THE EFFECT OF RESIDUAL SUBSTRATE UTILIZATION ON SLUDGE SETTLING IN ANENHANCED BIOLOGICAL PHOSPHORUS REMOVAL PROCESS

The simultaneous process requirements of phosphorus removal and bulkin g control were demonstrated in this study via a unified explanation al ong with an introduction of the parameter q(re) i.e., specific residua l substrate utilization rate. Pilot-plant experiments using synthetic wastewater were performed at different SRTs (5,10,15) and anaerobic:ae robic volume ratios, V-an:V-a (1:9,1:4,1:2.3). These results indicated that more than 75% of phosphorus removal and 94% of COD removal can b e achieved during experimental periods. However, sludge settling prope rties in terms of SVI varied significantly, and a higher phosphorus re moval did not necessarily imply a better sludge settling. Nevertheless , SVI-values highly correlated with q(re) - regardless of different SR Ts and V-an:V-a ratios. This correlation would imply that the specific . utilization of residual substrate left for filaments in oxic zone is the primary factor influencing SVI. Furthermore, eliminating the acce ss of filaments to substrate plays a more influential role on SVI than favouring the poly-p microorganisms : the main floc-formers in EBPR p rocess. Based on these findings we can infer that when in the design a nd/or operation stage of the EBPR process, the carbon sequestration by poly-p microorganisms in anaerobic zone can be as much as possible so as to obtain a lower q(re) in the oxic zone. That is, if phosphorus r emoval and bulking control is achieved simultaneously. Copyright (C) 1 996 IAWQ.