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The beginning of biological phosphorus removal

This paper, based on Dr. Levin’s doctoral dissertation, demonstrated that an activated sludge mixed liquor culture could be induced to take up dissolved orthophosphate in excess of metabolic needs and reported seminal research describing the enhanced biological phosphorus removal process. Levin and Shapiro used the term “luxury uptake” to describe this phenomenon. The authors demonstrated that luxury uptake was induced by carefully altering the concentration of dissolved oxygen between aerobic and anoxic conditions. The phenomenon of luxury uptake was the basis for the development of the Phostrip process (Shapiro, Levin, & Zea, 1967) for phosphorus removal. The Phostrip process combined biological removal along with chemical addition. Luxury uptake was achieved in an aerobic aeration tank and released in an anoxic stripper tank. The eluent from the stripper had elevated (concentrated) levels of phosphorus, which were removed by lime addition. At that time, lime was the conventional chemical of choice for phosphorus removal. Since the lime dosage was proportional to wastewater volume rather than phosphorus concentration, a lower dosage could be used saving chemical and residual management costs. A number of fullscale Phostrip installations were implemented in the late 1970s and early 1980s. The conclusions of this paper were not accepted by a significant number of the academic and practicing engineering communities. Several papers rebutted their conclusions and stated that what was observed was not biological but was actually physical/chemical phenomena that caused phosphorus precipitation (Menar & Jenkins, 1970). In the early 1980s, subsequent research showed the importance of maintaining proper microbiological/ecological conditions within a biological phosphorus removal process. One important development was the recognition that phosphorusaccumulating organisms (PAOs) required true fermentative conditions for the release of phosphorus rather than merely the absence of oxygen (i.e., anoxic conditions with alternative electron acceptors, such as nitrate, prevented the release of phosphorus in the stripper tank). At the same time, various other biological phosphorus removal processes were developed, which eliminated the need for a stripper tank (Metcalf and Eddy, 2013). Most of these were based on configurations, which promoted the growth of PAOs. This can be achieved using anaerobic (fermentative) reactors in series with aerobic reactors. The key is to remove the phosphorusrich PAOs from the aerobic reactor before phosphorus release under anaerobic conditions. The work of Comeau, Hall, Hancock, and Oldham (1986) was arguably the first to describe the presently accepted biochemical model for enhanced biological phosphorus removal. Over time, greater emphasis was placed on nutrient removal. Success in fullscale plant biological phosphorus removal has resulted in greater use of the process to realize the advantages of reduced chemical cost and lower residual production. More recently, greater emphasis is being placed not only on removal, but also on recovery of valuable nutrients from domestic wastewater. The “luxury uptake” phenomenon initially developed for removal is often a part of contemporary phosphorus recovery scenarios (Salehi, Cheng, Heitz, & Ginige, 2018). In conclusion, our present enhanced biological nutrient removal technologies and more recent advances in phosphorus recovery owe much to the pioneering work of Levin and Shapiro (1965).