The activated sand filter is a continuously operating depth filtration equipment that integrates filtration, backwashing, and sand layer regeneration. With its high efficiency, automation, and low energy consumption, it has become one of the core equipment in the fields of municipal sewage advanced treatment, industrial wastewater purification, and tap water pretreatment. It breaks the intermittent mode of "filtration-stop and backflush" of traditional filters, achieves 24-hour continuous operation, and significantly improves water treatment efficiency.
1. Core working principle: continuous filtration and sand regeneration simultaneously
The core advantage of the activated sand filter lies in the synchronization of filtration and backwashing. Its working process can be divided into two parallel links:
1. Filtration process
Raw water enters the filter tank through the bottom water distribution system and flows upward through a multi-layer sand bed (quartz sand is the main medium, with a particle size of usually 0.8-1.2mm). The sand layer removes suspended solids (SS), colloids, phosphorus (through chemical precipitation or adsorption), algae and other pollutants in the water through physical interception, adsorption and biological action (if it is bioactive sand, microorganisms can also be attached to degrade organic matter). The filtered clean water is discharged through the top water collection system and enters the subsequent treatment unit.
2. Backwash and sand regeneration process
While filtering, a part of the filtered clean water is diverted as backwash water, and the "dirty sand" (sand that absorbs a large amount of pollutants) at the bottom of the filter tank is lifted to the sand cleaner at the top through an air lift pump. In the cleaner, the dirty sand is scrubbed under the dual action of water flow and air, the pollutants are separated from the sand particles, and the dirty water is discharged through the sewage outlet; the clean sand particles after cleaning fall back to the top of the sand bed by gravity, completing the regeneration cycle of the sand layer. The entire backwash process only consumes 1%-3% of the treated water volume, which is much lower than the 5%-10% of traditional filters.
2. Key structural components: core units that ensure efficient operation
The structural design of the activated sand filter revolves around "continuous operation" and mainly consists of the following parts:
1. Filter tank
It is usually a cylindrical vertical tank (the material can be carbon steel anti-corrosion, stainless steel or FRP), which provides filtering space and maintains the stability of the sand bed. The inner wall of the tank needs to be anti-corrosion treated to adapt to different water qualities (such as acidic wastewater).
2. Sand bed
As the core of the filter media, the thickness of the sand layer is generally 1.2-1.8m, which is divided into upper fine sand (main filter area) and lower coarse sand (support layer). The particle size gradient of the sand ensures a balance between filtration efficiency and water permeability.
3. Water distribution and collection system
- Water distribution system: Located at the bottom of the tank, it uses perforated pipes or water distributors to ensure that raw water enters the sand bed smoothly and evenly, and avoids excessive local flow rates from damaging the sand layer structure.
- Water collection system: Located on the top of the tank, it collects filtered clean water through the water collection tank or porous plate to ensure uniform water output.
4. Backwash system
- Air lift pump: Using air buoyancy to lift the dirty sand at the bottom to the cleaner, it is a key component to achieve continuous backwash.
- Sand cleaner: adopts vortex or mechanical scrubbing design to efficiently separate sand particles and pollutants.
- Backwash water circuit: Return part of the clean water to the cleaner to provide backwash force.
5. Control system
Automated operation is realized through PLC (programmable logic controller), which can monitor inlet and outlet water quality (such as SS concentration), sand layer height, backwash pressure and other parameters in real time, automatically adjust the backwash intensity, and reduce manual intervention.
3. Main application scenarios: covering water treatment needs in multiple fields
Activated sand filters have strong adaptability and are widely used in the following scenarios:
1. Municipal sewage treatment
As an advanced treatment unit, it removes SS (to less than 5 mg/L) and total phosphorus (TP to less than 0.5 mg/L) in the secondary effluent, helping the sewage plant to meet Class A discharge standards; it can also be used in the reclaimed water reuse system to improve the quality of recycled water.
2. Industrial wastewater treatment
- Electric power industry: bypass filtration of circulating cooling water to remove suspended solids and prevent heat exchanger scaling;
- Chemical industry: remove colloids, organic matter and heavy metal ions from wastewater;
- Printing and dyeing industry: reduce the chroma and SS in wastewater and reduce the subsequent biochemical treatment load.
3. Tap water pretreatment
Remove algae, sediment, colloids, etc. from raw water, reduce subsequent coagulant dosage, and improve drinking water safety.
4. Rainwater recycling
Filter suspended solids and impurities in initial rainwater to make it meet reuse standards (such as greening, flushing toilets).
4. Core advantages: Comparing the outstanding features of traditional filters
Compared with traditional quartz sand filters, activated sand filters have the following advantages:
- Continuous operation: No need to shut down for backflush, processing efficiency increased by more than 30%;
- High degree of automation: PLC control, reducing manual operations and reducing operation and maintenance costs;
- Water and energy saving: backwash water consumption is only 1%-3% of the treated water volume, and energy consumption is 20% lower than traditional equipment;
- Small footprint: no backup filter is required, and the footprint is reduced by 50% for the same treatment capacity;
- Stable filtration effect: the sand layer is continuously regenerated to avoid "penetration" phenomenon, and the effluent quality has small fluctuations.
5. Daily maintenance points
In order to ensure the long-term stable operation of the equipment, the following maintenance needs to be paid attention to:
1. Sand layer management: Check the sand loss every six months and replenish new sand (the annual replenishment amount is about 5%-10%);
2. Equipment inspection: regularly clean the blockage of the water distributor and check the air pressure and flow rate of the air lift pump;
3. Water quality monitoring: Regularly detect the inlet and outlet water SS, TP and other indicators, and adjust the backwash parameters;
4. Anti-corrosion maintenance: Regular anti-corrosion coating inspection and repair of carbon steel tanks.
Activated sand filters have become important technical equipment in the field of modern water treatment due to their high efficiency, environmental protection and intelligence. As environmental protection requirements continue to improve, its application scenarios will be further expanded to provide strong support for water resource recycling.
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