Industry: Environmental protection industry

Monitoring scheme for toxic and hazardous gases in wastewater treatment plants

Industry Pain Points

The gas risk in urban industrial wastewater treatment plants manifests as the dual characteristics of "odor superposition + oxygen-deficient deep wells": sudden H2S concentrations in the intake section can reach 500-1000 ppm (with a lethal concentration of just 100 ppm for 30 minutes exposure), long-term NH3 concentrations in the biochemical section at 30-50 ppm affecting employee health, and the coexistence of CH4, H2S, and CO2 in the sludge digestion section (with biogas content of 60-65%/1000-3000 ppm/35%), as well as dust + NH3 + thermophilic bacteria pollution in the sludge dewatering room. Employees frequently encounter accidents when entering confined spaces such as grating wells, collection wells, and sludge wells (with over 50 confined space accidents occurring in wastewater treatment plants nationwide each year). At the environmental regulatory level, the HJ 1098-2020 odor emission standards strictly control H2S < 0.06 ppm and NH3 < 1.5 ppm at the plant boundary, with exceeding standards resulting in penalties from the ecological environment bureau + production restrictions for rectification. Operating units often incur annual losses of hundreds of thousands of yuan due to "accidental production shutdowns + emergency sprinkling + petition complaints".

Solution Overview

Youri'an provides a comprehensive process chain + boundary odor joint prevention and control solution: ① **Inlet section** (coarse screen / lift pump room / grit chamber): H2S + LEL + O2 + NH3 multi-component fixed monitoring + portable monitoring for confined space operations (4-in-1); ② **Biochemical section** (AAO / oxidation ditch / SBR): aeration tank NH3 + dissolved oxygen feedback + H2S edge monitoring + methane diffusion monitoring in anaerobic zone; ③ **Sludge treatment section** (digestion tank / dewatering machine room / sludge silo): CH4 + H2S + CO2 tri-gas fixed monitoring + biogas tank pressure + biogas sulfur content (< 100 ppm for boiler feeding); ④ **Boundary odor joint control**: 8-12 boundary odor monitoring stations (H2S + NH3 + VOC + wind speed and direction + PM2.5), real-time source tracing + automatic diffusion range calculation; ⑤ **Central monitoring platform**: all data aggregation + intelligent linkage deodorization facilities (biofilter air volume / chemical scrubbing spray solution ratio) + SMS alarm + historical data compliance reporting.

## Key Monitoring Node Configuration

### Water Inlet Section (Highest H2S Risk)

– Coarse grating well (underground depth of 8-12m): fixed H2S (range 0-500 ppm) + LEL + O2 + wind speed
– Sand trap: H2S + NH3
– Inlet water pump room: combustible gas LEL + oxygen deficiency O2
– Employees must undergo a mandatory 30-second confirmation using a portable 4-in-1 (O2 + LEL + H2S + CO) device before entering

### Biochemical Section

– AAO anaerobic zone: CH4 + H2S (methane produced through anaerobic reaction)
– Anoxic / Aerobic Zone: NH3 + Dissolved Oxygen (Aeration Feedback)
– Secondary sedimentation tank: NH3 + boundary odor sampling

### Sludge Treatment Section (Biogas Specialty)

– Sludge thickener: H2S + CH4
– Anaerobic digestion tank: fixed CH4 (range 0-100% LEL) + H2S (range 0-3000 ppm) + CO2 + gas storage tank level + pressure
– Inlet/outlet of biogas desulfurization tower: H2S online continuous monitoring (control desulfurizer dosing + verify desulfurization effect)
– Biogas boiler room: LEL × 25% to cut off the main gas supply valve + flame detector
– Sludge dewatering room: NH3 + dust

### Boundary odor (core of environmental compliance)

– 8-12 boundary monitoring stations: H2S (trigger at < 0.06 ppm) + NH3 (< 1.5 ppm) + VOC (PID 0-1000 ppb) + wind direction and speed
– Automatic traceability: abnormal concentration + wind direction inversion → locate the leakage area → automatically notify the on-site team for investigation

## Key Technical Parameters

– H2S electrochemical sensor range: 0-500 ppm (calibrated with standard gas every 6 months + components replaced every 12 months)
– CH4 infrared principle (unaffected by H2S poisoning, a must-have for marsh gas scenarios)
– Protection level: IP68 (high humidity in wastewater treatment plant + splash)
– Explosion-proof grade Ex d IIB T4 (Zone 1 of marsh gas area)
– Communication: 4G wireless + LoRa backup, data upload with < 30 seconds delay
– The boundary station is powered by solar and wind energy, and is independently deployed (not reliant on the plant's power grid)

## Implementation Key

1. **Standard Operating Procedure (SOP) for Operations in Confined Spaces**: Conduct testing to ensure compliance → Perform forced ventilation for ≥ 15 minutes → Re-test → Attach safety ropes + have a guardian outside → Enter; Re-check must be conducted after 30 minutes
2. **Biogas desulfurization and boiler protection**: The H2S concentration at the outlet of the desulfurization tower must be less than 100 ppm before entering the biogas boiler, otherwise it will corrode the boiler and cause emissions to exceed standards
3. **Integrated odor removal and dosing**: When H2S concentration exceeds 30 ppm, automatically increase the dosage of NaOH in the chemical scrubber; when NH3 concentration exceeds 20 ppm, increase the dosage of H2SO4
4. **Environmental Compliance**: The odor concentration at the factory boundary is automatically reported to the local ecological environment bureau's monitoring platform, ensuring compliance with unannounced inspections
5. **Carbon Trading**: Biogas Utilization + Emission Reduction Data can be used as Application Materials for CCER Voluntary Emission Reduction Projects

## Regulatory Basis

– GB 50014-2021 "Standard for Design of Outdoor Drainage"
– CJJ 60-2011 "Technical Regulations for Operation, Maintenance, and Safety of Urban Sewage Treatment Plants"
– HJ 1098-2020 "Emission Standards for Odor Pollutants from Wastewater Treatment Plants"
– GB/T 14554-93 "Emission Standards for Odor Pollutants"
– Chapter 11: Confined Spaces in GB 30871-2022 "Safety Code for Special Operations in Hazardous Chemical Enterprises"
– GBZ 2.1-2019 Limit Values

## Applicable Customers

Municipal wastewater plants (with a capacity of over 100,000 tons), wastewater treatment in industrial parks, village and town wastewater stations, reclaimed water plants, wastewater lift stations, landfill leachate treatment plants, sludge disposal centers, and self-built wastewater treatment in printing and dyeing/food/pharmaceutical industries.

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