Regulatory mechanism of humic substances on microbially induced carbonate precipitation

To further apply microbially induced carbonate precipitation (MICP) in the environmental civil engineering, this study explored how the widely present humic substances (HS), typically humic acid (HA) and fulvic acid (FA), tailor the strength and microstructures of the MICP-based bio-cement. The presence of HA was found to reduce the yield of bio-precipitates, lower the strength of the resulting cemented sandstone by 27 %, and reduce the particle sizes and surface smoothness of the precipitates. By further examining the biomineralization in the solution system, a similar inhibitory effect on MICP was confirmed and found to be 50 % more substantial when tailored by FA (which possesses more densely distributed functional groups) than HA. Furthermore, HS was found to reduce the crystal sizes by chelating with calcium ions and serving as nucleation sites, and prolonged the existence of the unstable bacteriogenic vaterite by serving as a crystal stabilizer.