Recycled Sewage: Coming to a Tap Near You?
Tasha Eichenseher in Stockholm, Sweden
for National Geographic News
|August 25, 2008|
Is recycled sewage water coming to a tap near you? If you live in certain parts of the developed world—including areas of the united States—the answer, perhaps surprisingly, is yes.
Persistent droughts and competition for resources are leading to increased use of recycled sewage for drinking water and fertilizer, water experts say.
In developing countries human waste is already used by an estimated 200 million farmers, according to a recent report by the Sri Lanka-based International Water Management Institute (IWMI).
Now wastewater use is gaining steam in the developed world too, though in rich countries, the water undergoes a cleansing process before being pumped out to taps.
"Wastewater recycling is something we will have to rely more heavily on," said Shivaji Deshmukh, program manager for the groundwater replenishment system at the Orange County Water District in southern California.
Orange County has been recognized for its innovative sewage system, which collects what people flush down the toilet, separates its components, then treats the wastewater to drinking-water standard.
The county water district pumps the treated wastewater into underground caverns, where it is stored and later used as tap water or irrigation water.
In the U.S. many federal and state laws require reclaimed water to sit in rivers or aquifers before it can be processed for drinking water.
This explains why water coming out of the Orange County facility doesn't flow directly to residents' taps, Deshmukh said.
The Groundwater Replenishment System facility, the largest of its kind, supplies 70 million gallons (265 million liters) of treated water a day, enough for 500,000 people.
Like many other regions, Orange County is struggling to find fresh water during prolonged periods of drought.
According to the UN-chartered International Panel on Climate Change, more than 1.4 billion people on the planet already face water shortages.
The hardest-hit areas include northern Africa, the Mediterranean, the Middle East, southern Asia, northern China, Australia, the U.S., and Mexico.
In Australia more than 10 percent of wastewater in drought-stricken cities is recycled, according to the IWMI report.
Deshmukh said the cost to treat reclaimed wastewater to drinking-water standard remains high, which is why large-scale facilities like his aren't readily built in developing countries.
Orange County's facility relies on reverse osmosis, a process that requires an enormous amount of energy to push water through a membrane that captures trace amounts of toxins, pollutants, household chemicals, and pharmaceuticals.
As energy costs rise, so do the costs of wastewater recycling, Deshmuhk noted.
He said, however, that recycling is still cheaper than pumping in water from water-rich areas in California.
In Orange County it takes 3,500 kilowatt hours of electricity to pump one acre-foot of water (a foot of water spread over an acre or 12 centimeters spread over a hectare) into the county. Recycling the same amount of local wastewater requires half as much energy.
Anders Finnson, deputy managing director of environmental wastewater issues for the Swedish Water and Wastewater Association (SWWA), said recycling wastewater brings other benefits—namely, nutrient-rich solids that can be turned into fertilizer.
Fertilizer prices jumped nearly 50 percent per metric ton over the last year in some places, making human waste a somewhat more attractive substitute.
Sewage sludge contains the same soil-enriching, plant-boosting elements found in expensive chemical fertilizers—nitrogen, phosphorous, and potassium.
Often referred to as biosolids, highly treated human feces is used in scattered areas throughout the developed world, where it must meet strict levels for pathogens and heavy metals.
Most biosolids are applied as fertilizer to cereal and grain crops, with occasional applications for forestry operations, golf courses, and other land uses, according to James Clark of Black and Veatch Corporation, a U.S. firm specializing in water recycling.
The practice has not spread widely, partly because of the public's concerns about human health or odors from neighboring farms, Clark said.
Despite such resistance, a handful of European countries have recently responded to a global phosphorus shortage by promoting sludge use.
Experts estimate that the world's reserves of the naturally occurring phosphorus, a critical element for plant growth, will be depleted in less than 200 years.
Sweden Pushes Biosolids
Sweden recently made phosphorus recycling a national environmental priority, with the goal of returning 60 percent of it back to the land by 2015.
Reaching that goal is possible through the use of biosolids to fertilize farms, the SWWA's Finnson said.
Hoping to convince farmers that biosolids are safe, the Swedish association launched a certification program highlighting wastewater facilities that produce high-quality, phosphorus-rich sludge ready for agricultural use.
The price of phosphorus, which has risen 400 percent in the last two years, has helped convince Swedish farmers to make the switch, Finnson said.
He estimates that as much as 20 percent of Swedish agricultural land is now treated with biosolids.
(Also see "Alcohol, Feces, Carcasses Fuel Green Vehicles in Sweden" [June 25, 2007].)
By comparison, biosolids are used on just one percent of U.S. farmland, according to the U.S. Environmental Protection Agency.
"In North America we sometimes go overboard with treatment," Clark, of Black and Veatch, said. "I think there are ways to meet halfway."
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