Cementation Of Sandy Soil By Shallow Mineralization Of Microbe Capturing Carbon Dioxide And Application In Fugitive Dust Suppresion

Fugitive dust is one of the most important factors causing air pollution,and the researchers at home and abroad have carried out a great deal of research work on its prevention and trement technologies.A variety of inorganic,organic and composite dust suppressants have been developed,which generally have a series of drawbacks such as single function,high price,even toxicity,corrosion,difficult degradation and secondary pollution.Microbe cement is a new type of cementitious materials based on microbe induced mineralization to form inorganic minerals to cement loose particles.It has many advantages such as efficient preparation process,easy control and environmental friendliness,which is expected to be used in fugitive dust control,desert treatment,foundation reinforcement,slope stability,and so on.At present,urinary enzyme microbe cement has been investigated widely,but ammonia will be released during the cementing process,which has a negative impact on the ecological environment.In this paper,the microbe,capturing carbon dioxide from the air as a carbon source and depositing carbonate minerals,is screened and cultivated.A new type of microbe cement for fugitive dust suppression,which is more ecological and suitable for shallow cementation,has been developed.In this paper,the technical route of cementation of sandy soil by shallow mineralization of microbe capturing carbon dioxide in fugitive dust suppression was innovatively proposed.Around the two key problems of formulation optimization and application method of microbe cement,mineralization mechanism of microbe capturing carbon dioxide in simulated pore solution of sandy soil and cementation mechanism of microbe shallow mineralization in sandy soil were thoroughly studied.The formula of microbe cement for fugitive dust suppression was optimized.The characterization methods and influence factors of shallow cementation of sandy soil by microbe capturing carbon dioxide were systematically studied,and the application method of microbe cement was refined.In view of the poor cementation effect in low temperature environment,low temperature resistant microbe was selected.Microbe cement suitable for low temperature was prepared,and the cementation effect was demonstrated.Finally,combined with three soil samples in three practical construction sites,the fugitive dust suppression effect and ecological compatibility of microbe cement were verified.The main research contents and conclusions of this paper include the following four aspects:?1?Revelation of mineralization mechanism of microbe capturing carbon dioxide in simulated pore solution of sandy soilThe spore germination ratio was improved by heat shock,germination agents and nutrients.Test results showed that the best temperature was 70?and the best time was 10 min for heat shock,then the best germination agent was alanine and its concentration was 6 mmol/L.Furthermore,nutrients had no obvious effects on improving spore germination ratio.From carbon source,nitrogen source,inorganic salt and growth factors which needed for microbe growth,the growth and reproduction efficiency of vegetative cells was improved,and the OD₄₀₀ value of microbe solution was increased from 0.43 to 0.83,which increased by about 93.0%.The enzyme protein expression was identified by electrophoretic and gel imaging system,and it was clear that the main enzyme protein in microbe solution was carbonic anhydrase.The effects of simulated solution,microbe culture solution and secretion solution on the ions formation rate in the mineralization process were compared and analyzed.The results showed that the carbonic anhydrase promoted the ions formation,and the bacterial bodies accelerated the deposition of mineralization products as nucleating sites.By means of X ray diffraction?XRD?,energy spectrum?EDS?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?analysis,it was concluded that the mineralization product was near-spherical calcite.Based on the characteristics of microbe growth and the formation process of mineralization product,mechanism model of microbe mineralization was established.?2?Explanation of shallow cementation mechanism of sandy soil by microbe capturing carbon dioxideThe microstructure between mineralization products and loose sandy soil particles was analyzed by SEM and TEM,and the difference of cementing effect between different methods was clarified.The feasibility of shallow cementation of sandy soil by microbe capturing carbon dioxide was demonstrated.Analysis of interaction between mineralization products and loose sandy soil particles by fourier transform infrared spectroscopy?FTIR?,thermogravimetric-differential scanning calorimetry?TG/DSC?and nuclear magnetic resonance?NMR?,the essential reason for microbe cement cemnting loose sandy soil particles was the formation of intermolecular hydrogen bonds.The formula of microbe cement was optimized by comparing the effect of microbe and calcium source on cementation properties.?3?Determination of the characterization methods and influence factors of shallow cementation of sandy soil by microbe capturing carbon dioxideBy studying the influence of cementing process,pH value,temperature and soil types on cementing effect,the pressureless spraying process could obtain higher cementing strength and more dense structure,which was easier to operate;The suitable pH environment of microbe cement was neutral and weak alkaline;With the increase of ambient temperature,the cementing effect was obviously improved,and the cementing effect in the low temperature environment was the worst.Under the same amount of microbe cement,the effect was the best cementing clay soil,followed by silt soil and sandy soil was the worst.According to the analysis of composition,calcite content,surface hardness and microstructure of cementing body at different depth,the calcite was present from the surface to the deep layer,calcite content and section hardness decreased gradually,and micro pores and defects of cross section increased gradually.The three-dimensional structure of cementing body and the pore distribution in the two-dimensional section were studied by X-ray computed tomography?X-CT?.With the increase of the amount of microbe cement,the pore number and pore size of cementing body decreased gradually,and cementing effect increased gradually.In the case of spraying different dosage of microbe cement,the pore number and pore size of cementing body at the surface were the lowest,showing the best cementation effect.The engineering properties of cementing soil were studied in terms of liquid limit,plastic limit,plasticity index,permeability coefficient,consolidation compression and direct shear,and it was concluded that microbe cement had no effect on engineering performance of soil.In view of the poor cementation effect in low temperature environment,low temperature resistant microbe was selected.Microbe cement suitable for low temperature was developed,and the cementation effect was demonstrated.?4?Demonstration of the fugitive dust suppression effect of microbe cement in field applicationAccording to different types of soil,the corresponding engineerings were selected for field application respectively.The field application results indicated that three types of soil could be cemented into cementing body,which were good at wind erosion resistance,rain resistance,moisture retention,aging resistance,freeze-thaw resistance,and ecological compatibility.When dealing with different types of soil,the amount of microbe cement should be adjusted appropriately.The amount of microbe cement could be increased when ccementing sandy soil,but it should be reduced when cementing clay soil.Compared with traditional method of fugitive dust suppression,microbe cement had superior economy and ecology.