AbstractIn a previous report it was concluded that steady‐state operation of completely mixed reactors for growth of heterogeneous microbial populations, i.e., activated sludge processes, was extremely difficult to attain if maintenance of a constant sludge recycle ratio,c, was required, and equations were devised in which the concentration of cells in the recycle,xR, rather than the recycle ratio, was constant. In this report the equations are developed and computational analysis shows the effect on substrate and cell concentrations in the reactor of operational variables such as inflowing feed concentration, hydraulic recycle ratio, recycle sludge concentration, dilution rate, and the biological “constants” μm,ks, andY. The stabilizing effect of operating with constantxRon the dilute‐out pattern