Anaerobic wastewater is frequently corrosive to materials it contacts, especially:

• A. Coal tar enamel
• B. Concrete
• C. Copper
• D. Plastic

Answer: (B)

Anaerobic wastewater creates hydrogen sulfide, a gas produced by sulfate-reducing bacteria in oxygen-poor sections of sewers. When this H2S encounters the oxygen-rich surface of concrete, sulfur-oxidizing bacteria convert it to sulfuric acid. That sulfuric acid aggressively attacks concrete because the cement paste (calcium hydroxide and related compounds) dissolves in sulfuric acid, causing surface deterioration and deep pits. Concrete is especially vulnerable due to its porosity and lime content, so it is the material most frequently corroded in these conditions. While other materials can be protected by coatings or may resist some exposure, the inherent susceptibility of concrete makes it the primary target in anaerobic wastewater environments.