Liming of District of Columbia raw or treated wastewater to pH 10 insolubilized the various forms of phosphorus in the wastewater, but removals to residuals of 0.3 mg./liter as P occurred only above pH 11.5, where precipitated magnesium hydroxide flocculated the turbidity. Nitrification of the wastewater during biochemical (secondary) treatment reduced the lime requirement for precipitation, the amounts of sludge from precipitation, and also improved phosphorus removals. Liming of organic free solutions insolubilized mixtures of ortho and polyphosphates by pH 10, although insolubilization of meta or tripolyphosphate alone required a pH above 11. The degree of biochemical oxidation significantly influenced the phosphorus removals, while temperature and ionic strength did not. (Author)