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Graywater study results can't be processed fast enough

April 2, 2009 | 12:24 pm

"It seems we needed to do this study three years ago," said Sybil Sharvelle, principal investigator on a graywater study that's been in the works since 2006 and won't be completed until mid-2011. "There's a huge rush right now for information, and we're just not at the point yet where we're ready to provide results."

Sharvelle is referring to "Long Term Effects of Landscape Irrigation Using Household Graywater," a $450,000, two-phase study conducted by the Virginia-based Water Environment Research Foundation. WERF, as the scientific research organization is known, is dedicated to wastewater and stormwater issues and is funded by hundreds of subscribers, including muncipal wastewater agencies, environmental groups, chemical companies and cleaning product manufacturers, all of which are clamoring for more information on what has become a hot topic of late: recycling wastewater.

Graywater is the wastewater generated from laundry machines, showers, baths and sinks (excluding kitchen sinks). About 50% of the wastewater generated inside an average American household is graywater, which makes it an attractive option for water agencies that are looking to not only reduce consumer demand for potable water, especially in areas that are prone to drought, but the amount of wastewater those consumers are sending to the sewers for treatment.

California's Department of Housing and Community Development is one of the many government agencies looking to the WERF graywater study for guidance as it works to revise the state's current graywater standard. A preliminary version of the revised California graywater code is expected in May. Interim results from WERF's analysis of existing graywater systems won't be available until June.

What, exactly, will those interim results entail? According to Sharvelle, it will be an analysis of the pathogens in soil samples that have been collected from four homes in three states (California, Colorado and Texas), all of which have been using graywater to irrigate their landscapes for more than five years. Most of those systems use graywater generated from laundry machines; some also incorporate the graywater generated from baths, showers and bathroom sinks. Only one kitchen sink system is included in the study, and it's at the home of a vegetarian; if meat is prepared in the kitchen, the resulting graywater "is typically contaminated with pathogens and viruses and is a more high-risk wastewater," Sharvelle said. "Overall, I think that the major concern [with graywater] really comes in terms of public health, but of all the systems that have been operating over very long durations, there haven't been cases of people getting sick," said Sharvelle. "We think that when drip lines are used for application of graywater, presence of pathogen indicators will be minimal at the surface of the soil. Results to be presented in June will confirm methods of graywater irrigation, which minimize potential human contact with pathogen indicators."

This spring, the WERF study will expand to four more homes in the same states -- homes that have installed graywater systems but have not yet started to use them.

"We've already taken the before samples," said Sharvelle. "Most of those houses will start irrigating this spring, and we'll start taking [after] samples over the next couple years."

Final results of the WERF graywater study are expected in spring 2011.

— Susan Carpenter