Application of Sludge Dewatering System in Waterworks

In the process of transforming the water resources into tap water, a lot of sewage will be produced in waterworks. The application of sludge dewatering system, not only can effectively improve the water quality, but also can protect the environment.

1. Sewage and Sludge Dewatering

The sewage produced by the waterworks mainly includes these substances:

(1) The coagulant retained in the sludge.

(2) The organic substances and suspended solids after concentration.

(3) The waste water produced by repeatedly washing the filter tank.

(4) The muddy water discharged from the sedimentation tank.

If the sewage was discharged directly into the ecological environment without strict treatment, it will not only pollute the water resources, but also result in a waste of water resources. Nowadays, water pollution and water shortage are becoming more and more serious, the waterworks should pay more attention to the sustainable development of ecological environment and water resources, and fully fulfill their social responsibilities.

Sludge dewatering refers to a kind of method which can remove the moisture contained in sludge, so as to transform sludge into solid mud and semi-solid mud. At present, granulation, mechanical dehydration and natural drying are widely used. Mechanical dehydration is mainly used in waterworks.

According to the relevant research results, the water content of sludge can be reduced by 50%-80% after sludge dewatering treatment. And then, the sludge will be dried by dryer, the water content will be reduced to no more than 10%.

2. Sludge Dewatering System

2.1 Main Components

The sludge will be pumped from the bottom of the sedimentation tank to sludge buffer tank. The sludge buffer tank can homogenize the sludge, so as to effectively improve the possibility and reliability of sludge dewatering. The the sludge will be pumped to the centrifugal dehydrator. After dewatering, the sludge will be transformed into mud cake, and the water which be separated will be returned for recycling.

2.2 Structure and Working Principle of Centrifugal Dehydrator

The centrifugal dehydrator is mainly composed of a central screw, a cylinder and a conical cylinder. The sludge will be injected into the central screw and discharged from the slag outlet.  The rotating speed of the central screw is higher than that of the cylinder, the sludge will be deposited on the cylinder wall, and transported towards the conical cylinder.

2.3 Conveying and Storage

After dewatering, the sludge will be transported for drying. Belt conveyor and screw conveyor are the main components of the conveying and storage unit used in sludge dewatering system. In addition, an important part of sludge dewatering system is the treatment of mud cake. At present , the common treatment method is outward delivery and centralized processing.

2.4 Sludge Dewatering Operation System

When the centrifugal dehydrator is running at full speed with a constant flow, it is necessary to open the dilution water valve and start the input pump to add the polymers. Gradually start the sludge supply pump, properly adjust the input quantity and input speed of polymers to achieve a constant torque value.

The rotating direction of the cylinder and the central screw is consistent, and the rotating speed of the central screw is faster than that of the cylinder, so a relative speed is formed, called differential speed. When the torque value decreases, the differential speed will rise, and the sludge will become thinner. When the torque value increases, the differential speed will fall, and the sludge will become drier.

In addition, the selection of polymer and its proportion play a decisive role in the flocculation effect.

3. Conclusion

For sludge dewatering system, the centrifugal dehydrator has the advantages of good dewatering effect, high separation efficiency, low agent consumption, high solid recovery rate, small area occupied, clean and tidy site, durable and can effectively prevent the filter belt from blocking. However, it also has the disadvantages of high investment cost, high power consumption and difficult to repair.