Ozone Disinfection Systems

Ozone disinfection systems generate and inject ozone gas (O3) into water to inactivate pathogens through powerful oxidation reactions that destroy cell walls and viral proteins. Ozone generators produce O3 from oxygen using corona discharge or UV methods, delivering the gas through fine-bubble diffusers in contact chambers with 10-20 minute detention times. Systems typically achieve 3-4 log reduction of viruses and bacteria at CT values of 0.5-1.6 mg-min/L for Giardia inactivation. The primary limitation is ozone's instability requiring on-site generation and immediate use, plus higher energy costs compared to chlorination.

• Primary Disinfection (Post-Secondary): Ozone contactors installed after secondary clarifiers provide 3-4 log virus inactivation with 2-4 mg/L dosing and 10-20 minute contact time. Selected for superior pathogen kill compared to chlorine, especially for Cryptosporidium and Giardia.
• Taste and Odor Control: Pre-ozonation at 1-2 mg/L before conventional treatment removes geosmin and MIB compounds. Applied upstream of coagulation/flocculation when raw water has seasonal algae issues.
• Color and Iron/Manganese Removal: Ozone oxidizes dissolved metals and organic color compounds at 0.5-1.5 mg/L doses. Installed before filtration to convert dissolved iron/manganese to filterable precipitates.
• Advanced Oxidation Process (AOP): Combined ozone/UV or ozone/hydrogen peroxide systems target micropollutants and pharmaceuticals. Typically 5-8 mg/L ozone with UV at 400-600 mJ/cm².

Daily Operations: Monitor ozone residual with continuous analyzers, typically targeting 0.1-0.3 mg/L contact chamber effluent. Adjust generator output based on water temperature, flow rate, and ozone demand. Check oxygen purity, generator cooling water temperature, and off-gas destruction efficiency. Log generator runtime hours and ozone production rates.

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Maintenance: Weekly cleaning of diffuser systems and ozone analyzer sensors. Monthly inspection of generator dielectric tubes and cooling systems. Quarterly replacement of ozone destruction catalyst media. Annual generator overhaul including dielectric replacement costs $15,000-25,000. Requires confined space entry training and respiratory protection for contact chamber work.

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Troubleshooting: Generator arcing indicates moisture infiltration or dielectric failure - immediate shutdown required. Low ozone transfer efficiency suggests diffuser fouling.

• Ozone Generator: Corona discharge units producing 50-500 lb/day ozone from oxygen feed gas. Stainless steel construction with dielectric tubes requiring 15-20 kV power supply. Sizing based on 1.5-2.0 transfer efficiency and peak hourly demand.
• Contact Chamber: Concrete or stainless steel tanks providing 10-20 minute detention with fine bubble diffusion. Typical dimensions: 4-6 serpentine passes, 12-18 feet deep. Baffling achieves plug flow with T10/T ratio >0.7.
• Ozone Destruction Unit: Thermal or catalytic destruction of off-gas ozone to <0.1 ppm before atmospheric release. Thermal units operate at 600-700°F. Catalytic units use manganese dioxide or hopcalite media.
• Oxygen Feed System: PSA oxygen generators or liquid oxygen supply providing 90-95% purity feed gas. PSA systems sized for 1.2-1.5x peak ozone demand.

• Contact Time Requirements: CT values: 0.5-6.0 mg-min/L depending on target log removal (Giardia: 0.5, Cryptosporidium: 1.6-10), Contact chamber detention time: 10-30 minutes at peak flow, Baffling factor: minimum 0.7
• Ozone Production: Ozone dose: 0.5-8.0 mg/L (typical 1.5-3.0 mg/L for 2-3 log removal), Generator capacity: 1.2-1.5x average day demand for redundancy, Power consumption: 8-15 kWh/lb O₃ (oxygen feed) or 15-25 kWh/lb O₃ (air feed)
• System Pressures: Generator operating pressure: 5-15 psig, Contactor pressure: atmospheric to 15 psig, Off-gas pressure drop: <2 psi across destruction unit
• Physical Parameters: Generator sizing: 50-500 lb/day capacity per unit, Contact chamber depth: 16-20 feet typical, Gas-to-liquid ratio: 1:10 to 1:20 (volume basis), Residual ozone: <0.1 mg/L at effluent

• Oxygen vs. Air Feed System Selection: Air feed threshold: <5 MGD plants, lower capital cost acceptable, higher operating costs tolerable. Oxygen feed threshold: >5 MGD plants, high CT requirements (>3.0), space constraints critical. Wrong choice impacts 20-year lifecycle costs by $500K-2M and footprint by 40-60%.
• Contact Chamber Configuration: Serpentine threshold: flows >2 MGD, high CT requirements, retrofit applications. Bubble column threshold: new construction, <10 MGD, moderate CT needs. Poor mixing reduces CT efficiency by 20-40%, requiring higher ozone doses.
• Redundancy and Turndown Requirements: Minimum 2 units for <5 MGD, 3+ units for >10 MGD plants. Each unit sized for 60-75% of peak demand to allow maintenance. Insufficient redundancy causes permit violations during maintenance.

• Primary: Division 46 23 61 - Ozone

• Material/Equipment Verification: Verify 316L stainless steel for all ozone contact surfaces, Confirm generator efficiency guarantees (8-12 kWh/lb O₃), Check contactor baffle materials and thickness specifications
• Installation Requirements: Dedicated HVAC with ozone destruction for equipment rooms, Separate electrical service with backup power provisions, Crane access for generator module replacement
• Field Challenges: Ambient leak detection system calibration and commissioning, Precise flow measurement for CT calculations, Generator cooling water quality requirements
• Coordination Issues: 16-24 week lead times for custom contactors, Early electrical coordination for high-voltage feeds

• Xylem WEDECO - DURON series (10-2,000 lb/day O₃) dominates North American municipal market
• Ozonia (Suez) - TOGC2E generators popular for 50-500 lb/day applications
• Mitsubishi Electric - strong in larger installations with OZAT series
• PRIMOZONE - Swedish technology gaining traction in 20-200 lb/day range with energy-efficient medium-frequency systems

• UV Disinfection - Lower O&M, no chemical storage, preferred for <5 MGD plants. Capital costs similar but simpler operations.
• Sodium Hypochlorite - 50% lower capital cost, easier operations, but requires chlorine contact time and dechlorination.
• Mixed Oxidants - On-site generation reduces chemical handling, good for 1-10 MGD range with moderate capital costs between UV and ozone.

Establish direct relationships with manufacturer service technicians early - they're invaluable for troubleshooting complex control sequences. Budget 15-20% contingency for unforeseen electrical upgrades; older plants often need panel modifications. Consider phased installations to maintain disinfection during construction. Negotiate service contracts including annual generator tune-ups and spare parts inventory to minimize downtime costs.