Effects of quantitative shock loadings on the constant recycle sludge concentration activated-sludge process

The reliability of the process of Ramanathau and Gandy (Biotechnical Bioeng., 13, 125 (1971) for the completely mixed activated-sludge process holding the recycle cell concentration, Xr, as a system constant with respect to step changes in hydraluic retention time was investigated. The experiments were run at initial dilution rates of 1/8, 1/6, 1/4, and 1/2 hr-1 treating a soft drink bottling wastewater. The influent substrate concentration was maintained at 1000 mg/liter chemical oxygen demand and the hydraulic recycle ratio at 0.3. The recycle sludge concentration was maintained at about 7000 mg/liter. It was found that the system could accomodate hydraulic shock loads up to 200% positive changes and down to 50% negative changes without disruption of the effluent quality. Shorter retention time of the range studied, from 2 to 8 hr, has the advantage of shorter response time with respect to the response of the concentration of biological solids in the reactor.