In the past, most enterprises used belt filter presses for sludge concentration and dehydration in urban sewage treatment plants. In recent years, the application of decanter centrifuges has the momentum to surpass belt filter presses. According to the usage survey of belt filter press and decanter centrifuge and combined with design experience, the selection of sludge concentration and dehydration equipment is discussed as follows.
The belt filter press is the mainstream of sludge dewatering in sewage treatment plants. The advantages of the decanter centrifuge mainly lie in its comparison with the belt filter press. The decanter centrifuge manufacturers believe that the decanter centrifuge has the following advantages compared with the belt filter press.
(1) The decanter centrifuge uses the principle of centrifugal sedimentation to separate solid and liquid. Since there is no filter screen, it will not cause blockage. The belt filter press uses a filter belt to separate solid and liquid. In order to prevent the filter belt from being blocked, the belt needs to be washed with high pressure water continuously.
(2) Decanter centrifuge is suitable for the concentration and dehydration of various types of sludge. Though belt filter press is also suitable for various types of sludge, for the remaining activated sludge, it needs a large dosage and the dehydration is difficult, so flocculants need to be added.
(3) When the concentration of the feed material changes during the dehydration process of the decanter centrifuge, the slip and torque of the rolling drum and the screw will be automatically tracked and adjusted, so there is no need for special operators. During the dehydration process of the belt filter, when the concentration of the feed material changes, the belt speed, belt tension, dosing amount, and flushing water pressure all need to be adjusted, which has relatively high operation requirements.
(4) In the decanter centrifuge, even the fine sludge can also be separated from water, so the dosage of flocculant is less. Generally, the dosage of mixed sludge during dewatering is: 1.2kg/t (dry mud) . The sludge recovery rate is above 95% and the moisture content of the mud cake after dehydration is about 65%-75%. However, because the filter belt cannot be woven too densely in the belt filter, in order to prevent the fine sludge from leaking out of the net, more flocculant needs to be added to make the sludge form larger flocs. Generally, the dosage of the mixed sludge during dewatering is greater than 3kg/L (dry mud), the sludge recovery rate is about 90%, and the moisture content of the mud cake after dehydration is about 80%.
(5) The decanter centrifuge china runs continuously for 24 hours a day. It does not require cleaning during operation other than downtime. And it does not require relaxation and maintenance. Generally, only two shifts are arranged every day. During the operation, the filter cloth needs to be washed with high-pressure water continuously.
(6) The decanter centrifuge occupies very small space and is easy to install and debug. The supporting equipment is only the dosing and feeding and discharging conveyors. The whole machine is fully sealed and the workshop environment is good, while the belt filter press occupies a large area and it also needs other supporting equipment like flushing pump, air compressor, sludge conditioner and so on in addition to the dosing and feeding and discharging conveyors. The sealing performance of the whole machine is poor, and the high-pressure cleaning water mist and odor can pollute the environment. If the management is not good, it will cause mud overflow.
(7) The wearing parts of the decanter centrifuge are bearings and seals, and the maintenance cycle of the discharge screw is generally more than 3a, while the wearing parts of the belt filter press, in addition to the bearings and seals, like the filter belts, also need to be replaced and are very expensive.
(8) Calculation of operating costs. Decanter centrifuge manufacturers are calculating operating costs for centrifugal dewatering and belt press dewatering.