What Is a Depth Filter?

The multi-media filter is a process in which one or more filter media is used to pass highly turbid water through a granular or non-granular material of a certain thickness under a certain pressure, thereby effectively removing suspended impurities and clarifying the water. The filter materials include quartz sand, anthracite, and manganese sand. They are mainly used for water treatment to remove turbidity, soften water, and pre-treatment of pure water. The turbidity of the effluent can reach below 3 degrees.

Multi-media filter

Chinese name

The meaning of filtration. In the process of water treatment, filtration generally refers to the process of trapping impurities suspended in the water with filter material layers such as quartz sand and anthracite, so that the water is clear. The porous material used for filtration is called filter material, and quartz sand is the most common filter material. Filter materials are granular, powdery and fibrous. Commonly used filter materials are quartz sand, anthracite, activated carbon, magnetite, garnet, porous ceramics, and plastic balls.

Multi-media filters are widely used in water treatment processes. Multi-media filters are mainly composed of the following parts: supporting pipelines and valves. The filter body includes: a cylinder body; a backwash air pipe; a water distribution component; a support component; filter material; exhaust valve (external)

Remove mud, suspended solids, colloids and other organisms in the water and algae and other organisms to reduce mechanical damage and pollution to reverse osmosis membrane elements.

The multi-media filter material in the filter is high-quality homogeneous gravel, quartz sand, magnetite, anthracite and other filter materials. These filter materials are scientifically and orderly distributed in the filter tank according to its specific gravity and particle size, such as small specific gravity. Anthracite with a larger particle size is placed in the uppermost layer of the filter bed, quartz sand with a moderate specific gravity and a small particle size is placed in the middle layer of the filter bed, and gravel with a larger specific gravity and a larger particle size is placed in the lower layer of the filter bed. Such a ratio ensures that the filter will not produce a disordered layer during backwashing, thereby ensuring the ability of the filter material to retain.

Multi-media filter (also known as mechanical filter) is a layer of anthracite, sand, finely divided garnet or other materials. It is a typical multi-media filter.

The top layer of the bed consists of the lightest and coarsest grades of material, while the heaviest and finest grades of material are placed in the lower part of the bed. The principle is to filter by depth-larger particles in the water are removed at the top layer and smaller particles are removed deeper in the filter medium. So that the water quality reaches the standard after coarse filtration.

The equipment is pressure type. The principle is that when raw water passes through the filter material from top to bottom, suspended matter in the water is trapped on the surface of the filter layer due to adsorption and mechanical blocking; when water flows into the middle of the filter layer, the filter material layer The sand particles are arranged more closely, so that the particles in the water have more chances to collide with the sand particles, so the floc, suspension and the surface of the sand particles adhere to each other, and the impurities in the water are trapped in the filter material layer to obtain a clear water quality. The filtered effluent suspension can be below 5 mg / L.

1. Porous media filters are widely used in water treatment processes and can be used alone, but most of them are pre-filtration for advanced water quality treatment (exchange resin, electrodialysis, reverse osmosis).

2. The multi-media filter is a commonly used pretreatment device for deep purification of water quality. Different filter materials can be added according to process requirements.

3. The material of the multi-media filter can be FRP, A3 steel anti-corrosion or rubber lining, and all stainless steel. There are two types of operation modes: full-automatic and manual. The automatic control is controlled by automatic controllers and gas and hydraulic valves imported from the United States. The operation is simple and easy to maintain. It is widely used in pretreatment devices for water treatment processes in various industries. .

4. The filter material of the multi-media filter (including dual-filter material filter) should have sufficient chemical stability, and the relative density and particle size of each medium should have a certain difference. The double-layer filter material composed of anthracite and quartz sand The relative density of anthracite used in the device is 1.4-1.6, the particle size is 0.8-1.8mm, the relative density of quartz sand is 2.6-2.65, and the particle size is 0.5-1.2mm; in addition to the above two types of filter media Heavy ore such as manganese sand and magnetite can be used. Its relative density is 4.7-5.0 and its particle size is 0.5-4mm.

The multi-media filter is mainly composed of a filter body, a supporting pipeline and a valve.

The filter body mainly includes the following components: simplified; water distribution component; support component; backwash gas pipe; filter material; exhaust valve (external) and so on.

(1) It must have sufficient mechanical strength to avoid rapid wear and tear during backwashing;

(2) Good chemical stability;

(3) Contains no harmful and toxic substances to human health, and does not contain substances harmful to production and affecting production;

(4) The selection of filter materials should be as far as possible using filter materials with high adsorption capacity, large interception capacity, high water production, and good effluent quality.

In the filter material, the pebble mainly plays a supporting role. During the filtering process, due to its high strength, the gap between each other is stable, and the pores are large, which is convenient for the normal washing process and the filtered water can pass smoothly; similarly, backwashing During the process, backwash water and backwash air can pass smoothly.

In the conventional configuration, the pebble is divided into four specifications, and the bedding method is bottom-up, first-large, then-small.

The relationship between filter particle size and filling height

The ratio of the height of the filter bed to the average particle size of the filter material is 800 to 1,000 (design specification).

The size of the filter material is related to the filtration accuracy.

The following table shows the function and structure of each component.

The structure of the quartz sand filter is divided into a filtering system and a control system. The filtration system usually consists of a high-efficiency filter unit, a three-way automatic valve, an inlet and outlet pipe, and a sewage pipe. The high-efficiency filter unit includes various filter media. The control system usually consists of PLC timing controller, differential pressure controller, electromagnetic three-way valve and control pipeline.

Common filter materials for multi-media filters are: anthracite, ceramsite, quartz sand, activated carbon, etc.

The filter material is activated carbon, which is used to remove color, taste, residual chlorine and organic matter. Its main mode of action is adsorption. Activated carbon is an artificial adsorbent.

The backwashing of the filter mainly refers to that after a certain period of use of the filter, the filter material layer traps and adsorbs a certain amount of debris and stains, which makes the quality of the effluent of the filter lower.

(1) If the dirt trapped on the surface of the filter layer cannot be effectively removed within a certain period, in the subsequent backwashing process, if the distribution of the backwashing air is uneven, the expansion height will be uneven. The scrubbing air, where the amount of rubbing is small, the impurities such as oil on the surface of the filter material cannot be effectively removed. After putting in the next normal filtration cycle, the local load increases, the impurities will sink into the interior from the surface, and the pellets gradually increase Large and simultaneously extend into the filter's filling depth until the entire filter fails.

Note : In actual operation, the phenomenon of uneven backwash air often occurs, mainly due to the perforation of the air distribution pipe at the bottom, the clogging or damage of the local filter cap, or the deformation of the grid tube spacing.

(2) The surface of the filter layer is small in particle size, and there is less chance of collision with each other during backwashing, and the momentum is small, so it is not easy to clean. The attached sand particles are easy to form small mud balls. When the filter layer is re-graded after backwashing, the mud ball enters the lower layer of filter material, and moves deeper as the mud ball grows.

(3) The oil contained in the raw water is trapped in the filter, and the residual part is accumulated over time after backwashing, which is the main factor leading to the sintering of the filter material.

When to perform backwashing can be determined based on the water quality characteristics of the raw water and the requirements of the effluent water quality, using standards such as limited head loss, effluent water quality, or filtration time.

(1) The parallel tolerance between the outlet tank and the filter plate is required to be not more than 2 mm.

(2) Both the level and unevenness of the filter plate are less than ± 1.5 mm. The structure of the filter plate is optimized for the whole process. When the diameter of the cylinder is large, or when it is restricted by raw materials, transportation, etc., two-flap splicing can also be used.

(3) The reasonable treatment of the joints between the filter plate and the cylinder is particularly important for the air backwashing link.

In order to eliminate the radial clearance between the filter plate and the cylinder due to errors in the processing of the filter plate and the rolling of the cylinder, generally circular arc plate welding is used. The contact area must be fully welded.

The method for processing the radial clearance of the central pipe and the filter plate is the same as above.

Note : The above measures ensure that filtering and backwashing can only be communicated through the filter cap or the gap between the exhaust pipes. At the same time, the uniformity of the distribution of the backwash and filtration channels is also guaranteed.

(4) The radial error of the through holes processed on the filter plate is ± 1.5 mm. The increase in the matching size between the filter cap guide rod and the filter plate through hole is not conducive to the installation or fixation of the filter cap. The machining of through holes must use mechanical equipment.

(5) The material of the filter cap is nylon, followed by ABS. Due to the filter material added on the top, the squeeze load on the filter cap is extremely large, and the strength is required to avoid deformation. The contact surfaces (upper and lower surfaces) of the filter cap and the filter plate need to be provided with elastic rubber pads.

Pretreatment of reverse osmosis, electrodialysis, ion exchanger, ultrafiltration and other systems

Pre-filtration treatment of raw water for power generation, chemical industry, papermaking, beverages, etc.

Decoloration and organic removal of feedwater in chemical plants

Pretreatment of domestic water

Industrial water treatment

Swimming pool water treatment

Circulating water filtration system

Turbidity and color removal of surface water and groundwater.

Wastewater treatment