Fate of Phosphorus in Waste Treatment Processes: Enhanced Removal of Phosphate by Activated Sludge SIR: The article by Menar and Jenkins [ENVIRON. Scr. TECHNOL., 4 (12), 1115 (1970)l purporting to show that phosphate removal by activated sludge is due largely to chemical precipitation is impressive, but we wish to emphasize that their data are not universal in application. In our own studies (Levin, 1963; Levin and Shapiro, 1965; Levin and Shaheen, 1967; Shapiro, 1967; Shapiro et al., 1967), we showed that the uptake of phosphate by activated sludge is inhibited by poisons such as 2,4-dinitrophenol, or mercuric chloride, and is thus far more likely to be a biological phenomenon than a chemical one. Similarly, the release of phosphate by anaerobic sludge is affected by poisons, being inhibited at low concentrations and stimulated at high concentrations of, for example, cyanide. Furthermore, whereas Menar and Jenkins claim that bubbling of an anaerobic sludge with nitrogen will cause apparent uptake of phosphorus due to calcium phosphate precipitation brought about by the stripping of COz from the system, we have actually used nitrogen bubbling to create and maintain anaerobic conditions to favor phosphate release. In fact, both vigorous bubbling with nitrogen and anaerobic mechanical stirring resulted in identical rates of phosphate release. Literature Cited Levin, G. V., PhD thesis, Johns Hopkins University, Baltimore, Md., 1963. Levin, G. V., Shapiro, J., J . Water Pollut. Contr. Fed., 37, 800-21 (1965).
280 Environmental Science & Technology
Levin, G. V., Shaheen, D. G., Biotechnol. Bioeng., Vol. IX, 457-70 (1967). Shapiro, J., Science, 155,1269-71 (1967). Shapiro, J., Levin, G. V., Zea, H., J. Water Pollut. Contr. Fed., 39,1810-18 (1967).
Gilbert V. Levin1 Biospherics Inc. 4928 Wyaconda Rd. Rockville, Md. 20852
Joseph Shapiro Limnological Research Center University of Minnesota Minneapolis, Minn . 1
To whom correspondence should be addressed.
SIR: I have no objections to Levin and Shapiro’s letter except to say that I do not claim that bubbling nitrogen gas has any significance with respect to removing soluble phosphate from activated sludge. It is the bubbling with C02free gas that is significant; argon, methane, helium, neon, or oxygen, etc., would be just as effective as long as they were C02-free.
David Jenkins Department of Civil Engineering University of California BerkeIey, Calif. 94720