Does H₂S in sewage treatment wells always play hide-and-seek?

I scene Pain Point: Why Does H₂S in Wells Always "Meet Standards on the Surface but Exceed Limits at the Bottom"?

During the maintenance of a grille well in a sewage treatment plant, the surface detection of H₂S at the wellhead was 7ppm (with a limit of 10ppm). However, when the detection device was extended to 3 meters below the well bottom, the concentration surged to 26ppm. This is because the density of H₂S is higher than that of air, and after being released from sewage and sludge, it accumulates at the well bottom. Detecting only the surface easily leads to missed detection.

II Core Detection Knowledge and Precautions

1. H₂S Hazard Thresholds

◦ ＞10ppm：Foul odor, eye pain, and headache;

◦ ＞50ppm：Difficulty breathing;

◦ ＞100ppm：Life-threatening risk.

2. Well Detection Difficulties

◦ The wellhead is narrow, and the well depth ranges from 2 to 5 meters, making it impossible for conventional probes to reach the well bottom;

◦ Water accumulation at the well bottom is likely to contaminate the sensor, and the release of H₂S increases by 3-5 times when sewage is agitated.

3. Operational Specifications

◦ Conduct detection within 30 minutes before entering the well, measuring at three points: "1 meter below the wellhead, the middle of the well, and the well bottom";

◦Calibrate the detector's zero point with 10ppm standard gas every day.

III Solutions: 3 Sets of Accurate H₂S Detection Schemes for Wells

• Wells Without Water Accumulation: Pump-suction detector + 2-5m extended hose + anti-clogging filter (prevents sludge from clogging the probe and actively extracts air for bottom detection);

• Waterlogged Wells: Pump-suction detector + extended pipe with float + waterproof probe (the float keeps the probe suspended above the water surface to prevent sewage contamination);

• Long-Term Monitoring: Fixed detection module at the well bottom + wellhead alarm (when the concentration exceeds 10ppm, the wellhead triggers an audible and visual alarm, eliminating the need for frequent manual detection).

• After the sewage treatment plant implemented the measures, the timely detection rate of H₂S leakage increased to 100%, and no more incidents of employee poisoning occurred.

Have you encountered problems such as "insufficiently long hoses" or "contaminated probes" when detecting H₂S in wells? Send a private message with the keyword "H₂S in Wells" to get tool selection recommendations for different well depths!