Shocks to the bioprocesses in the form of sudden changes in concentrations of nutrients can cause upsets. If the concentrations or flow rates of the waste vary greatly, dosages for treatment must be constantly be readjusted. If the input flow increases suddenly, the settling patterns will be upset to lower collection efficiency. Equalization dampens fluctuations. Flow equalization can improve performance of subsequent steps significantly.
Equalization allows reactions in the equalization tank.
There may be aeration both to keep the fluid from becoming anaerobic and smelly and to biodegrade some of the organic compounds present. More important for industrial wastes that can have wide swings in pH is the reaction of acids with bases because otherwise each would have to be neutralized with costs for equipment and reagents. Early in the process, usually following the initial step of collecting debris from the input stream from the sewer.