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Time within Cycle, min.

Figure 7.43 Performance of an SBR during a single cycle. The SBR was operated in a manner to mimic the performance of the MLE system shown in Figure 7.28. Effective HRT = 6 hr; effective SRT = 10 days; biomass recycle ratio = 0.5; mixed liquor recirculation ratio = 2.0; aerobic fraction = 50%. Influent flow = 1000 m'/day. Influent concentrations are given in Table 6.6. Paramelers are listed in Table 6.3. The dissolved oxygen concentration was zero during the anoxic period and 2.0 mg/L during the aerobic period.

Figure 7.43 Performance of an SBR during a single cycle. The SBR was operated in a manner to mimic the performance of the MLE system shown in Figure 7.28. Effective HRT = 6 hr; effective SRT = 10 days; biomass recycle ratio = 0.5; mixed liquor recirculation ratio = 2.0; aerobic fraction = 50%. Influent flow = 1000 m'/day. Influent concentrations are given in Table 6.6. Paramelers are listed in Table 6.3. The dissolved oxygen concentration was zero during the anoxic period and 2.0 mg/L during the aerobic period.

within 25 minutes, after which little occurred due to lack of an electron acceptor. Furthermore, complete nitrification was not achieved during the aerobic period. Consequently, for this SRT, it would have been better to devote less time to anoxic conditions and more to aerobic conditions. The effects of the acrobic fraction of the fill plus react period will be addressed later.

The effect of SRT on the performance of this SBR system is shown by the solid lines in Figure 7.44. For comparison, the performance of an analogous MLE system is shown by the dashed lines. They are the same as the second bioreactor curves in Figure 7.29. The similarity in the performance of the two systems is apparent; the differences are due to the plug-flow nature of the SBR which allows it to achieve better removal of the soluble constituents. The particulate constituents are very similar, however, for the same reason that the particulate constituents were the same in the CSTR and tanks-in-series systems. This emphasizes the point that continuous flow and batch systems with the same effective SRT will contain the same amount of biomass, thereby making the biomass concentrations the same when the effective HRTs are the same. Consequently, the simple analytical model for a CSTR

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