Systematic optimization of a novel, cost-effective fermentation medium of Sporosarcina pasteurii for microbially induced calcite precipitation (MICP)

Abstract

• The fermentation medium and conditions of Sporosarcina pasteurii are optimised. • A cheap nitrogen source, corn-steep liquor, replaces soybean peptone in the medium. • The medium cost was reduced by 50.5%, and the urease activity was increased by 24.2%. • The unconfined compressive strength of MICP-treated samples was increased by 21.3%. • XRD diagram shows that calcite was formed in the MICP-treated samples. Microbially induced calcite precipitation (MICP) is a promising technology for sand fixation, ground stabilisation, concrete crack repairment, and contaminated soil remediation. Sporosarcina pasteurii is the most used urease-producing bacterium for MICP applications. This study proposes a novel, cost-effective culture medium for S. pasteurii using corn-steep liquor as a cheaper nitrogen source, partially replacing the soybean peptone, decreasing the medium cost by 50.5 %. The optimal fermentation conditions were determined by single-factor experiments at a temperature of 30℃, an initial pH of 8.0, and an inoculation amount of 0.5 %. The optimal medium composition was determined by orthogonal experiments at 15 g/L soybean peptone, 30 g/L corn-steep liquor, 10 g/L urea, and 3 g/L sodium dihydrogen phosphate. As a carbon source, lactose was found to inhibit urease activity and should not be added. The novel medium increased the urease activity by 24.2 % and enhanced the unconfined compressive strength (UCS) of the MICP-treated sample to 2.39 MPa, which increased by 21.3 %. XRD analysis shows that calcite, the most stable crystal form of calcium carbonate, was formed in the samples. ESEM images show more calcium carbonate generated on the sample surface, and the cementation between sand particles was better. Therefore, this novel, cost-effective medium made the Sporosarcina pasteurii show satisfying MICP performance and alleviated economic concerns about the large-scale application of MICP.