Plate and frame filter press was the first mechanical application in chemical dehydration. Although plate and frame filter presses are generally operated intermittently, require large investment in infrastructure equipment, and have low filtration capacity, they are still widely used in some small-scale sewage treatment plants due to their advantages such as high filtration driving force, high solid content of filter cake, clear filtrate, high solid recovery rate, and low consumption of conditioning drugs.
After concentration and digestion, the sludge still has a moisture content of about 95% to 97% and a large volume. Sludge dewatering can further remove pore water and capillary water from sludge, reducing its volume. After dehydration treatment, the moisture content of sludge can be reduced to 70%~80%, and its volume is 1/10~1/4 of the original volume, which is beneficial for subsequent transportation and treatment. The mechanical dewatering methods for sludge include filtration dewatering, centrifugal dewatering, and press dewatering. Filtration dewatering also includes vacuum filtration and pressure filtration; Centrifugal dehydration is the process of dehydrating using a centrifuge; Squeezing dehydration is carried out using a screw press or rolling press for dehydration. The commonly used methods are pressure filtration and centrifugal dehydration. Sludge filtration dewatering is achieved by using the pressure difference between the two sides of the filter medium as a driving force, forcing the water in the sludge to pass through the filter medium to form a filtrate, while solid particles are trapped on the medium to form a filter cake, thus achieving the purpose of sludge dewatering. Plate and frame filter press was the first mechanical application in chemical dehydration. Although plate and frame filter presses are generally operated intermittently, require large investment in infrastructure equipment, and have low filtration capacity, they are still widely used in some small-scale sewage treatment plants due to their advantages such as high filtration driving force, high solid content of filter cake, clear filtrate, high solid recovery rate, and consumption of conditioning drugs.