Operation of full-scale biological phosphorus removal plant

Full-scale operation of a new process to remove phosphorus has shown the method to be reliable, efficient, and cost effective. The method uses activated sludge to concentrate and transfer influent phosphorus into a substream from which it is chemically precipitated. The high concentration of phosphorus and the small volume of wastewater in which it is contained make the use of lime highly efficient. The essential feature is cycling of the activated sludge through aerobic and anaerobic phases. Sludge organisms take up phosphorus in the aerobic mixed liquor. After settling in the secondary clarifier, the sludge is transferred to a holding tank in which it becomes anaerobic. Upon further settling, it produces a phosphorus-rich supernatant. Lime readily precipitates the phosphorus from the supernatant. The process is fully compatible with activated sludge treatment.