ABSTRACT

Consider first the concentrations of MLSS and heterotrophic biomass shown in parts d and e of Figure 7.26. For an SRT of 10 days, the mass of each in the system is relatively constant over the range of relative tank sizes considered. This suggests that the changes in the concentrations of each shown in the figure are due primarily to their distributions within the system. Consequently, the concentration curves must satisfy two criteria. First, the sum of the masses in each tank, i.e., volume times concentration, must be relatively constant. Second, the concentration in the stabilization tank must be related to the concentration in the contact tank in approximately the same way that the concentration in the biomass recycle flow is related to the concentration entering the settler, i.e., through Eq. 7.7. In other words, as more volume is shifted to the contact tank, a smaller percentage of the system biomass is at the concentration of the biomass recycle and thus the concentration in the system must increase in order to contain the same mass in the same total volume. Those changes in biomass concentration, in turn, impact on the concentrations of soluble constituents leaving the contact tank.