Abstract
Wastewater treatment plant (WWTP) components generally experience both atmospheric and immersion corrosion. The corrosion intensive components include buried piping, handrails, gratings, ladders, electrical junction boxes, clarifier rake arms, concrete walls, etc. Hydrogen sulfide, which is usually present, has wide-ranging effects in wastewater systems, most notably causing corrosion and odor problems.
Severe immersion corrosion of WWTP components were recently identified in and around the primary and secondary clarifiers at two Army Installations. The corroding components included: rake arms, weir and other metallic components, such as skimmers and valve handles. Also the concrete clarifier structure itself has shown sign of deterioration. In addition, steel lamp posts within the vicinity of one of the wastewater treatment plant were found to be corroding due to hydrogen sulfide in the atmosphere, in addition to moisture and high humidity.
The corrosion problems have been mitigated by a combination of strategies, including judicious selection and implementation of emerging corrosion resistant coatings, corrosion resistant materials selection, and cathode protection. For example, impressed current cathodic protection using ceramic anodes has been employed for protection of the immersed metallic components in several clarifiers. Coal tar epoxy coatings are being used on light post within the WWTP, and corrosion resistant steels alloys are being substituted as corrosion resistant alternatives for low carbon steel in valve handles and electrical junction boxes and polymers are being implemented in electrical junction boxes. The benefits of the implementing corrosion control technologies at the wastewater treatment plants are restoration of the plant to optimum operating condition, reduced maintenance, and increased safety.
