In residential buildings, between 50 to 80 percent of the wastewater produced is graywater; for commercial buildings, the range is lower, at 20 to 40 percent. “If you had an apartment complex for about 1,000 people, you’re looking at payback between three and four years,” Lohan estimates.
Living Machine Systems’ graywater and blackwater treatment system at the new headquarters for the San Francisco Public Utilities Commission, designed by Seattle’s KMD Architects, clocked in at about $1 million, or 0.5 percent of the total building cost. The 5,000-gallon-per-day capacity system pumps wastewater through a series of five hydroponic cells, which are embedded in the building lobby and the surrounding sidewalk outside.
The system includes two tidal-flow, first-stage treatment cells and three vertical-flow, second-stage treatment cells. The two types of treatment cells operate similarly. Above grade, the treatment cells resemble large planters, and each contains shade-friendly, leafy plants indoors or low-maintenance, native plants outdoors. The planters drain to a series of below-grade tanks that perform specific functions: a settling tank for organic material; a collection tank for discharging solid waste to the sewer; and tanks to equalize flow, recirculate water, and store water for toilet flushing.
Wastewater is pumped into the treatment cells and then drained into a reuse tank a dozen times each day, mimicking tidal action. As the water rises and falls, the plants, bolstered by naturally occurring, beneficial bacteria, consume the nutrients in the water. The planting medium—coarse, lightweight, expanded shale—ensures that wastewater levels stay 6 inches below the top surface of each cell, out of reach of building users and passersby.
From each hydroponic cell, the wastewater is piped to a two-stage filtration system, which is followed up by UV and chlorine disinfection. The Living Machine treatment system is expected to reduce the building’s water use by 70 percent and to save about 750,000 gallons of water per year.
Washing Away Conventions
Despite the science behind the design of wastewater treatment systems, some designers, building officials, and occupants still view them with skepticism. The widespread installation and use of such systems relies on more than simply perfecting the technical details; it also demands an awareness of water scarcity and reuse. “As we become more aware of changes relating to water availability and water supply on the treatment side of things, graywater systems will be more accepted and perhaps encouraged,” Spataro says. “The shift will really come when the building industry feels that water is a precious resource, and that our lightly tainted graywater shouldn’t be going off miles away to a water treatment plant. Water has value in reuse within the boundaries of the site.”
Going one step beyond wastewater treatment systems that clean water to a state suitable for nonpotable uses are graywater and blackwater recycling systems that can treat and clean wastewater to potable standards. But designers should not expect these systems to become standard callouts in architectural drawings anytime soon. They still cause regulators, building owners, and occupants to squirm.
Everyone will first need to reevaluate their preconceptions about wastewater itself, says Dan Hellmuth, AIA, principal and co-founder of Maplewood, Mo.–based Hellmuth+Bicknese Architects. “We need to eliminate the concept of waste, and no longer talk about it that way.” Instead, he says, people need to transition their perception of graywater as a potential source of pathogens to a source of valuable nutrients that can benefit the earth. “It’s basically nutrient conversion.”
As a result, while regulations currently restrict or even outlaw the use of on-site wastewater treatment systems, the solution to water scarcity ultimately does not lie in codebooks or technical drawings. The solution begins with us.