Element Screens

Element screens are self-cleaning fine screening systems that remove suspended solids and debris from municipal water and wastewater streams using rotating drum or disc elements with mesh openings typically ranging from 0.5 to 6mm. The rotating elements continuously lift captured solids above the water surface where spray wash systems remove debris into collection troughs. These screens typically achieve 85-95% removal of suspended solids larger than their mesh size while handling flows from 0.1 to 25 MGD per unit. The primary trade-off is higher capital and maintenance costs compared to static screens, requiring regular spray nozzle cleaning and mechanical component servicing.

• Primary Headworks Screening: Element screens serve as the first line of defense in municipal plants (2-25 MGD), positioned after bar racks but before grit removal. They capture 3-6mm debris that passes through coarse screening, protecting downstream pumps and process equipment.
• Secondary Effluent Polishing: Installed before disinfection in plants with stringent TSS limits (<10 mg/L), element screens remove residual floc and biological solids. Their fine screening capability (1-3mm) provides reliable tertiary treatment without chemical addition.
• Influent Pump Station Protection: Element screens protect high-service pumps in facilities with combined sewer systems, where debris loads vary dramatically during wet weather events.

Daily Operations: Operators monitor differential pressure across elements (typically <2 psi during normal operation) and observe cleaning cycle frequency. Visual inspection of spray patterns and screenings discharge quality indicates system performance. Flow rate verification ensures hydraulic capacity matches design parameters, with adjustments made to cleaning intervals based on debris loading.

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Maintenance: Weekly lubrication of drive mechanisms and monthly inspection of spray nozzles for plugging. Quarterly element removal for detailed cleaning and wear assessment. Annual drive motor service and control system calibration. Requires confined space training for internal access and lockout/tagout procedures. Standard PPE includes safety harnesses, chemical-resistant gloves, and eye protection.

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Troubleshooting: High differential pressure indicates element blinding or spray system failure. Reduced cleaning effectiveness suggests worn elements (typical 3-5 year life) or inadequate backwash pressure. Motor overload conditions often result from debris accumulation on elements or drive mechanism binding. Warning signs include irregular cleaning cycles, visible element damage, and increased screenings moisture content.

• Filter Elements: Stainless steel wedge-wire or perforated plate elements with 1-6mm openings. Sized based on peak flow (typically 2-4 gpm/sq ft loading). Elements range from 12-48 inches in municipal applications.
• Drive Mechanism: Gear-reduced motors (0.5-2 HP) rotate elements at 1-3 rpm for continuous cleaning. Variable speed drives optimize cleaning cycles based on differential pressure.
• Backwash System: High-pressure spray nozzles (60-100 psi) with automated sequencing remove captured solids. Flow rates typically 5-15% of process flow.
• Control System: PLC-based controls with differential pressure monitoring, timer-based cleaning cycles, and alarm functions. Integration with plant SCADA for remote monitoring.

• Flow Rate Parameters: Design flow: 0.1-15 MGD per unit (typical municipal range), Peak hydraulic capacity: 1.5-3.0x design flow, Minimum turndown ratio: 3:1 for variable speed drives
• Physical Loading Criteria: Surface loading rate: 5-15 gpm/ft² of effective screen area, Through-flow velocity: 0.5-2.0 ft/s at design conditions, Approach velocity: 1-3 ft/s in inlet channel
• Hydraulic Parameters: Operating head loss: 6-24 inches at design flow, Maximum allowable head loss: 36-48 inches before cleaning cycle, Backwash pressure: 15-40 psi, Backwash flow rate: 2-5% of forward flow
• Removal Performance: TSS removal: 10-40%, Particle size cutoff: 20-100 microns, Turbidity reduction: 15-35% typical
• Physical Constraints: Footprint: 8-20 ft² per MGD capacity, Operating temperature range: 35-100°F, Minimum straight pipe: 5D upstream, 3D downstream

• What influent TSS concentration and particle size distribution will the screens handle? Requires 6-month influent characterization data. TSS >200 mg/L may require pre-screening or frequent cleaning cycles.
• Should the system include automated backwash with dedicated pumps or rely on gravity cleaning? Flows >2 MGD typically require automated systems. Manual cleaning acceptable for <1 MGD plants with adequate staffing.
• What redundancy level is required - single unit, duplex, or N+1 configuration? Depends on downstream process sensitivity and bypass capabilities. Critical applications require N+1.
• What cleaning waste disposal method will be used - to plant headworks or separate handling? Determines backwash pump sizing and piping requirements.

• Primary: Division 40 - Process Integration (40 05 00 - Common Work Results for Process Integration)
• Secondary: Division 46 - Water and Wastewater Equipment (46 07 00 - Packaged Water and Wastewater Treatment Equipment)
• Element screens are packaged treatment units requiring process integration specifications for controls, interconnections, and performance requirements

• Material/Equipment Verification: Verify 316SS construction for all wetted parts, Confirm screen element spacing matches design (typically 6mm), Check motor specifications and electrical requirements
• Installation Requirements: Requires 8-12 week lead times for custom channel configurations, Needs precise channel dimensions for proper fit, Requires 480V/3-phase power and control panel coordination
• Field Challenges: Channel modifications often needed for retrofits, Screenings conveyance system integration critical, Access requirements for maintenance often overlooked
• Coordination Issues: Early coordination with electrical contractor for control integration, Screenings handling equipment must be sized together

• Huber Technology - ROTAMAT RoK4 series, widely installed in North American plants 1-20 MGD capacity
• Headworks International - BioMag Element screens, popular for smaller facilities 0.5-5 MGD
• Lakeside Equipment - Raptor Element screens, common in retrofit applications
• JWC Environmental - Auger Monster Element series, known for robust construction in challenging applications

• Static wedge wire screens cost 30-40% less but require manual cleaning and higher headloss. Preferred for smaller facilities under 2 MGD with consistent flows.
• Rotating drum screens handle higher flows (10-50 MGD) but cost 50-70% more than element screens.
• Traditional bar screens with manual raking remain viable for very small plants under 1 MGD where labor costs are acceptable and simplicity is prioritized.

Establish relationships with local manufacturer reps early - they provide valuable sizing verification and troubleshooting support. Many offer free preliminary sizing for serious projects. Consider standardizing on one manufacturer across multiple facilities for parts inventory and operator familiarity. Negotiate service contracts during equipment purchase for better rates. Request factory training for operators during commissioning to maximize equipment life.