Filter Air Scour Equipment

Filter air scour equipment provides compressed air injection beneath filter media to enhance backwash cleaning effectiveness in gravity sand and anthracite filters. During the air scour cycle, compressed air is distributed through lateral piping or porous plates at the filter bottom, creating vigorous agitation that loosens accumulated solids from media grains. Typical air scour rates range from 3-5 scfm/ft² of filter area, reducing backwash water consumption by 30-40% compared to water-only backwashing while achieving superior cleaning. The primary trade-off is increased energy costs for air compression and more complex control systems requiring careful sequencing to prevent media loss.

• Gravity Sand Filtration (Most Common): Air scour systems are integrated into rapid sand filters at 2-25 MGD plants, positioned beneath filter media with dedicated air distribution piping. Selected for superior cleaning efficiency compared to water-only backwash, reducing backwash water consumption by 30-40%

• Dual-Media Filtration: Essential for anthracite/sand filters where media stratification requires aggressive cleaning. Air scour prevents media intermixing during backwash cycles. Typically sized for 3-5 SCFM per square foot of filter area

• GAC Filter Regeneration: Used in 5-50 MGD plants with granular activated carbon contactors. Air scour removes accumulated biofilm and particulates without carbon attrition

• Membrane Bioreactor Pre-filtration: Applied in advanced treatment trains where cloth media filters require frequent cleaning to maintain 2-5 micron particle removal efficiency

Daily Operations: Operators monitor air flow rates via SCADA, typically 4-6 SCFM per square foot during backwash cycles. Key parameters include blower amperage, discharge pressure (10-15 PSI), and cycle timing. Manual adjustments involve flow rate optimization based on turbidity breakthrough and headloss development. Most systems operate automatically with 15-30 minute backwash cycles every 24-72 hours.

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Maintenance: Blower oil changes every 2,000-4,000 hours, requiring confined space entry procedures and lockout/tagout protocols. Air filter replacement monthly, involving basic mechanical skills. Orifice cleaning quarterly using compressed air or wire brushes. Valve actuator lubrication semi-annually. PPE includes hearing protection, safety glasses, and fall protection for elevated equipment access.

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Troubleshooting: Common failures include blower bearing wear (indicated by vibration/noise increase), orifice plugging (uneven air distribution patterns), and control valve sticking (erratic cycle timing). Warning signs: reduced backwash effectiveness, increased filter runtime, elevated blower temperatures above 180°F. Typical blower service life: 15-20 years with proper maintenance.

• Air Blowers: Positive displacement or centrifugal units delivering 3-8 SCFM per square foot filter area. Typical municipal sizing: 25-150 HP for 0.5-10 MGD plants. Selection based on required pressure (8-15 PSI) and continuous duty rating

• Air Distribution Piping: Schedule 40 PVC or stainless steel headers with orificed laterals. Sized for 15-25 FPS velocity in mains, 8-12 FPS in laterals. Includes pressure regulation and flow measurement

• Control Valves: Pneumatic or electric actuated butterfly/ball valves for sequenced air introduction. Sized 6-24 inches for municipal applications with 3-5 second opening/closing times

• Air Flow Meters: Thermal mass or differential pressure instruments monitoring 50-500 SCFM ranges. Critical for optimizing scour intensity and detecting blockages

• Pressure Relief Systems: Safety valves preventing over-pressurization of filter structures, typically set 2-3 PSI above normal operating pressure

• Air Flow Rate: 3-5 scfm/ft² of filter bed area is standard for municipal rapid sand/anthracite filters. For 10-ft deep beds, use 4-5 scfm/ft²; shallow beds (6-8 ft) require 3-4 scfm/ft²

• Air Pressure: 5-15 psig at filter underdrain headers. Higher pressures (12-15 psig) needed for deep beds or high-rate filters. Include 3-5 psi pressure drop allowance through piping and valves

• Blower Sizing: Size for simultaneous operation of 25-50% of filters during normal backwash cycles. Include 10-15% safety factor for motor sizing. Positive displacement blowers preferred for consistent air delivery

• Underdrain Design: Air scour-compatible underdrains required. Wheeler bottom systems handle 4-6 scfm/ft² effectively. Avoid older gravel/pipe systems - retrofit costs $15-25/ft²

• Control Sequencing: Air scour typically runs 2-5 minutes before water backwash initiation. Programmable timing with 0.1-minute resolution standard. Include air flow measurement ±5% accuracy for optimization

• Pipe Sizing: Size air mains for 15-20 fps velocity. Use Schedule 40 minimum for buried applications. Include air release valves at high points and drains at low points

• 1. Simultaneous vs. Sequential Filter Operation? Can existing blower capacity handle multiple filter backwash (>2 filters)? Simultaneous operation requires 2-4x larger blower but reduces cycle time. Sequential operation uses smaller equipment but extends plant downtime

• 2. Retrofit Existing Underdrains or Replace? Will current underdrain system handle 4+ scfm/ft² without media loss? Gravel/pipe systems typically fail - $20-30/ft² replacement cost. Wheeler bottoms retrofit well. Poor decision leads to media carryover and shortened filter runs

• 3. Centralized or Dedicated Blower System? Should one large blower serve all filters or individual units per filter? Centralized systems cost 20-30% less initially but create single point of failure. Need redundancy requirements and maintenance philosophy

• 4. Air Flow Measurement Location? Measure at blower discharge or individual filter headers? Header measurement provides better control (±2% vs ±10%) but costs $3,000-5,000 per filter. Inadequate measurement leads to ineffective cleaning and shortened filter runs

• Primary: Division 40 - Process Integration

• Section 40 30 00 - Water Treatment Equipment

• Secondary: Division 23 - Heating, Ventilating, and Air Conditioning

• Section 23 34 00 - Dedicated Outdoor-Air Units (for blower equipment)

• Air scour systems integrate water treatment processes with mechanical air handling, requiring coordination between process and HVAC specifications

• Material/Equipment Verification: Verify stainless steel grade (316L minimum) for air piping and nozzles; Confirm blower capacity at site elevation and temperature conditions; Review underdrain compatibility with existing filter media

• Installation Requirements: Coordinate electrical for blower systems (typically 480V, 3-phase); Plan for compressed air piping routing through filter gallery; Ensure adequate blower room ventilation (heat removal)

• Field Challenges: Limited access in existing filter boxes during retrofits; Coordinating shutdowns with plant capacity requirements; Managing concrete cutting dust in operational facilities

• Coordination Issues: Interface with filter control systems and SCADA integration; Sequencing with backwash pump operations; Lead times: 12-16 weeks for custom underdrain systems, 6-8 weeks for standard blowers

• Parkson Corporation - AirLift air scour systems with rotary lobe blowers, widely used in municipal retrofits

• WesTech Engineering - AirWash underdrain systems with integrated air distribution

• Evoqua/USFilter - Leopold air scour underdrains with proprietary nozzle designs

• Tonka Water - AirBurst systems featuring pulse-style air delivery for smaller municipal plants

• Surface wash systems cost 40-60% less than air scour but provide inferior cleaning in deep bed filters

• High-rate backwash pumps (15-20 gpm/sf) can substitute air scour in shallow bed applications under 24 inches

• Combination air/water wash offers superior performance but increases capital costs 25-35%

• Surface wash preferred for anthracite-only filters; high-rate backwash suitable for single-media applications under 2 MGD capacity

Specify manual isolation valves on individual filter air lines - automatic valves fail frequently in municipal environments. Oversize blower systems by 15-20% beyond calculated requirements; actual pressure losses often exceed theoretical values due to underdrain fouling. Establish service agreements with blower manufacturers early - rotary lobe blowers require skilled technicians for maintenance that most municipal staff lack.