Selection of Sludge Concentration and Dewatering Equipment

In the past, belt filter press was used for sludge concentration and dewatering in most of the domestic urban sewage treatment plants. Decanter centrifuge was rarely used due to loud noise, high energy consumption and low processing capacity. However, in recent years, the application of decanter centrifuge has begun to surpass that of belt filter press.

Based on the survey of the use of belt filter press and decanter centrifuge, combined with design experience, this article will discuss the selection of sludge concentration and dewatering equipment.

1. Comparison Between Belt Filter Press and Decanter Centrifuge

(1) Under the action of centrifugal force, the solid and liquid phase will be separated by decanter centrifuge. Since there is no filter screen in the drum, the drum will rarely be blocked. However, in order to prevent the belt filter press from blockage, high pressure water is needed to continuously flush the filter belt.

(2) Decanter centrifuge is suitable for the concentration and dewatering of various types of sludge. So is the belt filter press, but for residual activated sludge, a large amount of flocculant is needed and the dewatering is difficult.

(3) During the dewatering process, when the feed concentration changes, the differential speed and torque between drum of screw of decanter centrifuge will automatically be adjusted by control system, so there is no need for manual operation. But the belt speed, belt tension, dosage and flushing water pressure of belt filter press should be adjusted, it requires high technological skills of site operator.

(4) For decanter centrifuge, sludge with small particles can also be separated from water, so the amount (1.2kg/tds) of flocculant is relatively less than belt filter press (3kg/tds).

(5) The energy consumption of decanter centrifuge is 1.2 kW/m3, noise level is 76-80 dB, 24 hours continuous running without flushing water. The energy consumption of belt filter press is 0.8 kW/m3, noise level is 70-75 dB. But the filter cloth needs to be loosened and maintained, beside, the filter cloth also needs to be continuously flushed with high pressure water.

(6) Decanter centrifuge has the advantages of small space usage, simple installation and commissioning, few supporting equipments, fully sealed operation and good workshop environment, etc. Belt filter press has a large space usage, supporting equipments includes dosing device, screw conveyor, flushing pump, air compressor, sludge conditioner, etc. Belt filter press is not fully sealed, high pressure flushing water and odors will pollute the environment, and the mud will overflow without proper management.

(7) The vulnerable parts of decanter centrifuge are bearings and seals, the maintenance period of the screw is generally more than 3 years. In addition to bearings and seals, the filter cloth of belt filter press should be replaced every 3-6 months, which will cost a lot.

2. Conclusion

The advantages of decanter centrifuge are small space usage, good operation environment and without flushing water. The advantages of belt filter press are low energy consumption and low noise. Sewage treatment plants should select the proper sludge concentration and dewatering equipment according to the actual demand.