Microbially induced CaCO3 precipitation through denitrification: An optimization study in minimal nutrient environment

• We achieved CaCO3 precipitation yields up to 18.9 g CaCO3/g NO3-N in 2 days.
• Repetitive CaCO3 precipitation can be achieved from single inoculation.
• Precipitation formed around the cells decreases nutrient uptake rate and activity.
• Denitrifiers removed Ca2+ from paper mill wastewater through CaCO3 precipitation.

So far, researchers investigated microbially induced CaCO3 precipitation (MICP) for soil reinforcement, self-repairing concrete and Ca2+ removal from industrial waste streams. Reported MICP yields were mainly achieved under nutrient-rich conditions. However, creating the tested nutrient-rich conditions in intended applications is both an economical and a practical issue. Therefore, investigation of MICP in more realistic conditions is necessary. This study presents optimization of MICP through denitrification in minimal nutrient conditions. To optimize their MICP performances, we isolated two strains, Pseudomonas aeruginosa and Diaphorobacter nitroreducens, by following an application oriented selection procedure. Upon performance optimization, in 2 days, D. nitroreducens and P. aeruginosa precipitated 14.1 and 18.9 g CaCO3/g NO3-N, respectively. Repetitive CaCO3 precipitation was also achieved from a single inoculum in both 2 days and 3 weeks intervals. Selected strains and the process were further evaluated for three MICP applications: (1) Ca2+ removal from paper mill wastewater (2) soil reinforcement, (3) crack repair in concrete. Overall, denitrification was found to be an effective process to remove Ca2+ from paper mill wastewater. P. aeruginosa and D. nitroreducens could be introduced as potential candidates for soil and concrete applications due to their enhanced precipitation yields, resilience and performance under minimal nutrient conditions.

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