| In recent years,microbially induced calcium carbonate precipitation(MICP)based on urease activity of ureolytic bacteria have been widely used for bioclogging and biocementation in geotechnical engineering.MICP technology has become a research hotspot in the field of geotechnical engineering reinforcement due to the fact that it is environment-friendly,green and low energy consumption.Among them,ureolytic bacteria with ability of inducing calcium carbonate precipitation are the key of MICP research.Therefore,it is more helpful to the research and application of MICP to select a new type of indigenous urea decomposition bacteria,which has higher urease activity and better environmental adaptability.First of all,we collected 47 different types of soil from different parts of China for isolation and purification,and identified by molecular biology methods.51 strains of the target strains were obtained.The isolates were mainly distributed in 7 genera,among which 2 strains of Acetobacter sp.,8 strains of Arthrobacter sp.,24 strains of Bacillus sp.,7 strains of Lysinibacillus sp.,2 strains of Oceanobacillus sp.,6 strains of Paenibacillus sp.,2 strains of Sporosarcina sp.,Among them,the strain HZ1 T and LZ2 T were identified as a new species of bacteria that could be decomposed by a number of taxonomic studies,named as Paenibacillus ripae and Sporosarcina terrae.Secondly,through the genetic stability of the strain,urease activity,calcium carbonate precipitation induced ability and growth characteristics in the alkaline environment and many other screening comparison found.The strain Sporosarcina sp.LZ3 had the best genetic stability and the highest urease activity,the strongest calcium carbonate precipitation ability and the high activity in the alkaline environment.All aspects were superior to the control strain S.pasteurii ATCC11859 and other strains.In the experiment of calcium carbonate deposition,the XRD,SEM and EDX analysis confirmed that the sediments are stable calcite crystals.Therefore,Sporosarcina sp.LZ3 can be used as an ideal strain for further research.Sporosarcina sp.LZ3 was cultured in YE-NH4 medium for 36 ~ 40 h under the conditions of 6% inoculation,30 ?,pH 9.0,100 ?M Ni2+ and then used to induce the calcium carbonate deposition.Four important influence factors and levels of MICP reaction system were optimized by response surface method: pH 7.0,Ca2+ 0.60 M,urea 0.60 M,bacterial liquid concentration 10.0%(OD600 = 1.0).Finally,under the above conditions,the sand samples were tested with the standard sand and the solidification effect of sand column was evaluated.The results show that: unconfined compressive strength reached 1.79 MPa;In the three axis compression test,the axial stress is 495 KPa and 750 KPa,respectively,when the ambient pressure is 100 KPa and 200 KPa;In the direct shear test,the average shear stress is 496.6 KPa,which is about 100 times of the wet sand control.After XRD,SEM and EDX analysis confirmed that the calcium carbonate and covered with sand around all the stable calcite crystals.The results show that the cured sand column has some engineering properties and has the potential of further application.To sum up,in this paper,the isolation and identification of ureolytic bacteria Sporosarcina sp.LZ3 has a strong urease activity,the ability to induce calcium carbonate precipitation,can be better tolerated alkaline environment.MICP optimizing reaction system which induces the precipitation of calcium carbonate can be successfully cured of loose sand into a sand column overall with a certain strength.The above studies systematically studied the whole MICP system from the aspects of strain selection,bacterial culture,reaction conditions,sand column condensation experiment and curing effect evaluation.It can provide a good theoretical basis and data reference for the later application research,which has potential application value in microbial geotechnical reinforcement and repair. |
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