Graywater Wetland Treatment for a Living Building

This paper discusses the graywater treatment wetland performance data for the Bullitt Center which is a six-story, 4645 m2 (50,000 ft2) office building located in Seattle, Washington. Graywater from sinks, dishwashers and showers is stored in a 1514 L (400 gal) tank in the basement. Graywater is pumped every four hours to a 44.5 m2 (479 ft2) recirculating gravel filter system (RGFS) wetland located on a third floor balcony. The wetland was designed to treat an average daily flow of 1305 L (345 gal), and it must meet a regulatory standard of 30 mg/L for both total suspended solids (TSS) and biochemical oxygen demand BOD5. The wetland was also required to meet a total fecal coliform concentration of 200 CFU/100-ml sample. After approximately three days of treatment, the graywater is discharged to an adjacent 325 m2 (375 ft2) drain field amended with a 1.07 m (42 in) mixture of C-33 sand and 35-40 percent compost. Due to low effluent flows that approached one-tenth of the design flow throughout the year, the wetland was able to meet mass discharge limits for both BOD5 and TSS. The system achieved concentration limits for BOD5 during the growing season. Decreasing the TSS loading on the system by adding a settling basin or pre-filter may enable the system meet BOD5 and TSS discharge concentration limits throughout the year. Ultraviolet light disinfection may also be required to meet fecal coliform discharge limits during the winter months.

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