quantity of phosphorus incor porated by activated sludge has been reported by several investigators1_3 to range normally between 2 and 3 percent, based on volatile suspended solids (vss) present in the sludge. In the 1960's, how ever, some activated sludge systems were reported to exhibit higher percentages of incorporated phosphorus, up to 7 percent in some cases.4'5 Two hypotheses for this abnormally high sludge phosphorus are 1. A biological incorporation in excess of required metabolic uptake by the bio mass present in the sludge, the so called "luxury uptake"; and 2. A physical-chemical formation of a solid species that subsequently is sorbed or becomes enmeshed in the sludge mass.

Phosphate incorporation in activated sludge

Phosphorus removal from domestic wastewater was investigated using four synthetic media, pilot trickling filters constructed at the Madison Nine-Springs Sewage Treatment Plant. Phosphorus removal was not correlated with the parameters of the experimental design of: hydraulic load, depth, recirculation, or waste strength; however, greater phosphorus removals were measured than could be attributed to biological requirements for phosphorus. Analysis of filter slime composition and phosphorus release studies suggested this bonus-removal of phosphorus was attributed to chemical precipitates of calcium apatite, aluminum phosphate, and iron (III) phosphate trapped in the filter slime. This trickling filter study supports the enhances-removal mechanism for bonus-removal of phosphorus from hard water wastewaters reported for the activated sludge process.

Harold J. Jebens

Papers

Enhanced Phosphorus Removal in Trickling Filters