Whether it is municipal sewage generate by toilets, kitchens, bathrooms, etc., or industrial, medical and agricultural wastewater by production and facilities, sewage should be treated before discharge into the river. In many countries, it is a crime to discharge sewage into nature without treatment. The sewage treatment plant separates solid pollutants and reduce organic pollutants and nutrients, thereby reducing the pollution of the sewage to the environment. The separated solid is called sludge.

The nature of the sludge has a dual character. On the one hand, it contains a large amount of organic material and nutrients such as NPK, which could be reused. On the other hand, some pollutants retained in the sludge, makes the sludge in high moisture, and includes a lot of harmful and carcinogenic substances (pathogenic bacteria, parasite eggs, heavy metals, etc. ) that are difficult to degrade. If not treated appropriately, it will easily cause secondary pollution to groundwater and soil, directly threatening the environment and public health. obviously that the most essential in sewage treatment is sludge treatment.

Sludge dewatering is the primary process of sludge treatment. After mechanical dewatering, the sludge moisture content could reduce to 55% to 80%, reduce the volume significantly, and easy to transport and further disposal and utilization. There are many types of sludge dewatering machines used in municipal sewage treatment plants and industrial wastewater treatment plants, but belt filter presses are the mainly used.

There are gravity and pressure in belt filter press dewatering process. Three main factors affect the gravity dewatering: the area of the gravity dewatering, the property of the filter belt, and the cleaning effect of the filter belt. The main affecting the press filter is the tension of the filter belts, obviously that the filter belt choice is crucial in press filter dewatering.

In recent years, to improve the dewatering performance of the filter belt and the sludge retaining ability, the single-layer and the double-layer mesh are most used. The upper layer uses a thinner yarn and has a tighter structure. The under layer uses a coarser yarn and a material having higher strength, which has a good interception effect on sludge and enhancing dewatering performance. Some manufacturers are weaving a double-layer with a four-yarn structure, which has good permeability and made mud not easily lost with water. However, no matter which kind of filter belt, it is necessary to increase the strength, otherwise the residual sludge in the deep layer is difficult to remove, which affects the dehydration effect.

With Increasing humanity and diminishing natural resources, environmental protection is urgent. We must start from all aspects to reduce environmental pollution and do what we can.

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