Assessment of Recirculation Ratio Impacts on Mixed Liquor Suspended Solids in the Activated Sludge Process
Control of the bacterial environment through efficient solid/liquid separation and operation of the biological processes with high biomass concentrations are likely to affect cell metabolism and limit the bacterial growth, and in turn the sludge production. This paper presents a simulation study with the objective to study the effect of recirculation ratio on Mixed Liquor Suspended Solids (MLSS) in plant design and operation strategy of activated sludge process. The simulation results indicated that an optimal combination of recirculation ratio and operation strategy, the performance in terms of MLSS and efficiency improves significantly when compared to current operational practice. The use of simulations, rather than experiments, to compare combinations of plant design and operation strategy excludes erroneous conclusions due to arbitrary events. Moreover, it would be practically impossible to make a fair experimental comparison between all the combinations of design and operation, which are compared in these simulations. The simulation results were verified by operating a bench scale reactor in the laboratory operated in the continuous mode with the recirculation ratio (R) varied in the range of 0.25 to 1.
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