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1.
Concentration of cementation solution (CCS) is one of the key factors influencing the cementation effect on soil improvement through the microbially induced carbonate precipitation (MICP) process. To precipitate more calcium carbonate per treatment, a higher CCS is needed. However, the MICP process may be retarded or even terminated with an increase in CCS. This retarding effect can be a major limitation for the MICP-based soil treatment and thus needs to be understood properly. This paper presents a systematic study on the conditions causing retarding and its effect on biocementation. The test results of this study have identified that there is retarding effect of CCS on the MICP process, showing that the calcium conversion efficiency, which represents the amount of calcium that has been converted into calcium carbonate in each treatment, reduces with the increase in CCS, and the concentration of calcium is the control factor. The retarding effect will dominate increasingly when CCS is higher than 1.0 M and the amount of calcium carbonate precipitation will reduce for the given amount and type of bacteria used in this study and become zero with CCS of 2.5 M. For the same calcium carbonate content, the unconfined compressive strength is greater for sand treated using a lower CCS as the contribution to the bonding strength by the calcium carbonate generated under a lower CCS is greater than that under a higher CCS. 相似文献
2.
Enzyme induced carbonate precipitation (EICP) is an emerging soil improvement method using free urease enzyme for urea hydrolysis. This method has advantages over the commonly used microbially induced carbonate precipitation (MICP) process as it does not involve issues related to bio-safety. However, in terms of efficiency of calcium carbonate production, EICP is considered lower than that of MICP. In this paper, a high efficiency EICP method is proposed. The key of this new method is to adopt a one-phase injection of low pH solution strategy. In this so-called one-phase-low-pH method, EICP solution consisting of a mixture of urease solution of pH?=?6.5, urea and calcium chloride is injected into soil. The test results have shown that the one-phase-low-pH method can improve significantly the calcium conversion efficiency and the uniformity of calcium carbonate distribution in the sand samples as compared with the conventional two-phase EICP method. Furthermore, the unconfined compressive strength of sand treated using the one-phase-low-pH method is much higher than that using the two-phase method and the one-phase-low-pH method is also simpler and more efficient as it involves less number of injections. 相似文献
3.
A homogeneous microfluidic chip was used to investigate the pore-scale characteristics during the process of microbially induced calcium carbonate precipitation (MICP). An image-processing scheme was developed to measure the projecting areas of the precipitated calcium carbonate. Calcium carbonate first precipitated on the bacterium side before spreading to the rest of the chip. The distribution of calcium carbonate was more uniform along the length of the microchip than along the width. Raman back-scattering spectroscopy was used to examine the chemical composition of the precipitate, identifying calcite and vaterite as the main mineral phases. Bacterium traces were noted on crystal surfaces in SEM images, suggesting a higher adsorptive capacity for irregular precipitates than well-shaped crystals. 相似文献
4.
文章对近年来基于生物固土技术的防风固沙研究进行了回顾和分析。常用于防风固沙的生物过程包括基于微生物或酶诱导碳酸钙沉积（MICP或EICP）的矿化固土技术,加入黄原胶等生物高聚物作为辅助剂,可获得更好的固土效果。土壤风蚀过程中,除了风力本身,风携带的跃移颗粒对土的撞击,也是侵蚀破坏的重要因素,这在生物固化土风蚀试验中体现明显。生物固化防风固沙的处理过程简单易行,以尿素和钙盐作为处理材料,用细菌或脲酶作为催化诱导媒介,对土体进行单遍喷洒处理即可获得很好的抗风效果。室内抗风试验中,将风蚀速率与临界起动风速两个指标结合是较为合理的评估方法。在室内和现场条件下,表面贯入强度测试可用来快速测定处理效果和抗风性能。目前的现场试验研究表明,生物固化土中植物可以生长,但是极端条件下生长受限。为了将该方法推向实用,需要从多重侵蚀因子作用下的抗风力侵蚀能力、生态恢复能力和现场施工技术等方面进一步研究探索。 相似文献
5.
The carbonate (CO 3 ?2 ) produced by Sporosarcina pasteurii was injected electrokinetically to enhance the mechanical properties of soft clay soils. In this method the Ca 2+ was injected into the anode chamber and moved towards the cathode by electromigration and electroosmotic flow. Then the released CO 3 ?2 from a blend of bacteria and urea was injected into the cathode chamber. The CO 3 ?2 ions were moved from the cathode to the anode under electromigration mechanism. The CaCO 3 was precipitated in the presence of calcium in porous medium of the soil, and consequently increased the shear strength of the soil. The polarity reversal was applied to have a homogeneous distribution of CaCO 3. 相似文献
6.
为了提升微生物诱导碳酸盐沉淀(MICP)技术在海洋环境下对钙质砂的加固效果,在以往研究的基础上,设计进行了人工海水环境下巴氏芽孢杆菌多梯度人工驯化培养试验,并结合MICP固化钙质砂柱的力学试验和微细观结构分析,对巴氏芽孢杆菌的驯化效果进行了综合评价。结果表明:(1)海水环境下五梯度驯化后细菌的菌液浓度可达到淡水环境的97%以上,其与胶结液作用后碳酸盐的生成量较淡水环境下有一定幅度提高;(2)驯化后的巴氏芽孢杆菌具有很好的温度适应能力,在10～30℃温度下均有较好的MICP性能;(3)海水环境下加固的钙质砂柱无论是碳酸盐生成量还是无侧限抗压强度均较未驯化前高,尤其是五梯度驯化后的细菌,驯化后的细菌菌体变小,在海水环境生成的碳酸盐(碳酸钙和碳酸镁)晶体更小,更加致密,能更好地填充钙质砂颗粒的孔隙并胶结相邻的钙质砂颗粒,具有更优异的MICP性能。相关研究思路和方法可为MICP技术在海洋环境钙质砂地基加固方面的研究与应用提供参考。 相似文献
7.
Wind erosion is a serious problem throughout the world which results in soil and environment degradation and air pollution. The main objective of this study was to evaluate feasibility of microbial-induced carbonate precipitation, as a novel soil-strengthening technique, to reduce wind erosion risk of a sandy soil. For this purpose, the erosion of biocemented soil samples was investigated experimentally in a wind tunnel under the condition of wind velocity of 45 km h ?1. The weight loss of treated samples relative to the weight loss of control treatment was 1.29 and 0.16 % for low and high bacterial mix concentrations, respectively, indicating a significant improvement in erosion control in biologically treated samples. The effect of biological treatment on wind erosion control was even superior at the higher velocities. Thereafter, the penetration resistance of the surface layers as a simple index of resistance against wind erosion was measured. Significant improvements in the penetration resistance of the treated soil samples were observed. Although low bacterial mix concentrations did not significantly improve the penetration resistance of the samples, significant improvements in the penetration resistance of the treated soil samples were observed reaching to the highest measured strength (56 kPa) in high bacterial mix concentrations samples. Finally, the morphology of precipitated CaCO 3 crystals using scanning electron microscopy and X-ray powder diffraction analysis showed that the CaCO 3 was mainly precipitated as vaterite crystals forming point-to-point contacts between the sand granules. 相似文献
8.
The enzyme urease drives the hydrolysis of urea leading to the release of ammonium ions and bicarbonate; in the presence of calcium, the rise in pH leads to increased calcium carbonate saturation and the subsequent precipitation of calcite. Although such alkalinizing ureolysis is widespread in nature, most studies have focussed on bacteria (i.e. indigenous communities or urease-active Sporosarcina pasteurii) for calcite precipitation technologies. In this study, urease-active jack bean meal (from the legume Canavalia ensiformis) was used to drive calcite precipitation. The rates of ureolysis ( k urea ), determined from measured NH 4 +, enabled a direct comparison to microbial ureolysis rates reported in literature. It is also demonstrated that a simple single reaction model approach can simulate calcite precipitation very effectively (3–6 % normalised root-mean-square deviation). To investigate the reduction of permeability in porous media, jack bean meal (0.5 g L ?1) and solutions (400 mM urea and CaCl 2) were simultaneously pumped into a borosilicate bead column. One-dimensional magnetic resonance profiling techniques were used, non-invasively, for the first time to quantify the porosity changes following calcite precipitation. In addition, two-dimensional slice selective magnetic resonance images (resolution of ~0.5 × 1.0 mm) revealed that the exact location of calcite deposition was within the first 10 mm of the column. Column sacrifice and acid digestion also confirmed that 91.5 % of calcite was located within the first 14 mm of the column. These results have important implications for the design of future calcite precipitation technologies and present a possible alternative to the well known bacterial approaches. 相似文献
9.
In order to reduce the cost of the microbial-induced carbonate precipitation, mixotrophic growth of Sporosarcina pasteurii was carried out at different yeast extract/sodium acetate concentrations and constant chemical oxygen demand for optimal production of urease enzyme. Optimization of cultivation conditions was also investigated using a 3-level central composite design approach based on the response surface methodology. A good agreement between predicted values of enzyme activity and experimental results was observed ( R 2 value of 0.973). All three chosen independent variables had statistically great effects on the efficiency of urease activity. The maximum activity of 2.98 mM urea min ?1 was achieved at yeast extract concentration of 5 g L ?1, NH 4 concentration of 9.69 g L ?1, and incubation time of 60 h as the optimal conditions. Thereafter, a novel injection procedure as sequencing batch mode injection has been proposed for bacteria and cementation fluid injection at obtained optimal urease activity. After fourth injection of bacteria and cementation fluid, uniform CaCO 3 distribution with unconfined compression strength of 795 kPa was obtained even for poorly graded sand. The presented experimental approach for optimizing urease activity and strength production in porous media can be used to design the treatment protocol for practical engineering applications. 相似文献
10.
崩岗是中国花岗岩地区危害最大的一种土壤侵蚀方式,坡面防护是崩岗侵蚀治理的重要措施。为研究微生物诱导碳酸钙沉淀（MICP）技术在花岗岩崩岗侵蚀区冲刷防护中应用的可行性,以福建省崩岗最为发育的安溪县官桥镇花岗岩土质覆盖层为研究对象,进行降雨条件下微生物治理崩岗的模型试验研究。采用喷洒加固法对崩岗坡面进行处理,然后利用降雨模拟系统冲刷坡面,最后分析了MICP加固技术对泥沙产量及坡面侵蚀深度的影响。结果表明：与未加固边坡相比,MICP固化边坡泥沙产量由未加固的7648.43 g下降至266.61 g,较加固之前降低了96.51%;最大侵蚀深度由未加固的60 mm下降至除个别侵蚀坑外边坡表面基本未发生侵蚀。 相似文献
11.
The deposition of natural dust in an area of 53 ha, situated in the northern Negev desert, is investigated in detail both in the wind tunnel (dust storm simulations over a topographic scale model) and in the field. The wind tunnel results and the field results show a high degree of agreement, indicating that scale-model simulation may be considered an important technique for future loess and desert research. More dust settles on windward slopes than on leeward slopes, which is in contradistinction with the widespread wind shadow concept. Air-flow separation zones immediately downwind of steep windward slopes have an important impact on dust deposition too. In the case of dust deposition on topographic scale models, a restricted height distortion of the model will not necessarily lead to serious problems. In addition, wind tunnel blockage percentages up to 13% may be allowed in order to obtain acceptable dust deposition patterns for the scale model. A mean gross dust deposition of about 200–250 g m ?2 year ?1 is calculated for the northern Negev desert for 1987. Thus, if the settled dust can be protected against erosion in the cultivated areas in the Negev, the dust content of the top soil will markedly increase with time. However, it has to be borne in mind that cultivation activities themselves may also contribute to a higher soil erosion and, hence, to a higher dust content in the atmosphere. At any rate, a higher dust content in the top soil will unquestionably have an important positive effect on agricultural yields. From the air dust concentration data and the dust deposition data, a deposition velocity of 4.7cms ?1 can be calculated for Avdat dust. 相似文献
12.
Ureolysis-driven calcite precipitation has potential to seal porosity and fracture networks in rocks thus preventing groundwater flow and contaminant transport. In this study urea hydrolysis and calcite precipitation rates for the model bacterium Sporosarcina pasteurii were compared with those of indigenous groundwater communities under conditions required to precipitate large volumes of calcite (up to 50 g L −1). We conducted microcosm experiments in oxic artificial and anoxic natural groundwaters (collected from the Permo-Triassic sandstone aquifer at Birmingham, UK) that were inoculated with aerobically grown S. pasteurii. The rate constants for urea hydrolysis, kurea, ranged between 0.06 and 3.29 d −1 and were only affected by inoculum density. Higher Ca 2+ concentration (50-500 mM Ca 2+) as well as differences in fO 2 did not inhibit the ureolytic activity of S. pasteurii and did not significantly impact kurea. These results demonstrate that S. pasteurii has potential to improve calcite precipitation in both oxic and anoxic groundwaters, especially if indigenous communities lack ureolytic activity. Urea hydrolysis by indigenous groundwater communities was investigated in anoxic, natural groundwaters amended with urea and CaCl 2. A notable increase in ureolysis rates was measured only when these communities were stimulated with dilute nutrients (with best results from blackstrap molasses). Furthermore, there was a considerable lag time (12-20 days) before ureolysis and calcite precipitation began. Calculated ureolysis rate constants, kurea, ranged between 0.03 and 0.05 d −1 and were similar to kurea values produced by S. pasteurii at low inoculum densities. Overall, this comparative study revealed that the growth of ureolytic microorganisms present within groundwaters can easily be stimulated to enhance rates of urea hydrolysis in the subsurface, and thus can be used to induce calcite precipitation in these environments. The time required for urea hydrolysis to begin is almost instantaneous if an inoculum of S. pasteurii is included, while it may take several weeks for ureolytic groundwater communities to grow and become ureolytically active. 相似文献
13.
Acta Geotechnica - Temperature is a key factor that contributes to microbially induced calcium carbonate precipitation. At low temperatures, low enzyme activity results in a lack of calcium... 相似文献
14.
Strontium incorporation into calcite generated by bacterial ureolysis was investigated as part of an assessment of a proposed remediation approach for 90Sr contamination in groundwater. Urea hydrolysis produces ammonium and carbonate and elevates pH, resulting in the promotion of calcium carbonate precipitation. Urea hydrolysis by the bacterium Bacillus pasteurii in a medium designed to mimic the chemistry of the Snake River Plain Aquifer in Idaho resulted in a pH rise from 7.5 to 9.1. Measured average distribution coefficients (D EX) for Sr in the calcite produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic calcites (0.02-0.4). They were also higher than values for calcite produced abiotically by ammonium carbonate addition (0.3). The precipitation of calcite in these experiments was verified by X-ray diffraction. Time-of-flight secondary ion mass spectrometry (ToF SIMS) depth profiling (up to 350 nm) suggested that the Sr was not merely sorbed on the surface, but was present at depth within the particles. X-ray absorption near edge spectra showed that Sr was present in the calcite samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of calcite precipitation, where faster precipitation was associated with greater Sr uptake into the solid. The presence of bacterial surfaces as potential nucleation sites in the ammonium carbonate precipitation treatment did not enhance overall precipitation or the Sr distribution coefficient. Because bacterial ureolysis can generate high rates of calcite precipitation, the application of this approach is promising for remediation of 90Sr contamination in environments where calcite is stable over the long term. 相似文献
15.
Evidence for glaciation during the mid-late Neoproterozoic is widespread on Earth, reflecting three or more ice ages between 730 Ma and 580 Ma. Of these, the late Neoproterozoic Marinoan glaciation of approximately 635 Ma stands out because of its ubiquitous association with a characteristic, microcrystalline cap dolostone that drapes glacially influenced rock units worldwide. The Marinoan glaciation is also peculiar in that evidence for low altitude glaciation at equatorial latitudes is compelling. Three models have been proposed linking abrupt deglaciation with this global carbonate precipitation event: (i) overturn of an anoxic deep ocean; (ii) catastrophically accelerated rates of chemical weathering because of supergreenhouse conditions following global glaciation (Snowball Earth Hypothesis); and (iii) massive release of carbonate alkalinity from destabilized methane clathrates. All three models invoke extreme alkalinity fluxes into seawater during deglaciation but none explains how such alkalinity excess from point sources could be distributed homogeneously around the globe. In addition, none explains the consistent sequence of precipitation events observed within cap carbonate successions, specifically: (i) the global blanketing of carbonate powder in shallow marine environments during deglaciation; (ii) widespread and disruptive precipitation of dolomite cement; followed by (iii) localized barite precipitation and seafloor cementation by aragonite. The conceptual model presented here proposes that low latitude deglaciation was so massive and abrupt that the resultant meltwater plume could extend worldwide, physically separating the surface and deep ocean reservoirs for ≥10 3 years. It is proposed that cap dolostones formed primarily by microbially mediated precipitation of carbonate whitings during algal blooms within this low salinity plumeworld rather than by abiotic precipitation from normal salinity seawater. Many of the disruption features that are characteristic of cap dolostones can be explained by microbially mediated, early diagenetic dolomitization and cementation. The re-initiation of whole ocean circulation degassed CO 2 into the atmosphere in areas of upwelling, triggering localized, abiotic CaCO 3 precipitation in the form of aragonite fans that overlie cap dolostones in NW Canada and Namibia. The highly oxygenated shallow marine environments of the glacial and post-glacial Neoproterozoic world provided consistently favourable conditions for the evolutionary development of animals and other oxygenophiles. 相似文献
16.
Acta Geotechnica - One-dimensional compression tests on quartz sands treated by microbially induced carbonate precipitation (MICP) were carried out to evaluate the effects of gradation and calcium... 相似文献
17.
Microbially induced calcium carbonate (CaCO3) precipitation (MICP) has been extensively studied for soil improvement in geotechnical engineering. The quantity and size of calcium carbonate crystals affect the strength of MICP-treated soil. In this study, microfluidic chip experiments and soil column experiments were conducted to optimize MICP treatment protocols for effective strength enhancement of MICP-treated sandy soils. The microscale experiments reveal that, due to Ostwald ripening, longer injection intervals allow crystals to dissolve and reprecipitate into larger crystals regardless of the concentration of cementation solution. Even though a cementation solution input rate of 0.042 mol/l/h is sufficient to maintain a high chemical transformation efficiency, a further reduction in the input rate by about four times resulted in an increase in the size of crystals produced by the end of treatment from about 40 to 60 μm. These findings were applied in soil column experiments. Results showed that significantly larger crystals and higher soil strength were achieved when the normalized rate of cementation solution injection was reduced from 0.042 to 0.021 mol/l/h. Crystal size and soil strength increased slightly more when the normalized input rate was further reduced from 0.021 to 0.010 mol/l/h. This study demonstrates how data from microscale microfluidic experiments that examine the effects of injection intervals and concentration of cementation solution on the properties of calcium carbonate crystals can be used to optimize MICP treatment in macroscale sand soil column experiments for effective strength enhancement. 相似文献
18.
Groundwater of the southern Jornada del Muerto Basin, an intermontane basin structure associated with the Rio Grande rift
located in south-central New Mexico, USA, was analyzed chemically and microbially. A microbial phospholipid fatty acids (PLFA)
analysis revealed a sparse microbial population consisting of relatively simple microorganisms with no major population changes
along the flow system. A nucleic acid (DNA) analysis of the groundwater resulted in the identification of ten eubacterial
and one archeal species. Chemical analyses revealed that sulfate along with calcium, magnesium, iron, and manganese is removed
by about an order of magnitude in concentration from the recharge area to the discharge area. The removal of iron, manganese,
magnesium, and to some extent calcium can be explained by oxidation reactions and the precipitation of dolomite. Sulfate and
additional calcium are most likely removed by the precipitation of gypsum. Thiobacillus spp. are oxidizing metal sulfides that occur as subsurface sulfide mineral deposits to sulfuric acid, which subsequently
reacts with calcium carbonate and water to precipitate gypsum. The presence of these sulfide deposits exposed to oxygenated
water in the deep groundwater flow system significantly alters its chemical and bacteriological composition.
Electronic Publication 相似文献
19.
In the Borrego Desert (California) and in the Sinai Desert (Israel) laminated, microbially mediated carbonate crusts have been found and analysed biologically and mineralogically, and further studied with scanning electron microscope methods combined with energy dispersive X-ray analyses. All morphological and biological features of the extant crusts justify the term ‘desert stromatolite’, a term applied to stromatolites from desert regions which form under permanent exposure to the atmosphere. These stromatolites are never covered by standing water, and running water (heavy rainfall) covers them for only a few hours during the year. Carbonate deposition is achieved principally by the cyanobacterium Pleurocapsa sp. which exhibits characteristic yet different stages of calcification. Calcification occurs in the sheaths of single cells (including baeocytes) as well as in mature colonies. The specificity for calcification in Pleurocapsa sp. is discussed. 相似文献
20.
重庆紫色土是一种砂质黏性土,地区降雨集中,水力冲蚀作用剧烈,极易产生水土流失,微生物诱导方解石沉积(MICP)技术因能耗低、污染小而广泛应用于土体加固中。通过正交试验优化了巨大芽孢杆菌(BNCC 336739)的培养基和培养条件,活菌数增长126%,活性良好。采用巨大芽孢杆菌,进行低水压(9.8kPa)灌注固化砂质黏性紫色土试验,探究了固化效果的变化规律。结果表明:随固化次数增加,碳酸钙生成量和干密度逐级增加,无侧限抗压强度与碳酸钙生成量正相关;碳酸钙有效沉积越来越少,强度提高趋于稳定,固化9次后强度提高77%;随孔隙被碳酸钙填充和上下碳酸钙硬壳的形成,渗透性不断降低,最终下降两个数量级;通过试样上、中、下三部分碳酸钙生成量C的样本标准差s来反映碳酸钙分布离散程度,发现割线弹性模量在s的影响下随C增加而波动上升,波动表现为在C相近或s相差很大时,s越小割线弹性模量越大。研究成果可以为MICP技术在紫色土地区的地基、边坡加固和水土流失防护等工程应用提供科学依据和参考。 相似文献
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