Cartridge Filters

Cartridge filters remove suspended solids and particulates from water using replaceable cylindrical filter elements housed in pressure vessels. Water flows radially through pleated media (typically polypropylene, cellulose, or polyester) with pore sizes ranging from 0.5 to 100 microns, achieving 95-99% removal of particles larger than the rated size. Municipal plants commonly use them for final polishing after conventional treatment, producing effluent turbidity below 0.1 NTU. The primary trade-off is frequent cartridge replacement costs, with elements lasting 2-12 weeks depending on influent quality and loading rates.

• Final Polishing in Membrane Plants: Cartridge filters (typically 1-5 micron) protect RO membranes downstream, removing residual particles after conventional pretreatment. Installed between media filters and high-pressure pumps, handling 2-15 MGD flows with 6-12 parallel vessels
• Laboratory Sample Preparation: 0.45 micron cartridges filter grab samples before analysis, ensuring accurate turbidity and particle count measurements. Single-cartridge housings handle intermittent flows of 1-5 GPM
• Chemical Feed System Protection: 25-50 micron cartridges protect chemical metering pumps and injection points from pipe scale and debris in polymer, coagulant, and disinfectant lines. Flows typically 5-50 GPM per system
• Potable Water Final Treatment: Post-GAC polishing using 1-10 micron cartridges removes carbon fines and residual particles before clearwell storage. Multiple vessel configurations handle 5-25 MGD with automated backwash sequences

Daily Operations: Monitor differential pressure gauges hourly during peak flows - typical starting pressure drop 2-3 PSI, replacement needed at 15-25 PSI. Check flow rates and adjust valve positions to maintain design hydraulics. Log cartridge installation dates and track service life patterns for predictive replacement scheduling.

​

Maintenance: Replace cartridges every 30-90 days depending on influent quality and loading rates. Requires confined space entry procedures for large vessels. Use nitrile gloves and safety glasses when handling used cartridges. Two-person team recommended for multi-cartridge systems. Inspect O-rings and housing threads during each changeout.

​

Troubleshooting: Rapid pressure rise indicates cartridge blinding from algae or fine particles - check upstream treatment effectiveness. Flow bypass around cartridges suggests O-ring failure or improper seating. Shortened service life typically indicates upstream process upsets or seasonal water quality changes requiring micron rating adjustment.

• Filter Cartridge Elements: Pleated polypropylene or cellulose media in 10", 20", or 40" lengths. Micron ratings from 0.45-100 μm. Municipal systems typically use 5-25 micron ratings with 2.5" diameter cartridges. Selection based on particle size distribution and required effluent quality
• Pressure Vessels: Stainless steel or fiberglass housings rated 150-300 PSI. Single cartridge vessels for <10 GPM; multi-cartridge vessels (6-40 elements) for 50-500 GPM municipal flows. Include inlet/outlet ports, pressure gauges, and vent/drain connections
• Differential Pressure Monitoring: Transmitters measure pressure drop across cartridge bank (typically replace at 15-25 PSI differential). Digital displays with 4-20mA outputs for SCADA integration
• Support Hardware: End caps, O-rings, and center cores maintain cartridge integrity. Stainless steel preferred for potable applications. Quick-disconnect fittings enable rapid cartridge changeouts during maintenance windows

• Flow Rate Parameters: Design flow rate: 0.1-25 MGD typical for municipal applications; Flux rate: 2-8 gpm/ft² of filter area (typical 4-6 gpm/ft²); Peak flow capacity: 150-200% of average daily flow
• Pressure Requirements: Operating pressure: 15-150 psi (typical 30-80 psi); Maximum allowable pressure drop: 25-35 psi across clean cartridge; End-of-run pressure drop: 40-50 psi before replacement required; Minimum upstream pressure: 20 psi above operating pressure
• Physical Parameters: Cartridge lengths: 10", 20", 30", 40" standard (20" most common); Housing diameter: 4"-24" for municipal applications; Micron ratings: 0.1-100 microns (1-50 microns typical for municipal); Service life: 30-180 days depending on water quality and loading
• Performance Criteria: Turbidity removal: >95% for ratings ≤5 microns; Particulate removal efficiency: 99%+ at rated micron size; Temperature range: 40-180°F (municipal typically 40-100°F)

• What micron rating is required based on downstream equipment protection or effluent quality targets? Need raw water particle size distribution analysis and downstream equipment manufacturer requirements. Wrong selection causes either inadequate protection (too coarse) or excessive pressure drop/short service life (too fine). Typical municipal applications: 5-25 microns for membrane pre-filtration, 1-5 microns for reverse osmosis protection
• What flux rate can be sustained given raw water quality and acceptable cartridge replacement frequency? Requires turbidity, TSS, and fouling index data. Conservative design at 3-4 gpm/ft² extends cartridge life but increases capital cost. Aggressive design at 6-8 gpm/ft² reduces footprint but may require weekly cartridge changes in high-fouling applications
• Should system use single-stage or multi-stage filtration configuration? Depends on particle size distribution and total loading. Multi-stage (coarse to fine) extends fine filter life but adds complexity. Single-stage appropriate when >90% of particles are within 2x of target micron rating
• What housing material and pressure rating is required for the specific application? Consider water chemistry (chlorine, pH), pressure requirements, and maintenance access. Stainless steel required for chlorinated applications >2 ppm or pH >8.5

• Primary: 40 05 23 - Cartridge Water Filters
• Secondary: 40 20 00 - Water Treatment Equipment (if part of larger treatment system), 40 05 00 - Common Work Results for Water Treatment (for installation requirements)

• Material/Equipment Verification: Verify NSF-61 certification for potable water contact; Confirm cartridge micron ratings match specifications; Check housing pressure ratings exceed system design pressure
• Installation Requirements: Provide adequate clearance for cartridge changeout (typically 1.5x cartridge length); Install pressure gauges upstream/downstream for monitoring; Specify quick-disconnect fittings for maintenance access
• Field Challenges: Housing alignment critical for proper sealing; Cartridge shipping damage common - inspect upon delivery
• Coordination Issues: Lead times typically 4-6 weeks for standard configurations, 8-12 weeks for custom housings

• Pentair - Pentek series housings with Big Blue and standard 2.5" cartridges, strong municipal chloramine removal applications
• 3M - Aqua-Pure whole house systems and commercial AP900 series, excellent sediment filtration track record
• Pall Corporation - Profile series pleated cartridges in stainless housings, proven in pre-RO applications
• Parker Hannifin - Fulflo cartridge systems, reliable performance in smaller municipal facilities under 5 MGD

• Bag Filters - Lower capital cost, easier maintenance for larger particles (>25 microns), roughly 40% less expensive than cartridge systems but higher labor costs
• Automatic Backwash Filters - Higher upfront cost (2-3x cartridge systems) but eliminate consumable costs, preferred for continuous high-flow applications above 1 MGD
• Multimedia Sand Filters - Traditional choice for primary filtration, lower operating costs but require more space and backwash infrastructure, typically 50% higher capital cost including backwash systems

Establish cartridge inventory agreements with local distributors - emergency replacements often needed during high turbidity events. Negotiate bulk pricing for annual cartridge purchases rather than per-order pricing; 20-30% savings typical. Maintain relationships with multiple cartridge suppliers since specific models frequently discontinued. Consider universal-fit cartridges to reduce inventory complexity. Track differential pressure daily - many operators wait too long between changeouts, reducing overall system efficiency and increasing pump energy costs.