Biological Nutrient Removal at the Blue Plains Wastewater Treatment Plant in Washington, D.C.

A pilot study was conducted to establish feasibility of biological nutrient removal at one of the most advanced wastewater treatments in the U.S. The results of the study revealed technical feasibility of biological phosphorus removal at extremely high F/M (0.84 1/day) and a short hydraulic detention time (2.2 hours) in the first stage activated sludge system. Due to phosphorus limitation of 0.18 mg/l, it was determined that none of the single sludge BNR processes was applicable at this facility. In the second stage, therefore, biological nitrogen removal was achieved with both methanol and primary effluent as a carbon source. Another significant finding was that after acclimation, the primary effluent exhibited the same rate of denitrification as with methanol (2.7 mg NO₃− N/gVSS·hr). Further pilot testing revealed correlations among such process variables as detention time, BOD to nitrogen ratio, and effluent nitrogen concentration.