Microbially Induced Carbonate Precipitation Technique Research Articles

Evaluation of urea hydrolysis for MICP technique applied in recycled aggregate: Concentration of urea and bacterial spores

Aggregate is an indispensable raw material for concrete. Microbial induced carbonate precipitation (MICP) is an environmentally friendly aggregate modification method, which could modify recycled aggregate (RA) to replace natural aggregate for the preparation of concrete in the future. The urea hydrolysis is the key to modified RA by MICP. Biological calcium carbonate is generated during mineralization reaction in modification solution to fill the weak part of aggregate, which will enhance the performance of RA. The bacterial solution and urea solution, as the sources of CO32- in biological CaCO3, jointly affect the modification effect of RA. In this paper, the different ratios of bacterial solution concentration (×108 cells/mL) to urea concentration (mg urea/mL) are used for exploring the improvement effect and the cooperative enhancement mechanism of recycled coarse aggregate (4.75 mm-9.5 mm). The results show that the bacterial mineralization efficiency is most improved when bacterial solution concentration/urea concentration (B/U) is in the optimal interval of 5–6 because 1 mg urea provides a moderate number of bacteria during the modification period. In the interval, the precipitation amount of biological CaCO3 and effective CaCO3 that could modify RA is larger, and the pores of the attached mortar of RA are better filled and blocked. Therefore, the macro performance of RA is greatly improved in the internal. When the B/U is outside the optimal interval, the modification effect is poor because the amount of biological CaCO3 and effective CaCO3 is too less to fill pores or too more to enter pores.

A Novel Mathematical Model for Repairing Rough Cracks Using the Microbially Induced Carbonate Precipitation (MICP)

Concrete cracks have an adverse effect on the strength properties and durability of concrete structures. Therefore, repairing concrete cracks to recover the concrete’s strength parameters is an important task in the civil engineering field. For repairing concrete cracks, the MICP technique has been widely analyzed in recent times; however, no research has been conducted to deeply investigate the repair effects of MICP on concrete cracks with a rough surface using a theoretical model. In the current research, MICP with a novel mathematical model was conducted considering the precipitation of calcium carbonate (CaCO3), ureolysis, suspended biomass, geochemistry, transport of solutes, and biofilm growth. Furthermore, crack repair experiments were performed to assess the performance of the new mathematical model. The results revealed that the calculated concentrations of suspended biomass in cracks gradually decreased during the test. The comparison between the experimental results and calculated results verified the precision of the migration behavior of the suspended biomass. At the inlet, the solute concentrations and volume fractions of biofilm were higher, causing an increase in the productive rates of calcium carbonate. The consumed concentrations of solutes were higher for cracks with a smoother surface, eventually leading to smaller values of sonic time; the upper parts of the cracks also had smaller values of sonic time, showing good repair effects. The proposed mathematical model provides a better solution to control the repair time and microbial metabolism process, allowing for adjustive bioremediation and biomineralization of concrete, which could provide a firm basis for the remediation of materials in the civil engineering field.

The Spatial Distribution of Microbially Induced Carbonate Precipitation in Sand Column with Different Grouting Strategies

For ground improvement via microbially induced carbonate precipitation (MICP), the spatial distribution of biocementation considerably affects the mechanical performance of soil. This study systematically assessed the CaCO3 spatial distribution in sand columns with various grouting strategies. CaCO3 dispersion along the radial and vertical directions was quantitatively evaluated. Furthermore, a series of biochemical monitoring experiments was conducted to investigate the MICP process in sand. The results indicated that the reversed and downward chemical solution grouting and high rates of microbial grouting all promoted CaCO3 vertical uniformity. Moreover, the grouting strategy slightly affected the dispersion degree of radially distributed CaCO3. The variation coefficient basically ranged from 0.1 to 0.3. However, the variation coefficient for radially distributed CaCO3 along the vertical direction was significantly affected by the chemical grouting direction. The biochemical monitoring results indicated that 38% Ca2+ was even consumed near the chemical solution outlet in the chemical solution grouting process. The initial Ca2+ concentration during the intermittent period gradually decreased along the chemical solution grouting direction. The CaCO3 vertical distribution was controlled by a combination of the total MICP reaction time, biomass, and Ca2+ availability in the intermittent phase. Different CaCO3 distributions resulted in each grouting strategy exhibiting specific applicable engineering requirements. Furthermore, the carbon footprint was preliminarily evaluated. The results in this study provide references for the selection of grouting strategies for the MICP technique in engineering applications.

Effects of microbially induced carbonate precipitation on diffuse double layer and particle fabric of oil sands fine tailings

Microbially induced carbonate precipitation (MICP) is a sustainable biological process that catalyzes carbonate mineral precipitation within geomaterials. This study evaluates the performance and mechanisms of the MICP treatment for flocculating the oil sands fine tailings (FT). Column tests showed that the untreated FT did not decant during the 31 days. However, the MICP technique shortened the dewatering process. To elucidate the mechanisms of the MICP-induced flocculation of the FT, the diffuse double layer (DDL) thickness and microstructure of the specimens were evaluated. Three chemical equilibrium scenarios that gradually considered the MICP-biochemical reactions were explored to analyze the change of the DDL thickness. The results showed that increasing of ionic strength by urea hydrolysis decreased the DDL thickness. The fabric observation indicated that the specimens with the most calcium carbonate precipitation had the densest fabric. In summary, the MICP technique densified the fabric of FT via the ureolysis process and precipitating minerals.

Application of microbially induced carbonate precipitation to form bio-cemented 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 artificially cemented 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 (0.25–0.4) of the artificial specimens fall in the same range of values reported for natural rocks. The strength gain was 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 the MICP 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. • MICP specimens were generated with a good degree of uniformity and repeatability. • The MICP strategy delivered specimens with controlled mechanical properties. • Properties of artificially cemented sands resemble those of natural soft sandstones. • Varying combinations of UCS and porosity are achieved through different grain sizes.

Solidification of loess using microbial induced carbonate precipitation

Microbial-induced carbonate precipitation (MICP) is a relatively innovative and environmentally-friendly soil reinforcement technology, primarily used on sand, but its application in loess has rarely been studied. This paper explores the viability of the MICP technique for improving the engineering properties of typical loess. Sporosarcina pasteurii was used to trigger carbonate precipitation. Factors such as reaction temperature, pH of the media, and the inoculation ratio were adopted to determine the optimum conditions. Different concentrations of Sporosarcina pasteurii and cementation reagent were selected for combination to treat the loess samples with a self-designed vacuum test device. The unconfined compressive strength and calcium carbonate content of the treated samples were tested and Scanning Electron Microscopy (SEM) was carried out to evaluate the improving effect. The results showed that the optimum conditions are reaction temperature of 30°C, pH of the media of 9, a higher inoculation ratio can produce higher enzyme activity and monomer enzyme activity. The engineering properties of the MICP-treated loess are significantly improved. The obtained unconfined compressive strength increases nearly 4 times when the OD600 is 1.5 and cementation reagent concentration is 1 mol/L. The test results of calcium carbonate content are consistent with unconfined compressive strength. Finally, the microstructure of loess samples was quantitatively analyzed by Pore (Particle) and cracks analysis system (PCAS). It was showed that MICP has a great influence on the surface porosity, followed by the pore fractal dimension and the probability entropy, but has little influence on the pore average form factor.

Microbially induced carbonate precipitation via methanogenesis pathway by a microbial consortium enriched from activated anaerobic sludge.

Various applications of microbially induced carbonate precipitation (MICP) has been proposed. However, most studies use cultured pure strains to obtain MICP, ignoring advantages of microbial consortia. The aims of this study were to: (i) test the feasibility of a microbial consortium to produce MICP; (ii) identify functional micro-organisms and their relationship; (iii) explain the MICP mechanism; (iv) propose a way of applying the MICP technique to soil media. Anaerobic sludge was used as the source of the microbial consortium. A laboratory anaerobic sequencing batch reactor and beaker were used to perform precipitation experiment. The microbial consortium produced MICP with an efficiency of 96·6%. XRD and SEM analysis showed that the precipitation composed of different-size calcite crystals. According to high-throughput 16S rRNA gene sequencing, the functional micro-organisms included acetogenic bacteria, acetate-oxidizing bacteria and archaea Methanosaeta and Methanobacterium beijingense. The methanogenesis acetate degradation provides dissolved inorganic carbon and increases pH for MICP. A series of reactions catalysed by many enzymes and cofactors of methanogens and acetate-oxidizers are involved in the acetate degradation. This work demonstrates the feasibility of using the microbial consortium to achieve MICP from an experimental and theoretical perspective. A method of applying the microbial-consortium MICP to soil media is proposed. It has the advantages of low cost, low environmental impact, treatment uniformity and less limitations from natural soils. This method could be used to improve mechanical properties, plug pores and fix harmful elements of soil media, etc.

Strength and Permeability of Bentonite-Assisted Biocemented Coarse Sand

To effectively stabilize coarse sand, bentonite was introduced in microbially induced carbonate precipitation (MICP) grouting. Varying concentrations (0 g/L, 20 g/L, 40 g/L and 80 g/L) of bentonite were added to bacterial suspensions (BSs), which were magnetically stirred to form bacterial-bentonite suspensions (BBSs). Then, coarse sand specimens were treated with BBSs and cementation solutions (CSs) to different cementation levels. The results showed that the addition of bentonite could increase the volume fractions of the precipitates consisting of calcium carbonate (CaCO3) and bentonite. The permeability decreased exponentially as the volume fraction of precipitates increased. As the active precipitates increased when a lower concentration (e.g., 20 g/L) of bentonite was added to the MICP grouting, the unconfined compressive strength (UCS) was substantially improved. However, detrimental effects were observed for specimens treated with a high concentration of bentonite. These results indicate that the effective concentration of natural clay aggregates used in MICP grouting was different for different engineering applications, e.g., seepage control and strength enhancement. The current work provides an encouraging method of improving the MICP technique.

Slope failure of biotreated sand embankments under rainfall conditions: experimental investigation and numerical simulation

Rainfall has become a main trigger of slope failure for embankments in most coastal areas in China. The microbially induced carbonate precipitation (MICP) technique has great potential to improve soil strength and slope stability. In this study, three small-scale biotreated sand embankments and one untreated embankment were first prepared using the injection method. Rainfall scouring tests were then conducted to investigate the slope failure of the embankments. Experimental results revealed that scouring/erosion resistance of biotreated sand embankments was significantly improved comparing to that of the untreated one. The failure time of the embankment increased as the treatment cycles increased. The failure mode of the untreated embankment was the general shear failure, whereas the failure was most likely to occur at shallow depth in biotreated embankments. Using the finite element method (FEM), flow analysis was conducted to simulate the rainfall infiltration in sand embankments and study the effect of biotreatment on the infiltration process. The simulation results were found to be consistent with the experimental results. This study preliminarily investigates the effectiveness of using the MICP technique to prevent slope failure of sand embankments. Considering the complicated environmental factors, more effort towards optimization is still needed for field implementation in the future.

Shear resistance of MICP cementing material at the interface between calcareous sand and steel

MICP (Microbially Induced Carbonate Precipitation) technique was firstly adapted to treat the interface between calcareous sand and steel. The influences of cementing material and surface roughness on the interface shear resistance were investigated experimentally. Results show that biomaterial produced by MICP exists mainly in the form of spherical and block crystals, which bonding and coating sand particles. The peak shear resistances of the interface treated by MICP and Gypsum are similar, while the resistance mobilized at 5 mm displacement of interface treated by MICP is the highest. The surface roughness plays a significant role in enhancing the interface cohesion of MICP-treated sample. This work proves that MICP technique is feasible to improve the calcareous sand-steel interface resistance in an environment-friendly way.

Microbial induced solidification and stabilization of municipal solid waste incineration fly ash with high alkalinity and heavy metal toxicity.

This paper presents an experimental study on the applicability of microbial induced carbonate precipitation (MICP) to treat municipal solid waste incineration (MSWI) fly ash with high alkalinity and heavy metal toxicity. The experiments were carried out on fly ashes A and B produced from incineration processes of mechanical grate furnace and circulating fluidized bed, respectively. The results showed that both types of fly ashes contained high CaO content, which could supply sufficient endogenous Ca for MICP treatment. Moreover, S. pasteurii can survive from high alkalinity and heavy metal toxicity of fly ash solution. Further, the unconfined compressive strength (UCS) of MICP treated fly ashes A and B reached 0.385MPa and 0.709 MPa, respectively. The MICP treatment also resulted in a reduction in the leaching toxicity of heavy metals, especially for Cu, Pb and Hg. MICP had a higher solidification and stabilization effect on fly ash B, which has finer particle size and higher Ca content. These findings shone a light on the possibility of using MICP technique as a suitable and efficient tool to treat the MSWI fly ash.

Laboratory method of microbial induced solidification/stabilization for municipal solid waste incineration fly ash

This paper presents a method to solidify/stabilize the municipal solid waste incineration (MSWI) fly ash by originally employing the microbial induced carbonate precipitation (MICP) technique. In this method, the rich endogenous calcium in the MSWI fly ash was utilized to induce calcite precipitation, which is different from the operation of adding extra calcium source in previous researches. The fly ash sample had a CaO content of 44.5%, and its leaching concentrations of Zn, Cr and Pb exceed the limits of the identification standard for hazardous wastes in China. The optical density at 600 nm (OD600) of the bacterial solution was about 1.0 after the processes of bacterial activation and reproduction. The prepared fly ash sample was well mixed with bacterial solution at an ash-liquid ratio of 1 kg: 0.3 L and cured at a temperature of 20 °C and a humidity of ≥95% for 7 days. After treatment, the heavy metal leachability significantly reduced to meet the standard for pollution control of landfill site, and the unconfined compressive strength increased approximately 40%. The precipitated carbonates were verified by SEM-EDS analysis and quantified by measurement of carbonate content via acid-dissolving method. The results shone a light on the possibility of using MICP technique as a useful and efficient tool to stabilize the MSWI fly ash before being reused or properly stored in landfills.•The MICP method is efficient to reduce the heavy metal leachability and increase the compressive strength of MSWI fly ash.•The endogenous calcium in MSWI fly ash was utilized to induce calcite precipitation.•The heavy metals in MSWI fly ash were well immobilized by the formation of carbonates.

Reducing the hydraulic erosion of sand using microbial-induced carbonate precipitation

Hydraulic erosion is one of the main causes of failure within earth dams and embankments. Various methods are used to mitigate against such erosion, a common approach being grouting with cement, clay or chemical materials. Biogrouting using the microbial-induced carbonate precipitation technique is a relatively new, cost-effective, technically appropriate and environmentally friendly soil improvement method. Bacteria injected into the soil produce urease enzyme, which converts urea to ammonium and carbonate, causing calcite precipitation that binds soil grains together. In this study, the erodibility parameters of dense silica sand specimens treated with different injection strategies were investigated at bench scale. More effective treatment – in terms of greater and more uniform calcite precipitation over the test-specimen length, and hence greater erosion resistance – was achieved by aeration during solution injections and by incorporating a drained stage between injection cycles. With the latter, calcite precipitated as larger crystals, accumulating extensively over grain surfaces and also formed integrated in the pore voids. The best-performing treatment strategy produced a 95% reduction in erodibility and a five-fold increase in critical shear stress relative to untreated sand. These findings were confirmed by scanning electronic microscopy and calcium carbonate titration tests.

Review of ground improvement using microbial induced carbonate precipitation (MICP)

ABSTRACTMechanical compaction and chemical grouting are the two most widely used methods in geotechnical engineering for ground improvement. However, the disadvantages of the methods including high cost, high energy consumption, and potential environmental pollution are obvious. A new ground treatment technique, i.e., microbial induced carbonate precipitation, was developed recently. Review of ground improvement using microbial induced carbonate precipitation technique was performed in this study. The mechanism of microbial induced carbonate precipitation-treated soils was first introduced followed by the review of many aspects of the microbial induced carbonate precipitation technique. Thereafter, the related engineering applications were presented and summarized. Moreover, some problems existing in current theoretical and experimental studies as well as the possible solutions for future development were also discussed. Some recommendations were proposed for a wider application of this technique.

Characterization of the Microbial Induced Carbonate Precipitation Technique as a Biological Cementing Agent for Sand Deposits

Characterization of the Microbial Induced Carbonate Precipitation Technique as a Biological Cementing Agent for Sand Deposits

Bio-cementation of sandy soil using microbially induced carbonate precipitation for marine environments

This study proposes and describes a novel approach for cementing sandy soils in marine environments by modifying the promising technique of microbially induced carbonate precipitation (MICP). In contrast to the usual MICP technique described in the literature, the method proposed herein relies on the calcium ions dissolved in seawater as the sole source of calcium for calcite formation. This proposed method involves flushing high-salinity-tolerant, urease-active bacteria followed by a mixture of urea and seawater through a porous sandy soil, leading to bacterial carbonate release from the urease reaction and precipitation of insoluble and semi-soluble carbonate salts including calcium carbonate and magnesium carbonate trihydrate. This precipitation method resulted in a physical stabilisation of sand that reached an unconfined compressive strength of up to 300 kPa, which is about two-fold higher (with same amount of crystals produced) than that of the MICP treatment in which highly concentrated calcium and urea solutions are used. Permeability was retained at about 30% for all MICP-treated samples, suggesting good drainage ability. This new exploration of MICP technology provides a high potential for using bio-cementation in marine environments, for applications such as mitigation of submarine sediment liquefaction and prevention of beach sand erosion and cliffs scouring.