is discharged into the base of the sludge return line the air discharged into the sludge return line rises to the top as this happens some of the liquid in the sludge return line is also forced up to the top of the pipe and out the discharge opening in the sludge return line the sludge return line is an air lift pump that pumps settled sludge and water from the bottom of the clarifier cone back into the aeration chamber the sludge return line flow rate is controlled by the needle valve 251 and a solenoid valve s for intermittent operation this arrangement allows more settling time for the sludge the liquid displaced from the aeration chamber flows into the clarifier through the 6 inch circular clarifier baffle pipe 177 this baffle pipe keeps the sludge in the liquid flowing into the clarifier separate from the clear water being discharged from the clarifier in addition any floating material will separate from the liquid flowing into the clarifier and float back up into the aeration chamber 159 because this material will be lighter than the liquid slowly flowing through the circular clarifier baffle pipe the clear liquid in the top of the clarifier is discharged from the clarifier through the crossover manifold 118 the clear liquid flows into the crossover manifold through openings in the top of the pipe the liquid then flows up through the pipe in the aeration chamber and down into the clarifier discharge chamber 183 through the external crossover manifold pipe 193 the elevated loop in the crossover manifold pipe provides a static liquid seal that keeps the liquid level in the aeration chamber 159 high enough so that there will be no air space in the top of the clarifier 173 that would allow.