The small purification tank of the anaerobic filter bed-biological filtration process consists mainly of the first chamber of the anaerobic filter bed tank, the second chamber of the anaerobic filter bed tank, the biological filtration tank, the treated water tank, and the disinfection tank, etc.

The upper section of the Anaerobic Filter Tank No.1 and Anaerobic Filter Tank No.2 serves as the flow regulation zone, where the effluent from the Anaerobic Filter Tank No.2 is pumped into the biological filter tank using an intermittent dosing pump.

The process recirculates treated water from the biological filter tank back to the anaerobic filter tank bed, where it removes BOD and undergoes biological denitrification under aerobic and anaerobic conditions.

To maintain the treatment efficiency of the biological filter tank, regular backwashing is conducted on the tank, with the backflushed water entering the first chamber of the anaerobic filter bed. Phosphorus removal can be achieved through ferric electrocoagulation.

Sludge primarily accumulates at the lower section of the first and second anaerobic filter bed chambers, and should be regularly discharged for treatment.