An Oregon facility tweaks its enhanced biological phosphorus removal system to cut costs and improve compliance

The Durham Advanced Wastewater Treatment Facility (Tigard, Ore.) must meet what is among the most stringent phosphorus limits in the nation: 0.07-mg/L total phosphorus. When the facility was upgraded in the early 1990s, the primary goal of its operations staff was to achieve reliable compliance with the new phosphorus limit; consequently, alum addition was used to remove phosphorus. By 1997, however, plant personnel had shifted their focus to achieving the phosphorus limit at the lowest operating cost. To do this, they needed to optimize enhanced biological phosphorus removal (EBPR) and stop using alum, except to polish effluent, because alum is more expensive than the chemical-free EBPR process. The wastewater treatment plant (WWTP) was modified to remove phosphorus using a combination of chemical precipitation, biological uptake, and effluent filtration. These continuous process improvements reduced alum consumption from 170 mg/L in 1993 to 60 mg/L in 1997.