Ozone Generator in Sewage Treatment Plant (STP)

Ozone (O₃) is generated from dry air or oxygen by corona discharge inside the OZ India ozone generator. The dielectric barrier discharge cell passes high-voltage AC current (6–10 kV, 500–1000 Hz) through a precision gap between two electrodes separated by a dielectric material. This creates micro-discharges (plasma channels) that dissociate O₂ molecules into oxygen radicals which recombine to form O₃. OZ India ozone generators for STP applications are sized from 10g/hr to 75g/hr (air-fed) or 25g/hr to 350g/hr (oxygen-fed), covering STP flows from 0.5 MLD to 50 MLD.

Generated ozone gas is introduced into the STP effluent through a Venturi injector or fine bubble diffuser system within the ozone contact chamber. The Venturi injector creates negative pressure that draws ozone gas into the water stream under turbulent mixing conditions — achieving ozone transfer efficiency of 85–95%. The contact chamber, sized for 15–20 minutes hydraulic retention time (HRT), provides the contact time (CT) required for pathogen inactivation. OZ India supplies PVDF Venturi injectors and 316L stainless steel contact chamber internals resistant to ozone attack.

Within the contact chamber, ozone attacks pathogens through two simultaneous pathways: direct molecular ozone reaction (redox potential 2.07V) and indirect hydroxyl radical (•OH) pathway (redox potential 2.80V). At pH 6.5–8.0 typical of STP effluent, both pathways operate concurrently. The ozone CT concept governs disinfection efficacy — for 4-log E. coli inactivation, a CT of 0.5–1.0 mg/L·min is required at neutral pH. The OZ India dissolved ozone monitor continuously measures residual ozone at the contact chamber outlet, ensuring the required CT is consistently achieved regardless of seasonal flow variations or organic load fluctuations.

Beyond disinfection, ozone simultaneously oxidises recalcitrant organic compounds that biological treatment cannot remove. Chromophoric groups in colour-causing compounds are destroyed, removing visible colour from effluent. Pharmaceutical compounds including hormones, antibiotics, and personal care products are oxidised and mineralised, preventing accumulation in receiving water bodies. Geosmin and 2-methylisoborneol (MIB) causing earthy odours are destroyed at ozone doses as low as 0.3 mg/L — making ozone-treated STP effluent suitable for reuse in residential landscaping without aesthetic concerns.

Odour control is addressed simultaneously. The OZ India Ozone Odour Control System doses ozone gas into STP vent gases above aeration tanks and sludge dewatering areas, oxidising H₂S (detectable at 0.008 ppm), mercaptans, ammonia, and other volatile organic sulphur compounds to non-odorous sulphate and nitrate. This eliminates odour complaints from residential and commercial areas surrounding urban STPs — a major compliance requirement under CPCB's Ambient Air Quality Standards for odour and NGT's penalty framework for odour nuisance.

System control is fully automatic. The dissolved ozone monitor output (4–20 mA) feeds back to the ozone generator control panel, which adjusts ozone production to maintain the set residual concentration of 0.2–0.5 mg/L at the contact chamber exit. During low-flow periods (night hours), ozone production reduces automatically, saving energy. Historical data logging with 30-day onboard memory provides compliance documentation for CPCB inspections. The ozone ambient air monitor in the operator room ensures safe working conditions per OSHA 0.1 ppm TWA limit.

OZ India Technology has been designing and commissioning ozone systems for STP tertiary treatment since 2014, with installations at hotel STPs, municipal STPs, industrial campus STPs, and research institute facilities across India. Our standard STP ozone package is a complete, skid-mounted system including: CE-certified ozone generator, air dryer or oxygen concentrator, ozone gas piping, Venturi injector, PVDF non-return valve, dissolved ozone monitor with automatic control panel, and ambient air safety monitor. All equipment is manufactured at our Greater Noida facility under ISO 9001:2015 quality management.

For STP flows up to 2 MLD, the OZ India 10-25g/hr Industrial Ozone Generator provides complete tertiary treatment meeting CPCB Class A. For 2–10 MLD STPs, the 30-50g/hr Heavy Industrial system is standard, with oxygen feed from our PSA Oxygen Generator for optimum energy efficiency. Large STPs above 10 MLD use the 75-350g/hr system in oxygen-fed configuration, with multiple units in parallel for N+1 redundancy. All systems include automatic dose control, fault alarms, and remote monitoring capability via Modbus/GSM.

OZ India dissolved ozone monitors provide real-time effluent quality data and automatic dose adjustment — critical for STPs with variable influent loads. The in-line amperometric dissolved ozone sensor (range 0–2 mg/L, ±2% accuracy) requires calibration every 3 months, with replacement membranes available ex-stock from our Greater Noida warehouse. Historical data is logged to SD card and can be downloaded as CSV for CPCB compliance reports. The ozone ambient air monitor protects operators per OSHA/NIOSH guidelines with audible alarm at 0.05 ppm and automatic shutdown at 0.1 ppm.

OZ India provides turnkey project delivery for STP ozone systems: site assessment, detailed engineering drawing submission, equipment supply, installation supervision, commissioning, operator training (2-day programme), and 1-year comprehensive warranty. Post-warranty Annual Maintenance Contracts (AMC) include 4 scheduled preventive maintenance visits and priority emergency response within 48 hours anywhere in India. Our STP ozone references include Leela Hotel Greater Noida, CSIR-NEERI Nagpur, and multiple Smart City STP projects — demonstrating project management experience that ensures smooth installation without disrupting STP operations.

Sizing an ozone system for STP begins with three inputs: design flow (MLD), secondary effluent quality (BOD, COD, TSS, coliform count from lab reports), and the target standard (CPCB Class A for reuse or Class B for discharge). The ozone dose in mg/L is determined from pilot testing data or standard design tables: 2–3 mg/L for effluent with BOD 20–30 mg/L and coliform 10⁵–10⁶ MPN/100mL; 3–5 mg/L for higher load effluent. Ozone generator capacity (g/hr) = Flow (m³/hr) × Dose (mg/L) × Safety factor (1.3) ÷ 1000.

Contact chamber volume is sized for 15–20 minutes HRT: Volume (m³) = Flow (m³/hr) × HRT (hr). For a 5 MLD STP at 20 min HRT, contact chamber volume = 208 × 0.33 = 69 m³. The existing chlorine contact tank can usually be repurposed as the ozone contact chamber — retrofitting ozone into STPs without major civil works. OZ India provides hydraulic calculations and contact chamber drawings for each project, ensuring cross-flow plug conditions that prevent short-circuiting and guarantee the design CT value is achieved.

Oxygen source selection significantly impacts operating cost and ozone yield. Air-fed generators (ambient air dried to -60°C dew point) are economical for systems below 25g/hr; oxygen-fed generators (using 90-93% O₂ from OZ India PSA Oxygen Generator) are recommended above 25g/hr, halving specific energy consumption from 15 kWh/kg to 8 kWh/kg ozone. For very large STPs (above 350g/hr requirement), bulk liquid oxygen from commercial suppliers provides the lowest cost per kg O₂. OZ India prepares a techno-economic analysis comparing air-fed vs oxygen-fed vs LOX options as part of every STP project proposal.