Phosphorus Balance: Field Studies of Two Sewage Treatment Plants
Abstract Removal of phosphates from wastewater will become an important requirement in the near future in order to arrest the eutrophication of our surface water supplies. Present day treatment plants are inefficient in removing phosphates. Additions of new and deletions or changes in existing processes will be required. Knowledge of the concentration and type of phosphorus compound in all streams of a conventional biological treatment plant will be required to make effective and economical changes. This work attempts a mass balance on phosphorus on unit operations of two activated sludge plants: The North Toronto Sewage Treatment Plant and the Penetanguishene Sewage Treatment Plant. Preliminary field studies were carried out over several weeks to establish background information on phosphorus concentration and type at each plant. From this information, the number of sampling streams, timing of sampling, and accuracy and precision of phosphate and flow measurements for short, in-depth, phosphorus studies on each plant was made. Two 2–3 day surveys were made at each plant. The data are presented in the form of phosphorus mass balances on important unit operations as well as on the entire plant. Balances were found to be within the combined experimental error of sampling, analytical technique, and flow measurement. Major phosphate streams in decreasing order are the return sludge, raw influent, primary sludge and digestor supernatant. Present phosphorus reduction is about 20–30%, as expected for biological treatment. The possible effect of operational changes and additions of phosphorus removal process is discussed.