Activity of sulfur oxidizing microorganisms and impacts on concrete pipe corrosion

Concrete is the foundation of modern infrastructure due to its broad availability and comparative ease of production. Rapid deterioration of concrete structures in sewage collection systems has a major impact on environmental health and safety in countries with warm climates. Using the Water Environment Federation database, the American Society of Civil Engineers (ASCE; Reston, Va.) evaluated wastewater infrastructure as poor in 2005, and cited a 2002 EPA analysis that estimated the United States will need to spend during the next 20 years nearly 390 billion to replace existing wastewater infrastructure and construct new facilities, including collection systems. The purpose of this research was to investigate the corrosion mechanism of concrete sewer pipes the major component in the deterioration of wastewater infrastructure. The practical implications of this research are improvements in the analysis and development of strategies for the prevention of concrete corrosion---strategies that will prevent the deterioration of sewer collection pipelines, saving costly replacement.; Microorganisms that produce sulfuric acid catalyze the deterioration of concrete sewer pipes in a process termed "microbially induced concrete corrosion" (MICC) [U.S.EPA, 1991]. The MICC process has been theorized to occur in the following manner:; In the first stage, chemical reactions with CO 2 and other acidic gasses in the headspace of sewers cause the pH of moisture condensing on concrete pipes to drop from 13 to about 9.; The second stage of MICC is the colonization of condensate on the pipe crown surfaces by sulfur oxidizing microorganisms (SOM), such as the neutrophilic SOM (NSOM). This population will then utilize reduced sulfur compounds such as hydrogen sulfide that are emitted from the sewage, producing elemental sulfur and polythionic acids, which further lower the pH of the concrete surface.; The third stage of concrete corrosion requires the establishment of acidophilic microorganisms (ASOM) in biofilm that grows on the sewer crown; their subsequent growth and copious acid production is the actual cause of sustained concrete corrosion. The acid front moves into the fresh concrete, reducing the pH and reacting with concrete binders, producing ettringite and gypsum, which severely compromise the imperviousness and strength of the pipe.; This research focused on improving the assessment and predictability of the MICC process. The scope included detailed study of the microbial communities associated with biogenic acid production, microbial interactions that occur in sewer pipe environments, and refining the processes that result in concrete corrosion.; Critical microbial kinetics of key sulfur-oxidizing bacteria associated with MICC were quantified for the express purpose of predicting in-situ sulfuric acid production rates. Sequenced batch reaction flasks that simulated conditions in corroding sewage collection systems were used along with a novel scanner-based image analysis method to non-destructively characterize corrosion of the concrete samples. A comparison with abiotic conditions were performed in order to validate the optical methodology and to quantify the importance of microbial activity.