WATER TREATMENT SLUDGES CAUSE PHOSPHORUS DEFICIENCY IN BIOLOGICAL WASTEWATER PROCESS

The removal of biologically available phosphorus caused by the discharge of water treatment coagulant sludge into the sewer created a nutrient deficiency at the Southeast Water Pollution Control Plant in Philadelphia. The investigation into the incident is detailed including the effects on the secondary system biology, the removal of phosphorus in both the sewer system and through the wastewater treatment plant, and the beneficial effect of adding phosphoric acid to the wastewater treatment process. The results of laboratory and full-scale testing are presented. The effects of both ferric chloride sludge and aluminum sulfate sludge entering the sewer system on phosphorus concentrations in the wastewater are described. A description of the phosphoric acid feed system, monitoring, and controls are discussed. The addition of approximately 1 part per million of phosphorus restored a healthy activated sludge biota and yielded an excellent settling sludge.