Seasonal phosphorus removal in a phostrip process—II. Phosphorus fractionation and sludge microbiology during start-up

This paper presents data related to the start-up of biological phosphorus removal in a plant exhibiting simultaneous nitrification and denitrification in the aerobic basin. No particular selection of bacterial species was observed during the start-up period, leading to the conclusion that the dephosphatation was carried out by the denitrifiers present in the sludge. The time necessary to promote phosphorus removal in the plant corresponded to about 2 anaerobic-aerobic cycles of the sludge. The maximum removal rate of phosphorus was equal to 7 mg P g−1 MLSS d−1, resulting in the sludge containing about 10% of phosphorus. Chemical speciation of phosphate fractions indicated that when no lime was added to the clarifier, organic phosphates contributed to 52% of the phosphorus present in the sludge. The remaining 48% is to be attributed to the process of co-precipitation. Dosing of lime caused a decrease in the polyphosphate fraction in the sludge and a simultaneous increase in the portion of other fractions. The conditions prior to lime addition were re-established within a few days of stopping the chemical dosing, indicating that the chemical process does not exert an irreversible influence on the enzymatic system of the biological luxury up-take.