Just add (gray) water
A Chinese university offers small-scale solutions to water pollution and scarcity.
2010 will be the year China embraces "toilet-to-tap" water treatment technology, predicts environmental engineering professor Siqing Xia. Until then, he continues to educate the public about the technology's benefits through a unique demonstration project at Tongji University in Shanghai.
His small-scale, 400 liter per day (L/day) treatment plant on the Tongji University campus turns wastewater from the College of Environmental Science and Engineering's lab building into pure water for scientific procedures and irrigation of the surrounding landscape. The end product is so pure it could be used for kidney dialysis, carbon-chip washing, or to replenish drinking-water supplies, according to Xia, who is also head of the State Key Laboratory of Pollution Control and Resource Reuse.
Although using recycled or gray water for agriculture and industrial applications is common in many parts of the world, direct consumption is still frowned upon, and the water at Tongji University does not end up in drinking glasses.
In 2010, Xia will set up another demonstration project, this one for the Shanghai World Expo, and he expects broad interest in, and even acceptance of, so-called toilet-to-tap, or direct potable reuse, technologies.
At Tongji University, wastewater from lab-building toilets and rainwater collected in tanks on campus is eventually funneled into a membrane bioreactor, which uses membrane technology and traditional biological treatment with bacteria to remove nutrients. The membrane component filters out silt, pollen, colloids, bacteria, protozoa cysts, and large viruses, among other things.
Most of the water leaving the membrane bioreactor is disinfected and reused as gray water in the lab-building toilets or for landscaping. The rest is treated with reverse osmosis and ion exchange, resulting in pure water that exceeds government drinking-water standards, according to Xia.
Such easy-to-assemble treatment plants can be quickly replicated and help in water-stressed regions, says Xia. He can deliver a 10,000 L/day facility for less than $14,000. So why aren't we seeing them everywhere? Negative public perception presents an enormous stumbling block. Even in a country that suffers from severe drought and pollution, people are not ready to drink water that is directly derived from the toilet bowl.
Nevertheless, says Xia, the Chinese government encourages such projects, and Tongji University is a step closer to making toilet-to-tap technology a viable solution to China's water woes.
China and the rest of world seem to be moving closer to accepting direct reclamation. At the end of last year, Orange County, Calif., christened a large-scale, 266 million L/day plant that treats sewage and uses the effluent to fill drinking-water aquifers relied on by some 2.3 million people. Orange County staged a sophisticated marketing and education campaign and earned the support of environmental groups and local officials, but state laws prevented direct reuse.
"Perception is a big issue, but permitting is also a big issue," says John Petersen, a professor of environmental studies and biology at Oberlin College. Oberlin pioneered on-site water reuse when its "living machine" went on-line nearly a decade ago to recycle gray water at the Adam Joseph Lewis Center for Environmental Studies. The living machine does not use membrane filtration, and effluent is used solely for toilet reuse and landscaping.
A handful of larger-scale projects exist around the world, but only one, according to experts, uses direct toilet-to-tap—a municipal facility in the Namibian capital, Windhoek.
The U.S. EPA is also beginning to embrace water reuse. "We are moving towards a more integrated approach to water resources management, and we know that water reuse and recycling will play a greater role," says agency spokeswoman Shakeba Carter-Jenkins.
A $480 million treatment plant, like the one in California, may not be feasible in other parts of the world, including rural China, but smaller-scale projects like the one at Tongji University present another option.
"It shows that local users and citizens can make a difference and take a part in improving the environmental quality of their own habitat," says University of Iowa hydrology professor Youkuan Zhang, who visited Tongji University last year. "Education is one of the important measures to effectively deal with environment problems." Petersen agrees: "I think the key value of the technology right now is probably as a tool to transform people's perception of what is waste and what is resource."
