Many of the proposed processes that reduce orthophosphate in the effluents from sewage treatment plants result in the extracted phosphate being concentrated in the digester supernatant. This phosphate must be removed prior to disposal of the supernatant or its recycle back to the head of the treatment plant. Digester supernatant was treated in two ways. The first was to add magnesia and elevate the pH to 9 to cause precipitation of the phosphorus. The other technique was to apply heat and/or vacuum to the digester supernatant which caused precipitation of the soluble orthophosphate. A 90% removal of orthophosphate can be achieved by either approach. The heat and/or vacuum process also yields a supernatant substantially lower in BOD, COD, and nitrogen concentration. The precipitated phosphorus (primarily a mixture of calcium phosphate and magnesium ammonium phosphate) was found available for plant food. Work was conducted by bench and pilot plant studies on digester supernatant.