The effect of silica fume on biodegradation of cement paste and its capacity to immobilize strontium during exposure to microbial sulfur oxidation

Increased Resistance of Nitrite-Admixed Concrete to Microbially Induced Corrosion in Real Sewers

Microbially induced concrete corrosion is a major deterioration process in sewers, causing a huge economic burden, and improved mitigating technologies are required. This study reports a novel and promising effective solution to attenuate the corrosion in sewers using calcium nitrite-admixed concrete. This strategy aims to suppress the development and activity of corrosion-inducing microorganisms with the antimicrobial free nitrous acid, which is generated in situ from calcium nitrite that is added to the concrete. Concrete coupons with calcium nitrite as an admixture were exposed in a sewer manhole, together with control coupons that had no nitrite admixture, for 18 months. The corrosion process was monitored by measuring the surface pH, corrosion product composition, concrete corrosion loss, and the microbial community on the corrosion layer. During the exposure, the corrosion loss of the admixed concrete coupons was 30% lower than that of the control coupons. The sulfide uptake rate of the admixed concrete was also 30% lower, leading to a higher surface pH (0.5-0.6 unit), in comparison to that of the control coupons. A negative correlation between the calcium nitrite admixture in concrete and the abundance of sulfide-oxidizing microorganisms was determined by DNA sequencing. The results obtained in this field study demonstrated that this novel use of calcium nitrite as an admixture in concrete is a promising strategy to mitigate the microbially induced corrosion in sewers.

Monitoring sulfide-oxidizing biofilm activity on cement surfaces using non-invasive self-referencing microsensors

Microbially influenced corrosion (MIC) in concrete results in significant cost for infrastructure maintenance. Prior studies have employed molecular techniques to identify microbial community species in corroded concrete, but failed to explore bacterial activity and functionality during deterioration. In this study, biofilms of different sulfur-oxidizing bacteria compositions were developed on the surface of cement paste samples to simulate the natural ecological succession of microbial communities during MIC processes. Noninvasive, self-referencing (SR) microsensors were used to quantify real time changes of oxygen, hydrogen ion and calcium ion flux for the biofilm to provide more information about bacterial behavior during deterioration. Results showed higher transport rates in oxygen consumption, and hydrogen ion at 4 weeks than 2 weeks, indicating increased bacterial activity over time. Samples with five species biofilm had the highest hydrogen ion and calcium ion transport rates, confirming attribution of acidophilic sulfur-oxidizing microorganisms (ASOM). Differences in transport rates between three species samples and two species samples confirmed the diversity between Thiomonas intermedia and Starkeya novella. The limitations of SR sensors in corrosion application could be improved in future studies when combined with molecular techniques to identify the roles of major bacterial species in the deterioration process.

Review of concrete biodeterioration in relation to nuclear waste

Storage of radioactive waste in concrete structures is a means of containing wastes and related radionuclides generated from nuclear operations in many countries. Previous efforts related to microbial impacts on concrete structures that are used to contain radioactive waste showed that microbial activity can play a significant role in the process of concrete degradation and ultimately structural deterioration. This literature review examines the research in this field and is focused on specific parameters that are applicable to modeling and prediction of the fate of concrete structures used to store or dispose of radioactive waste. Rates of concrete biodegradation vary with the environmental conditions, illustrating a need to understand the bioavailability of key compounds involved in microbial activity. Specific parameters require pH and osmotic pressure to be within a certain range to allow for microbial growth as well as the availability and abundance of energy sources such as components involved in sulfur, iron and nitrogen oxidation. Carbon flow and availability are also factors to consider in predicting concrete biodegradation. The microbial contribution to degradation of the concrete structures containing radioactive waste is a constant possibility. The rate and degree of concrete biodegradation is dependent on numerous physical, chemical and biological parameters. Parameters to focus on for modeling activities and possible options for mitigation that would minimize concrete biodegradation are discussed and include key conditions that drive microbial activity on concrete surfaces.