Biological Uptake of Phosphorus by Activated Sludge

Abstract

The ability of activated sludge to remove phosphates was studied by adding carrier-free 32 P to raw sewage and measuring incorporation of the radioactivity into the cells over a period of time. Radioisotope determinations indicated that 48% of the 32 P radioactivity was removed by 12 hr. However, chemical methods indicated that only 30% of the orthophosphate apparently disappeared from the sewage during this period. Experiments with sludge prelabeled with 32 P indicated that considerable phosphate turnover occurred. The cells released large amounts of radioactivity as they were incorporating fresh phosphates. Starvation in isotonic saline for 18 hr caused the sludge to dump phosphate. When introduced into fresh sewage containing 32 P, the starved sludge removed about 60% of the radioactivity in 6 hr with little phosphate turnover. The ability of sludge to remove 32 P was inhibited approximately 83% by 10 −3 m 2,4-dinitrophenol. This inhibition was at the expense of the cell fraction that contained ribonucleic acid and deoxyribonucleic acid. The sludge cells released orthophosphate when exposed to the chemical agent. Experiments using 45 Ca indicated that calcium phosphate precipitation plays a minor role in phosphate removal under our experimental conditions.

Finding the key to enhanced biological phosphorus removal (EBPR)

“…No release was observed in the final clarifier. A literature search showed that “luxury uptake” of phosphorus occurred in several plants in the USA and India but those were all high‐rate plants with limited or no nitrification (Levin & Sharpiro, 1965; Milbury et al, 1971; Srinath et al, 1959; Vacker et al, 1967; Yall et al, 1970). The author concluded that the release of phosphorus in the second anoxic zone resulted from anaerobic conditions in that zone.…”