Remove the outlet of the excess sludge air-lift pump from the sludge tank into the accumulation tank (so that the outlet of the aif-lift pump would be higher, than the height of water level in the activation tank). After about 2 months of the WWTP operation, put the air-lift pump back.

Take the outlet of the air-lift pump for settling tank filling from the stilling cylinder of the settling tank and put it into the activation tank. After about one month of the WWTP operation, put the outlet of the air-lift pump back into the stilling cylinder of the settling tank.