The discharge of phosphorus to surface waters causes accelerated eutrophication of lakes, reservoirs, and ponds. Surface waters discharged in municipal and industrial wastewater has been identified as one of the principal sources of phosphorus, readily available for uptake by aquatic micro-organisms (algae). Since the 1970s phosphorus has been identified as the most important rate-limiting factor for algal growth in freshwater systems, and its removal from these wastewaters has therefore become increasingly important.
Phosphorus removal from wastewater effluents can be achieved in two fundamentally different ways: (1) physical-chemical precipitation and (2) using enhanced biological removal (although both, in essence, entail the creation of particulate matter that can be separated from the water). The former utilizes the solubility of phosphorus-metallic compounds to precipitate the phosphorus down to levels approaching the solubility product of the compounds, and then employs a physical separation process to remove the precipitate from the wastewater. The latter takes advantage of the “luxury uptake” of phosphorus by poly- phosphate accumulating organisms (PAOs). Depending upon the level of phosphorus removal to be achieved, one can use physical-chemical processes, the biological process, or a blend of the two.