Crisis and What to Do About Information technology, Americans use 24 gallons of h2o each day to flush their toilets—approximately 5.8 billion gallons. What a waste! Equally the global population continues to grow and climate change results in more h2o crises, where volition nosotros observe plenty water to meet our needs?

In the U.S., we spend billions of dollars treating h2o to drinking h2o quality when we use only 10% of information technology for drinking and cooking, then flush most of the rest downward the toilet or drain. So the growing utilise of recycled wastewater for irrigation, landscaping, industry and toilet flushing, is a good way to conserve our fresh water resources. Recycled water is also used to replenish sensitive ecosystems where wild animals, fish and plants are left vulnerable when h2o is diverted for urban or rural needs. In littoral areas, recycled water helps recharge groundwater aquifers to prevent the intrusion of saltwater, which occurs when groundwater has been over pumped.

Photo credit: notcub

The use of recycled water for drinking, however, is less common, largely considering many people are repelled by the thought of water that'south been in our toilets going to our taps. Simply a few countries like Singapore, Commonwealth of australia and Namibia, and states such every bit California, Virginia and New Mexico are already drinking recycled h2o, demonstrating that purified wastewater tin can be condom and clean, and help ease water shortages.

The term "toilet to tap," used to drum up opposition to drinking recycled h2o, is misleading because recycled water that ends up in drinking water undergoes all-encompassing and thorough purification. In addition, it is usually added to groundwater or surface water for further cleansing before beingness sent to a drinking water supply where it is again treated. In fact, it has been shown to have fewer contaminants than existing treated h2o supplies.

At that place are a number of technologies used to recycle water, depending on how pure it needs to exist and what it will be used for. Here's how information technology's washed at the Indicate Colina Wastewater Treatment plant in San Diego—the city is currently studying the feasibility of recycling water for drinking.

Sewage start goes through advanced main treatment in which water is separated from large particles, then enters sedimentation tanks where chemicals are used to make main sludge settle to the lesser and scum rise to the acme. Once the water is separated out, 80% of the solids accept been removed, and the wastewater is clean enough to be discharged to the sea. (Though wastewater is a potentially valuable resource, virtually wastewater produced along our coasts ends upwardly in the ocean.)

In secondary treatment, bacteria are added to the wastewater to ingest organic solids, producing secondary sludge that settles to the bottom.

Tertiary treatment filters the h2o to remove whatsoever solids remain, disinfects information technology with chlorine, and removes the salt. In California, 3rd-treated water is called "recycled water" and tin be used for irrigation or industry.

For Indirect Potable Reuse (IPR)—recycled water that somewhen becomes drinking water—tertiary-treated water undergoes advanced water technology, so spends fourth dimension in groundwater or surface water, such as a reservoir, earlier being sent to drinking h2o supplies. Advanced water engineering outset involves microfiltration that strains out any remaining solids.

Reverse osmosis. Photograph credit: fhemerick

Next, reverse osmosis, which applies pressure to water on 1 side of a membrane allowing pure water to pass through, eliminates viruses, leaner, protozoa, and pharmaceuticals. The water is and so disinfected by ultra violet light (UV) or ozone and hydrogen peroxide. Finally it is added to groundwater or surface h2o reservoirs where information technology stays for an boilerplate of 6 months to be further purified past natural processes. (This is done mainly to assuage public anxiety about drinking recycled h2o.) Once drawn from the groundwater or reservoir, the recycled water goes through the standard h2o purification procedure all drinking water undergoes to encounter U.S. Ecology Protection Bureau standards.

In fact San Diego is already drinking recycled water because information technology imports 85% of its water from Northern California and the Colorado River, into which upstream communities like Las Vegas belch wastewater that is later treated for drinking purposes. Considering of recent restrictions on Northern California water and drought on the Colorado River, San Diego, which recycles sewage water for irrigation, invested $11.viii million into an IPR study. The demo project at the North City Water Reclamation Plant will end in 2013. During this fourth dimension, its Advanced H2o Purification Facility is producing 1 meg gallons of purified h2o each 24-hour interval, though no h2o is being sent to the reservoir.

IPR is more economic for San Diego than recycling more sewage for irrigation would be because recycled irrigation water must be conveyed through special purple pipes to separate it from potable water; expanding the purple pipe infrastructure would cost more than IPR. Recycled water is also less expensive than desalinating seawater. In Orange County, for example, IPR costs $800-$850 to produce plenty recycled water for 2 families of 4 for a year. Desalinating an equal corporeality of seawater would require $ane,200-$one,800 because of the corporeality of energy needed.

To bargain with its growing population and salt intrusion into the groundwater, the Orangish Canton Water District in California opened its $480 1000000 state-of-the-art h2o reclamation facility, the largest in the U.S., in January 2008. It costs $29 one thousand thousand a twelvemonth to operate. Later avant-garde water treatment, half the recycled water is injected into the aquifer to create a bulwark confronting saltwater intrusion. The other half goes to a percolation pond for farther filtration by the soils, and then afterward virtually vi months, ends up in drinking water well intakes. By this year, it's expected to produce 85 million gallons a day.

Singapore, with no natural aquifers and a small landmass, has struggled to provide a sustainable h2o supply for its residents for decades.

Photo credit: Jerry Wong

In 2003, it opened the commencement plants to produce NEWater, recycled drinking water purified by advanced membrane techniques including microfiltration, reverse osmosis and UV disinfection. Subsequently treatment, the h2o is added to the reservoirs. NEWater, which has passed more than 65,000 scientific tests and surpasses Earth Wellness Organisation drinking water standards, is clean enough to be used for the electronics manufacture and to be bottled as drinking water. It is expected to produce 2.five% of Singapore's total daily consumption this year.

Namibia, the nearly arid country in southern Africa, has been drinking recycled water since 1969. The water reclamation plants produce 35% of the h2o for Windhoek, the capital urban center. To date, there have been no negative health impacts connected with the consumption of recycled water.

In 2001, a $55 million h2o recycling project for water-stressed Los Angeles was scuttled past the public'due south revulsion at the idea of drinking recycled h2o and the term "toilet to tap" was born. Are the public's fears grounded?

A recent scientific discipline advisory console report examined the potential homo health implications of "chemicals of emerging business organisation" (CECs) such every bit pharmaceuticals, pesticides, and industrial chemicals, in recycled water. The scientists reviewed epidemiological and other studies of recycled water from the final forty years. While some early studies reported the presence of chlorine disinfection byproducts, the panel noted that treatment methods at that time were less sophisticated. Electric current methods take been refined and disinfection byproducts have decreased. More recent studies of recycled h2o found no agin health effects in populations using recycled h2o. Though the scientists best-selling that the furnishings of long-term exposure (over generations) to CECs and to substances that have not all the same been detected are unknown, they concluded that there was "robust evidence that recycled water represents a source of safe drinking water."

Hopefully public opinion is starting to turn. Dr. Shane Snyder, Professor of Environmental Applied science at the University of Arizona and a member of the science advisory console, is at present studying public perception of recycled water and is finding that "if they trust the utility, the majority of people understand that recycling water is unavoidable."

The truth is that all h2o is existence recycled over and over—no h2o on earth is truly pristine. Snyder concludes, "We're going to drink recycled water one mode or another, whether it comes from downstream flow or groundwater. I strongly believe we should to do it through engineered systems where we tin actively control the process."

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Columbia Water Centre demonstrates inquiry-based solutions to global freshwater scarcity.  Follow Columbia Water Center on Facebook and Twitter