In municipal sludge treatment, the spiral centrifugal pump has played its soft conveying characteristics, and can transport activated sludge without damage. Therefore, it is widely used in the process sections such as primary sedimentation sludge, digestion sludge, and return activated sludge.

1) Transportation of primary sludge and digested sludge

The spiral centrifugal pump can transport medium with high solid content due to its good non clogging performance, which can well solve the problems of clogging, abrasion and inability to transport caused by high solid content and viscosity of primary sedimentation and digested sludge in the transport process; Ordinary centrifugal pumps can not normally and stably transport primary sludge and digested sludge with high solid content and high viscosity. Although positive displacement pumps (such as screw pumps) can deliver normally, due to the wear of impurities in sludge on the stator and rotor, the stator and rotor of the screw pump fail too quickly, resulting in high maintenance costs. In addition, screw pumps use screw thrust to deliver, which has extremely low efficiency, high energy consumption and high operating costs.

2) Transportation of returned sludge

At present, in most domestic sewage treatment plants, the activated sludge treatment process using microorganisms for sewage treatment is widely used. In this process, the spherical bacteriocolloids (flocs) formed by bacteria bonding are the main components of the activated sludge aeration tank. The dissolved pollutants in the sewage can easily approach the bacteria and be preyed on. The colloidal pollutants must first be adsorbed on the surface of the bacteriocolloids (flocs), and then gradually moved around the bacteria in the flocs. After the colloidal pollutants are hydrolyzed into small molecules of soluble substances by bacteria, They can be decomposed together with other soluble pollutants. Therefore, in this process, the sludge is returned to the aeration tank from the final sedimentation tank in a fixed amount, which can effectively shorten the microbial culture time. In order to achieve this goal, the efficiency and speed of sewage treatment can be improved only by not breaking the microbiota in the activated sludge as much as possible in the process of activated sludge return, so that the microorganisms in the aeration tank can reach the effective concentration quickly. Otherwise, the treatment effect will be seriously affected. The spiral centrifugal pump has significant advantages in the process section of returning activated sludge. Its unique impeller design, low head, large flow, and low speed characteristics make it neither easy to break the activated sludge flocs nor cause blockage, ensuring the activity of the returned sludge and improving the treatment efficiency. The characteristics of the sludge flocs have hardly changed, and the structure is basically intact. The sudden 90 degree turning of the centrifugal pump during the conveying process is easy to cause obvious collision, which will seriously damage the flocs.