Active sand filter

Active sand filter

Product model: HSLQ type

Active sand filter function

Activated sand filter is a type of water filter that has the following functions:

Intercept organic matter, suspended solids, colloidal particles, microorganisms, etc. in water
nitrogen and phosphorus removal
Reduce COD content in water

Working principle of activated sand filter

Water: The water to be filtered is sent into the sand filter through the inlet pipe ①, and then enters the sand bed through the inlet pipe ② and the water distributor ③. The water is purified during the upward process of passing through the sand bed, and the filtrate is discharged at the upper part of the filter ⑤

Sand: While water flows upwards, the sand bed continuously moves downwards. Dirty sand ⑥ is extracted from the bottom of the sand bed and cleaned before being placed back at the top ⑦ of the sand bed

Air: The sand circulation is based on the principle of gas. The air lift pushes the mixture of dirty sand and water upwards through the central tube ⑧, and the strong friction separates the dirty suspended solids and sand particles. Released at the top of the riser, dirty water is discharged, and sand settles and falls in the cleaner. The amount of sand transported through the riser depends on the amount of compressed air entering the riser

Sand washer: The washer 10 has excellent hydraulic characteristics in design. At the upper part of the air lift pipe, sand particles fall through the annular space of the washer's labyrinth structure, and are finally cleaned by a small amount of clean filtered water in the opposite direction of the sand's falling direction. The flow of the filter fluid is driven by the liquid level difference between the filter fluid ⑪ and the washing water ⑨. The liquid level of the filter fluid is equal to the liquid level of the filter fluid overflow, and the liquid level of the washing water is equal to the top height of the washing water discharge pipe.

Active sand filter appearance video

High efficiency: The activated sand filter works continuously for 24 hours without the need for shutdown and backwashing.
Low operating costs: No need for high head and large flow backwash water pumps, and can adopt program controlled intermittent sand washing control operation mode, greatly reducing operating costs.
Low maintenance costs: The activated sand filter has no rotating parts during operation, with a low failure rate and low maintenance costs.
Low one-time investment: No need for facilities such as coagulation tanks and clarification tanks, high filter utilization rate, and low one-time investment.
◆ Loose requirements for inlet water quality: able to withstand a long-term SS concentration of 150mg/L in the inlet water. It can withstand an SS concentration of 250mg/L in the short term without affecting the effluent quality.
Small head loss: Due to the use of single-stage filter material for timely cleaning, the head loss can be reduced to 0.5m.
Good filtration effect and stable effluent quality: Due to the timely cleaning of the filter material, a stable and efficient filtration effect can be ensured, and the effluent quality has no periodic fluctuations.
◆ Easy to renovate and expand: The unit operation mode adopted by the activated sand filter can flexibly change the number of filters according to changes in water quality and quantity, making it easy to renovate and expand existing facilities.

Application scope of activated sand filter

Applied to township water supply, waterworks, urban sewage treatment, industrial sewage treatment, circulating cooling water treatment, process water treatment, seawater purification treatment, algae containing water treatment, and other filtered water.

Gas extraction method

External circulation: The air compressor uses compressed air to lift the sand water mixture through an external air pipe to the sand washer
Internal circulation: Compressed air enters from the bottom of the equipment to lift the sand water mixture from the internal center pipe to the sand washer

Design parameters of activated sand filter

The surface load is expressed as the amount of impurities intercepted per unit filter surface per unit time, measured in mgSS/m2h.
The recommended surface load values for activated sand filters are as follows:
Activated sand filters can withstand surface loads higher than the above values in a short period of time.
The filtration area of the filter can be determined based on the maximum surface load and the quality and quantity of the raw water. For safety reasons, a slightly larger filtration area than the calculated value can be used in actual selection.
The working flow rate can be calculated based on the raw water flow rate and the service area of the filter being washed. It should be noted that when the flow rate reaches a certain limit, the biological flocs will disintegrate or the filter will disintegrate or the filter will produce fluidization phenomenon. In the design, it should be ensured that the working flow rate of the filter is below this limit value.
The quality of the filtration effect should also consider temperature factors, and in low-temperature areas, the depth of the filter bed should generally be greater than 2 meters.
Under normal operation, the activated sand filter can ensure the following effluent effects:
SS<5mg/l (adding flocculant)
<10mg/l (without adding flocculant)
BOD removal rate: 0.3-0.6mg/mgSS
COD removal capacity: 0.8-1.6mg/mgSS
Chromaticity:<5 degrees
Turbidity:<0.3NTU
Algae removal rate approaching 100%

Specification and model of activated sand filter

Note:
1. The height of the filter bed is determined based on the quality of the incoming and outgoing water.
2. Type B is a concrete structure pool body, and Type T is a movable active sand filter; The material can be 304 stainless steel, 316 stainless steel, fiberglass, high chromium alloy steel, carbon steel (anti-corrosion), or other specified materials.
3. The gas extraction method can be either internal circulation or external circulation

The effluent quality of the activated sand filter

SS: ≤ 5mg/l (adding flocculant)
SS: ≤ 10mg/l (without adding flocculant)
Total phosphorus removal rate: 70-95% (with flocculant added)
Total phosphorus removal rate: 5-20% (without adding flocculant)
COD removal rate: 20-45%
Ammonia nitrogen removal rate: 10-20%
Note: To improve the removal efficiency of COD and ammonia nitrogen, biological treatment methods need to be used

Bioactive sand filter

2. HSLQ series denitrification activated sand filter
The HSLQ series denitrification activated sand filter is a filter designed specifically for denitrification, integrating filtration and denitrification, and is commonly used in applications such as renovation and expansion projects.
Using quartz sand homogeneous filter material ensures both filtration efficiency and biological treatment effectiveness.
The top cover plate of the filter can prevent the interference of oxygen in the external air on the denitrification process.

Process flow of supporting activated sand filter

1、 Conventional processing techniques
Process Description
Add a flocculant in front of the activated sand filter and mix the reagent and raw water thoroughly through a pipeline mixer. When water flows into the activated sand filter, tiny suspended particles and colloidal particles in the water undergo coagulation, forming larger and more easily precipitated flocs (particle size>20um), which are generally treated with PAC.

2、 Biochemical treatment process

Process Description
Add a carbon source in front of the activated sand filter and cultivate microorganisms (denitrifying bacteria) in the activated sand system to convert nitrate nitrogen in the water into nitrogen gas, thereby achieving denitrification. If two filters are connected in series, with the front unit undergoing nitrification and the rear unit undergoing denitrification, nitrogen (organic nitrogen, ammonia nitrogen, nitrate nitrogen) in the water can be better removed.

3、 Denitrification treatment process:

Process Description of Activated Sand Filter

The pre treated water passes through an anoxic tank, which reduces some of the nitrate ions in the raw water to nitrogen gas in advance, playing a role in pre denitrification. Then, through the aeration tank, oxygen can be added to the water to decompose some degradable organic matter in the water, and oxidize ammonium nitrogen and organic nitrogen in the water into nitrate nitrogen. After passing through the secondary sedimentation tank, the activated sludge flowing through the aeration tank can be intercepted, and finally enter the activated sand denitrification filter. Methanol is added to convert nitrate nitrogen into nitrogen gas, completing the denitrification process.

Nitrification reaction:

NH₃+O₂→NO₂-+3H++2e-

NO₂-+H₂O→NO3-+2H+2e-

Denitrification reaction:

6NO₃-+5CH₃OH→5CO₂+3N₂+7H₂O+6OH-