Dewatering Filter Bag for Removing Sediment and Pollutants

I. Core Characteristics and Working Principle

1. Key Materials and Structure

• Materials:
  • Primarily made of polypropylene (PP) or polyester (PET) fibers, offering acid-alkali resistance and wear resistance;
  • Special scenarios (e.g., high temperature, strong corrosion) may use nylon (PA) or polytetrafluoroethylene (PTFE).
• Structural Design:
  • Multi-layer composite filter cloth: Coarse outer layer intercepts large particles, while a fine inner layer captures tiny impurities to improve dewatering efficiency;
  • High-strength stitching: Reinforced stitching on bag openings and edges prevents tearing during filtration.

2. Working Principle

• Filtration Stage: Sewage containing sediments enters the filter bag, where solid particles are trapped by the filter cloth, and water drains through the cloth pores;
• Dewatering Stage: External forces (e.g., pressure, vacuum, or gravity) squeeze the bag to further extract water from between particles, forming a filter cake with a moisture content of 50–80% (depending on the application).

II. Main Application Scenarios

1. Industrial Wastewater Treatment

• Scenarios: Heavy metal ion precipitates (e.g., copper hydroxide, iron hydroxide), slag particles in wastewater from chemical, metallurgical, and electroplating industries;
• Role: Reduces SS (suspended solids) concentration in wastewater to meet subsequent treatment or discharge standards, while recovering valuable metal particles.

2. Municipal and Environmental Engineering

• Scenarios: Sludge thickening tanks in wastewater treatment plants, river dredging slurry, construction piling wastewater, etc.;
• Role: Rapidly separates water from slurry, reducing sludge volume (volume reduction ratio up to 3:1) and lowering transportation and disposal costs.

3. Mining and Quarrying Industry

• Scenarios: Dewatering of tailings slurry, ore washing wastewater treatment, mine pit drainage purification, etc.;
• Role: 截留 ore particles and heavy metal pollutants, enabling water recycling and reducing environmental risks in tailings ponds.

4. Food and Chemical Industries

• Scenarios: Separation of fruit pulp residues in food processing wastewater, crystallization products in chemical reactions, etc.;
• Role: Recovers solid raw materials (e.g., starch, sugar residue) while purifying wastewater.

III. Key Selection Parameters

1. Filtration Precision and Pore Size

• Precision Range: Typically 5–200 microns, matched to sediment particle size:Pore Size Distribution: Choose surface filtration (uniform pores) or deep filtration (gradient pores). The former suits uniform particle 污水，while the latter fits complex water with multiple particle sizes.
  • Coarse particles (e.g., sand): 50–200 microns;
  • Fine suspended matter (e.g., colloids): 5–50 microns.

2. Dewatering Performance Indicators

• Water Permeability: Water flux per unit filter cloth area (L/m²·h). Higher permeability speeds up filtration but requires balancing with interception efficiency;
• Water Retention: The ability to retain water in the filter cake. Poor water retention improves dewatering efficiency (e.g., when used with flocculants).

3. Pressure Resistance and Strength

• Operating Pressure: Matches the pressure type of dewatering equipment (e.g., plate-and-frame filter presses can reach 0.6–1.0MPa, while vacuum filtration uses negative pressure);
• Tear Resistance: Select filter cloth with warp and weft tensile strength ≥1500 N/m to avoid damage under high pressure.

4. Chemical Compatibility

• pH Tolerance:Solvent Resistance: Choose PET or PTFE for oily wastewater to prevent PP from swelling and damaging.
  • PP material: Suitable for pH 1–14 (resistant to strong acids and alkalis);
  • PET material: Suitable for pH 4–10 (resistant to weak acids and alkalis, not concentrated acids).

IV. Supporting Equipment and Processes

1. Common Dewatering Equipment

• Plate-and-Frame Filter Press: Exerts hydraulic pressure to squeeze filter bags, suitable for high-concentration slurry dewatering with low filter cake moisture content (≤60%);
• Vacuum Filter: Uses negative pressure to suction water, suitable for fine-particle sludge with high processing efficiency but higher energy consumption;
• Centrifugal Filter: Separates solid-liquid via centrifugal force, suitable for uniform particle sediments with small footprint.

2. Pretreatment Processes

• Flocculant Addition: Adds polyaluminum chloride (PAC) or polyacrylamide (PAM) to sewage to agglomerate fine particles into large flocs, improving filter bag interception efficiency and dewatering speed;
• Pre-Filtration: Uses coarse filter bags (e.g., 200 microns) to remove large particles, protecting fine filter bags and extending service life.

V. Maintenance and Environmental Considerations

1. Maintenance Tips

• Cleaning Frequency:Damage Inspection: Regularly check stitching and the bottom of the bag, and replace promptly if damage is found to prevent material leakage.
  • Reusable filter bags: Backwash with high-pressure water after each dewatering to remove residual particles in filter cloth pores;
  • Disposable filter bags: Replace immediately when saturated to avoid clogging and reduced filtration efficiency.

2. Environmental Treatment

• Filter Cake Disposal: Filter cakes with high heavy metal content must be treated as hazardous waste (e.g., stabilized landfilling); general industrial filter cakes can be used for brick-making, landfilling, or incineration;
• Filter Bag Recycling: Choose recyclable materials (e.g., PP, PET) and send them to professional recycling companies to reduce white pollution.

VI. Comparison with Other Filtration Methods