MAINTENANCE AND DECAY IN ENHANCED BIOLOGICAL PHOSPHOROUS REMOVAL IN ACTIVATED SLUDGE DURING LONG-TERM STARVATION

摘要

Operational problems in plants performing Enhanced Biological Phosphorus Removal (EBPR)under dynamic loading are often linked to an overall decay of active biomass or to an unbalanceddecay of storage products in phosphorus accumulating organisms (PAO). Decay processesoccurring during starvation of biomass decrease the amount of active PAO and their organic(PHA) and inorganic (poly-P) storage products. In this study, the effects of long-term starvationperiods on EBPR activity of activated sludge were examined. The main objectives were: i)quantification of the change in EBPR activity due to starvation under anaerobic and aerobicconditions and ii) identification of the mechanisms occurring under starvation conditions andtheir relation to currently used mathematical modeling approaches. An anaerobic-aerobicSequencing Batch Reactor (SBR) was operated with synthetic wastewater under steady stateloading. Sludge was withdrawn from the SBR and deprived from external substrate underanaerobic and aerobic conditions for 1, 7, 14, 21 or 28 days. Phosphorus release and uptake rateswere measured before and after starvation, together with viability staining. A first order decayrate for PAO of 0.15 d-1 was obtained from the aerobic starvation experiments. Approximately25% of EBPR activity was measured after 28 days of anaerobic starvation, although the reasonfor this decreased activity was not completely clear. Further studies showed that cell lysis andprotozoan predation are enhanced under aerobic starvation. Decay of PAO is greatly reducedunder anaerobic storage as compared to aerobic storage conditions.