A new interpretation of ASM2d for modeling of SBR performance for enhanced biological phosphorus removal under different P/HAc ratios.

This study evaluated the prediction capability of Activated Sludge Model No. 2d (ASM2d), for the enhanced biological phosphorus removal (EBPR) performance of a sequencing batch reactor (SBR) receiving variable influent phosphate load. For this purpose, a laboratory-scale SBR was operated with a synthetic feed containing acetate as the sole carbon source. The experiments were conducted in four different Runs to ensure a range of different phosphate/acetate ratios in the influent. Model evaluations were carried out using concentration profiles measured throughout a representative cycle at steady state. An iterative calibration methodology was developed based on sensitivity analysis and applied to four different sets of experimental data on relevant model parameters reflecting SBR performance. ASM2d was able to predict the steady state behavior of the SBR system receiving variable influent phosphate loads only with the recalibrated parameter set. The regular changing pattern of the coefficients could be interpreted with the ability of the SBR system to sustain glycogen accumulating microorganisms, GAOs, which can store substrate under anaerobic conditions without polyphosphate energy, but deriving energy from the degradation of glycogen. Thus they are capable of prevailing at lower P/Ac ratios. The results indicate the need to include glycogen and GAOs as model components for processes involving both phosphate accumulating organisms, (PAOs) and GAOs, in order to obtain a better prediction of X(PHA) and oxygen uptake rate (OUR) profiles in the system.

The effect of nitrate and different substrates on enhanced biological phosphorus removal in sequencing batch reactors.

Enhanced biological phosphorus removal (EBPR) requires an anaerobic-aerobic sequence and short chain fatty acids, namely acetate. It is also known that the presence of nitrate in the anaerobic phase inhibits EBPR. This study describes a lab-scale experimentation carried out to study the effect of different substrates on EBPR and behaviour of PAOs under anoxic conditions in a sequencing batch reactor operated using synthetic wastewater. Experimental data show that the EBPR performance is significantly affected by glucose rich influent. Low COD/TKN ratios caused lower phosphorus removal performance since nitrate entering the anaerobic zone consumes substrate for denitrification. The results also show that anoxic phosphate uptake took place together with nitrate reduction when there was no external substrate. However, the uptake rate under anoxic conditions was lower than that under aerobic conditions.