The control of the sludge thickening tank includes the control of incoming mud volume and the control of the discharge of concentrated sludge volume. Under normal circumstances, there is no sludge storage tank before the concentration tank. In this way, the sludge discharged from the sewage treatment system will directly enter the concentration tank. Therefore, the control of the concentration tank mainly refers to the control of the discharge of concentrated sludge. The control methods for the discharge of concentrated sludge mainly include:

(1) Control the starting and stopping of the sludge pump with the timer;

(2) Use timers and preset counters to control daily discharge of a certain amount of concentrated sludge;

(3) Control the start of the sludge pump with the timer, and stop the pump when the concentration of the sludge is reduced to a certain concentration with the sludge concentration meter;

(4) Use a timer to control the start of the pump. Use a sludge concentration meter, flow meter, and preset counter to stop the pump each time a certain amount of solids (to dry sludge mass) is discharged.

Large-scale sewage treatment plants often use control methods (1). For semi-continuous operation control, the control method (2) is generally adopted for small-scale sewage treatment. The control process and required hardware for the control methods (3) and (4) of the sludge concentration detector are not complicated, but it is not widely used currently.