Industry: Municipal engineering

Monitoring Solution for Hydrogen Sulfide and Combustible Gases in Municipal Wastewater Treatment Plants

Fixed and portable dual coverage, integrated with SCADA exhaust linkage, ensuring zero accidents in confined space operations

Industry Pain Points

Municipal wastewater treatment plants are sites with a quadruple risk combination of H2S (hydrogen sulfide), CH4 (methane), NH3 (ammonia), and hypoxia. The concentration of H2S in the intake pump room, coarse screen well, and anaerobic section of the regulating reservoir can suddenly reach 500-1000 ppm (with a lethal concentration of just 100 ppm for 30 minutes). Frequent confined space accidents occur when employees enter and exit the screen well, clean the sludge well, and maintain the digestion tank. The methane recycling system has a CH4 concentration of 60-65% (with an explosion lower limit of 5%), and pipeline leaks can cause devastating explosions. The aeration tank and sludge dewatering room present complex working conditions with NH3, dust, and noise. Traditional single-point detectors have incomplete coverage, high maintenance costs, and severe data isolation issues. Operators face annual compliance fines and accident losses ranging from hundreds of thousands to millions of yuan

Solution Overview

U-Right provides a full process chain gas monitoring solution for the "inlet section + biochemical section + sludge digestion section + outlet section": a fixed multi-component monitoring network for H2S, LEL, O2, NH3, and CO2, covering coarse screen wells, grit chambers, regulating reservoirs, AAO tanks, secondary sedimentation tanks, sludge digestion tanks, gas storage tanks, and biogas boilers. Key equipment includes corrosion-resistant and waterproof probes (IP68, suitable for H2S + high humidity environments), electrochemical sensors resistant to NH3 cross-talk, portable 4-in-1 confined space detectors (one for each employee), and a three-tier protection system consisting of fixed, portable, and inspection systems. A digital twin process dashboard is provided as a supporting tool, which is linked with SCADA/DCS to control aeration volume, fan frequency conversion, and emergency exhaust. The distribution density follows the standards of GB 50014-2021 + CJJ 60-2011, with at least one set in the intake pump room for every 50m² and at least one set in the digestion tank gas storage tank for every 30m².

## Key Monitoring Nodes

– **Intake lift pump room / coarse screen well**: H2S 0-500 ppm pre-alarm 10 ppm (PC-STEL) + LEL 25%
– **Biochemical treatment (AAO / oxidation ditch)**: NH3 + H2S dual-parameter + dissolved oxygen feedback in aeration tank
– **Sludge digestion system**: CH4 + H2S (biogas containing 1000-3000 ppm H2S, desulfurization required before reuse) + gas storage tank level + pressure interlock
– **Sludge Dewatering Room**: NH3 0-100 ppm + dust
– **Marsh gas boiler room**: LEL × 25% high alarm → automatic shut-off of main gas supply valve

## Confined Space Operations (Key Safety Control)

Employees must undergo a mandatory 30-second detection test using a portable 4-in-1 (O2 + LEL + H2S + CO) device before entering digestion tanks, biogas tanks, or underground well chambers. Only those who meet the standards are allowed to enter. Once inside, external monitoring, escape masks, and SCBA backups are required.

## Implementation Key Points

1. **The lifespan of the H2S sensor is short (high H2S concentration is prone to poisoning), and a service package is promised that includes 6 months of calibration and 12 months of replacement.**
2. The biogas main pipeline must be dual-metered (flow rate + concentration) to facilitate the calculation of carbon reduction and carbon trading
3. Interlock with PLC: H2S > 50 ppm → automatically activate emergency ventilation + close water inlet valve; LEL > 25% → immediately shut off the main biogas pipeline

## Regulatory Basis

– GB 50014-2021 “Standard for Design of Outdoor Drainage”
– CJJ 60-2011 “Technical Regulations for Operation, Maintenance, and Safety of Urban Wastewater Treatment Plants”
– HJ 1098-2020 Emission Standards for Odor Pollutants from Wastewater Treatment Plants
– GBZ 2.1-2019 H2S PC-TWA 10 mg/m³ / PC-STEL 15 mg/m³

## Applicable Customers

Municipal wastewater plants (with a capacity of over 10,000 tons), industrial park wastewater treatment, village and town wastewater stations, reclaimed water plants, and wastewater lift stations.

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