Coupled multiphysical model for investigation of influence factors in the application of microbially induced calcite precipitation

The study presents a comprehensive coupled thermo-bio-chemo-hydraulic(T-BCH)modeling framework for stabilizing soils using microbially induced calcite precipitation(MICP).The numerical model considers relevant multiphysics involved in MICP,such as bacterial ureolytic activities,biochemical reactions,multiphase and multicomponent transport,and alteration of the porosity and permeability.The model incorporates multiphysical coupling effects through well-established constitutive relations that connect parameters and variables from different physical fields.It was implemented in the open-source finite element code OpenGeoSys(OGS),and a semi-staggered solution strategy was designed to solve the couplings,allowing for flexible model settings.Therefore,the developed model can be easily adapted to simulate MICP applications in different scenarios.The numerical model was employed to analyze the effect of various factors,including temperature,injection strategies,and application scales.Besides,a TBCH modeling study was conducted on the laboratory-scale domain to analyze the effects of temperature on urease activity and precipitated calcium carbonate.To understand the scale dependency of MICP treatment,a large-scale heterogeneous domain was subjected to variable biochemical injection strategies.The simulations conducted at the field-scale guided the selection of an injection strategy to achieve the desired type and amount of precipitation.Additionally,the study emphasized the potential of numerical models as reliable tools for optimizing future developments in field-scale MICP treatment.The present study demonstrates the potential of this numerical framework for designing and optimizing the MICP applications in laboratory-,prototype-,and field-scale scenarios.

A comparative study of using two numerical strategies to simulate the biochemical processes in microbially induced calcite precipitation

In this study,we carried out a comparative study of two different numerical strategies for the modeling of the biogeochemical processes in microbially induced calcite precipitation(MICP)process.A simplified MICP model was used,which is based on the mass transport theory.Two numerical strategies,namely the operator splitting(OS)and the global implicit(GI)strategies,were adopted to solve the coupled reactive mass transport problems.These two strategies were compared in the aspects of numerical accuracy,convergence property and computational efficiency by solving the presented MICP model.To look more into the details of the model,sensitivity analysis of some important modeling parameters was also carried out in this paper.

The Reduction of the Permeability of a Lateritic Soil through the Application of Microbially Induced Calcite Precipitation

Lateritic soils are frequently utilised in tropical areas of the developing world as an engineering material in the construction of rural earth roads, usually in the form of engineered natural surface (ENS) roads. The heavy, seasonal rainfalls common to the tropics results in ENS roads becoming quickly saturated with rainwater, and no longer accessible to motorised transportation. Microbially induced calcite precipitation (MICP) has been successfully used as a treatment process to decrease the permeability of clean, cohesionless sands by studies trying to impede the movement of groundwater, and any pollutants they may contain. In order to see if MICP treatment can also reduce the susceptibility of ENS road lateritic soils to rainwater saturation, this study has treated a Brazilian sample extracted from an ENS road in Espirito do Santo, Brazil, using the MICP bacterium Sporosarcina pasteurii contained within a urea-calcium chloride solution inoculum. Investigation, by means of a Rowe cell, of the post-treatment permeability, to untreated control samples, has shown an average decrease in the vertical coefficient of permeability of 83%, from 1.15 × 10-7 m/s for the untreated control samples, to 1.92 × 10-8 m/s in treated samples.

Physical-mechanical properties of microbially induced calcite precipitation-treated loess and treatment mechanism

Loess disintegration can lead to geotechnical engineering problems,e.g.,slope erosion,wetting-induced landslide,and hydroconsolidation.Microbially induced calcite precipitation(MICP)technique is a potential loess reinforcing method.This study investigated the physical-mechanical properties of MICP-treated loess and then explored the mechanism of loess modification by MICP.Here,loess first underwent MICP treatment,i.e.,mixing loess with Sporosarcina pasteurii and cementation solution(CS).Then,the effects of the CS concentration(0.2,0.6,0.8,and 1 M)on the physical and mechanical properties of the MICP-treated loess were tested.Finally,the static contact angle test,scanning electron microscopy(SEM),and X-ray diffractometry(XRD)were conducted to study the mechanism of MICP treatment on loess.Results showed the following property changes of loess after MICP treatment:the liquid limit decreased by 1.7%,the average particle size increased from 6 to 47μm,the specific gravity decreased from 2.65 to 2.43,the unconfined compressive strength increased from 37 to 71 k Pa,and the disintegration time increased from 10 to 25 min.Besides,the shear strength also increased,and the shear strength parameters(cohesion c and internal friction angle?)varied with the CS concentration.The static contact angle tests indicated that the water absorption ability of loess was reduced after MICP treatment.SEM and XRD results verified that the CaCO_(3)from MICP was attributed to the above results.The above findings explained the mechanism of MICP treatment of loess:the CaCO_(3)coats and cements the particles,and fills the pores of loess,improving the strength and water stability of loess.

MICP增强改性煤矸石在水稳材料中应用的试验研究

为解决煤矸石集料强度低、吸水率高、易崩解等问题,采用微生物诱导碳酸盐沉积(MICP)技术对煤矸石进行了增强改性。通过表观密度、吸水率、压碎值和超声波质量损失率的测试,同时结合SEM,EDS和XRD微观表征,研究了微生物矿化时间、菌液浓度和煤矸石粒径对MICP增强改性煤矸石性能的影响,并揭示了MICP增改性煤矸石的机理。将MICP增强改性煤矸石应用于水稳材料,通过无侧限抗压强度、间接抗拉强度和抗压回弹模量的测试,对比了MICP增强改性煤矸石水稳材料与普通煤矸石水稳材料的性能。结果表明:采用MICP增强改性技术可以提升煤矸石的物理力学性能,并且煤矸石的粒径越大增强改性效果越明显;在菌液OD600值(溶液在600 nm波长处的吸光值)为0.8、矿化改性7 d的条件下,MICP增强改性煤矸石比普通煤矸石的表观密度增加了14.66%,吸水率降低了40.94%,压碎值降低了7.93%;经MICP增强改性后的煤矸石表面包裹的生物CaCO_(3)方解石使得煤矸石的表观密度增加,吸水率和压碎值降低,强度提高,从而提升了煤矸石的性能;水泥稳定MICP增强改性煤矸石混合料最佳含水量比普通煤矸石水稳材料降低了17.3%,最大干密度增加了7.9%;MICP增强改性煤矸石水稳材料各龄期的无侧限抗压强度、间接抗拉强度和抗压回弹模量比普通煤矸石水稳材料均显著提升,表现出更高的强度、更好的抗裂性能和抗变形能力。

MICP加固花岗岩残积土的渗透特性

MICP技术可以显著降低固化土壤的渗透系数,然而目前没有关于MICP固化土壤渗透系数的理论计算方法。基于理论推导和试验验证的方法,研究MICP加固花岗岩残积土的渗透特性,提出MICP加固花岗岩残积土的碳酸钙生成量和渗透系数理论表达式。假设MICP的反应速率线性衰减,通过酶促反应动力学方程得到MICP加固土体的CaCO3生成量,估算CaCO3晶体的粒径和个数,从而获得加固后试样的孔隙比、迂曲度和颗粒比表面积,代入修正的Kozeny-Carman方程,得到加固后土体的渗透系数理论表达式。与试验数据对比分析结果表明:CaCO3的产量早期增加快,后期增加变缓并逐渐趋于稳定;MICP加固土体的渗透系数其具有早期降低快,后期趋于平稳的特征。胶结液浓度为0.50、0.75、1.00、1.25 kmol/m3的试样渗透系数最终分别降低了35%、40%、45%和55%。提出的CaCO3含量表达式和渗透系数表达式与试验结果拟合良好,可为微生物加固的设计计算提供参考。

Experimental study on mitigating wind erosion of calcareous desert sand using spray method for microbially induced calcium carbonate precipitation

Wind erosion is one of the significant natural calamities worldwide, which degrades around one-third of global land. The eroded and suspended soil particles in the environment may cause health hazards, i.e.allergies and respiratory diseases, due to the presence of harmful contaminants, bacteria, and pollens.The present study evaluates the feasibility of microbially induced calcium carbonate precipitation(MICP)technique to mitigate wind-induced erosion of calcareous desert sand(Thar desert of Rajasthan province in India). The temperature during biotreatment was kept at 36℃ to stimulate the average temperature of the Thar desert. The spray method was used for bioaugmentation of Sporosarcina(S.) pasteurii and further treatment using chemical solutions. The chemical solution of 0.25 pore volume was sprayed continuously up to 5 d, 10 d, 15 d, and 20 d, using two different concentration ratios of urea and calcium chloride dihydrate viz 2:1 and 1:1. The biotreated samples were subjected to erosion testing(in the wind tunnel) at different wind speeds of 10 m/s, 20 m/s, and 30 m/s. The unconfined compressive strength of the biocemented crust was measured using a pocket penetrometer. The variation in calcite precipitation and microstructure(including the presence of crystalline minerals) of untreated as well as biotreated sand samples were determined through calcimeter, scanning electron microscope(SEM), and energydispersive X-ray spectroscope(EDX). The results demonstrated that the erosion of untreated sand increases with an increase in wind speeds. When compared to untreated sand, a lower erosion was observed in all biocemented sand samples, irrespective of treatment condition and wind speed. It was observed that the sample treated with 1:1 cementation solution for up to 5 d, was found to effectively resist erosion at a wind speed of 10 m/s. Moreover, a significant erosion resistance was ascertained in15 d and 20 d treated samples at higher wind speeds. The calcite content percentage, thickness of crust,bulk density, and surface strength of biocemented sand were enhanced with the increase in treatment duration. The 1:1 concentration ratio of cementation solution was found effective in improving crust thickness and surface strength as compared to 2:1 concentration ratio of cementation solution. The calcite crystals formation was observed in SEM analysis and calcium peaks were observed in EDX analysis for biotreated sand.

基于高密度电阻率成像技术的MICP浆液入渗过程监测研究

微生物诱导碳酸钙沉淀(MICP)技术是一种生态环保、前景广阔的土体改性方法,其改性效果与浆液的入渗特征密切相关。为此,提出将高密度电阻率成像(ERT)技术用于MICP浆液入渗过程监测。文章通过开展模型试验,对石英砂试样进行混合一步注浆法MICP处理,同时对试样持续进行ERT监测及电导率分析,获取了试样的三维电阻率变化特征,处理完成后测定了试样中碳酸钙含量的空间分布。结果表明:(1)MICP反应过程中,砂土与注浆液电导率随尿素分解而逐渐升高;(2)注浆液的迁移分布对砂土内部低电阻区的分布规律起主导作用,而碳酸钙沉淀的影响较小;(3)在MICP处理过程中,碳酸钙沉淀的生成与注浆液的迁移渗透相互作用,共同影响改性效果;(4)ERT技术可有效监测MICP处理区电阻率的时空演化特征,准确反映注浆液渗透迁移情况,进而评价改性效果。研究结果表明,采用ERT技术监测MICP改性土体过程具有可行性,为评价和优化微生物矿化改性效果提供了新的技术思路和方向。

Application of microbially induced carbonate precipitation to form biocemented artificial sandstone

It is difficult to collect and characterise well-preserved samples of weakly-cemented granular rocks as conventional sampling techniques often result in destruction of the cementation.An alternative approach is to prepare synthetic geomaterials to match required specifications.This paper introduces microbially induced carbonate precipitation(MICP)as a method to reliably deliver artificiallycemented specimens with customised properties,closely resembling those of soft carbonate sandstones.The specimens are generated from materials with two highly different particle size distributions(PSDs)to access a range of achievable combinations of strengths and porosities.The MICP parameters are kept constant across all samples to obtain similar calcium carbonate characteristics(size of individual crystals,type,etc.),while injected volume is varied to achieve different cementation levels.Although uniform cementation of very coarse sands has been considered very difficult to achieve,the results show that both the fine and coarse sand specimens present high degrees of uniformity and a good degree of repeatability.The unconfined compressive strengths(UCSs)(less than 3000 kPa)and porosities(0.25e0.4)of the artificial specimens fall in the same range of values reported for natural rocks.The strength gainwas greater in the fine sand than that in the coarse sand,as the void size in the latter was significantly larger compared to the calcium carbonate crystals’size,resulting in precipitation on less effective locations,away from contacts between particles.The strengths and porosities obtained for the two sands in this work fall within ranges reported in the literature for natural soft rocks,demonstrating theMICP technique is able to achieve realistic properties and may be used to produce a full range of properties by varying the grain sizes,and possibly the width of PSD.

冻融循环作用下MICP固化铅污染土的强度与浸出特性研究

微生物诱导碳酸钙沉淀(MICP)技术可用于重金属污染土固化稳定修复。本文通过开展无侧限抗压强度、离子浸出及微观试验,主要研究MICP固化铅污染土在冻融循环作用下的强度与化学稳定性,并揭示其微观作用机理。结果表明:随着铅离子浓度的增加,土体的无侧限抗压强度先增大后减小,铅离子浸出浓度增大;随冻融循环次数的增加,土体的强度逐渐降低并趋于稳定,铅离子浸出浓度增大。冻融循环作用后,固化土的主要矿物成分未发生变化;土中的小孔隙数量增加,大孔隙数量基本保持不变。冻融循环作用损伤固化土的碳酸钙胶结与铅离子沉淀结构,致使土体性能劣化。

MICP技术在地下水封油库渗控注浆中的应用潜力

地下水封油库在建设及运营过程中洞室涌水量大小是影响洞库水封安全和运营成本的重要因素。目前地下水封油库工程建设中采用传统的注浆方式难以将围岩渗透性降低到设计要求,因此洞室涌水量得不到很好的控制。微生物诱导碳酸钙沉淀(MICP)技术具有注浆黏度低、环境适应性强、生成矿化物质稳定等显著优点,引起了学术界与工程界广泛的兴趣和研究。本文首先分析了地下水封油库涌水量控制中存在的相关问题,然后阐述了MICP技术对裂隙渗流控制的机理、影响因素以及对裂隙渗透性的影响效果,最后探讨了MICP技术在地下水封油库中应用的关键问题。通过分析表明,MICP作为地下水封油库渗流控制的一种辅助注浆方式,可以较为准确地控制围岩渗透性变化,达到对洞室涌水量有效控制的目的。

椰壳纤维-MICP复合改良膨胀土膨胀特性研究

采用椰壳纤维联合微生物诱导碳酸钙沉积(MICP)技术对南水北调中线工程南阳段的膨胀土进行试验改良,对素土、纤维土、MICP土以及椰壳纤维-MICP复合改良土开展无荷膨胀率试验和有荷膨胀率试验,研究改良前后膨胀土无荷膨胀率、有荷膨胀率随纤维掺量的变化规律,并对比分析单一改良方式和复合改良方式下纤维掺量对膨胀土膨胀特性的影响,最后通过电镜扫描试验,观察土样微观结构,揭示纤维-MICP复合改良膨胀土特性的内在机理。结果表明:单掺椰壳纤维和MICP技术改良均可抑制膨胀土的膨胀性能,而椰壳纤维-MICP复合改良土的改良效果最明显,且随着纤维掺量的增加,纤维土和复合改良土的无荷膨胀率和有荷膨胀率呈现出先减后增的趋势,纤维最佳掺量为0.5%,电镜扫描试验显示椰壳纤维可发挥桥联的作用以增强MICP膨胀土的改良效果。

天然海水环境下离子浓度对MICP反应的影响

微生物岩土技术通过生物矿化过程改善基础材料的力学性质,使其更适用于建筑或解决多学科领域的环境问题。微生物矿化过程中产生的碳酸钙是改善基础材料力学性质的主要成分,但其生成量及形态等受多种因素的影响。通过离子计、pH计、SEM、EDS和XRD等手段探究天然海水和去离子水环境在矿化过程中氯化钙和尿素浓度、比例及菌液和胶结液(氯化钙、尿素)体积比等因素对沉淀物质形貌及晶体组成的影响。结果表明:钙离子和尿素浓度及比例低时,碳酸钙的产率较高,但当初始钙离子、尿素浓度超过1.0 mol/L时,离子浓度增大对细菌产脲酶有抑制作用,浓度越高对脲酶的抑制作用越明显,沉淀物产率也随之减小,海水环境总体沉淀量与沉淀效率均高于去离子水环境。菌胶结液体积比去离子水中为1∶4、海水中不高于1∶10时,碳酸钙生成量较高,去离子水环境晶型以方解石为主,海水环境晶型以球霰石为主且沉淀中含有镁盐。

采煤地裂缝MICP修复规律及影响因素实验研究

西北黄土覆盖区采煤地裂缝造成浅表水资源漏失和土体失稳,为此开展黄土覆盖区采煤地裂缝微生物诱导碳酸钙(CaCO_(3))沉淀(Microbial Induced Carbonate Precipitation,MICP)修复实验研究。以陕北柠条塔煤矿为研究背景,对采煤地裂缝特征进行观测,揭示采煤地裂缝发育特征。结合矿山压力观测,划分黄土采煤地裂缝类型。基于采煤地裂缝分类和特征,采用无侧限抗压实验、三轴抗压实验、变水头渗透实验及三轴渗透实验,对比测试了两类裂缝黄土MICP修复样品的力学和水理参数。基于修复体pH、MICP CaCO_(3)产量和扫描电镜测试结果,剖析采煤地裂缝MICP修复影响因素。结果表明:黄土覆盖区采煤地裂缝可分为边界地裂缝和内部地裂缝2种类型。边界地裂缝条件下,菌液和胶结液的最佳比例为1.2∶1.0。内部地裂缝条件下,裂缝充填物中风积沙与黄土的最佳比例为1∶1,菌液和胶结液的最佳比例为1∶1。黄土覆盖区不同类型采煤地裂缝的开度差异,造成CaCO_(3)产率相差31.2%,因此,边界地裂缝较内部地裂缝最佳MICP修复液中胶结液成分所占比例更大。裂缝充填物中风积沙与黄土为1∶1时,充填物与修复液混合体的pH为9.2。该pH环境CaCO_(3)产率可达88%,促进了MICP高效运行。研究成果为黄土覆盖区采煤地裂缝修复提供了参考。

采用MICP加固不同掺砂比例粉土的试验研究

针对微生物诱导碳酸钙沉积(MICP)处理对象多为单一级配土体的现状,开展颗粒级配对MICP加固效果影响的试验研究.通过在粉土中掺入不同比例的标准砂来配置5种不同级配的土样.选用巴氏芽孢杆菌作为微生物,尿素和氯化钙作为胶结液来进行MICP处理.由于制样的密实程度会影响加固效果,将每种级配试样的干密度控制为5个水平.通过试验研究掺砂比例、密实水平等对加固效果的影响.结果表明:试样经过MICP处理得到了整体加固,在粉土中掺入一定比例砂土有助于提高水稳定性.掺砂比例和密实水平对CaCO_(3)生成量和无侧限抗压强度都有影响.在粉土中掺入适量的砂土颗粒有利于提高加固强度;但当砂土掺量过高时,对加固效果有不利影响.增加制样干密度在一定程度上有助于获得更高的强度,但加固强度并不完全取决于初始干密度或孔隙比.

MICP加固粉土的渗透特性及微观机理

针对黄河冲积平原地区的粉土颗粒均匀、黏聚力低、水稳性差,雨季时易出现水害,然而现有加固方法环保性不足的问题,利用绿色环保的微生物诱导碳酸钙沉淀(Microbially Induced Calcite Precipitation,MICP)技术进行加固.首先,选用巴氏芽孢杆菌作为微生物,通过多轮注浆制得MICP加固土样.然后,采用三轴渗透试验研究其渗透特性.最后,结合其内部碳酸钙含量测定、电镜扫描结果揭示微观机理.研究结果表明:MICP加固可使粉土渗透系数降低96%;渗透系数和其内部平均碳酸钙产量之间呈线性关系,且渗透系数随胶结液浓度和加固轮数的增加而降低,但趋势逐渐变缓.MICP反应在粉土中产生的碳酸钙晶体为菱形聚合物,且主要分布在粉土颗粒表面、土颗粒间孔隙及孔喉处,起到覆膜、粘连和封堵作用,进而降低渗透系数.相关研究成果可为MICP技术在改良加固粉土中的应用提供理论支持和技术参考.

胶结液浓度对MICP固化残积土力学性能影响及机理研究

为分析微生物诱导碳酸钙沉淀(MICP)技术对加固花岗岩残积土的适宜性,以及胶结液浓度对固化效果的影响,通过开展无侧限压缩和三轴剪切试验,对5组不同胶结液浓度的固化土试样进行力学测试,并基于扫描电镜图像和X射线衍射图谱分析MICP固化机理。试验结果表明:当胶结液浓度为2 mol/L时,固化土的无侧限抗压强度和弹性模量分别提高47.15%和82.08%,残积土的破坏模式从局部压裂破坏转变为整体剪切破坏;MICP固化残积土的抗剪强度随胶结液浓度增加得到较大程度提升,在2 mol/L胶结液作用下,黏聚力和内摩擦角增幅分别为127.62%和36.50%;碳酸钙晶体主要分布在土颗粒表面、孔隙以及接触点上,在土体内部分别发挥着包裹、填充和胶结作用;细菌与胶结液反应生成的碳酸钙沉淀主要以方解石晶体的形式存在。研究成果可为花岗岩残积土的改性提供参考,拓宽了MICP在非均质土中的应用范围。

椰壳纤维-MICP复合改良膨胀土强度特性

采用椰壳纤维联合微生物诱导碳酸钙沉积(MICP)技术对南水北调中线工程南阳段的膨胀土进行试验改良,开展无侧限抗压强度试验,对比分析素土、纤维土、MICP土以及复合改良土的应力应变特征曲线和破坏形态,并利用响应面法试验研究了椰壳纤维掺量、处理液掺量和胶结液浓度对改良膨胀土无侧限抗压强度的影响,得其最优配比。结果表明:单掺纤维和MICP技术改良均可提升膨胀土的无侧限抗压强度,而复合改良土强度提升最明显,纤维最佳掺量为0.5%;在轴向压力作用下,素土破坏形态表现为“脆性破坏”,MICP土表现为“完全脆性破坏”,纤维土表现为“塑性破坏”,复合改良土表现为“弹塑性破坏”;经统计软件方差分析,对复合改良土强度影响最主要因素是胶结液浓度,其次为处理液掺量、纤维掺量。

MICP加固钙质砂的耐久性试验研究

南海岛礁建设中,钙质砂是易于获取的原材料,但也存在孔隙多、易破碎等不足。为保证岛礁建设的安全稳定,设计经微生物诱导碳酸钙沉积(MICP)加固后钙质砂试样在海水、纯水环境下分别进行浸泡与干湿循环试验,以探究不同环境与处理方式对MICP加固钙质砂样耐久性能的影响。结果表明:(1)经MICP加固的钙质砂具有较好的抗侵蚀能力,通过增加钙质砂的加固轮次能够有效地提高试样的耐久性能,其在海水中干湿循环时劣化最快,在纯水中浸泡时劣化最慢;(2)持续浸泡与干湿循环均会对试样耐久性造成不利影响,干湿循环的劣化作用更大;(3)控制其余变量不变时,海水环境下试样耐久性能的劣化比纯水环境下更严重。

Biochar-bacteria partnership based on microbially induced calcite precipitation improves Cd immobilization and soil function

Microbially induced calcite precipitation(MICP)technique utilizes ureolytic bacteria to decompose urea and generate carbonate ions for metal combination.MICP can remediate heavy metal(e.g.,Cd)contaminated soils while maintaining or even improving soil functions,but its efficiency in agricultural soil practical application still needs to be enhanced.Here,we constructed a biochar-bacteria(2B)partnership in which biochar provides high nutrition and diverse sorption sites.Using the 2B system,Cd immobilization effectiveness and the underlying mechanism were examined along with the soil properties and soil functions.Results showed that compared to the single biochar and ureolytic bacteria systems,soil Cd mobility was reduced by 23.6%and 45.8%through co-precipitating with CaCO_(3) as otavite(CdCO_(3))in the 2B system,whereas soil fertility,bacterial diversity,and richness increased by 11.7-90.2%,5.4-16.1%,and 6.8-54.7%,respectively.Moreover,the abundances of Proteobacteria and Firmicutes were enhanced in the 2B system.Notably,Sporosarcina and Bacillus(Firmicutes genus)that carry the ureC gene were boosted in the system,further implicating the microbiological mechanism in reducing Cd migration and its bioavailability in soil.Overall,the constructed 2B system was efficient in soil Cd immobilization by strengthening the ureolytic bacteria growth and their nutrient supply in the bacteria-rich soil ecosystem.