Continuous Sand Filter

Operating Principle

The sand filter operates on the principle of countercurrent flow. Raw water or wastewater enters the filter from the top through the inlet pipe and flows downward. After being evenly distributed by the distributor, it rises through the filter medium, achieving microflocculation and filtration. The filtered water accumulates at the top of the active filter and is discharged into the clear water channel through an overflow weir. During the filtration process, the raw water or wastewater is filtered, reducing the content of pollutants in the water. Consequently, the content of pollutants in the quartz sand increases, with a higher concentration in the lower filter medium layer than in the upper layer. Simultaneously, an air compressor supplies air to the air control cabinet, which then provides the appropriate air pressure to the air-lifting pump located in the middle and lower part of the filter. Under the pressure of the air-lifting pump, the polluted quartz sand at the bottom of the filter is lifted to the top of the washing sand chamber for cleaning. After cleaning, the sand particles sink back to the filter bed, while the pollutants generated during cleaning are discharged outside through the flushing water. Throughout this process, the sand at the bottom is continuously lifted to the top washing chamber by the air-lifting pump. Inside the active filter, the sand outside the filter core sinks, while the raw water or wastewater rises after being released by the distributor. Therefore, the flow direction of the sand and the filtered water is relative and opposite, which is why the active sand filter is said to operate on the principle of countercurrent flow.

Overview

A sand filter is a continuous contact filtration device that integrates flocculation, clarification, and filtration. It is widely used in various water treatment applications requiring filtration.

Raw water enters the activated sand filter through the inlet pipe, is evenly distributed by the distributor, and flows upstream through the filter bed, exiting via the filtrate outlet. Filter media contaminated with pollutants at the bottom is lifted to the sand cleaner located at the top of the filter by the air-lifting pump. After cleaning, it returns to the surface of the filter bed, entering the next cycle. The cleaning water for the filter media is directly drawn from the filtrate within the filter, eliminating the need for dedicated cleaning water.

The filter media moves against the flow of the water to be treated, thus acting as a stirrer. When coagulants are added to the raw water, the coagulation process can be completed directly within the tank.

Due to the elimination of the need for additional flocculation, clarification, and air flotation equipment, the active sand filter has a total volume reduction of 7-80% compared to a standard filtration system.

The continuous operating mode of the slurry filter means that auxiliary equipment such as the backwash pump, automatic backwash valve, and backwash control system can be eliminated. This results in reduced maintenance and operating costs, with the entire filter system only requiring an air compressor for operation, with no additional power consumption.

Technical Features

High efficiency: The sand filter operates continuously for 24 hours without the need for shutdown for backwashing.

Low operating costs: No need for high-head, high-flow backwash pumps; instead, a program-controlled intermittent sand washing operation can be adopted, significantly reducing operating expenses.

Low maintenance cost: The activated carbon filter has no rotating parts during operation, resulting in a low failure rate and low maintenance cost.

Low initial investment: No need for concrete ponds, sedimentation tanks, and other facilities; high filter utilization rate, with a low initial investment.

◆ Lenient water quality requirements: Can withstand 150 mg/L incoming SS concentration for long periods. Short-term exposure to 250 mg/L incoming SS concentration does not affect effluent water quality.

    ◆ Head loss minimized: With timely cleaning of the single-stage filter material, the head loss can be reduced to 0.5 meters.

    ◆ Excellent filtration performance, stable water quality output: Thanks to timely cleaning of the filter media, consistent filtration results are ensured, with no periodic fluctuations in water quality.

    ◆ Easy to modify and expand: The unit operation method of the activated sand filter can be flexibly adjusted according to changes in water quality and quantity, making it easy to modify and expand existing facilities.