Isolation And Screening Of Carbonate Mineralization Bacteria And Biogrouting Experiments In Sand

High energy consumption and high pollution of traditional rock and soilreinforcement materials have become the focus of attention for the whole world. So,developing low energy consumption and environment-friendly rock and soilreinforcement technologies has an important practical significance. Microbial-inducedcarbonate precipitation (MICP) technology has become a research hotspot in the fieldof geotechnical engineering reinforcement due to the fact that it isenvironment-friendly, green and low energy consumption.In this thesis, isolation and screening of carbonate mineralization bacteria andbiogrouting experiments were carried out. The main achievements are summed asfollows.Five ureolytic strains were isolated from soil using selective enrichment cultureand plate screening techniques. The growth characteristics of the five strains were investigated, and the optimal culture conditions were determined as follows: initial pH9,inoculation volume4％, culture temperature35℃and rotation rate200r/min.The urease activity and the ability of bacterial-induced mineralizationdeposition of the ureolytic strains were tested. Then, a strain which could producehigher urease activity and induce more deposition than other strain was selected. Thedeposition induced by the stain was determined through scanning electron microscopy(SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). And theresults showed that the deposition was calcium carbonate. Furthermore, the strain wasidentified as Sporosarcina pasteurii based on morpHology, Gram stain and16S rDNAsequence analysis. Maximum urease activity of the stain was1.05mmol/(min·OD) inthe mid and late-logarithmic stages, and an appropriate amount of Ni2+couldsignificantly improve the level of the urease activity. More than66%of activity wasincreased at10mg/L concentration of NiCl2. The type and concentration of calcium source affected the ability of theSporosarcina pasteurii to induce calcium deposition. When Ca2+concentration was0.5mol/L using CaCl2and Ca(NO3)2as calcium source, respectively, the amount ofcalcium carbonate induced was maximum within48h. At the same concentration ofCa2+, mixing calcium source provided more calcium carbonate precipitation than thesingle source of calcium.Finally, biogrouting experiments in sand were carried out. After grouting of12cycles, the sand in all columns were consolidated. As a whole, the maximum uniaxialcompressive strength of the sand samples in column was3.2MPa, increasing with theincrease in calcium carbonate content. However, the uniformity of calcium carbonatedeposition in sand had a significant impact on the uniaxial compressive strength.