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Greening Graywater

By Office of Communication Services    Published on 04/30/2015 More stories >>

Eunsung Kan (right) and MS student Stuart Watson demonstrate
a system for neutralizing emerging contaminants.

Eunsung Kan (right) and MS student Stuart Watson demonstrate a system for neutralizing emerging contaminants.

Schoolchildren learn about the natural water cycle: clouds, rain, streams, ocean, evaporation. In the municipal water cycle, water from the tap is used for drinking/ cooking, bathing, washing, and irrigation; the resulting “graywater” runs to the sewer, is taken to a wastewater treatment plant, and is purified to be used again.

It’s in the purification process that things can get problematic. Assistant Professor Eunsung Kan works with emerging contaminants, adulterants of the water that appear in such small concentrations that they are often ignored—and therefore not removed. But these contaminants, including endocrine disrupters such as BPA, synthetic hormones, antibiotics and pain relievers, and certain chemicals in makeup and sunscreen, can cause a host of problems even in tiny amounts, including a higher incidence of breast, thyroid, and prostate cancers and hormone disruptions. Other problems include drug resistance—and not only in humans. Since the water is also used for irrigation, trace amounts of antibiotic collect and concentrate in the tissues of the plants, leading to pesticide resistance in the pests that eat them—and thus to the need for stronger pesticides.

Biochar made from locally grown greenwaste (left) is used as
a substrate for locally collected waterpurifying bacteria (right).

Biochar made from locally grown greenwaste (left) is used as a substrate for locally collected waterpurifying bacteria (right).

Dr. Kan looks at the entire municipal water cycle, but the core of the research in his Bio/Green Engineering Lab in the Department of Molecular Biosciences and Bioengineering is on removing emerging contaminants. He explains that several processes in use pose problems of their own, such as adding extra chemicals to neutralize those already present. His techniques, both cheaper and “greener,” include a photocatalytic process and one using specially selected and cultured bacteria.

In the first process, rods of biochar, or biologically active charcoal, are impregnated with titanium oxide and placed in the water. Sunlight excites the titanium oxide, which catalyzes, or breaks down, and neutralizes the trace contaminants. In the second process, a particular strain of bacteria that also breaks down the contaminants is isolated from the soils surrounding UH Manoa and encouraged to grow in a thick biofilm on the surface of biochar. The ideal system, Dr. Kan explains, combines the techniques: a photocatalytic system can be fitted to any area where wastewater is outflowing, after which the water is directed through a column treated with the bacteria, emerging contaminant free. With their green and sustainable focus, his techniques are contributing to detoxification and agricultural reuse of water.