The rotary disc filter with outward-in and inward-out consists of a series of horizontally installed rotating filter discs, each filter disc is composed of an even number of fan-shaped filter plates, and the rotary disc is equipped with a removable filter cloth made of fiber, with a filtration pore size of 10um.

The operating states of the fiber-cloth disc filter include: filtration, backwashing, sludge discharge state.

（1）Filtration

The sewage flows into the filter by gravity, and a water distribution weir is equipped in the filter tank. The filter cloth is fully submerged. The sewage enters through the outer side of the filter cloth. The filtrate is collected through the hollow pipe and flows out of the filter through the weir by gravity. The entire process is continuous.

（2）Washing

Some of the sludge in the filtration is adsorbed on the outside of the filter cloth, gradually forming a sludge layer. With the accumulation of sludge on the filter cloth, the filtration resistance of the filter cloth increases and the water level in the filter gradually rises, monitoring the changes in the liquid level in the tank through a pressure sensor. When the liquid level in the tank reaches the washing set value (high water level), the PLC can start the reverse suction pump to begin the washing process. During the washing process, the filter tank continues to filter.

During filtration, the filter disc is static, which is conducive to the sedimentation of sludge at the bottom of the tank. During washing, the filter disc rotates at a rate of 1 turn /2 minutes. The negative pressure shaft of the suction pump sucks the surface of the filter cloth, removes the accumulated sludge particles on the filter cloth, and the water in the filter disc is simultaneously drawn from the inside out and backwashes the filter cloth. The instantaneous flushing area is only about 1 percent of the total area of the filter disc. The backwashing process is intermittent.

During the washing process, two filter discs form a group and are controlled by an electric valve on the pipeline of the automatic switching suction pump. In a complete washing process, the washing of each group alternates while the suction pump operates continuously. When the quality of the incoming water deteriorates suddenly and the liquid level in the tank rises rapidly to the backwash liquid level, all backwash pumps are activated simultaneously during the washing process, which can backwash several groups of filter discs at the same time until the backwash cycle returns to normal.

（3）Sludge discharge system

The fiber disc filter has a bucket bottom under the filter disc to facilitate the collection of sludge at the bottom. Sludge deposition at the bottom reduces the amount of sludge on the filter cloth, which can extend the filtration time and reduce the amount of backwash water. After a set period of time, the PLC starts the sludge pump, and the sludge is returned to the plant drainage system through the perforated sludge pipe at the bottom of the tank. Among them, the interval and duration of sludge discharge can be adjusted.