The effect of the enhanced phosphorus removal process (EBPR) on the waste activated sludge production and the type of phosphorus storage were investigated in two continuous flow activated sludge systems on semi-technical scale. One of the plants (plant II) was operated with the A/O process, whereas the other plant (plant I) was operated in a conventional, fully aerobic mode and served as a control. By monitoring the elementary composition of the activated sludge solids in plant II it was proved that a major part of the enhanced phosphorus removal was due to a storage as polyphosphate (poly-P). The additional uptake of phosphorus resulted in an increase of the inorganic sludge mass which was determined as 3.05 g SS/g P using the results of the measurements of the non volatile solid fraction. This value was also experimentally confirmed by the measurement of the difference between the WAS production of plant I and plant II. Based on the specific WAS production, an additional dry solids production of 3.14 g SS/g P was calculated. No indications for a significant difference of the organic sludge production between both plants were found, although the organic WAS production was slightly higher in experimental periods with a relatively high phosphorus content of the activated sludge solids of plant II.

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