Microbiologically influenced corrosion of concrete in sanitary sewers: Processes and control mechanisms

Microbiologically influenced corrosion (MIC) of concrete sanitary sewers is a common problem that demands a large rehabilitation investment every year. MIC is the result of dilute sulfuric acid (H₂SO₄) dissolving the cement matrix. The acid is produced by a complex series of chemical and biochemical reactions. Hydrogen sulfide (H₂S) is produced by sulfur-reducing bacteria (SRB) in the liquid phase, and then in time, this gas is converted by sulfur-oxidizing bacteria (SOB) into H₂SO₄. The last conversion occurs above the liquid level under aerobic conditions. The objectives of this paper are (1) to present a literature review of MIC processes and factors influencing them, and (2) to discuss control mechanisms and authors’ experience on development over years in understanding MIC of concrete (MICC) in a sanitary sewerage environment (SSE). Published papers were identified that reported MICC in SSE for the past 30 years. The literature review and authors’ on-site and laboratory investigations suggest that MIC of concrete is a complex process that involves varied surface interactions. The addition of liquid antimicrobial additive as per standard procedure shows the resistance of concrete to MIC and its direct relation with the mixing time of admixture. Many empirical inputs like corrosion areas, corrosion rates, the impact of cement, and aggregate types varying with installation and repair of sewer structures are identified. The review results show variation in corrosion rates and other empirical inputs obtained on-site and through laboratory studies due to different testing procedures. Further research is needed to establish quantitative relations between empirical inputs related to MICC in SSE. Identification and development of more effective coatings and safe antibacterial agents will help inhibit colonization of SOB overexposed sewers and better understand environmental microbiology.