Backwashing for Filter Cleaning
The V-type filter is widely used in water treatment plants due to its strong pollutant interception capacity of the filter layer, long backwashing cycle, and good effluent quality. However, unreasonable backwashing parameters during operation can affect filter media stability and cause problems such as excessive energy consumption.
The V-type filter is widely used in water treatment plants due to its strong pollutant interception capacity of the filter layer, long backwashing cycle, and good effluent quality. Its operation includes two parts: filtration and backwashing, among which efficient backwashing is the key to ensuring filtration effectiveness. Combined air-water backwashing is currently a widely adopted backwashing method in water treatment plants both domestically and internationally, and its good backwashing performance has been proven by many practices. However, in actual engineering applications in China, problems such as filter media loss and excessive energy consumption caused by unreasonable backwashing parameters are common.
The filter uses homogeneous quartz sand filter media with an effective particle size of 0.85 mm, a single-cell effective filtration area of 136 m2, and a backwashing cycle of 52 h; the filter support layer is coarse sand with a thickness of 100 mm and a particle size of 2–3 mm; the filter water and air distribution system uses long-handle filter nozzles.
In the separate air backwashing stage, an air scour intensity of 13.4 L/(s·m2) is appropriate, and the backwashing time should be 3 min; in the combined air-water backwashing stage, vw/vmf should preferably be 0.40–0.60, and the backwashing time should be 6 min, which not only has a strong stripping effect on impurities on the filter media particles but also has good sludge transport capacity; in the separate water backwashing stage, according to the expansion rate test, when the water scour intensity is 6.38 L/(s·m2) and the backwashing time is 4 min, the stripped impurities can be promptly discharged out of the tank.
In the separate air backwashing stage, the air scour intensity is 6.6 L/(s·m2), and in the combined air-water backwashing stage, the air scour intensity is 3.6 L/(s·m2), which can avoid the problem of sand loss from the filter. While ensuring a good backwashing effect of the filter, it reduces the water consumption of the entire backwashing process and achieves energy saving and consumption reduction.
