1. OverviewThe role of sludge dewatering is to remove the capillary water and surface attached water in the sludge, thereby reducing its volume and weight. Basic principle: Mechanical dewatering of sludge is driven by the pressure difference on both sides of the filtering medium, forcing the water in the sludge to be expelled through the filtering medium, termed as the filtrate, while the solids are retained on the medium, known as the cake, thus achieving the goal of dewatering the sludge.
2. Mechanical Dewatering Equipment
1) Dewatering equipment using the filtration method
(1) Vacuum filter: This is a widely used method, employing a vacuum drum filter machine, also referred to as a drum vacuum filter. The GP-type drum vacuum filter is commonly used in China. It is primarily applied for the dewatering of primary sedimentation sludge and digested sludge. Its features include the ability to operate continuously and smoothly, with automatic control capability. However, its disadvantages include the tightly packed filtering medium on the drum, which complicates regeneration and cleaning, making it prone to blockage and affecting production efficiency; it also requires many auxiliary devices, resulting in a complex process and high operating costs. The key factors affecting vacuum filtration are both process and mechanical aspects.
(2) Plate and Frame Filter Press: The mechanical device used for pressure filtration and dewatering is called a plate and frame filter press. It can be divided into manual and automatic plate and frame filter presses. It can handle various types of sludge, primarily using simple inorganic flocculants for pretreatment, and its dewatering effect is better than vacuum filtration and centrifuges. The drawbacks are that it cannot operate continuously, is cumbersome to operate, and has a low yield. Its filtering capacity is related to the characteristics of the sludge, the thickness of the mud cake, the filtration pressure, the filtration time, and the type of filter cloth.
(3) Belt Filter Press: The mechanical device used for rolling dewatering is the belt filter press, which is characterized by not requiring vacuum or pressurized equipment. There are two modes of pressing: the rolling shafts are oppositely oriented up and down; the rolling shafts are staggered up and down. The pretreatment flocculants are high polymer organic flocculants. The walking speed of the filter belt and the pressing pressure affect the production capacity of the belt filter press and the moisture content of the mud cake. It cannot handle oil-containing sludge because it causes the filter cloth to become waterproof, easily squeezing the mud cake out from the side of the equipment. The equipment for sludge centrifugation and dewatering: primarily centrifuges. The general suitable type for sludge dewatering is the horizontal screw centrifuge. Its characteristics include the ability to produce continuously, ease of operation, automatic control, good sanitation conditions, and a small footprint, but the requirements for sludge pretreatment are high, requiring the use of high molecular polymer electrolytes as flocculants.
3.Operation and maintenance of sludge dewatering facilities:
1). Sludge conditioning is an important measure to ensure dewatering effectiveness, and the operational steps of sludge conditioning should be well controlled.
2). Before operating the sludge dewatering machine, the filter cloth should be soaked first, which helps the mud cake to detach easily.
3). Regularly check the operating status of the dewatering machine and take corrective measures for any abnormalities to ensure normal operation.
4). According to the requirements of the type of dewatering machine used, carefully perform regular maintenance and upkeep of the equipment, frequently check for wear on easily worn parts of the dewatering machine, and replace them when necessary, such as the dewatering machine’s rotating shaft and filter cloth.
5). Conduct thorough analysis, measurement, and recording of the inlet sludge amount, mud cake amount, sludge solid content, dosage of chemicals, and energy consumption.
