Microbially Induced Carbonate Precipitation Research Articles

Enhancing clay soil reinforcement using MICP-BIN method with biochar-induced nucleation

The microbially induced carbonate precipitation (MICP) method has gained extensive use in the realm of soil stabilisation. This study presents a novel microbial solidification technique known as the biochar-induced nucleation (MICP-BIN) method for reinforcing clay soil. Corn stover biochar was employed as an auxiliary material, mixed with dry clay powder, and subsequently reinforced using the MICP technique. Direct shear tests, drying experiments, X-ray diffraction, and scanning electron microscopy were also conducted to investigate the efficacy of the MICP-BIN method. Compared with that of the remoulded soil, the shear strength of the treated soil exhibited a substantial increase of 22.4%, the CaCO3 content increased by 30%, and the shear strength improved by 389.5%. Similarly, the internal friction angle exhibited increases of 22.7% and 405.2%, while the cohesion showed improvements of 9.4% and 344.3%, respectively. The MICP-BIN method is found to increase suction for a given water content. Furthermore, biochar-amended soil possesses highest water-retention ability (especially at lower suction magnitude), followed by MICP-amended soil, MICP-BIN-amended soil, and untreated soil. This study demonstrated the promising results achieved by combining biochar and the MICP-BIN technique, providing a novel approach for reinforcing soft ground.

Synergistic mechanisms of humic acid and biomineralization in cadmium remediation using Lysinibacillus fusiformis.

Heavy metal pollution, particularly cadmium, poses severe environmental and health risks due to its high toxicity and mobility, necessitating effective remediation strategies. While both microbially induced carbonate precipitation (MICP) and humic acid adsorption are promising methods for heavy metal mitigation, their combined effects, particularly the influence of humic acid on the MICP process, have not been thoroughly investigated. This study explores the interaction between humic acid and MICP, revealing that humic acid significantly inhibits the MICP process by reducing urease activity, with the 10% humic acid treatment resulting in a 23.8% reduction in urease activity compared to the control. Additionally, while higher concentrations of humic acid did not significantly reduce cadmium ion concentrations, they did result in a slight increase in organically bound cadmium, indicating an interaction that could alter metal speciation in the soil. These findings provide important insights into the mechanisms by which humic acid affects MICP, offering a foundation for optimizing combined remediation approaches. Future research should aim to fine-tune the balance between MICP and humic acid to enhance the overall efficiency of cadmium remediation strategies. This study contributes to the development of more effective and sustainable methods for addressing cadmium contamination.

Improving non-uniform gravelly sand using microbially induced carbonate precipitation: An outdoor cubic-meter scale trial by engineering contractors

Soil improvement using microbially induced carbonate precipitation (MICP) remains largely confined to the laboratory, with only a very small number of large-scale experiments having been completed under field conditions and none by engineering contractors. This study presents a cubic-meter scale improvement of heterogeneous natural sand collected from a local quarry, with a wide variation in grain size, via MICP. The MICP trial was conducted by engineering contractors in a cubic test cell under variable temperatures ranging from 5 °C to 19 °C. The upscaling of cultivation of Sporosarcina pasteurii (600 L for each treatment cycle) under non-sterile conditions, as performed by engineering contractors, achieved an optical density (OD600) of 0.89 and a specific urease activity of 2.5 mM urea/min/OD600. Post-MICP-treated sands were subjected to a series of coring, block sampling and laboratory tests. The block sampling process indicated that the majority of sand was effectively cemented, with a small region near a side wall forming a less well-cemented zone, likely induced by less effective fluid delivery in this region. The unconfined compressive strengths of three cores (diameter: 10 cm, length: 22 cm) were 3.6, 4.4, and 7.6 MPa. Consolidated-drained triaxial tests on sub-sampled cores also demonstrated rock-like material behaviour, with a peak friction angle of 43.6° and peak cohesion of 0.64 MPa, and ultimate state frictional angles of 42.0° and ultimate cohesion of 0.12 MPa. The increased shear parameters of the bio-cemented samples (relative to the untreated samples) have many implications for mitigation of geotechnical hazards such as soil liquefaction. The study marks a step forward industrial implementation of MICP for soil improvement by engineering contractors without prior knowledge of MICP.

Carbonic anhydrase-mediated phosphogypsum degradation and enhanced CO2 sequestration: a promising sustainable strategy for biological resource utilization of phosphogypsum.

This study continues our previous investigation of the intrinsic degradation of phosphogypsum (PG) by indigenous microorganisms on amending adequate nutrients. We aim to unravel the intricate mechanisms involved in PG biotransformation by a bacterial consortium. We isolated and characterized seven multi-metal-resistant bacterial strains from a nutrient-amended PG-contaminated microcosm and identified them through 16S rRNA gene sequencing. Primarily aerobic, Gram-positive chemolithotrophs, these strains demonstrated significant heavy metal uptake and PG degradation potential. Further analysis revealed that all strains produced carbonic anhydrase (CA), while six also produced urease, which may facilitate microbial-induced carbonate precipitation. Microstructural and elemental analysis using scanning electron microscopy-energy-dispersive X-ray and X-Ray Diffraction (XRD) confirmed the PG bio-transformation, indicating substantial increases in carbonate concentrations and reductions in sulfate levels. The consortium, composed of seven urease- and CA-producing bacterial strains, effectively degraded PG, transforming it from an acidic to an alkaline state and significantly enhancing CO2 sequestration.

Experimental study on the products of coupling effect between microbial induced carbonate precipitation (MICP) and the pozzolanic effect of metakaolin

In this paper, the performance of the products resulting from of coupling effect between microbial induced carbonate precipitation (MICP) and the pozzolanic effect of metakaolin in the same system is analyzed and discussed in depth. The inoculation parameters of the bacterial solution were optimized, and a method of increasing pH of medium step by step was used to acclimate the alkali tolerance adaptation of Sporosarcina pasteurii. Mixed slurries (MC-M) were prepared and cured for 30 days and 180 days using a ratio of metakaolin (MK) to calcium hydroxide (CH) of 1:1, the bacterial solution as mixing water and calcium acetate as the source of introduced calcium. The compressive strength of the specimens was compared and the properties of the products cured for 180d were analyzed based on test methods such as nanoindentation, SEM, XRD, and TG-DSC. The test results show that the macroscopic mechanical properties of the MC-M specimens were effectively improved and the discrete degree of the micromechanical property parameters was reduced. The particle size distribution of the products increased, within 0.9–12 μm. The decomposition temperature of calcium carbonate in the products decreased, and the water loss temperature of the hydrated products increased. CaCO3 contains both aragonite and calcite phases, and the phase compositions of the hydrated products became more stable. This work demonstrates that MICP accelerates the depletion of CH in the pozzolanic reaction system and promotes the transformation of the hydration product phase composition. The pozzolanic effect reduces the particle size and degree of accumulation of calcite produced by MICP, resulting in a denser cured product. This phenomenon is referred to as the “coupling effect” of the two reactions and positively affects the mechanical properties, providing a new research idea on materials and methods for repairing concrete cracks.

Experimental Study of Erosion Prevention Model by Bio-Cement Sand

Microbially induced carbonate precipitation (MICP) technology is employed to reinforce the surface soil of a dam, aiming to prevent erosion caused by water flow and damage to the dam slope. The relationship between penetration depth, calcium carbonate content, and bonding depth was investigated at eight measuring points on the sand slope surface of a mold under different reinforcement durations. It was observed that as grouting reinforcement times increased, there was a gradual increase in calcium carbonate content but a rapid rise in penetration resistance. Moreover, the bonding depth of sand on the bio-reinforced sand slope increased with higher levels of calcium carbonate content. Microbial grouting reinforcement enhanced soil particle bonding force, requiring water flow to overcome this force for activation of sand particles. Consequently, microbial grouting reinforcement significantly improved shear strength and critical starting flow velocity on sand slope surfaces. The experimental results demonstrated that after MICP surface treatment through spraying, a dense and water-stable hard shell layer composed of bonded calcium carbonate and soil particles formed continuously on sample surfaces, effectively enhancing the strength and erosion resistance of sandy soils. These findings provide reliable evidence for silt slope reinforcement and dam erosion prevention.

Comparison and mechanism study on solidification of loose pisha sandstone by indigenous bacteria and sporosarcina pasteurii

Pisha sandstone is a kind of sandstone which is easy to collapse by water in Shanxi, Shaanxi and Inner Mongolia of China, and suffers from hydraulic erosion all the year round. In recent years, some scholars have used microbial induced calcium carbonate precipitation (MICP) technology to solidify Pisha sandstone to improve the water erosion resistance of Pisha sandstone. However, for the climate environment with low average temperature in Pisha sandstone area, the commonly used Sporosarcina pasteurii are not well adapted. The purpose of this study is to use the indigenous strainsto solidify the loose Pisha sandstone, and to compare the growth adaptability, mechanical properties and water erosion resistance of the solidified layer with Sarcina pasteurii at different temperatures, and to explore the mechanism of different temperatures and strains affecting the microbial solidification of Pisha sandstone from the micro scale. At the same time, a mixed bacterial liquid solidification test was also set up. The results showed that the solidified thickness of indigenous strains was 4.65 % higher than that of Sporosarcina pasteurii, and the thickness and strength of mixed strains were increased by 19.57 % and 36.62 %, respectively. The growth and solidification effect of indigenous strains were less affected by low temperature. Compared with Sporosarcina pasteurii, at low temperature, the bacterial concentration decrease of indigenous strains was reduced by 26.13 %, the thickness loss of solidified layer was reduced by 13.04 %, and the strength loss of solidified layer was reduced by 13.39 %. The effect of low temperature on the growth of bacteria is mainly reflected in affecting the maximum concentration of bacteria and the growth rate. The effect on MICP mainly reflected in affecting the life activities of bacteria and the crystal form and morphology of calcium carbonate. The research results provide a theoretical basis for the MICP technology application of indigenous strains and multi-strains in Pisha sandstone area soil reinforcement and solidification slope.

Innovative and environmentally friendly MICP surface curing: Enhancing mechanical and durability properties of concrete

Concrete curing is a critical factor influencing its mechanical properties and durability. Traditional curing methods, such as water curing and plastic film curing, have significant limitations, including high water consumption and environmental pollution. This study introduces Microbial Induced Carbonate Precipitation (MICP) as an innovative, environmentally friendly curing method for ready-mixed concrete, addressing the urgent need for sustainable construction practices. The feasibility of MICP surface curing is investigated through comprehensive mechanical and durability tests, coupled with microscopic analyses to understand the underlying mechanisms. The results demonstrate that MICP curing substantially enhances concrete performance. Compared to traditional water curing, the samples cured using MICP have increased compressive strength and splitting tensile strength by up to 31.69% and 24.66%, respectively. Additionally, MICP surface curing significantly reduced capillary water absorption, electric flux, and chloride ion migration coefficient by 12.83%, 15.50%, and 17.36%, respectively. It is found that the optimal concentration of Ca2+ in the MICP solution initially improves concrete performance, which then diminishes at higher concentrations due to bacterial activity inhibition. Spraying the MICP solution at appropriate intervals and increasing the number of treatments further improved concrete properties by ensuring a more extensive and dense deposition of CaCO3. Microscopic analyses, including XRD, TG, and SEM-EDS, revealed that MICP surface curing leads to the formation of vaterite and calcite, which densely cover and fill microscopic cracks and pores, ensuring adequate hydration and simultaneously enhancing the concrete's mechanical and durability properties. This study concludes that MICP surface curing provides superior performance than traditional methods and offers a more sustainable and environmentally friendly curing method.

Two factors facilitate the cost-effective and harmless cementation of rare earth slags through MICP technology: Carbonic anhydrase bacteria and endogenous calcium ions

Microbially induced carbonate precipitation (MICP), a solidification/stabilization technique that doesn't interfere with recycling and can reduce the migration of pollutants, has been employed to cement rare earth slags (RES). Currently, the MICP process of the urease/carbonic anhydrase pathway has attracted considerable attention. However, the MICP process of the urease pathway may produce high concentrations of ammonia, which can cause secondary contamination; the addition of a calcium source (calcium chloride) may increase the cost of the treatment process. In this study, two factors, carbonic anhydrase bacteria and endogenous calcium ions (Ca²⁺), facilitated the MICP technology to cost-effectively and harmlessly cement RES and stabilize contaminants. The findings indicated that strain Z1 could utilize endogenous Ca²⁺ to cement the RES, thereby enhancing its unconfined compressive strength, reducing the disintegration rate, radiation dose, and wind erosion intensity, and facilitating the stabilization of heavy metals and radionuclides. In comparison to the CK group, the leaching concentrations of Cu2+, Pb2+, Zn2+, Cd2+, Th(Ⅳ), and U(Ⅵ) in the C1 group were reduced by 42.37 %, 20.20 %, 18.77 %, 22.53 %, 12.32 %, and 23.66 %, respectively. The treatment effect can be further enhanced by adding exogenous Ca2+. This study's findings can help reduce the potential environmental risks in the long-term sequestration of RES, while also providing technical support for the sustainable development of the rare earth industry.

Heavy metal immobilisation with microbial-induced carbonate precipitation: a review

Microbial-induced carbonate precipitation (MICP) is a promising bioremediation technology for heavy metal immobilisation. This review explores the applications and efficacy of MICP in environmental challenges. It provides a comprehensive overview of the mechanism, primarily through ureolysis, detailing the process from urea hydrolysis to heavy metal precipitation as carbonate minerals. Alternative pathways like photosynthesis and nitrate reduction are also discussed, highlighting the broad applicability of MICP. The review covers the historical evolution and advancements of MICP as a sustainable solution for heavy metal contamination. Recent studies demonstrate the efficiency of MICP in achieving high removal rates in diverse environments. The sustainable operation, precise targeting of heavy metal species, and versatility of MICP are examined. Challenges such as high copper concentrations, acidic conditions, and cost considerations are addressed. The article provides future directions and solutions to these challenges, including leveraging machine learning for optimal performance and enhancing cost considerations through detailed analyses. This review improves understanding of MICP’s potential, provides a valuable resource for researchers in environmental engineering and the built environment, and encourages innovative approaches within these fields.

Cd2+ Sequestration by Ureolytic Bacteria Isolated from Goat Faeces and Nursery Wastewater

As modern industrial production makes extensive use of heavy metals, a significant amount of sewage and solid wastes containing heavy metals are released into the environment. There is significant potential for bioremediation of multiple heavy metal contamination using biomineralization to immobilise the toxic metal. In this study, microbially induced carbonate precipitation (MICP) technology was used to treat Cd2+ contamination on plants, humans, and the environment. Ureolytic bacteria that collected from goat faeces and nursery wastewater were stimulated using enrichment technique. Next, physicochemical properties of the bacteria including urea agar base test, biomineralization test, conductivity & pH measurement test and optical density test were examined through enrichment subculturing of the bacteria. The morphological characterization of precipitate formed from both samples were analayzed by using scanning electron microscopy- energy dispersive x-ray diffraction method. Ureolytic bacteria of the goat faeces sample demonstrated greater tolerance to Cd2+ concentration compared to the nursery wastewater sample by obtaining a higher optical density values and larger amounts of precipitate produced by the goat faeces sample across all tested Cd2+ concentrations. As a result, from the atomic absorption spectrophotometry (AAS) analysis, the goat faeces sample showed higher efficiency in removing Cd2+ compared to the nursery wastewater sample, with a removal efficiency of 89.06% for the goat faeces sample and 77.75% for the nursery wastewater sample. Hence, this study confirmed that the interaction between ureolytic bacteria isolated from waste sources and heavy metal ions is vital for the overall effectiveness of heavy metal removal.

Immobilization of Cadmium Via Ureolytic Bacteria Isolated from Greywater Waste and Horse Faeces

With the constant growth of technology and pollution caused by urban expansion, heavy metal contamination has become an alarming concern. The performance of Microbial induced carbonate precipitation technology in immobilizing heavy metal has been demonstrated by several researchers. While various studies have successfully isolated ureolytic bacteria from a variety of sources, there are very limited studies that have focused on isolating them from local waste sources, specifically Greywater and Horse Faeces for MICP application, which benefits in terms of economical, sustainability, and efficiency for engineering purposes. The study aims to investigate the effect of urease-producing bacteria derived from Greywater and horse faeces on heavy metal immobilization. The methods include collecting waste samples, isolating and subculturing of ureolytic bacteria, testing the physiological characteristics of ureolytic bacteria, examining the tolerance test and evaluating heavy metal removal efficacy through Atomic Absorption Spectrophotometry (AAS) analysis, and last but not least, Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) analyses of morphological and mineralogical properties of biominerals formed after heavy metal immobilization treatment. The study found that bacteria from Greywater were more effective at heavy metal immobilization than those from Horse Faeces. Additionally, AAS analysis indicates the greywater-derived bacteria from the residential area sample's exceptional competence in Cd2+ removal, with a significant 80.19% removal rate exceeding the horse faeces bacteria sample's removal rate of 65.26%. The morphological analysis confirmed the presence of heavy metal carbonate in treated heavy metal samples, as well as presenting insight into the effectiveness and application of local ureolytic bacteria's potential for heavy metal toxicity degradation.

AC-assisted microbially induced carbonate precipitation for sand reinforcement: An experimental study

Microbially induced carbonate precipitation (MICP) is a promising method for transforming natural soils into a rock-like material, enhancing soil strength and creating an environmentally friendly engineered geomaterial for load-bearing purposes. Applying alternating current (AC) for enhancing precipitation including changing the crystalline form of the calcium carbonate precipitates appeals as a possible solution to break the upper limit of the unconfined compressive strength (UCS) of bio-treated specimens. To assess the viability of AC-assisted MICP, a series of experiments were designed and conducted under various combination of conditions. The UCS, calcium carbonate content and permeability of the bio-fabricated specimens were obtained to evaluate the treatment effectiveness of AC-assisted MICP. The results demonstrate that the UCS of the sand column exhibits a linear increase with the applied voltage from 10 V to 30 V (i.e., electric field strength from 0.91 V/cm to 2.73 V/cm). The UCS value of the bio-specimen reaches 9.4 MPa after 3 treatments at a concentration of 1.00 mol/L, a voltage of 30 V, and a frequency of 100 Hz. With the assistance of an AC electric field, the adverse impacts caused by high chemical concentrations in the MICP process can be mitigated. We report that a more uniform distribution of the calcium carbonate content of the treated specimen is obtained under an optimal AC frequency of approximately 100 Hz in the current series of experiments. The induced ion vibration under the action of AC results in a change in crystalline form and an increase in the amount and uniformity of crystals precipitated on the surface of the soil grains, supported by X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images. For reference, the energy consumption and the cost for increasing the UCS of the bio-treated specimen to 5 MPa is estimated at 375.86 kWh and 676.55 HK$ per cubic meter, respectively. The findings from our experimental investigation and analysis provide compelling evidence that utilising AC electric field holds great potential for achieving an enhanced treatment effect of MICP and hence a stronger bio-soil.

Remediation of heavy metal contaminated soil in mining areas with vaterite-type biological calcium carbonate

In recent years, research on the remediation of heavy metal contaminated soil by microbially induced carbonate precipitation (MICP) technology has yielded significant findings. However, when utilizing MICP for remediation in situ, urea and calcium chloride may produce high concentrations of NH4+ and Cl-, which subsequently cause secondary pollution. If the biological calcium carbonate (Bio-CaCO3) produced by MICP is employed as a highly efficacious adsorbent, secondary pollution can be avoided while remediating heavy metal pollution. In this study, vaterite-type Bio-CaCO3 was prepared under the regulation of sophorolipids, and the remediation effect and mechanisms for heavy metal contaminated soil were investigated. The results demonstrated that sophorolipids facilitate the formation and stabilization of vaterite-type Bio-CaCO3. The addition of vaterite-type Bio-CaCO3 could notably increase the content of soil organic matter, enhance soil urease activity, and reduce soil catalase activity. On the 30th day of remediation with vaterite-type Bio-CaCO3, the active state content of Pb and Cd in the soil exhibited a decrease of 41.23% and 35.00%, respectively. Additionally, the exchangeable state content demonstrated a reduction of 6.61% and 8.48%, while the carbonate-bound state exhibited an increase of 12.05% and 13.89%, respectively. The principal mechanisms for the remediation of heavy metal contaminated soil by vaterite-type Bio-CaCO3 may be attributed to ion exchange, chemical precipitation, physical adsorption, and complexation reactions. The analysis of the microbial community structure demonstrated that vaterite-type Bio-CaCO3 could enhance the abundance of multiple genera with urease-producing genes, including Pseudomonas, Staphylococcus, and Bacillus while maintaining the soil biodiversity. This study provides a new idea for the remediation of heavy metal contaminated soil around the mining area and offers technical support for the construction of green mines.

Cationic-Modified diatomite as a novel carrier Material for enhanced Microbial-Induced carbonate precipitation in soil reinforcement

To address the low loading efficiency of mineralizing bacteria on conventional bio-carriers, a novel microbial carrier (SMD) was developed by cationically modifying diatomite with amino-modifying agents. The modification degree and surface potential of SMD were assessed using FT-IR and Zeta potential analysis, while thermogravimetric analysis and SEM evaluated the immobilization of mineralizing bacteria. The results indicated that SMD successfully grafted abundant –NH2 groups and, due to their protonation characteristics, carried a positive charge in solutions with a pH below 8.26. A significant amount of negatively charged Sporosarcina pasteurii (S.p) was firmly adsorbed onto the surface of SMD through Coulombic interactions. Compared to the unmodified carrier, the calcium carbonate content generated on the SMD surface after microbial-induced carbonate precipitation (MICP) treatment increased from 12.6% to 23.7%. Furthermore, soil reinforcement experiments demonstrated that this innovative bio-carrier significantly enhanced the repair efficiency of large-diameter pores in the soil, outperforming traditional MICP treatments.

Use of rise husks to improve the efficiency of MICP-based soil improvement technique

Biogrouting has been identified as the best alternative approach for the conventional cement and chemical grouts. Among the various types of biogrouting techniques, microbial induced carbonate precipitation (MICP) has been recently recognized as a promising pathway for producing biogrout material, hence densifying the weak soils. In MICP, calcium carbonate (CaCO3) biocement is produced through biochemical reactions induced by the urease enzyme. The efficiency and productivity of MICP can be further improved by introducing various additives, including fibers, organic polymers, powders, waste materials, etc. In this research, rice husk was sustainably incorporated into the MICP process, and (i) the effect of the rice husk content, (ii) the concentration of the cementation solution and (iii) the treatment time on the unconfined compressive strength (UCS) of the sandy soil were investigated at the laboratory-scale. Cementation solutions with higher concentrations exhibited a higher UCS values than solutions with lower concentrations. Interestingly, the content of rice husk had a marked influence on the UCS, and the optimum rice husk content was 15%. Compared to that of the control sample (0% rice husk), a threefold greater UCS was obtained for 15% of the rice husk content sample. The outcomes further suggested that longer treatment with lower concentration of cementation solution was the best combination for achieving effective cementation within the sand matrix. Rice husk acted as the template for CaCO3 crystals to nucleate while promoting the efficient formation of CaCO3, indicating that the rice husk is an excellent additive to improve the efficiency of the MICP biocementation in a sustainable way.

Field investigation of the feasibility of MICP for Mitigating Natural Rainfall-Induced erosion in gravelly clay slope

Rainfall-induced erosion on slopes is a prevalent natural process leading to soil loss. One promising application of microbially induced carbonate precipitation (MICP) is to mitigate rainfall-induced erosion. Conducting field tests is an essential step to verify and improve its performance. In the current work, field tests were conducted to assess the feasibility of using MICP to mitigate rainfall-induced erosion on a gravelly clay slope in Longyan, Fujian, China. A temporary laboratory was set up to cultivate bacteria, and a non-sterilizing method was employed to prepare large volumes of bacterial suspensions in a single batch. Slopes were treated by spraying solutions onto their surfaces. The amount of discharged soils and 3D surface scanning results were used for evaluating the erosion intensity of the slopes. The results demonstrated that the method could effectively mitigate the surface erosion caused by natural rainfall and prevent erosion-induced collapse. Notably, approximately one year after the treatment, the grass had started to grow on the heavily cemented slope, indicating that the MICP method is both effective and eco-friendly for soil stabilization method. However, further improvements are needed to enhance the uniformity and long-term durability of the MICP treatment.

Magnesium polypeptide combined with microbially induced calcite precipitation for remediation of lead contamination in phosphate mining wasteland soil

Soil Pb contamination is inevitable, as a result of phosphate mining. It is essential to explore more effective Pb remediation approaches in phosphate mining wasteland soil to ensure their viability for a gradual return of soil quality for cultivation. In this study, a Pb-resistant urease-producing bacterium, Serratia marcescens W1Z1, was screened for remediation using microbially induced carbonate precipitation (MICP). Magnesium polypeptide (MP) was prepared from soybean meal residue, and the combined remediation of Pb contamination with MP and MICP in phosphate mining wasteland soil was studied. Remediation of Pb using a combination of MP with MICP strain W1Z1 (WM treatment) was the most effective, with the least exchangeable Pb at 30.37% and the most carbonate-bound Pb at 40.82%, compared to the other treatments, with a pH increase of 8.38. According to the community analysis, MP moderated the damage to microbial abundance and diversity caused by MICP. Total nitrogen (TN) was positively correlated with Firmicutes, pH, and carbonate-bound Pb. Serratia inoculated with strain W1Z1 were positively correlated with bacteria belonging to the Firmicutes phylum and negatively correlated with bacteria belonging to Proteobacteria. The available phosphate (AP) in the phosphate mining wasteland soil could encapsulate the precipitated Pb by ion exchange with carbonate, making it more stable. Combined MP-MICP remediation of Pb contamination in phosphate mining wasteland soil was effective and improved the soil microenvironment.

Effectiveness and mechanism of microbial dust suppressant on coal dust with different metamorphosis degree.

The extraction of coal from open-pit mines significantly contributes to environmental degradation, posing grave risks to human health and the operational stability of machinery. In this milieu, microbial dust suppressants leveraging microbially induced carbonate precipitation (MICP) demonstrate substantial potential for application. This manuscript undertakes an exploration of the dust mitigation efficiency, consolidation attributes, and the fundamental mechanisms of microbial dust suppressants across coal dust samples with varying metamorphic gradations. Empirical observations indicate that, in resistance tests against wind and rain, lignite coal underwent mass losses of 7.43g·m-2·min-1 and 98.62g·m-2·min-1, respectively. The production of consolidating agents within the lignite dust, attributable to the microbial suppressants, was measured at 0.15g per unit mass, a value of 1.25 and 1.07 times greater than that observed in bituminous coal and anthracite, respectively. Scanning electron microscopy coupled with X-ray energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) analyses illuminated that the consolidating products within the coal dust predominantly constituted calcite and vaterite forms of calcium carbonate. The consolidation mechanism of coal dust via microbial suppressants is articulated as follows: Subsequent to the application on coal dust, the suppressants induce the formation of carbonate precipitates with inherent adhesive properties. These carbonates affix to the surfaces of coal dust particles, progressively encapsulating them. Furthermore, they play a pivotal role in bridging and filling the interstices between adjacent dust particles, thereby culminating in the genesis of a dense, cohesive mass capable of withstanding erosive forces.

Effect of sticky rice on the strength and permeability of bio-cemented sand

Microbially induced carbonate precipitation (MICP) is an eco-friendly soil improvement technique. However, this method still has some drawbacks, such as low conversion efficiency of CaCO3 crystallization, insufficient strength for certain applications, and requiring multiple treatments. Previous studies have reported that sticky rice can regulate CaCO3 crystals (i.e., chemical CaCO3) in the sticky rice-lime mortar, showing potential for improving the bio-cementation. Therefore, this study explored the possibility of using sticky rice to enhance the biocementation effect. Tests were carried out to assess the strength and permeability of bio-cemented sand with the inclusion of sticky rice. The results indicated that sticky rice may regulate the type and size of bio-CaCO3 crystals, and the use of an appropriate amount of sticky rice as additive could increase the strength of sand columns by regulating CaCO3 crystallization. Polyhedral calcites may be more favourable for the increasing strength than some vaterites with a hollow spherical structure. The combination of MICP and sticky rice can significantly decrease the coefficient of permeability to a value that was much lower than that by using sticky rice and MICP alone. Bio-CaCO3 immobilized the sticky rice on one end on sand particles, and the reticulated structure of sticky rice divided large pores into small pores, which may be the important cause of the decrease in permeability coefficient. Finally, this study proposed that the MICP with the sticky rice as an additive may enhance the MICP effect and prevent the surface erosion of coarse-grained sand slopes.