Disc Cloth Filters

Disc Cloth Filters provide tertiary filtration in municipal wastewater treatment plants, removing suspended solids and phosphorus to achieve effluent quality below 5 mg/L TSS and 0.5 mg/L total phosphorus. These systems use vertically-mounted fabric discs that rotate slowly through the wastewater flow, with solids captured on the cloth surface and removed via backwash cycles. Typical installations handle 0.5-20 MGD with filtration rates of 2-4 gpm/ft² of cloth area. The primary trade-off is higher capital cost compared to sand filtration, offset by smaller footprint and lower maintenance requirements in space-constrained municipal facilities.

• Secondary Clarifier Effluent Polishing: Disc cloth filters serve as tertiary treatment following secondary clarifiers, reducing TSS from 15-25 mg/L to <5 mg/L. They're selected for consistent effluent quality and compact footprint, typically sized at 2-4 gpm/sf. Connected downstream of clarifiers and upstream of disinfection systems.
• Biological Nutrient Removal (BNR) Polishing: In plants with biological phosphorus removal, disc filters capture residual biomass and precipitated phosphorus, achieving <1 mg/L TSS. Essential where discharge limits require <10 mg/L total phosphorus. Installed after final clarifiers in BNR configurations.
• Peak Flow Management: During wet weather, disc filters handle 2-3x design flows while maintaining effluent quality. Selected over sand filters for faster startup and consistent performance during flow variations. Typically configured with automated backwash systems for unmanned operation.
• Membrane Bioreactor (MBR) Pretreatment: Protects downstream RO membranes by removing particles >10 microns, extending membrane life 30-50%. Selected for reliability and automated operation in advanced treatment trains.

Daily Operations: Operators monitor differential pressure across cloth media (typical range 2-8 inches), effluent turbidity (<2 NTU), and backwash frequency (every 15-60 minutes). Flow distribution between sectors requires visual inspection for even loading. Automated systems require verification of backwash cycle timing and spray pressure readings.

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Maintenance: Weekly cloth inspection for tears or blinding, quarterly drive mechanism lubrication, and semi-annual backwash pump maintenance. Cloth replacement every 2-4 years costs $15,000-25,000 per unit. Requires confined space entry procedures and lockout/tagout for rotating equipment. Basic mechanical skills sufficient for routine maintenance.

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Troubleshooting: Shortened backwash cycles indicate cloth blinding from grease or biological growth - treatable with chemical cleaning. Uneven sector loading suggests drive problems or debris accumulation. Cloth tears cause immediate TSS breakthrough, requiring emergency bypass. Expected service life: 15-20 years for mechanical components, 2-4 years for filter media.

• Filter Discs: Woven polyester cloth media (10-20 micron openings) mounted on rotating sectors. Standard disc diameters range 8-12 feet for municipal applications. Media selection based on required particle removal and backwash frequency - tighter weaves for enhanced phosphorus capture.
• Backwash System: High-pressure pumps (60-80 psi) with spray nozzles provide inside-out cleaning. Sized at 15-25% of forward flow capacity. Includes automated sequencing controls and filtrate storage tanks (typically 15-30 minutes of backwash supply).
• Drive Mechanism: Variable-speed gear reducers rotate sectors at 0.1-0.5 rpm during backwash. Sized for continuous duty with stainless steel construction. Speed control allows optimization of cleaning effectiveness versus power consumption.
• Effluent Collection System: Stainless steel piping and channels collect filtered water from each sector. Includes flow measurement and level controls for automated operation. Designed for 4-6 gpm/sf peak hydraulic loading.

• Hydraulic Loading Rate: 2-8 gpm/ft² of cloth area (typical 4-6 gpm/ft² for secondary effluent)
• Solids Loading Rate: 0.5-3.0 lb TSS/ft²/day (design at 1.5-2.0 lb/ft²/day for reliable operation)
• Influent TSS Concentration: 15-50 mg/L (optimal range 20-35 mg/L for consistent performance)
• Operating Head Loss: 6-24 inches across cloth media (backwash typically initiates at 12-18 inches)
• Backwash Flow Rate: 15-25 gpm/ft² of cloth area for 15-30 seconds duration
• Disc Rotational Speed: 0.5-2.0 rpm (typically 1.0 rpm for municipal secondary treatment)
• Cloth Mesh Size: 10-20 microns (10-micron standard for tertiary filtration, 15-20 microns for polishing)
• Design Flow Range: 0.1-15 MGD per filter unit (multiple units for larger plants)
• Minimum Submergence: 12-18 inches above top disc for proper hydraulics
• Temperature Range: 32-104°F operational (cloth material dependent)
• Power Requirements: 0.5-2.0 HP per MGD capacity for disc rotation and backwash pumps

• What peak hourly flow multiplier should be used for sizing? Standard practice uses 2.5-3.0x average daily flow for peak sizing. Undersizing (using <2.5x) results in hydraulic overload during peak events, causing breakthrough and permit violations. Oversizing (>3.5x) increases capital costs unnecessarily. Engineers need 5-year flow projections and existing plant peaking factors.
• Should cloth media be 10-micron or 15-micron rating? 10-micron cloth achieves <5 mg/L TSS consistently but requires 20-30% more backwash water and higher head loss. 15-micron cloth reduces operating costs but may struggle meeting <10 mg/L TSS limits. Decision depends on effluent permit limits and plant's existing filter performance data.
• How many filter units provide optimal redundancy? Minimum three units for plants >5 MGD allows one unit offline for maintenance while meeting peak flows. Two-unit systems risk permit violations during maintenance. Single units acceptable only for <1 MGD plants with adequate upstream storage. Consider maintenance frequency and peak flow duration.
• What backwash water source and disposal method? Plant effluent backwash requires 2-3% of forward flow but avoids potable water costs. Dedicated backwash pumps add complexity but ensure consistent pressure. Gravity backwash limits installation flexibility. Engineers need backwash water quality analysis and return flow handling capacity assessment.

• Primary: Division 46 - Water and Wastewater Equipment, Section 46 55 13 - Cloth Disk Filters

• Material/Equipment Verification: Verify cloth media specifications (micron rating, material compatibility), Confirm backwash system capacity and automation controls, Check structural steel ratings for seismic/wind loads
• Installation Requirements: Requires 12-18 month lead times for custom configurations, Foundation depth typically 8-12 feet below grade, Overhead clearance needed for media replacement (15+ feet)
• Field Challenges: Cloth tensioning requires factory technician supervision, Backwash piping alignment critical for uniform cleaning, Control system integration with existing SCADA
• Coordination Issues: Early electrical coordination for VFD requirements, Structural engineer review for dynamic loading during backwash cycles

• Veolia - ACTIFLO Turbo series (0.5-50 MGD capacity)
• Ovivo - SIROFLOC cloth media systems (municipal retrofits specialist)
• Huber Technology - RoDisc series (proven in 200+ installations)
• Parkson Corporation - DynaSand cloth upgrades (strong North American presence)

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All maintain dedicated municipal references and standardized package configurations for typical 1-20 MGD applications.

• Sand Filters: Lower capital cost ($150-200/gpm vs $250-350/gpm) but higher footprint and backwash volumes. Preferred for smaller plants (<2 MGD) with available land.
• Membrane Bioreactors: Higher treatment quality but 3-4x capital cost. Justified for stringent discharge limits or water reuse applications.
• Dissolved Air Flotation: Better for high-solids applications (>200 mg/L TSS) but requires chemical addition and skilled operators.

Operations: Establish spare cloth inventory (10-15% extra) - media replacement typically needed every 3-5 years depending on loading. Vendor Relations: Negotiate service agreements including annual inspections and emergency response within 48 hours. Cost Savings: Consider standardizing cloth specifications across multiple units to reduce spare parts inventory. Pre-purchase critical wear components during initial procurement when pricing is most favorable.