Sustainable wastewater infrastructure systems are vital for civilizations to protect public health. Most of the structural elements of wastewater infrastructure are constructed using concrete owing to its versatility, low cost, and durability. Concrete structures that are exposed to wastewater can experience Microbially Induced Corrosion of Concrete (MICC), which is a multi-stage biodeterioration process. The service life of concrete wastewater infrastructure can be significantly shortened by MICC with considerable associated costs for repair and rehabilitation.
MICC is a multi-disciplinary subject that draws on civil engineering, environmental engineering, material science, and microbiology. The complex nature of MICC has made its comprehensive investigation difficult because of the challenges associated with creating the field conditions in laboratories. Therefore, although MICC has been studied for over 70 years, there is still a need for realistic tests methods to assess MICC in laboratory settings. The primary goal of this thesis is to develop practical laboratory test protocols to assess the performance of concrete against MICC.
The first part of this study hypothesizes that the performance of antimicrobial products is influenced by the pH of the environment, the bacterial population, and the level of bacterial activity. To test this hypothesis, three bacterial activity-population levels were tested in environments with different pH levels to evaluate the efficacy of an antimicrobial product against planktonic bacteria. The tested antimicrobial product was successful in delaying or preventing MICC with low and moderate bacterial populations and activity for all pH levels greater than 4. Antimicrobial products were successful in delaying or preventing MICC with severe bacterial populations and activity for all pH levels tested greater than 6. The results support the main hypothesis of the research.
In the second part of the thesis, an accelerated testing protocol, which has been developed for assessing the performance of cementitious materials and antimicrobial additives during the bacterial attachment phase of MICC, is presented. The proposed method is based on biogenic acidification and is practical, realistic, and safe. The test was designed to represent the pH range associated with the bacterial attachment phase of MICC by using neutrophilic sulfur-oxidizing bacteria (NSOB) and controlling the pH lower bound. Measurement of pH, sulfate concentration, optical density, and SEM observations were used to assess the microbial colonization. Deterioration evaluation was made by investigating the reduction in flexural strength, calcium leaching, and microstructural change. The resistance of admixed and/or topically applied antimicrobial additives against bacterial propagation and the deterioration of samples during the bacterial attachment stage of MICC was evaluated.
The last part of the thesis focuses on comparing biogenic sulfuric acid attack and chemical sulfuric acid attack. Both tests were performed on paste specimens that are exposed to solutions with an initial pH of 2. The maintenance of the pH of the solution in the desired range was highly challenging in chemical acid attack test, which required continuous monitoring and regular acid addition. Calcium leaching measurements showed that biofilm on the surface of specimens exposed to biogenic acidification restricted excessive leaching of calcium from the samples. XRF results showed that biogenic acid attack caused higher changes in the chemical composition of the specimens. Flexural strengths tests did not show a significant difference between the chemical and biogenic acid attack; however, this could be attributed to the short test duration.