Recently, the ability of microbial-induced calcium carbonate precipitation (MICP) to remediate heavy metals has been widely explored. Sporosarcina pasteurii was selected to remediate heavy metal-contaminated solution and aged refuse, exploring the feasibility of Sporosarcina pasteurii bioremediation of heavy metals and analyzing the changes in heavy metal forms before and after bioremediation, as well as the mechanism of remediation. The results showed that Sporosarcina pasteurii achieved remediation rates of 95%, 84%, 97%, and 98% for Cd, Pb, Zn, and Cr (III) in contaminated solution, respectively. It also achieved remediation rates of 74%, 84%, and 62% for exchangeable Cd, Pb, and Zn in aged refuse, respectively. The content of exchangeable Cr (III) before bioremediation was almost zero. The content of heavy metals with exchangeable form and carbonate-bounded form in aged refuse decreased after bioremediation, while the content of heavy metals with iron–manganese oxide binding form and residual form increased. Simultaneously, the presence of Fe and Al components in aged refuse, as well as the precipitation of calcium carbonate produced during the MICP process, jointly promotes the transformation of heavy metals into more stable forms.

Cohesive soil in the reservoir area is vulnerable to natural disasters because of its poor erosion resistance and low strength. Therefore, it needs to be reinforced. Microbially induced calcium carbonate precipitation (MICP) is a sustaibable soil reinforcement technique with low energy consumption and no pollution. Different combinations of Bacillus subtilis bacterial solution (BS) concentrations and cementing solution (CS) concentrations were set to perform MICP solidification treatment. The characterization of cohesive soil before MICP was carried out by means of Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), and Laser Particle Size Analyzer (LPSA). The results showed that the unreinforced soil showed an amorphous state with low strength and the particle size distribution was dominated by powder particles. However, with the addition of BS concentrations and CS concentrations, SEM results showed that spherical and rhombohedral minerals filled the pores of the cohesive soil, which increased the content of precipitations and enhanced the cementitious characteristics. When the concentrations of CS or BS were fixed, CaCO₃ content, deviatoric stress, shear strength, cohesive force, and internal friction angle all showed a trend of first increasing and then decreasing with the increase in CS or BS concentration. The optimal combination of CS and BS concentration was 1.5 mol/L and OD₆₀₀ = 1.8. Thermochemical analyses showed an improved thermal stability of the reinforcing cohesive soil, with the lowest mass loss (32%) and the highest pyrolysis temperature (812 °C) of the samples at the optimal combination of BS and CS concentration. This study is expected to improve the understanding of the MICP reinforcement process and contribute to the optimal design of future biologically mediated soil amendments, promoting bioremediation.

The mechanism of dolomite has been a major hotspot in geological research. However, most of the current studies mainly focus on single microorganisms and fail to fully consider the influence of marine microbial diversity on the precipitation of carbonate rock minerals. In this paper, two marine microorganisms (Bacillus sp. and Virgibacilus oceani), which can induce dolomite precipitation, were selected to induce dolomite precipitation in a culture solution that simulated the Mg²⁺/Ca²⁺ of modern oceans. Four systems were set up in this experiment, including the Bacillus sp. system, the Virgibacilus oceani system, the co-precipitation system (Bacillus sp. and Virgibacilus oceani), and the control system. The synergistic promotion of the dolomite was analyzed by comparing the changes in solution pH, ion consumption, morphology, mineralogical phase, and thermal stability in each experimental group. The experimental results show that the increase in pH value and the consumption of Mg²⁺ and Ca²⁺ in the coexistence of Bacillus sp. and Virgibacilus oceani are greater than those in the single microorganism system. The minerals induced by Bacillus sp. and Virgibacilus oceani were mostly small calcium carbonate particles and a small amount of proto-dolomite. However, the faster precipitation rates, larger particle diameters, higher proportion of proto-dolomite, and higher thermal stability of the calcium carbonate and proto-dolomite induced by the two microorganisms suggest that biomineralization facilitates the formation of stable dolomite and accelerates the precipitation of Mg²⁺ and Ca²⁺ for bioremediation purposes.

This study was conducted to determine the optimal mineralization enhancement period for recycled aggregates, and to elucidate the mechanisms underlying the mineralization enhancement of recycled aggregates and the self-healing of concrete cracks. Microbial-induced calcium carbonate precipitation enables the self-healing of concrete cracks: microbial carriers can effectively increase the survival rate of microorganisms within the concrete matrix, thereby enhancing the self-healing performance of the concrete. However, current carriers suffer from poor mechanical properties, poor compatibility with cement-based materials, and high costs. This study proposed a crack-self-healing concrete based on a mixed culture of microorganisms immobilized in recycled aggregate, and investigated the effects of the time of recycled aggregate incorporation on the concrete’s compressive strength and self-healing performance. The results showed that the optimal adsorption and incubation times for the recycled aggregates were 15 min and 9 days, respectively. Following mineralization and reinforcement, the water absorption and crushing index of the recycled aggregates was 11.4% and 20.4%, respectively. Moreover, the precipitates at the concrete cracks were in the form of regular cubes and clusters, and the crystals were calcite and aragonite. Small amounts of phosphorus were detected, originating from extracellular polymers produced by microbial metabolism, indicating that the organic matrix was involved in the crystal nucleation and growth processes. The compressive strength of the concrete increased by 35%. After repair and curing, the crack healing rate of the concrete reinforced with microorganisms immobilized on the recycled aggregates reached 70%.