During the decomposition of organic matter in wastewater treatment plants, gases such as hydrogen sulfide (H₂S), ammonia (NH₃), and methane (CH₄) are produced. Among these, hydrogen sulfide is the most corrosive, as it converts to acid in the presence of moisture and damages metal equipment, cables, and electrical panels. Ammonia can also damage copper and its alloys.
Effects of corrosive gases on equipment:
Prolonged exposure can lead to:
- Corrosion of electrical panels and equipment housings
- Blackening or sulfation of terminals and busbars
- Increased connection resistance and overheating at joints
- Failure of electronic boards and PLC equipment
- Reduced accuracy of sensors and transmitters
- Shortened lifespan of cables and electrical connections
These issues may seem minor at first but can, over time, lead to production stoppages, higher maintenance costs, and even safety hazards.
Mitigation strategies for H₂S:
Key preventive measures include proper ventilation and continuous gas concentration monitoring, installation of H₂S detectors and alarm systems, use of panels and equipment with appropriate IP ratings and anti-corrosion coatings, corrosion-resistant instrumentation and stainless steel components in sensitive areas, and regular inspection and servicing.
Operational experience:
After years of operation, the following practical lessons have been recorded:
- Replacing corroded terminals before overheating or shutdowns occur
- Distinguishing genuine sensor faults from connector corrosion or moisture ingress into junction boxes, which can send false data to the PLC
- Using 316 stainless steel or plated brass cable glands instead of standard ones
- Annual grounding resistance measurement and periodic inspection of connections
- Relocating electrical and instrumentation panels to areas with lower gas concentrations
- Using suitable resins to minimize gas effects on copper AC refrigerant lines
Conclusion:
Corrosive gases in wastewater treatment plants gradually reduce the lifespan of electrical and instrumentation equipment and increase maintenance costs. A regular inspection program, preventive maintenance, resistant equipment, and proper ventilation can prevent most of these issues and improve the reliability of plant operations.
Author: Mohsen Bakhtiarizadeh
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