Wedge Wire Screens

Wedge wire screens provide continuous mechanical screening for municipal water and wastewater treatment plants by removing suspended solids through precisely-sized triangular wire openings. The wedge-shaped profile creates self-cleaning action as flow passes over the smooth downstream face, preventing clogging while maintaining consistent hydraulic capacity. These screens typically achieve 85-95% solids removal efficiency for particles larger than the slot opening, with standard municipal applications using 0.5mm to 6mm slot widths. The primary trade-off is higher capital cost compared to static bar screens, though this is offset by reduced maintenance requirements and consistent performance in high-solids applications.

• Headworks Screening: Wedge wire screens serve as fine screening (1-6mm openings) after preliminary bar screens, removing debris, rags, and small solids before primary treatment. Selected for self-cleaning capability and consistent slot openings that prevent plugging. Upstream: bar screens and grit removal. Downstream: primary clarifiers or membrane bioreactors.
• Tertiary Filtration: Used as cloth media washers in tertiary cloth disk filters, cleaning fabric with 0.5-2mm slots to remove lint and debris from wash water. Selected for durability and precise slot geometry. Upstream: cloth disk filters. Downstream: wash water return to plant head.
• Solids Dewatering: Integrated into rotary drum thickeners and screw presses as cylindrical screens (0.25-1.5mm slots) for municipal biosolids processing in 2-25 MGD plants. Selected for structural strength under pressure and consistent dewatering performance.

Daily Operations: Operators monitor rotation speed, spray wash pressure, and differential head loss across screens. Visual inspection for unusual debris accumulation or spray pattern irregularities occurs during routine plant rounds. Speed adjustments made based on influent solids loading, typically maintaining 2-4 inches head loss differential.

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Maintenance: Weekly bearing lubrication and spray nozzle inspection required. Monthly drive chain/coupling alignment checks prevent premature wear. Quarterly wedge wire inspection for damage or slot plugging. Requires basic mechanical skills, standard PPE (safety glasses, gloves), and lockout/tagout procedures. Annual drive motor and gearbox servicing by qualified technicians.

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Troubleshooting: Excessive head loss indicates plugged slots or failed spray system - check nozzle pressure and cleaning patterns. Unusual noise suggests bearing wear or drive misalignment. Blinding occurs from grease or fine particles - increase wash frequency or chemical cleaning. Typical service life 15-20 years for wedge wire elements, 10-15 years for mechanical components with proper maintenance.

• Wedge Wire Elements: Triangular-profile stainless steel (316L) wires welded to support rods, creating precise slot openings. Slot widths range 0.25-6mm for municipal applications. Selection based on target particle removal and flow capacity requirements.
• Support Structure: Carbon or stainless steel framework providing structural integrity. Sized for hydraulic loads and cleaning forces in municipal installations.
• Drive Mechanism: Variable speed motors (0.5-3 HP) with gear reducers for rotating drum applications. Rotation speeds typically 1-6 RPM for optimal cleaning and solids capture.
• Spray System: High-pressure wash nozzles (80-120 PSI) for cleaning wedge wire surfaces. Stainless steel construction with 1/8" to 1/4" orifices depending on application.
• Collection Hopper: Stainless steel trough collecting removed solids, sized for 2-8 cubic feet capacity in typical municipal installations.

• Slot Opening: 0.5-6.0mm (0.02-0.24") - most municipal applications use 1.0-3.0mm for primary screening
• Surface Loading Rate: 5-20 gpm/ft² (0.2-0.8 m³/hr/m²) for gravity applications; up to 40 gpm/ft² for pressure applications
• Approach Velocity: 0.5-2.0 ft/s (0.15-0.6 m/s) to minimize blinding and plugging
• Open Area: 25-60% depending on slot width and support rod spacing
• Maximum Head Loss: 6-12 inches clean, 18-24 inches fouled before cleaning cycle
• Wire Profile: Triangular cross-section with 2:1 to 4:1 width-to-height ratio for self-cleaning
• Support Rod Spacing: 4-12 inches on center, typically 6" for municipal applications
• Panel Dimensions: Standard 2'×4' to 4'×8' panels; custom sizing available up to 8'×12'
• Materials: 316L stainless steel standard; 2205 duplex for high-chloride environments
• Flow Capacity: 0.1-15 MGD per screen assembly depending on configuration and slot size
• Cleaning Frequency: Manual cleaning every 1-4 weeks; automated systems clean every 15-60 minutes

• What slot opening is required based on downstream equipment protection requirements? Critical threshold: Pumps typically need 3-6mm protection; membrane systems need 0.5-1.0mm. Wrong selection causes either inadequate protection (costly pump repairs, membrane fouling) or excessive maintenance (frequent cleaning cycles). Need influent characterization data and downstream equipment specifications.
• Should you specify gravity-fed or pressure-fed configuration? Threshold: Available head >4 feet favors gravity; <2 feet requires pressure. Gravity systems cost 40-60% less but need more civil work. Pressure systems fit tight spaces but require pumping costs. Need site hydraulic profile and space constraints.
• What cleaning method - manual, backwash, or mechanical brush? Manual acceptable for <2 MGD with weekly cleaning tolerance. Backwash systems needed for >5 MGD or when labor is limited. Brush systems for heavy debris loading >100 mg/L TSS. Wrong choice impacts O&M costs by 200-400%.
• What materials are required for site-specific corrosion conditions? 316L adequate for typical municipal water (pH 6.5-8.5, <250 mg/L chlorides). 2205 duplex needed for >500 mg/L chlorides or pH <6.0. Wrong material selection leads to premature failure within 5-8 years versus 20+ year design life.

• Division 40 - Process Integration
• Section 40 30 00 - Water Treatment Equipment Primary section for municipal water treatment wedge wire screen assemblies, including mechanical cleaning systems and controls integration with plant SCADA systems.

• Material/Equipment Verification: 316L stainless steel certification required, Slot opening tolerance verification (±0.002"), Weld quality documentation per AWS D1.6
• Installation Requirements: Precise alignment critical for rotating equipment, Grouting specifications for static screens, Access requirements for maintenance
• Field Challenges: Shipping damage to delicate wedge wire surfaces, Alignment issues with concrete structures
• Coordination Issues: 12-16 week lead times typical, Early structural coordination essential

• Hendrick Screen Company - HSC Static Screens for 0.5-50 MGD applications
• Johnson Screens (Aqseptence Group) - V-Wire intake screens and cylinders
• WesTech Engineering - Rotary drum screens with wedge wire panels
• Evoqua Water Technologies - Leopold static screens for municipal intakes

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All maintain strong municipal references and provide standard AWWA-compliant materials.

• Bar screens - Lower cost ($15-25K vs $40-60K), suitable for coarser solids removal, higher maintenance
• Rotary drum screens - Better for high solids loading, 2-3x higher cost, more complex maintenance
• Traveling water screens - Preferred for large intake applications >25 MGD, significantly higher capital cost but automated operation

Establish direct relationships with manufacturer field service teams early - they provide invaluable startup support and troubleshooting expertise. Specify spare wedge wire panels (10-15% of total) during initial procurement rather than emergency orders. Consider stainless steel upgrade costs upfront; carbon steel false economy in municipal applications due to corrosion maintenance requirements.