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Low-cost cultivation and sporulation of alkaliphilic Bacillus sp. strain AK13 for self-healing concrete

Journal of Microbiology and Biotechnology 2019년 29권 12호 p.1982 ~ 1992
홍민영 ( Hong Min-Young ) - Korea University Department of Environmental Science and Ecological Engineering

 ( Kim Won-Jae ) - Korea University Department of Environmental Science and Ecological Engineering
박우준 ( Park Woo-Jun ) - Korea University Department of Environmental Science and Ecological Engineering

Abstract


The alkaliphilic, calcium carbonate precipitating Bacillus sp. strain AK13 can be utilized in concrete. Two types of screening experiment were first conducted to identify substrates that promote the growth of the AK13 strain: the first followed a one-factor-at-a-time factorial design and the second a two-level full factorial design. Based on these screening experiments, barley malt powder and mixed grain powder were identified as the substrates that most effectively promoted the growth of the AK13 strain from a range of 21 agricultural products and by-products. A quadratic statistical model was then constructed using a central composite design and the concentration of the two substrates was optimized. The proposed low-cost medium was approximately 45 times more effective than the commercial medium in terms of the number of cultivatable bacteria per unit price. The spores were then powdered via a spray-drying process to produce a spore powder with a spore count of 2.0 ± 0.7 x 109 CFU/g. The yeast extract and calcium lactate generated the highest CFU/ml for AK13 at a 0.4:0.4 ratio compared to 0.4:0.25 (the original ratio of the B4 medium) and 0.4:0.8. Twenty-eight days after the spores were mixed into the mortar, the number of vegetative cells and spores of the AK13 strain had reached 106 CFU/g within the mortar. Cracks in the mortar under 0.29 mm were healed in 14 days. Calcium carbonate precipitation was observed on the crack surface. The mortar containing the spore powder was thus concluded to be effective in terms of healing micro-cracks.

키워드

Economical medium; agricultural products; statistical design of experiments; spray dryer; crack healing material; calcium carbonate precipitation
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