Ion-exchange Media

Ion-exchange media removes dissolved contaminants from water by exchanging undesirable ions for acceptable ones through specialized resin beads. Cationic resins exchange calcium, magnesium, or heavy metals for sodium or hydrogen, while anionic resins replace sulfates, nitrates, or organics with chloride or hydroxide. Typical municipal applications achieve 90-99% removal efficiency for targeted ions at service flow rates of 2-8 gpm/ft². The primary limitation is regeneration chemical costs and waste brine disposal, making ion exchange most economical for specific contaminant removal rather than general water treatment in municipal plants.

• Softening for Corrosion Control - Ion-exchange softening removes calcium and magnesium hardness at 2-15 MGD plants where lime softening isn't economical. Reduces hardness from 150-300 mg/L to <85 mg/L CaCO3.
• Nitrate Removal - Selective anion resins remove nitrate in groundwater systems serving 0.5-5 MGD plants. Reduces NO3-N from 15-45 mg/L to <10 mg/L.
• Demineralization for Boiler Makeup - Mixed-bed polishing units provide ultra-pure water for plant boiler systems, reducing TDS to <1 mg/L.
• PFAS Removal - Emerging application using specialized anion resins for PFOA/PFOS removal, achieving 90%+ removal from 50-500 ng/L influent.

Daily Operations

Operators monitor service flow rates, pressure drop across beds (typically 5-15 psi), and effluent quality parameters. For softening, hardness breakthrough indicates regeneration need - usually when effluent hardness exceeds 2-5 mg/L CaCO3. Flow totalizers track throughput against expected capacity (15,000-30,000 gallons per cubic foot for softening). Automatic controllers handle most operations, but operators verify regeneration cycles complete properly and chemical feed systems maintain proper concentrations.

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Maintenance

Regeneration occurs every 1-7 days depending on influent quality and bed capacity. Monthly resin sampling checks for fouling, breakage, or capacity loss. Quarterly backwash system inspection ensures proper bed expansion and fines removal. Annual resin replacement typically 5-10% for softening, 10-15% for selective systems. PPE includes chemical-resistant gloves, eye protection, and respirators when handling regenerant chemicals.

• Resin Media - Synthetic polymer beads (0.3-1.2mm diameter) with functional groups. Municipal systems typically use 8x30 or 16x40 mesh sizes. Capacity ranges 1.8-2.2 eq/L for SAC, 1.0-1.4 eq/L for SBA resins.
• Pressure Vessels - FRP or steel tanks sized for 6-12 minute contact time at design flow. Typical municipal sizes: 8-12 ft diameter, 12-20 ft height for 2-10 MGD applications.
• Regeneration System - Includes chemical storage, metering pumps, and distribution piping. Salt dissolvers for softening (10-15% brine), acid/caustic systems for demineralization.
• Backwash/Rinse System - Separate piping for bed expansion and regenerant displacement. Backwash rates 4-8 gpm/ft², rinse rates 1-2 gpm/ft².

• Hydraulic Loading Rate: 2-8 gpm/ft² for softening applications, 1-4 gpm/ft² for nitrate removal
• Bed Depth: 30-36 inches minimum for strong acid cation (SAC) resins, 36-48 inches for weak base anion (WBA) resins
• Empty Bed Contact Time (EBCT): 2-5 minutes for hardness removal, 5-15 minutes for nitrate removal
• Operating Pressure: 15-60 psi typical, with 10-15 psi pressure drop across resin bed at design flow
• Backwash Rate: 4-8 gpm/ft² for standard resins, 6-12 gpm/ft² for high-capacity resins
• Freeboard: 50-100% of settled bed depth to accommodate backwash expansion
• Regenerant Dosage: 6-15 lbs salt per cubic foot of resin for softening, 4-8 lbs for selective resins
• Service Flow Velocity: 2-6 gpm/ft² to prevent resin attrition while maintaining adequate contact time
• Temperature Range: 35-120°F operating range for standard resins

• What removal efficiency is required and what target effluent quality must be achieved? Different resin selection needed for hardness removal to <1 grain/gallon versus 3-5 grains/gallon. Wrong selection results in permit violations or oversized systems.
• Should the system use co-current or counter-current regeneration? Counter-current systems achieve 20-30% better regeneration efficiency but require more complex piping and controls.
• What regeneration frequency balances chemical costs with operational complexity? Daily regeneration minimizes resin inventory but increases labor, while weekly cycles reduce O&M but require 40-60% larger resin beds.
• How will spent regenerant be managed? High-TDS brine disposal costs $2-8 per 1,000 gallons. Zero liquid discharge systems cost $500K-2M but eliminate disposal fees.

• Primary: 40 05 23 - Ion Exchange Water Treatment Equipment
• Secondary: 40 05 13 - Disinfection and Sterilization Water Treatment Equipment (when resin systems include disinfection capabilities)
• Related: 40 05 19 - Packaged Water Treatment Equipment (for skid-mounted systems <2 MGD)

• Material/Equipment Verification: Verify NSF-61 certification for all resins, confirm resin mesh size and uniformity coefficient specifications, review backwash flow rate requirements
• Installation Requirements: Underdrain system must prevent resin loss during backwash, adequate freeboard (typically 50-75%) for bed expansion, proper gravel support bed gradation critical
• Field Challenges: Resin fines removal during initial service requires extended rinse cycles, temperature limitations during shipping and storage, chlorine exposure during startup can damage anion resins
• Coordination Issues: Coordinate resin delivery with vessel completion (6-8 week lead times typical), regeneration chemical storage and feed system integration, waste disposal permits for spent regenerant solutions

• Purolite - A830 and A500P strong base anion resins widely used for nitrate removal in 2-20 MGD municipal plants. Strong municipal reference base including installations in California and Florida.
• DuPont Water Solutions - AMBERLITE IRN150 mixed bed resins for polishing applications. AMBERJET 4200 Cl for municipal softening applications up to 50 MGD.
• ResinTech - SIR-100 and MBD-15 resins popular in smaller municipal systems (0.5-10 MGD). Cost-effective alternative with good technical support.
• Lanxess - LEWATIT resins including MonoPlus M500 for municipal softening applications, particularly in hard water regions.

• Reverse Osmosis - Preferred for high TDS removal or multiple contaminant treatment. Higher energy costs but lower chemical usage. Capital costs 30-50% higher than IX.
• Electrochemical Treatment - Emerging option for selective ion removal without regeneration chemicals. Limited municipal track record but promising for specialized applications.
• Lime Softening - Traditional alternative for hardness removal in large plants (>25 MGD). Lower operating costs but higher sludge production and complexity.

Establish relationships with multiple resin suppliers early - municipal projects often require custom blends or specific certifications that can extend delivery times. Negotiate resin replacement costs upfront as part of long-term service agreements. Consider piloting with actual plant water rather than relying solely on lab analysis - municipal water chemistry variations can significantly impact resin performance and regeneration frequency, affecting lifecycle costs by 20-30%.