Ultrafiltration Systems

Ultrafiltration (UF) systems remove suspended solids, bacteria, viruses, and high molecular weight compounds from water using semi-permeable membranes with 0.01-0.1 micron pore sizes. Water is forced through hollow fiber or flat sheet membranes under 10-80 psi pressure, physically screening contaminants while allowing dissolved salts and low molecular weight organics to pass through. Typical municipal UF systems achieve >4-log virus removal and produce turbidity consistently below 0.1 NTU. The primary limitation is membrane fouling requiring regular backwashing and chemical cleaning, reducing net production capacity by 10-15%.

• Primary Water Treatment: UF replaces conventional clarification/filtration at 2-15 MGD plants, particularly with challenging raw water (high turbidity, algae, Cryptosporidium concerns). Systems typically follow coagulation/flocculation, feeding directly to disinfection. Selected for consistent 0.01-0.1 NTU effluent regardless of source water variability and 4-log Crypto removal credit

• Membrane Bioreactor (MBR) Applications: Immersed UF membranes in activated sludge process for 0.5-10 MGD plants with space constraints or stringent effluent requirements. Replaces secondary clarifiers and tertiary filtration, producing <2 mg/L TSS, <5 mg/L BOD effluent suitable for direct reuse applications

• Tertiary Treatment/Reuse: UF polishing after secondary treatment for indirect potable reuse or industrial supply, typically 1-25 MGD capacity. Positioned upstream of RO systems, providing consistent <0.1 NTU feed water while removing bacteria, protozoa, and most viruses before advanced treatment

Daily Operations: Operators monitor transmembrane pressure (TMP) trends, typically maintaining <15 psi differential. Flow rates, backwash frequency (every 15-60 minutes), and permeate quality (turbidity <0.1 NTU) require hourly logging. Air scour timing and chemical feed rates need adjustment based on seasonal fouling patterns. Most systems operate automatically with SCADA oversight.

​

Maintenance: Membrane integrity testing monthly using pressure decay or bubble point methods. Quarterly cleaning-in-place cycles require confined space entry procedures and chemical handling PPE. Annual membrane replacement typically 5-10% of total modules. Pump maintenance every 2,000-4,000 hours. Requires Level 2-3 operators with membrane system certification and basic mechanical skills.

• Membrane Modules: Hollow-fiber or flat-sheet configurations in pressurized vessels or immersed tanks. PVDF or PES materials with 0.01-0.1 micron pore size. Pressurized systems: 4-8 inch diameter vessels, 40-80 modules per rack. Immersed systems: cassette-style modules in concrete tanks. Selection based on fouling characteristics and cleaning requirements

• Feed/Backwash Pumps: Variable frequency drive centrifugal pumps sized for 6-12 gpm/sf flux rates plus 15-25% backwash flow. Typically 10-150 HP for municipal applications. Stainless steel or coated carbon steel construction with mechanical seals rated for continuous duty

• Air Scour System: Blowers providing 3-8 scfm/sf membrane surface area for physical cleaning. Positive displacement or centrifugal blowers, 5-75 HP typical range. Critical for controlling biological fouling in immersed systems and enhancing backwash effectiveness in pressurized configurations

• Chemical Cleaning Systems: Automated CIP skids with separate tanks for caustic (NaOCl, NaOH) and acid (citric, oxalic) solutions. Heated recirculation capability, typically 1-3% chemical concentration, 4-8 hour cleaning cycles every 30-90 days depending on fouling rates

• Flux Rate: 20-60 GFD (gallons per square foot per day) typical for municipal applications, with 35-45 GFD most common for surface water treatment. Higher flux rates (50-60 GFD) acceptable for groundwater with minimal fouling potential

• Transmembrane Pressure (TMP): Operating range 5-25 psi, with chemical cleaning triggered at 20-25 psi for hollow fiber systems. Design for maximum 30 psi to prevent membrane damage

• Recovery Rate: 90-98% typical, with 95% standard for municipal surface water treatment. Lower recovery (90-93%) required for high-fouling source waters

• Backwash Frequency: Every 15-60 minutes depending on source water quality. Surface water typically requires 20-30 minute cycles, groundwater 45-60 minutes

• Plant Capacity Sizing: 0.5-2.0 MGD: 2-4 trains; 2-10 MGD: 4-8 trains; 10-50 MGD: 8-16 trains. Minimum 3 trains for redundancy in plants >1 MGD

• Pretreatment Requirements: Coagulation dosing 1-5 mg/L aluminum or iron salts for surface water. Chlorine residual <0.5 mg/L at membrane inlet to prevent oxidation

• 1. Inside-out vs. outside-in flow configuration? Inside-out (pressurized) suitable for >5 MGD with flux rates 40-60 GFD. Outside-in (submerged) preferred for <5 MGD plants with 20-35 GFD flux. Wrong choice affects energy costs by 15-25% and maintenance complexity

• 2. What membrane material and pore size? PVDF or PES membranes with 0.01-0.1 micron pores standard. Tighter pores (0.01-0.02 micron) for Cryptosporidium/Giardia removal, larger pores (0.05-0.1 micron) for turbidity control only. Requires source water characterization and regulatory requirements analysis

• 3. How many trains for redundancy and cleaning cycles? Minimum N+1 redundancy for plants >2 MGD, with one train always available for cleaning. Plants >10 MGD typically use N+2 configuration. Insufficient trains cause production shortfalls during maintenance

• 4. What chemical cleaning system capacity? Size CIP tanks for 1.5-2.0x membrane volume with heating to 104-140°F. Inadequate cleaning systems reduce membrane life from 7-10 years to 3-5 years, increasing replacement costs significantly

• Primary: Division 46 23 00 - Membrane Water Treatment Equipment

• Secondary: Division 40 30 00 - Water Treatment Equipment (for integrated treatment plants with multiple processes)

• Material/Equipment Verification: Membrane material certification (NSF 61), Skid structural calculations for seismic/wind loads, Electrical classification verification

• Installation Requirements: Concrete pad thickness (typically 12" minimum), Overhead crane provisions (10-ton capacity), Utility routing coordination (power, air, chemical feeds)

• Field Challenges: Module shipping damage inspection critical, Piping stress analysis for thermal expansion, CIP system integration complexity

• Coordination Issues: 16-20 week lead times standard, Chemical feed system timing coordination

• Suez - ZeeWeed 1000 series (municipal standard, 0.04 micron PVDF)

• Evoqua - Memcor CP series (proven in 50+ MGD plants)

• Pentair X-Flow - Aquaflex modules (compact footprint design)

• Toray - HFU series (high-flux hollow fiber, growing US presence)

​

All offer municipal references and standardized skid packages for 0.5-20 MGD applications.

• Conventional Treatment - Preferred for high turbidity (>50 NTU), lower capital cost but higher chemical/labor costs

• Ceramic Membranes - Better for challenging waters, 3-4x capital cost but longer life

• Reverse Osmosis - Required for dissolved contaminants, 2-3x operating cost. UF optimal for 1-20 NTU source water needing pathogen removal without significant dissolved contaminant issues

Establish direct technical contact with manufacturer's process engineer during design - they'll provide realistic flux rates and cleaning frequencies based on your specific water quality. Negotiate spare membrane pricing upfront (typically 20-30% of original cost). Consider phased installation for larger plants to spread capital costs and gain operational experience before full buildout.