MODELING THE PERFORMANCE OF ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL SYSTEMS UNDER DYNAMIC LOADING CONDITIONS USING DIFFERENT MATHEMATICAL MODELS

摘要

The Activated Sludge Model No. 2 (ASM2) (Gujer et al. 1995) and the Activated Sludge ModelrnNo. 3 combined with the EAWAG Bio-P Module (EAWAG model) (Rieger et al. 2001) werernevaluated under dynamic loading conditions. These models differ mainly in their approach tornmodel decay processes. While the ASM2 model uses the death-regeneration concept, thernEAWAG model uses the endogenous respiration approach. In our modeling study, we found thatrnduring and after low loading conditions the specific approach of modeling decay significantlyrnaffected model predictions. The two models predicted different levels of the effluent PO4rnconcentrations during and after the 3-day period of low loading. One structural differencernbetween both models found to be important was that ASM2 assumes decay processes to occurrnboth under aerobic and anaerobic conditions, whereas the EAWAG model assumes decay to takernplace only under aerobic conditions. Both models predicted an increase in effluent PO4 duringrnthe low loading period, which does not agree with experimental results and is assumed to be anrnartifact. This artifact can be linked to a basic assumption in both ASM2 and the EAWAG modelrnwhere the decay of polyphosphate accumulating organisms (PAOs) and their storage products isrnassumed to occur at identical rates. Our experimental observations suggest that the rate of decayrnfor active PAOs is larger compared to the rate of decay for poly-P.