Filter Clogging Analysis and Its Solutions

Filters are widely used in industrial production, water treatment, and daily life. Whether filtering water or other liquids, filters play a crucial role. However, filter clogging has always been a common problem in equipment operation. It not only directly affects filtration efficiency but also increases energy consumption, and can even cause system shutdowns, bringing various inconveniences and economic losses to users. Therefore, understanding the causes of filter clogging and taking effective measures is crucial to ensure the normal operation of filters.

Analysis of Filter Clogging Causes

The causes of filter clogging are diverse, involving fluid characteristics, equipment defects, operational management, and environmental factors. Only by fully understanding these causes can targeted solutions be developed to effectively prevent and resolve clogging issues. Detailed analysis is as follows:

1. Fluid Characteristic Factors

Excessive concentration of suspended solids and particles: One common reason for clogging is when the concentration of suspended solids and particles in raw water or process fluids exceeds the filter's design treatment capacity. For example, in industrial circulating water systems, if no pretreatment is conducted, mud, rust, and other impurities will rapidly accumulate on the filter surface. Excessive impurities will block the mesh pores, reducing filtration efficiency. The solution is to install a hydrocyclone or multimedia filter before the filter to reduce the incoming impurity concentration.

Presence of viscous substances: Viscous substances in the fluid, such as oil, colloids, and microbial slime, easily adhere to the filter surface to form a dense filter cake. For example, in food processing wastewater, proteins and fats reduce the mesh porosity and increase filtration resistance. In this case, adding demulsifiers or flocculants for pretreatment, or using mesh material with hydrophobic surface modification, can reduce the adhesion of viscous substances.

2. Equipment Defects

Improper mesh size selection: Choosing the wrong mesh size can allow many small particles to enter the deeper layers of the mesh or cause large particles to directly block surface pores. For example, using a 50 μm mesh to filter fluid containing 10 μm particles easily causes deep-layer clogging. The correct approach is for the mesh pore size to be 2–3 times the particle size of impurities and adjusted according to fluid characteristics. Using a laser particle size analyzer to measure impurity distribution and selecting a matching mesh, such as a gradient pore mesh, can effectively prevent this problem.

Mesh material and structure issues: Insufficient corrosion resistance of the mesh material (such as 304 stainless steel in chlorine-containing environments) or low mesh open-area ratio (<30%) resulting in excessive flow resistance can also lead to clogging. Selecting corrosion-resistant materials (such as Hastelloy or titanium) according to the chemical properties of the fluid, or using sintered mesh with a high open-area ratio (>50%), can effectively resolve these problems.

3. Operational Management Issues

Backwash system problems: Insufficient backwash intensity (backwash flow rate <1.5 m/s), too short backwash time (<30 s), or leaking waste valves will cause residual impurities. Monitoring backwash flow with flow meters and pressure difference with pressure gauges to ensure backwash intensity meets standards is an effective solution. In addition, insufficient motor power, worn transmission mechanisms, or control system failure can prevent scrapers/brushes from effectively removing impurities. Regularly checking motor current, transmission component gaps, and upgrading to intelligent drive systems with torque sensors can improve backwash effectiveness.

Differential pressure settings and cleaning intervals: Setting differential pressure too high (>0.2 MPa) or extending cleaning intervals can compact impurities on the mesh surface. Dynamically adjusting differential pressure settings according to fluid characteristics and adding timed cleaning functions can prevent impurity compaction. Moreover, failing to regularly inspect mesh integrity, clean waste pipes, or replace worn components can cause secondary contamination. Regular maintenance, cleaning, and timely replacement of components are important measures to ensure normal filter operation.

4. Environmental Factors

Fluid parameter fluctuations: Flow fluctuations exceeding the design range (e.g., ±20%), sudden temperature changes causing impurity precipitation, or pressure surges damaging the mesh structure can all affect normal filter operation. Installing pressure stabilizers and temperature compensation valves, and leaving 20% flow reserve during system design, can effectively address these situations.

Changes in water quality: Variations in raw water hardness, pH, or dissolved oxygen content can increase scaling or corrosion products. For example, high-hardness water tends to form calcium carbonate scale after heating. Adding scale inhibitors, adjusting pH, or installing softening devices can effectively prevent scaling. In addition, microbial biofilms forming on the mesh surface can reduce filtration efficiency. Using UV sterilizers, non-oxidizing biocides, or periodic chemical cleaning can effectively control biofilm formation.

External impurity intrusion: Dust, willow fluff, and other external impurities entering the system through equipment gaps, or extreme temperatures causing filter material brittleness, can also lead to clogging. Installing protective covers and seals, and selecting mesh materials with strong weather resistance, can effectively prevent external impurity intrusion and filter material damage.

Methods for Handling Multimedia Filter Clogging

Multimedia filters are commonly used in water treatment systems and mainly capture suspended impurities through multiple layers of media, such as quartz sand, anthracite, and manganese sand. Clogging is a common problem, and treatment methods need to be targeted based on the cause of clogging, such as impurity deposition, media compaction, or biological contamination.

1. Mild Clogging Treatment

Conventional backwash: When the inlet-outlet differential pressure slightly rises (not exceeding 1.5 times the design value) or effluent turbidity slightly increases, backwash is preferred. Steps: close inlet and outlet valves, open waste valve and backwash inlet valve, and use raw water or clean water (pressure 0.1–0.15 MPa) to backwash the media layer, suspending media particles and causing mutual friction to flush attached impurities. Washing time: 5–10 minutes, until turbidity at the waste outlet ≤5 NTU.

Air-water combined backwash: If water-only backwash is ineffective, “air-water combined backwash” can be used. Compressed air (intensity 10–15 L/(m²·s)) is first injected to loosen the media for 5–8 minutes, followed by water backwash. Backwash frequency is adjusted according to incoming water turbidity, generally 1–2 times daily; for high-turbidity water (such as surface water), frequency can be shortened to once every 4–6 hours.

2. Moderate Clogging Treatment

Chemical cleaning: If differential pressure remains high after backwash (exceeding twice the design value) or adhesive impurities form on the media surface (such as organic matter or iron/manganese oxides), chemical cleaning is required. Methods:

Acid cleaning: For iron/manganese scales and inorganic precipitates, use 5–10% hydrochloric acid or 3–5% citric acid, with a small amount of corrosion inhibitor (e.g., urotropine). Close inlet and outlet valves, open exhaust and cleaning liquid circulation valves, pump in prepared acid solution, soak for 2–4 hours (or circulate for 1 hour), and rinse with clean water until effluent pH = 6–7.

Alkaline cleaning: Use 2–5% sodium hydroxide or 0.5–1% sodium hypochlorite (effective chlorine). Similar to acid cleaning, soak 1–2 hours (sodium hypochlorite must avoid light to prevent decomposition), rinse with clean water until effluent is odorless and pH ≈7. Before chemical cleaning, check the filter lining (e.g., rubber, FRP) for corrosion resistance to prevent equipment damage. Waste solutions after cleaning must be neutralized (acid-base neutralization to pH 6–9) and meet environmental standards before discharge.

3. Severe Clogging Treatment

When the media layer shows obvious compaction (clumping, cannot loosen), backwash still leaves dead spots, or media particle size has increased due to wear (e.g., quartz sand effective diameter exceeds 1.2 mm), media replacement or refurbishment is required. Steps:

Drain the filter water, open the manhole, and remove compacted media (use high-pressure water gun to break hard clumps if necessary).

Clean the filter's bottom distribution system (such as perforated plate or distributor), check for blockage or damage (e.g., filter cap dislodgement, gap blockage), and repair promptly.

Layer new media according to design specifications (e.g., top layer: anthracite 1–2 mm; middle layer: quartz sand 0.5–1 mm; bottom layer: support layer 2–4 mm), flatten each layer to avoid mixing.

After filling, perform forward washing (inlet direction) for 10–15 minutes, then backwash once to ensure clear effluent.

Recommendations for Preventing Filter Clogging

Strengthen pretreatment: Add pretreatment equipment before the filter, such as hydrocyclones or multimedia filters, to effectively reduce incoming impurities and relieve filter load.

Regular maintenance: Regularly check the filter's operational status, including differential pressure, backwash system, motors, and transmission components. Clean mesh and waste pipes promptly and replace worn components to ensure normal operation.

Optimize operating parameters: Dynamically adjust differential pressure settings and cleaning intervals based on fluid characteristics, ensuring backwash intensity and time meet requirements. Avoid drastic fluctuations in flow, temperature, and pressure, install pressure stabilizers and temperature compensation valves, and reserve sufficient flow capacity.

Control water quality: Add scale inhibitors, adjust pH, or install softening devices to prevent scaling. Use UV sterilizers, non-oxidizing biocides, or periodic chemical cleaning to control biofilm formation.

Protective measures: Install protective covers and seals to prevent external impurity intrusion. Choose weather-resistant filter media to avoid filter material damage from extreme temperatures.

Conclusion

Through the above analysis and recommendations, we can better understand and address filter clogging issues. Whether considering fluid characteristics, equipment defects, operational management, or environmental factors, taking targeted measures can effectively extend filter life, improve filtration efficiency, and reduce operational costs. These insights aim to provide valuable guidance for filter maintenance and management.