Modified one-phase-low-pH method for bacteria or enzyme-induced carbonate precipitation for soil improvement

Acta Geotechnica - One of the latest developments in biocementation is the use of one-phase-low-pH MICP or EICP method as a more effective and efficient alternative to the traditional two-phase...     

酶诱导碳酸钙沉淀加固遗址土动力特性试验研究

中国西北地区地震频发,土遗址长期受到地震活动的不利影响。为了研究酶诱导碳酸钙沉淀技术（EICP）加固遗址土的动力特性,对1.55、1.65、1.75 g/cm³这3种初始干密度的遗址土进行EICP处理,并设置未经EICP处理的对照组。开展了不同围压、振动频率下的动三轴试验。结果表明：在相同动应力作用下,相比对照组,试验组的动应变更小,耗散的能量更少,阻尼比更小;在EICP加固后,随着干密度、围压、振动频率增大,可以降低动应变的产生,但这种效果依次减弱。动本构关系符合Hardin模型,干密度、围压、振动频率对模型参数a（动弹性模量）的影响程度逐渐减小;微观分析发现,EICP加固后,碳酸钙沉淀在土颗粒表面附着,填充孔隙,并与土颗粒相互胶结成致密结构,土体结构强度增强。     

Improvement in silty sand with enzyme-induced carbonate precipitation: laboratory model experiment

Acta Geotechnica - Enzyme-induced carbonate precipitation (EICP) is a promising method for the improvement in soil properties. In this study, a model test using a meter-scale soil model was carried...     

基于生物诱导碳酸钙沉淀的土体固化研究进展

基于微生物或脲酶诱导碳酸钙沉淀（MICP/EICP）的土体固化技术是近年来岩土和地质工程领域的研究热点之一。在系统回顾基于生物诱导碳酸钙沉淀的土体固化技术发展历程的基础上,重点阐述了MICP/EICP固化机制、土体孔隙结构、菌液和脲酶性质、胶凝液性质和固化方式等方面对碳酸钙特性影响的研究进展。研究结果表明：土体孔隙越小,越不利于微生物或脲酶入渗,固化均匀性越差;土颗粒接触点越多,可为碳酸钙提供的沉积点位越多,碳酸钙与土颗粒间的黏结和桥接作用越强,固化效果越好;一定菌液或脲酶浓度或脲酶活性范围内,碳酸钙的生成速率和生成总量随浓度及活性的增大而增大,但过高的浓度或活性易导致碳酸钙生成速率过快,从而在土体注入端发生堵塞;低浓度胶凝液得到的碳酸钙晶体更小,在土体中的分布更均匀;采用合适的注浆饱和度可提高具有黏结作用的碳酸钙的占比;采用多层交替注入或单相低pH值注入可提高碳酸钙在试样中分布的均匀性。基于碳酸钙沉淀特性的影响因素,提高固化土体的均匀性,验证其耐久性,室内试验结果在现场尺度的适应性和改进方案应该成为以后研究的重点。     

Polymer-modified microbially induced carbonate precipitation for one-shot targeted and localized soil improvement

Acta Geotechnica - The viscous nature of certain hydrophilic polymer solutions and the tendency of these solutions to retain moisture may make them suitable carriers for the process of microbially...     

One-phase-low-pH enzyme induced carbonate precipitation (EICP) method for soil improvement

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.

     

Performance of microbial-induced carbonate precipitation on wind erosion control of sandy soil

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 CaCO₃ crystals using scanning electron microscopy and X-ray powder diffraction analysis showed that the CaCO₃ was mainly precipitated as vaterite crystals forming point-to-point contacts between the sand granules.     

生物膜脂参与的非晶碳酸钙形成和稳定

非晶碳酸钙(amorphous calcium carbonate,ACC)是碳酸钙矿物体系中极不稳定的矿物相。但由海鞘类动物的研究表明,ACC可作为碳酸钙晶体矿物的前驱体在生物体内稳定存在,并且这些生物成因的ACC常常是由膜包裹着的。文中选用生物膜的主要成分卵磷脂(PC)为主要矿化调节剂,通过调控与碳酸钙矿化过程密切相关的无机离子Mg2+的浓度,模拟生物膜表面碳酸钙矿化作用过程。在空气/水界面处的膜脂调控下合成出可在溶液中稳定存在数天的非晶碳酸钙。该结果有力地证明了在生物矿化过程中,除了受生物体中可溶性有机大分子调控外,生物膜可能对ACC的形成和稳定也有显著的调控作用。     

Mechanical properties of biocement formed by microbially induced carbonate precipitation

Acta Geotechnica - The failure of biocemented sand can be attributed to the breakage of biocement and the exfoliation of precipitates from sand surfaces. Therefore, optimizing the mechanical...     

Kitchen waste for Sporosarcina pasteurii cultivation and its application in wind erosion control of desert soil via microbially induced carbonate precipitation

Kitchen waste and wind erosion are two worldwide environmental concerns. This study investigated the feasibility of using kitchen waste for Sporosarcina pasteurii cultivation and its application in wind erosion control of desert soil via microbially induced carbonate precipitation (MICP). Enzymatic hydrolysis was adopted to improve the release and recovery of protein in kitchen waste for subsequent microorganism production. After conditions optimized, the maximum biomass concentration (OD₆₀₀) and urease activity of Sporosarcina pasteurii in the kitchen waste-based medium reached 4.19, and 14.32 mM urea min^?1, respectively, which were comparable to those obtained in conventional standard media. The harvested Sporosarcina pasteurii was then used to catalyze the precipitation of calcium carbonate in the desert soil, and its performance in wind erosion control was evaluated through wind tunnel tests. The microbially mediated calcium carbonate could significantly decrease wind erosion loss of the desert soil even after 12 wet–dry or freeze–thaw cycles. Scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) confirmed the bridge effect of calcium carbonate crystals in the soil matrix. The kitchen waste, as a cost-effective alternative nutrient for bacterial cultivation and carbonate precipitation, showed great potential for large-scale applications in wind erosion control of desert soils.

     

Calcium isotope evidence for suppression of carbonate dissolution in carbonate-bearing organic-rich sediments

Pore fluid calcium isotope, calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep-sea sediments containing abundant clay and organic material. This type of study of deep-sea sediment diagenesis provides unique information about the ultra-slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo-environmental information in carbonate fossils. For this study, calcium isotope ratios (δ^44/40Ca) of pore fluid calcium from Ocean Drilling Program (ODP) Sites 984 (North Atlantic) and 1082 (off the coast of West Africa) were measured to augment available pore fluid measurements of calcium and strontium concentration. Both study sites have high sedimentation rates and support quantitative sulfate reduction, methanogenesis and anaerobic methane oxidation. The pattern of change of δ^44/40Ca of pore fluid calcium versus depth at Sites 984 and 1082 differs markedly from that of previously studied deep-sea Sites like 590B and 807, which are composed of nearly pure carbonate sediment. In the 984 and 1082 pore fluids, δ^44/40Ca remains elevated near seawater values deep in the sediments, rather than shifting rapidly toward the δ^44/40Ca of carbonate solids. This observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate-rich sites. The data are fit using a numerical model, as well as more approximate analytical models, to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material. Our models give mutually consistent results and indicate that calcite dissolution rates at Sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate-rich sites, and the rate correlates with the abundance of clay. Our calculated rates are conservative for these sites (the actual rates could be significantly slower) because other processes that impact the calcium isotope composition of sedimentary pore fluid have not been included. The results provide direct geochemical evidence for the anecdotal observation that the best-preserved carbonate fossils are often found in clay or organic-rich sedimentary horizons. The results also suggest that the presence of clay minerals has a strong passivating effect on the surfaces of biogenic carbonate minerals, slowing dissolution dramatically even in relation to the already-slow rates typical of carbonate-rich sediments.     

An experimental study of mitigating coastal sand dune erosion by microbial- and enzymatic-induced carbonate precipitation

Acta Geotechnica - Due to more extreme weather events and accelerating sea-level rise, coastal sand dunes are subjected to more frequent storm wave inundation and surge impacts, which contribute to...     

微生物诱导碳酸盐沉积改善裂隙岩石防渗性能和强度的试验研究

微生物诱导碳酸盐沉积(MICP)技术主要利用微生物生命活动与环境反应形成的碳酸盐来修复岩土体。为了研究该技术改善含裂隙岩石防渗性能和强度的效果,利用巴氏芽孢杆菌开展了裂隙黄砂岩的修复试验,并对修复后的裂隙黄砂岩进行了无侧限抗压、核磁共振和电镜扫描(SEM)等测试,分析了巴氏芽孢杆菌对裂隙黄砂岩的修复效果和修复机制。研究表明:巴氏芽孢杆菌对裂隙黄砂岩具有较好的修复效果;修复时间越长,巴氏芽孢杆菌的修复效果越好。修复42d后,裂隙黄砂岩的孔隙率下降36.41%,防渗性能提升94.62%,抗压强度增加30.52%。巴氏芽孢杆菌具有较好修复效果原因在于,其诱导产生的碳酸钙能够胶结填充物与试样,大幅降低试样的孔隙率,改善其内部孔隙结构的均质性。     

Element fractionation by sequential extraction in a soil with high carbonate content

The influence of carbonate and other buffering substances in soils on the results of a 3-step sequential extraction procedure (BCR) used for metal fractionation was investigated. Deviating from the original extraction scheme, where the extracts are analysed only for a limited number of metals, almost all elements in the soils were quantified by X-ray fluorescence spectroscopy, in the initial samples as well as in the residues of all extraction steps. Additionally, the mineral contents were determined by X-ray diffractometry. Using this methodology, it was possible to correlate changes in soil composition caused by the extraction procedure with the release of elements. Furthermore, the pH values of all extracts were monitored, and certain extraction steps were repeated until no significant pH-rise occurred. A soil with high dolomite content (27%) and a carbonate free soil were extracted. Applying the original BCR-sequence to the calcareous soil, carbonate was found in the residues of the first two steps and extract pH-values rose by around two units in the first and second step, caused mainly by carbonate dissolution. This led to wrong assignment of the carbonate elements Ca, Mg, Sr, Ba, and also to decreased desorption and increased re-adsorption of ions in those steps. After repetition of the acetic acid step until extract pH remained low, the carbonate was completely destroyed and the distributions of the elements Ca, Mg, Sr, Ba as well as those of Co, Ni, Cu, Zn and Pb were found to be quite different to those determined in the original extraction. Furthermore, it could be shown that the effectiveness of the reduction process in step two was reduced by increasing pH: Fe oxides were not significantly attacked by the repeated acetic acid treatments, but a 10-fold amount of Fe was mobilized by hydroxylamine hydrochloride after complete carbonate destruction. On the other hand, only small amounts of Fe were released anyway. Even repeated reduction steps did not destroy the amorphous Fe oxides completely, showing that 0.1 mol L⁻¹ hydroxylamine hydrochloride was not strong enough to attack these oxides effectively.The extraction sequences were carried out not only on the soil samples, but also on their coarse and fine fractions (> or <2 μm). The fine fraction of the calcareous soil contained only 10% dolomite, but was enriched in organic matter and clay minerals, which also resulted in increased extract pH-values during the sequential extraction. Hence, the effects on ion release in the fine fraction were similar to those of the whole soil. Since the destruction of the organic matter was incomplete after regular oxidation, the H₂O₂-treatment of the fine fraction had to be repeated. The addition of the extractable amounts of the two fractions showed good agreement to the results obtained for extraction of the whole soils. Likewise the pH-values of the carbonate-free soil extracts did not increase significantly, therefore it was concluded that repetitions of extraction steps for this soil were not necessary.Extract-pHs should always be controlled so that extraction conditions are comparable; to be able to use the BCR extraction scheme or similar ones for carbonate- and organic-rich samples this is mandatory. Single extraction steps should be repeated if pH rises too much; additionally the oxidizing step should be performed more than twice for samples rich in organic substances, depending upon the violence of the reaction with H₂O₂. If these precautions are neglected the validity of the extraction data is likely to be questionable.     

Calcium carbonate precipitation induced by a bacterium strain isolated from an oligotrophic cave in Central China

A heterotrophic Bacillus sp. strain (5C-1) was isolated from Heshang cave, an oligotrophic karst cave in the middle reaches of Yangtze River, and identified by BIOLOG and 16S rDNA sequencing. Bacterially induced formation of calcium carbonate by 5C-1 was investigated in several comparative experimental sets with or without the cell and extracellular enzymes. The temporal variations of both the amount of the precipitates and the pH values of the solution were measured by a spectrophotometer and a pH meter, respectively. The morphological characteristics of the calcium carbonate precipitates were observed with environmental scanning electronic microscopy (ESEM). The growth of 5C-1 was found to greatly promote the pH value of the liquid medium in the first 2 days, which favors the formation of calcium carbonate. No precipitates were formed with the pH value lower than 8.6, though the pH value was demonstrated to be not the only factor controlling the formation of the calcium carbonate. The accumulation of extracellular polysaccharide substance was observed to favor the precipitate formation. Only when both factors reached a threshold did the precipitates form with the addition of CaCl₂. Cells and extracellular enzymes were not the factors that limit the precipitate formation in our microbial systems. The precipitates of a variety of morphological features including dumb bells, peanuts, irregular and spherical and rhombic forms were mainly observed in our microbial systems but not in the chemical control system. Interestingly, imprints of bacterial cells and spores were observed to be present on the surface of the precipitates of a peanut or a dumb bell form, probably indicative of the microbial escaping mechanism during the mineralization of calcium carbonate.     

Trace elements in natural organic-rich surface soils： Contributions from natural and anthropogenic sources

A large part of the Northem Hemisphere is covered by podzols and similar soil types, which have a surface layer characterized by high organic matter content. This layer is extremely important because it is the main source of plant nutrients. The elemental composition of the surface soil however is often strongly different from that of the underlying mineral soil, which may be due to a combination of natural processes and anthropogenic influence. Research in Norway over the last 30 years has contr/buted to the understanding of the relative importance of different factors in modifying the chemistry of the surface soil. The country is relatively pristine, but is substantially influenced in the south by atmospheric supply of pollutants from other parts of Europe. Vegetation is relatively uniform over large parts of the country, but climatic variations related to oceanic influence are considerable.     

Removal of heavy metals from mine water by carbonate precipitation in the Grootfontein-Omatako canal, Namibia

Water from the Kombat mine was delivered to the Omatako dam via the 263-km-long Grootfontein-Omatako canal during test runs in 1997. It is intended to supply water from Kombat and other underground mines in the Otavi Mountain Land to the capital Windhoek. The Cu-Pb-Zn orebodies are hosted by carbonate rocks and the mine waters are supersaturated with respect to calcite and CO₂. Along the length of the canal, the CO₂ partial pressure drops from 10^−2.1 atm at the inlet of the Kombat mine to 10^−3.5 atm at the end of the canal. This is accompanied by a drop in Ca concentration from about 60 to about 20 mg/l. The heavy metal concentrations (Cd, Cu, Mn, Pb and Zn) drop along the course of the canal to values far below the national drinking-water standard. Scavenging by calcium carbonate precipitation is the major depletion mechanism. Received: 21 June 1999 · Accepted: 29 August 1999     

酸活化坡缕石对土壤中Cd的钝化效果研究

为探究不同浓度H2SO4溶液活化的坡缕石对土壤中Cd的钝化效果,使用浓度分别为5％、7.5％、10％、12.5％、15％的H2SO4溶液对坡缕石进行活化,加入Cd污染土壤进行钝化实验和盆栽实验.结果表明:施加不同浓度H2SO4溶液活化的坡缕石均能显著降低土壤有效态Cd含量,10％的H2SO4活化的坡缕石钝化效果最显著,...     

Near-surface soil carbon detection for monitoring CO<Subscript>2</Subscript> seepage from a geological reservoir

The promise of the Brookhaven National Laboratory (BNL) Inelastic Neutron Scattering (INS) System was evaluated for use as a long-term, in-field monitor to detect cumulative changes in belowground carbon resulting from the leakage of CO₂ stored in deep geological reservoirs. This system underwent tests at a facility constructed specifically for testing, under controlled conditions, various detection systems for monitoring near-surface transport and accumulations of CO₂ fluxes emanating from a shallow buried, slotted horizontal well. The INS System was assessed by comparing the results from placing it above the horizontal well at a spot with a known high CO₂ leak identified and quantified the previous years, with those obtained from background readings adjacent to the well. At two different “Hot Spots”, a suppression of about 14% in 2008 and about 7% in 2009 in carbon content above the well in comparison to the background signal was observed. An overview of these results is presented.     

Soil stabilization with microbially induced desaturation and precipitation (MIDP) by denitrification: a field study

Acta Geotechnica - A field trial was performed to test the feasibility of microbially induced desaturation and precipitation (MIDP) by denitrification for the stabilization of a silty soil....