Two laboratory batch aeration units were operated under similar conditions using synthetic feed with and without phosphates. With synthetic feed, the normal activated sludge flocs after being washed off of their cations exhibited a phosphorus storage between 2.5% and 2.9% based on the mixed liquor volatile suspended solids (MLVSS). The storage of phosphorus was found to be independent of MLSS and organic load levels. The phosphorus starved activated sludge flocs also exhibited identical phosphorus storages. The units were subdivided and fed with the same standard synthetic feed except that different amounts of cations (Ca(++), and Fe(+++) were added to it to obtain the increase in the percent phosphorus in the cell mass due to the cations in the feed. The percent phosphorus incorporated in the volatile mass was increased from an average of 2.89% to 3.44% with 40 mg/ of Ca(++) and from 2.89% to 4.27% with 120 mg/ of Ca(++) in the feed. The corresponding calcium content of the sludge was 3.1% and 5.1% on the volatile mass basis. Similarly 15 mg/ and 30 mg/ of Fe(+++) in the feed enhanced the percent phosphorus in the volatile mass. (Author)