Chlorination Systems

Chlorination systems disinfect water and wastewater by injecting chlorine compounds to destroy pathogens and maintain residual protection throughout distribution networks. These systems dose liquid sodium hypochlorite, chlorine gas, or on-site generated hypochlorite based on flow-paced control and residual monitoring feedback loops. Typical municipal systems achieve 99.9% pathogen reduction with contact times of 15-30 minutes at dosages ranging from 1-4 mg/L. The primary trade-off involves balancing adequate disinfection against formation of regulated disinfection byproducts like trihalomethanes, which increase with higher chlorine doses and longer contact times.

• Primary Disinfection (Post-Secondary Treatment): Applied after secondary clarifiers or membrane bioreactors at 2-8 mg/L dosing rates. Selected for reliable pathogen inactivation meeting EPA CT requirements. Upstream connections from chemical feed pumps; downstream to contact basins with 30-120 minute detention times before distribution

• Distribution System Residual Maintenance: Booster chlorination at pump stations and storage tanks maintaining 0.2-4.0 mg/L free chlorine residuals per EPA regulations. Critical for preventing regrowth in 6-48 inch distribution mains. Connects upstream from high-service pumps with downstream monitoring at system extremities

• Odor Control: Pre-chlorination at headworks (1-3 mg/L) controlling septicity and H2S in collection systems. Applied upstream of screening/grit removal when influent dissolved oxygen drops below 1 mg/L. Downstream processes benefit from reduced corrosion and improved settling

• Emergency Disinfection: Temporary chlorination during UV system failures or main breaks. Portable feed systems delivering 5-15 mg/L for pipeline disinfection per AWWA C651 standards

Daily Operations: Operators monitor chlorine residuals hourly using DPD colorimetric testing or online analyzers, adjusting feed pump rates based on flow-paced control algorithms. Typical adjustments range 10-50% of setpoint responding to demand variations, influent quality changes, or distribution system requirements. Visual inspection includes checking solution levels, pump stroke rates, and injection point performance.

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Maintenance: Weekly calibration of feed pumps and analyzers using standard solutions. Monthly inspection of pump diaphragms, tubing replacement every 3-6 months depending on chemical concentration. Safety protocols require full PPE (chemical-resistant gloves, safety glasses, aprons) when handling 12.5% sodium hypochlorite. Requires Grade 2-3 operator certification and annual safety training for chemical handling procedures.

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Troubleshooting: Common failures include pump diaphragm rup

• Chemical Feed Pumps: Diaphragm or peristaltic pumps delivering 0.1-200 GPH sodium hypochlorite solution. Wallace & Tiernan, Grundfos, or LMI models with 4-20mA control and turndown ratios of 100:1. Selection based on required dosage range and redundancy requirements

• Storage Systems: HDPE or fiberglass tanks (50-5,000 gallon capacity) with secondary containment meeting EPA SPCC requirements. Includes level sensors, mixers for 12.5% sodium hypochlorite solutions, and emergency eyewash stations within 10 feet

• Injection Points: Chlorine contact chambers, pipeline injection quills, or flash mixers providing rapid dispersion. Materials include 316SS or CPVC rated for pH 11-13 solutions. Sizing based on detention time calculations and hydraulic mixing energy

• Monitoring Equipment: Online chlorine analyzers (Hach CL17, YSI 9300) with membrane or amperometric sensors. Includes flow-proportional control loops, data logging, and alarm systems for residual maintenance between 0.1-4.0 mg/L

• Safety Systems: Emergency shower/eyewash stations, chlorine leak detectors, and ventilation systems meeting OSHA requirements for hypochlorite handling areas

• Flow Capacity: 0.1-75 MGD typical municipal range; gas chlorinators sized 20-30% above peak hourly flow

• Dosage Range: 0.5-8.0 mg/L for disinfection; 1.0-4.0 mg/L typical finished water

• Chlorine Residual: 0.2-4.0 mg/L free chlorine; 2.0-4.0 mg/L combined chlorine for distribution

• Feed Rate Accuracy: ±2% of setpoint for gas systems; ±5% for liquid hypochlorite

• Turndown Ratio: 10:1 minimum for gas feed equipment; 20:1 preferred for variable demand

• Operating Pressure: 5-15 psig chlorine gas; 15-50 psig for solution injection

• Contact Time: CT values 0.5-6.0 mg·min/L depending on pH, temperature, target organism

• Storage Capacity: 15-30 days chlorine gas supply; 7-14 days liquid hypochlorite

• Ambient Temperature: 60-80°F chlorinator room; freeze protection required for solution lines

• pH Range: 6.5-8.5 optimal for free chlorine efficacy

• Backup Systems: 100% redundancy required; automatic switchover capability

• Safety Systems: Gas leak detection at 1 ppm; emergency scrubber sizing for largest container

• Gas vs. Liquid Chlorination Selection: Plants >5 MGD typically justify gas systems for lower chemical costs ($0.85/lb gas vs. $1.20/lb hypochlorite equivalent). Consider operator certification requirements, safety infrastructure costs, and delivery logistics. Wrong choice increases 20-year O&M costs by $200,000-500,000

• Chlorinator Sizing Strategy: Size for peak hourly demand plus 25% safety factor, or maximum day demand? Peak sizing prevents residual loss during high-demand periods but increases capital costs 30-40%. Requires accurate demand projections and redundancy analysis

• Contact Basin Configuration: Serpentine vs. straight-through design affects CT compliance and construction costs. Serpentine provides 15-20% better contact efficiency but costs 25% more. Critical for meeting CT requirements at design flows without overchlorination

• Residual Monitoring Location: Continuous monitoring at plant effluent vs. distribution entry points? Plant effluent monitoring is cheaper but may miss residual decay. Distribution monitoring adds $15,000-25,000 per location but ensures regulatory compliance and customer satisfaction

• Primary: Division 40 - Process Integration (40 05 00 - Common Work Results for Process Integration)

• Secondary: Division 46 - Water and Wastewater Equipment (46 71 00 - Disinfection Equipment)

• Alternative: 11 46 00 - Water and Wastewater Treatment Equipment (legacy numbering still common in municipal specifications)

• Material/Equipment Verification: Verify chlorine compatibility ratings (Hastelloy C for gas systems), Confirm analyzer calibration certificates and NIST traceability

• Installation Requirements: Gas chlorine rooms require exhaust fans, leak detectors, emergency scrubbers; Hypochlorite systems need secondary containment, freeze protection

• Field Challenges: Chlorine gas leaks during startup commissioning, Analyzer fouling from high turbidity in finished water

• Coordination Issues: HVAC coordination for gas room ventilation requirements, Electrical coordination for emergency power to safety systems, Lead times: 12-16 weeks for gas chlorinators, 8-12 weeks for analyzers

• Capital Controls (Evoqua): Series 1000 gas chlorinators, dominant in gas systems

• Wallace & Tiernan (Evoqua): V-100 vacuum regulators, legacy installations

• Hach (Xylem): CL17 analyzers with integrated control

• ProMinent: DULCO flex peristaltic pumps for sodium hypochlorite, growing municipal market share in smaller plants

• UV Disinfection: $200-400/GPM installed, preferred for plants with seasonal chloramine formation issues or high organics

• Ozone Systems: $300-600/GPM, used when simultaneous oxidation needed

• Chlorine Dioxide: 2-3x chemical cost versus hypochlorite, specified for taste/odor control or Cryptosporidium inactivation requirements

• UV gaining market share in secondary disinfection applications

Maintenance Access: Specify removable analyzer assemblies - cleaning electrodes weekly is critical but often overlooked during design. Vendor Relationships: Establish service contracts early; chlorine analyzer calibration drift causes more compliance issues than feed system failures. Cost Savings: Bulk hypochlorite delivery (4,000-gallon minimum) reduces chemical costs 15-20% versus tote delivery for plants >2 MGD.