Effects of bacterial inoculation and calcium source on microbial-induced carbonate precipitation for lead remediation

β-tricalcium phosphate enhanced biomineralization of Cd2+ and Pb2+ by Sporosarcina ureilytica HJ1 and Sporosarcina pasteurii HJ2

Microbiologically induced CaCO3 precipitation (MICP) has been proposed as a potential bioremediation method to immobilize contaminating metals. In this study, carbonate mineralizing bacteria HJ1 and HJ2, isolated from heavy metal contaminated soil, was employed for Cd2+ and Pb2+ immobilization with or without β-tricalcium phosphate addition. Compared with the only treatments amended with strains, the combined application of β-tricalcium phosphate and HJ1 improved the immobilization rates of Cd and Pb by 1.49 and 1.70 times at 24 h, and the combined application of β-tricalcium phosphate and HJ2 increased the immobilization rates of Cd and Pb by 1.25 and 1.79 times. The characterization of biomineralization products revealed that Cd2+ and Pb2+ primarily immobilized from the liquid phase as CdCO3 and PbCO3, and the addition of β-tricalcium phosphate facilitated the formation of Ca4.03Cd0.97(PO4)3(OH) and Pb3(PO4)2. Also, the calcium source was related to the speciation of carbonate precipitation and improved the Cd and Pb remediation efficiency. This research demonstrated the feasibility and effectiveness of MICP combined with β-tricalcium phosphate in immobilization of Cd and Pb, which will provide a fundamental basis for future applications of MICP to mitigate soil heavy metal pollutions.

Sulfate-reducing consortium HQ23 stabilizes metal(loid)s and activates biological N-fixation in mixed heavy metal-contaminated soil

Sulfate-reducing bacteria (SRB) are used in the remediation of mine pollution; however, the mechanism of stabilizing multiple heavy metal(loid)s by the SRB consortium under low oxygen conditions needs further study. Indigenous microflora were extracted from non-ferrous metal-contaminated soil co-inoculated with enriched SRB consortium and assembled as the HQ23 consortium. The presence of Desulfovibrio (SRB) in HQ23 was confirmed by 16S rRNA sequencing and qPCR. The effects of culture media, dissolved oxygen (DO), SO42¯, and pH on the HQ23 growth rate, and the SO42¯-reducing activity were examined. Data indicates that the HQ23 sustained SRB function under low DO conditions (3.67 ± 0.1 mg/L), but the SRB activity was inhibited at high DO content (5.75 ± 0.39 mg/L). The HQ23 can grow at pH 5 to pH 9 and can decrease mobile or bioavailable Cr, Cu, and Zn concentrations in contaminated soil samples. FTIR revealed that Cu and Cr adsorbed to similar binding sites on bacteria, likely decreasing bacterial Cu toxicity. Increased abundances of DSV (marker for Desulfovibrio) and nifH (N-fixation) genes were observed, as well as an accumulation of nitrate-N content in soils suggesting that HQ23 stimulates the biological N-fixation in soils. This study strongly supports the future application of SRB for the bioremediation of heavy metal-polluted sites.

Microbial-induced carbonate precipitation effectively prevents Pb2+ migration through the soil profile: Lab experiment and model simulation

Due to the inappropriate disposal of waste materials containing lead (Pb) and irrigation with sewage containing Pb, the migration of Pb2+ within the soil profile has been extensively investigated. The conventional Pb2+ block method is challenging to implement due to its complex operational procedures and high construction costs. To address this issue, this study introduces the microbial-induced carbonate precipitation (MICP) technique as a novel approach to impede the migration of Pb2+ in the soil profile. Soil acclimatization with urea resulted in an increased proportion of urease-producing microorganisms, including Bacillus, Paenibacillus, and Planococcaceae, along with heightened expression of urea-hydrolyzing genes (UreA, UreB, UreC, and UreG). This indicates that urea-acclimatized soil (Soil-MICP) possesses the potential to induce carbonate precipitation. Batch Pb2+ fixation experiments confirmed that the fixation efficiency of Soil-MICP on Pb2+ exceeded that of soil without MICP, attributed to the MICP process within the Soil-MICP group. Dynamic migration experiments revealed that the MICP reaction transformed exchangeable lead into carbonate-bound Pb, effectively impeding Pb2+ migration in the soil profile. Additionally, the migration rate of Pb2+ in Soil-MICP was influenced by varying urea amounts, pH levels, and pore flow rates, leading to a slowdown in migration. The Two-site sorption model aptly described the Pb2+ migration process in the Soil-MICP column. This study aims to elucidate the MICP biomineralization process, uncover the in-situ blocking mechanism of MICP on lead in soil, investigate the impact of Pb on key genes involved in urease metabolism, enhance the comprehension of the chemical morphology of lead mineralization products, and provide a theoretical foundation for MICP technology in preventing the migration of Pb2+ in soil profiles.

Struvite and ethylenediaminedisuccinic acid (EDDS) enhance electrokinetic-biological permeable reactive barrier removal of copper and lead from contaminated loess

Removal of heavy metals using the electrokinetic (EK) remediation technology is restricted by soils containing a fraction of clay particles above 12%. Furthermore, it is also affected by hydroxide precipitation (focusing phenomenon) close to the cathode. A modified EK reactor containing a permeable reactive barrier (PRB) was proposed herein where the enzyme-induced carbonate precipitation (EICP) treatment was incorporated into the PRB. Despite that, NH4+-N pollution induced by the urea hydrolysis resulting from the EICP treatment causes serious threats to surrounding environments and human health. There were four types of tests applied to the present work, including CP, TS1, TS2, and TS3 tests. CP test neglected the bio-PRB, while TS1 test considered the bio-PRB. TS2 test based on TS1 test tackled NH4+-N pollution using the struvite precipitation technology. TS3 test based on TS2 test applied EDDS to enhance the removal of Cu and Pb. In CP test, the removal efficiency applied to Cu and Pb removals was as low as approximately 10%, presumably due to the focusing phenomenon. The removal efficiency was elevated to approximately 24% when the bio-PRB and the electrolyte reservoir were involved in TS1 test. TS2 test indicated that the rate of struvite precipitation was 40 times faster than the ureolysis rate, meaning that the struvite precipitate had sequestered NH4+ before it started threatening surrounding environments. The chelation between Cu2+ and EDDS took place when EDDS played a part in TS3 test. It made Cu2+ negatively surface charged by transforming Cu2+ into EDDSCu2-. The chelation caused those left in S4 and S4 to migrate toward the bio-PRB, whereas it also caused those left in S1 and S2 to migrate toward the anode. Due to this reason, the fraction of Cu2+ removed by the bio-PRB and the electrolyte reservoir is raised to 32% and 26% respectively, and the fraction of remaining Cu was reduced to 41%. Also, the removal efficiency applied to Pb removal was raised to 50%. Results demonstrate the potential of struvite and EDDS-assisted EK-PRB technology as a cleanup method for Cu- and Pb-contaminated loess.

Effect of biopolymer chitosan on manganese immobilization improvement by microbial‑induced carbonate precipitation

Microbially induced carbonate precipitation (MICP), as an eco-friendly and promising technology that can transform free metal ions into stable precipitation, has been extensively used in remediation of heavy metal contamination. However, its depressed efficiency of heavy metal elimination remains in question due to the inhibition effect of heavy metal toxicity on bacterial activity. In this work, an efficient, low-cost manganese (Mn) elimination strategy by coupling MICP with chitosan biopolymer as an additive with reduced treatment time was suggested, optimized, and implemented. The influences of chitosan at different concentrations (0.01, 0.05, 0.10, 0.15 and 0.30 %, w/v) on bacterial growth, enzyme activity, Mn removal efficiency and microstructure properties of the resulting precipitation were investigated. Results showed that Mn content was reduced by 94.5 % within 12 h with 0.15 % chitosan addition through adsorption and biomineralization as MnCO3 (at an initial Mn concentration of 3 mM), demonstrating a two-thirds decrease in remediation time compared to the chitosan-absent system, whereas maximum urease activity increased by ∼50 %. Microstructure analyses indicated that the mineralized precipitates were spherical-shaped MnCO3, and a smaller size and more uniform distribution of MnCO3 is obtained by the regulation of abundant amino and hydroxyl groups in chitosan. These results demonstrate that chitosan accelerates nucleation and tunes the growth of MnCO3 by providing nucleation sites for mineral formation and alleviating the toxicity of metal ions, which has the potential to upgrade MICP process in a sustainable and effective manner. This work provides a reference for further understanding of the biomineralization regulation mechanism, and gives a new perspective into the application of biopolymer-intensified strategies of MICP technology in heavy metal contamination.

Deterioration phenomenon of Pb-contaminated aqueous solution remediation and enhancement mechanism of nano-hydroxyapatite-assisted biomineralization

Modern metallurgical and smelting activities discharge the lead-containing wastewater, causing serious threats to human health. Bacteria and urease applied to microbial-induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) are denatured under high Pb2+ concentration. The nano-hydroxyapatite (nHAP)-assisted biomineralization technology was applied in this study for Pb immobilization. Results showed that the extracellular polymers and cell membranes failed to secure the urease activity when subjected to 60 mM Pb2+. The immobilization efficiency dropped to below 50% under MICP, whereas it due to a lack of extracellular polymers and cell membranes dropped to below 30% under EICP. nHAP prevented the attachment of Pb2+ either through competing with bacteria and urease or promoting Ca2+/Pb2+ ion exchange. Furthermore, CO32- from ureolysis replaced the hydroxyl (-OH) in hydroxylpyromorphite to encourage the formation of carbonate-bearing hydroxylpyromorphite of higher stability (Pb10(PO4)6CO3). Moreover, nHAP application overcame an inability to provide nucleation sites by urease. As a result, the immobilization efficiency, when subjected to 60 mM Pb2+, elevated to above 80% under MICP-nHAP and to some 70% under EICP-nHAP. The findings highlight the potential of applying the nHAP-assisted biomineralization technology to Pb-containing water bodies remediation.

Application and mechanism of carbonate material in the treatment of heavy metal pollution: a review

Among the many heavy metal pollution treatment agents, carbonate materials show strong flexibility and versatility by virtue of their high adsorption capacity for heavy metals and the characteristics of multiple and simple modification methods. It shows good potential for development. This review summarizes the application of carbonate materials in the treatment of heavy metal pollution according to the research of other scholars. It mainly relates to the application of surface-modified, activated, and nano-sized carbonate materials in the treatment of heavy metal pollution in water. Natural carbonate minerals and composite carbonate minerals solidify and stabilize heavy metals in soil. Solidification of heavy metals in hazardous waste solids is by MICP. There are four aspects of calcium carbonate oligomers curing heavy metals in fly ash from waste incineration. The mechanism of treating heavy metals by carbonate in different media was discussed. However, in the complex environment where multiple types of pollutants coexist, questions on how to maintain the efficient processing capacity of carbonate materials and how to use MICP to integrate heavy metal fixation and seepage prevention in solid waste base under complex and changeable natural environment deserve our further consideration. In addition, the use of carbonate materials for the purification of trace radioactive wastewater and the safe treatment of trace radioactive solid waste are also worthy of further exploration.

Biogenic calcium improved Cd2+ and Pb2+ immobilization in soil using the ureolytic bacteria Bacillus pasteurii

Bioremediation based on microbial-induced carbonate precipitation (MICP) was conducted in cadmium and lead contaminated soil to investigate the effects of MICP on Cd and Pb in soil. In this study, soil indigenous nitrogen was shown to induce MICP to stabilize heavy metals without inputting exogenous urea. The results showed that applying Bacillus pasteurii coupled with CaCl2 reduced Cd and Pb bioavailability, which could be clarified through the proportion of exchangeable Cd and Pb in soil decreasing by 23.65 % and 12.76 %, respectively. Moreover, B. pasteurii was combined separately with hydroxyapatite (HAP), eggshells (ES), and oyster shells (OS) to investigate their effects on soil heavy metals' chemical fractions, toxicity characteristic leaching procedure (TCLP)-extractable Cd and Pb as well as enzymatic activity. Results showed that applying B. pasteurii in soil significantly decreased the heavy metals in the exchangeable fraction and increased them in the carbonate phase fraction. When B. pasteurii was combined with ES and OS, the content of carbonate-bound Cd increased by 114.72 % and 118.81 %, respectively, significantly higher than when B. pasteurii was combined with HAP, wherein the fraction of carbonate-bound Cd increased by 86 %. The combination of B. pasteurii and biogenic calcium effectively reduced the leached contents of Cd and Pb in soil, and the TCLP-extractable Cd and Pb fractions decreased by 43.88 % and 30.66 %, respectively, in the BP + ES group and by 52.60 % and 41.77 %, respectively, in the BP + OS group. This proved that MICP reduced heavy metal bioavailability in the soil. Meanwhile, applying B. pasteurii and calcium materials significantly increased the soil urease enzyme activity. The microstructure and chemical composition of the soil samples were studied, and the results from scanning electron microscope, Fourier transform infra-red spectroscopy, and X-ray diffraction demonstrated the MICP process and identified the formation of CaCO3, Ca0.67Cd0.33CO3, and PbCO3 in heavy metal-contaminated soil.

The interplay between microbial communities and soil properties

In recent years, there has been considerable progress in determining the soil properties that influence the structure of the soil microbiome. By contrast, the effects of microorganisms on their soil habitat have received less attention with most previous studies focusing on microbial contributions to soil carbon and nitrogen dynamics. However, soil microorganisms are not only involved in nutrient cycling and organic matter transformations but also alter the soil habitat through various biochemical and biophysical mechanisms. Such microbially mediated modifications of soil properties can have local impacts on microbiome assembly with pronounced ecological ramifications. In this Review, we describe the processes by which microorganisms modify the soil environment, considering soil physics, hydrology and chemistry. We explore how microorganism-soil interactions can generate feedback loops and discuss how microbially mediated modifications of soil properties can serve as an alternative avenue for the management and manipulation of microbiomes to combat soil threats and global change.

Synergistic promotion of sludge reduction by surfactant-producing and lysozyme-producing bacteria: Optimization and effect of Na. BIORESOURCE TECHNOLOGY 2024;393:130065. [PMID: 37984671 DOI: 10.1016/j.biortech.2023.130065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

To improve the efficiency of aerobic digestion, this investigation utilized the synergistic effect of lysozyme-producing strain YH14 and surfactant-producing strain ZXY4 to promote sludge hydrolysis, and added NaCl to enhance this promoting effect. The best performance in promoting sludge hydrolysis was achieved when the inoculum of functional bacteria was 12 % (inoculum ratio of strain YH14: strain ZXY4 = 1:3) and the dosage of NaCl was 5 g L-1, which caused an increase of 19.25 % in the SS removal rate and 2588.21 mg L-1 in the SCOD release, as compared with the control. Fluorescence region integral analysis shows that the synergy of two functional bacteria and NaCl can enhance the biodegradability of sludge. Protein secondary structure analysis shows that strain ZXY4 and Na+ cause the EPS structure to loosen, increasing the chances of lysozyme lysis of bacteria. Nucleotide metabolism, metabolism of other amino acids and membrane transport enhanced in a co-processing system.

Microbial induced carbonate precipitation for remediation of heavy metals, ions and radioactive elements: A comprehensive exploration of prospective applications in water and soil treatment

Improper disposal practices have caused environmental disruptions, possessing by heavy metal ions and radioactive elements in water and soil, where the innovative and sustainable remediation strategies are significantly imperative in last few decades. Microbially induced carbonate precipitation (MICP) has emerged as a pioneering technology for remediating contaminated soil and water. Generally, MICP employs urease-producing microorganisms to decompose urea (NH2CONH2) into ammonium (NH4+and carbon dioxide (CO2), thereby increasing pH levels and inducing carbonate precipitation (CO32-), and effectively removing remove contaminants. Nonetheless, the intricate mechanism underlying heavy metal mineralization poses a significant challenge, constraining its application in contaminants engineering, particularly in the context of prolonged heavy metal leaching over time and its efficacy in adverse environmental conditions. This review provides a comprehensive idea of recent development of MICP and its application in environmental engineering, examining metabolic pathways, mineral precipitation mechanisms, and environmental factors as well as providing future perspectives for commercial utilization. The use of ureolytic bacteria in MICP demonstrates cost-efficiency, environmental compatibility, and successful pollutant abatement over tradition bioremediation techniques, and bio-synthesis of nanoparticles. limitations such as large-scale application, elevated Ca2+levels in groundwater, and gradual contaminant release need to be overcome. The possible future research directions for MICP technology, emphasizing its potential in conventional remediation, CO2 sequestration, bio-material synthesis, and its role in reducing environmental impact for long-term economic benefits.

Mechanisms of ammonia, calcium and heavy metal removal from nutrient-poor water by Acinetobacter calcoaceticus strain HM12

An Acinetobacter calcoaceticus strain HM12 capable of heterotrophic nitrification-aerobic denitrification (HN-AD) under nutrient-poor conditions was isolated, with an ammonia nitrogen (NH4+-N) removal efficiency of 98.53%. It can also remove heavy metals by microbial induced calcium precipitation (MICP) with a Ca2+ removal efficiency of 75.91%. Optimal conditions for HN-AD and mineralization of the strain were determined by kinetic analysis (pH = 7, C/N = 2.0, Ca2+ = 70.0 mg L-1, NH4+-N = 5.0 mg L-1). Growth curves and nitrogen balance elucidated nitrogen degradation pathways capable of converting NH4+-N to gaseous nitrogen. The analysis of the bioprecipitation showed that Zn2+ and Cd2+ were removed by the MICP process through co-precipitation and adsorption (maximum removal efficiencies of 93.39% and 80.70%, respectively), mainly ZnCO3, CdCO3, ZnHPO4, Zn3(PO4)2 and Cd3(PO4)2. Strain HM12 produces humic and fulvic acids to counteract the toxicity of pollutants, as well as aromatic proteins to increase extracellular polymers (EPS) and promote the biomineralization process. This study provides a experimental evidence for the simultaneous removal of multiple pollutants from nutrient-poor waters.

Immobilized bioreactor for enhanced ammonia, phosphorus, and phenol removal and effects of phenol on microbial communities, potential functions, and nitrogen metabolism

In the present study, an immobilized bioreactor was established to remove ammonia (NH4+-N), phosphate (PO43--P), and phenol using composite mycelium spheres (CMP) as the immobilization material in combination with Pseudomonas sp. Y1. Under optimal operating conditions, the bioreactor achieved 98.07, 91.71, and 92.57 % removal of NH4+-N, PO43--P, and phenol, respectively. The results showed that the bioreactor removed PO43--P by biomineralization and co-precipitation. Phenol removal relied on a Fenton-like reaction achieved by CMP-induced quinone redox cycling. High-throughput sequencing analysis and functional gene prediction indicated that Pseudomonas was the dominant genus and that the bioreactor had much potential for nitrogen removal, respectively. In addition, phenol affected the performance of functional genes and the associated enzymes, which influenced the nitrogen metabolism process in the bioreactor. This work serves as a guideline for the development of more stable and sustainable composite pollution removal technologies and fungal-bacterial symbiotic systems.

Applying the first microcapsule-based self-healing microbial-induced calcium carbonate materials to prevent the migration of Pb ions

Lead (Pb) accumulation can lead to serious threats to surrounding environments and damage to the liver and kidneys. In the past few years, microbial-induced carbonate precipitation (MICP) technology has been widely applied to achieve Pb immobilization due to its environmentally friendly nature. However, harsh pH conditions can cause the instability of the carbonate precipitation to degrade or dissolve, increasing the potential of Pb2+ migration into nearby environments. In this study, microcapsule-based self-healing microbial-induced calcium carbonate (MICC) materials were applied to prevent Pb migration. The highest sporulation rate of 95.8% was attained at 7 g/L yeast extract, 10 g/L NH4Cl, and 3.6 g/L Mn2+. In the germination phase, the microcapsule not only prevented the bacterial spores from being threatened by the acid treatment but secured their growth and reproduction. Micro analysis also revealed that cerussite, calcite, and aragonite minerals were present, while extracellular polymeric substances (EPSs) were identified via Fourier transform infrared spectroscopy (FTIR). These results confirm their involvement in combining Pb2+ and Ca2+. The immobilization efficiency of above 90% applied to MICC materials was attained, while it of below 5% applied to no MICC use was attained. The findings explore the potential of applying microcapsule-based self-healing MICC materials to prevent Pb ion migration when the calcium carbonate degrades under harsh pH conditions.

Study on Cu- and Pb-contaminated loess remediation using electrokinetic technology coupled with biological permeable reactive barrier

Although the electrokinetic (EK) remediation has drawn great attention because of its good maneuverability, the focusing phenomenon near the cathode and low removal efficiency remain to be addressed. In this study, a novel EK reactor was proposed to remediate Cu and Pb contaminated loess where a biological permeable reactive barrier (bio-PRB) was deployed to the middle of the EK reactor. For comparison, three test configurations, namely, CG, TG-1, and TG-2, were available. CG considered the multiple enzyme-induced carbonate precipitation (EICP) treatments, while TG-1 considered both the multiple EICP treatments and pH regulation. TG-2 further considered NH4+ recovery based on TG-1. CG not only improved Cu and Pb removals by the bio-PRB but also depressed the focusing phenomenon. TG-1 causes more Cu2+ and Pb2+ to migrate toward the bio-PRB and aggravates Cu and Pb removals by the bio-PRB, depressing the focusing phenomenon. TG-2 depressed the focusing phenomenon the most because Cu2+ and Pb2+ can combine with not only CO32- but PO43-. The removal efficiency of Cu and Pb is 34% and 36%, respectively. A NH4+ recovery of about 100% is attained.

Biopolymer-assisted enzyme-induced carbonate precipitation for immobilizing Cu ions in aqueous solution and loess

Wastewater, discharged in copper (Cu) mining and smelting, usually contains a large amount of Cu2+. Immobilizing Cu2+ in aqueous solution and soils is deemed crucial in preventing its migration into surrounding environments. In recent years, the enzyme-induced carbonate precipitation (EICP) has been widely applied to Cu immobilization. However, the effect of Cu2+ toxicity denatures and even inactivates the urease. In the present work, the biopolymer-assisted EICP technology was proposed. The inherent mechanism affecting Cu immobilization was explored through a series of test tube experiments and soil column tests. Results indicated that 4 g/L chitosan may not correspond to a higher immobilization efficiency because it depends as well on surrounding pH conditions. The use of Ca2+ not only played a role in further protecting urease and regulating the environmental pH but also reduced the potential for Cu2+ to migrate into nearby environments when malachite and azurite minerals are wrapped by calcite minerals. The species of carbonate precipitation that are recognized in the numerical simulation and microscopic analysis supported the above claim. On the other hand, UC1 (urease and chitosan colloid) and UC2 (urea and calcium source) grouting reduced the effect of Cu2+ toxicity by transforming the exchangeable state-Cu into the carbonate combination state-Cu. The side effect, induced by 4 g/L chitosan, promoted the copper-ammonia complex formation in the shallow ground, while the acidic environments in the deep ground prevented Cu2+ from coordinating with soil minerals. These badly degraded the immobilization efficiency. The Raman spectroscopy and XRD test results tallied with the above results. The findings shed light on the potential of applying the biopolymer-assisted EICP technology to immobilizing Cu ions in water bodies and sites.

Heavy metals remediation through bio-solidification: Potential application in environmental geotechnics

Heavy metals are pervasive pollutants found in water, soil, and solid wastes. Bio-solidification offers an environmentally friendly approach to immobilize heavy metal ions using two types of bacteria: urease-producing bacteria (UPB) and phosphatase-producing bacteria (PPB). UPB, exemplified by Sporosarcina pasteurii, secretes urease to hydrolyze urea and generate CO32- ions, while PPB, like Bacillus subtilis, produces alkaline phosphatase to hydrolyze organophosphate monoester (ROP) and produce PO43- ions. These ions react with heavy metal ions, effectively reducing their concentration by forming insoluble carbonate or phosphate precipitates. The success of bio-solidification is influenced by various factors, including substrate concentration, temperature, pH, and bacterial density. Optimal operational conditions can significantly enhance the remediation performance of heavy metals. UPB and PPB hold great potential for remediating heavy metal pollution in diverse contaminated areas such as tailings ponds, electroplating sewage, and garbage incineration plants. In conclusion, harnessing the power of these microbial methods can provide effective solutions for remediating heavy metal-induced pollution across a range of environmental conditions.

Bioreduction and mineralization of Cr(VI) by Sporosarcina saromensis W5 induced carbonate precipitation

The microbial reduction of Cr(VI) to Cr(III) is widely applied, but most studies ignored the stability of reduction products. In this study, the Cr(VI)-reducing bacterium of Sporosarcina saromensis combined with microbially induced carbonate precipitation (MICP) was used to explore the reduction and mineralization mechanisms of Cr(VI). The results indicated that the high concentration of Ca2+ could significantly enhance the reduction and mineralization of Cr(VI). The highest reduction and mineralization efficiencies of 99.5% and 55.9% were achieved at 4 g/L Ca2+. Moreover, the urease activity of S. saromensis in the experimental group was up to 13.28 U/mg NH3-N. Besides, the characteristic results revealed that Cr(VI) and reduced Cr(III) were absorbed on the surface or got into the interspace of CaCO3, which produced a new stable phase (Ca10Cr6O24(CO3)). Overall, the combination of S. saromensis and MICP technology might be a high-efficiency and environmentally friendly strategy for further application in the Cr(VI)-containing groundwater.

Microbial functionalities and immobilization of environmental lead: Biogeochemical and molecular mechanisms and implications for bioremediation

The increasing environmental and human health concerns about lead in the environment have stimulated scientists to search for microbial processes as innovative bioremediation strategies for a suite of different contaminated media. In this paper, we provide a compressive synthesis of existing research on microbial mediated biogeochemical processes that transform lead into recalcitrant precipitates of phosphate, sulfide, and carbonate, in a genetic, metabolic, and systematics context as they relate to application in both laboratory and field immobilization of environmental lead. Specifically, we focus on microbial functionalities of phosphate solubilization, sulfate reduction, and carbonate synthesis related to their respective mechanisms that immobilize lead through biomineralization and biosorption. The contributions of specific microbes, both single isolates or consortia, to actual or potential applications in environmental remediation are discussed. While many of the approaches are successful under carefully controlled laboratory conditions, field application requires optimization for a host of variables, including microbial competitiveness, soil physical and chemical parameters, metal concentrations, and co-contaminants. This review challenges the reader to consider bioremediation approaches that maximize microbial competitiveness, metabolism, and the associated molecular mechanisms for future engineering applications. Ultimately, we outline important research directions to bridge future scientific research activities with practical applications for bioremediation of lead and other toxic metals in environmental systems.

Clean-Up of Heavy Metals from Contaminated Soil by Phytoremediation: A Multidisciplinary and Eco-Friendly Approach

Pollution from heavy metals is one of the significant environmental concerns facing the world today. Human activities, such as mining, farming, and manufacturing plant operations, can allow them access to the environment. Heavy metals polluting soil can harm crops, change the food chain, and endanger human health. Thus, the overarching goal for humans and the environment should be the avoidance of soil contamination by heavy metals. Heavy metals persistently present in the soil can be absorbed by plant tissues, enter the biosphere, and accumulate in the trophic levels of the food chain. The removal of heavy metals from contaminated soil can be accomplished using various physical, synthetic, and natural remediation techniques (both in situ and ex situ). The most controllable (affordable and eco-friendly) method among these is phytoremediation. The removal of heavy metal defilements can be accomplished using phytoremediation techniques, including phytoextraction, phytovolatilization, phytostabilization, and phytofiltration. The bioavailability of heavy metals in soil and the biomass of plants are the two main factors affecting how effectively phytoremediation works. The focus in phytoremediation and phytomining is on new metal hyperaccumulators with high efficiency. Subsequently, this study comprehensively examines different frameworks and biotechnological techniques available for eliminating heavy metals according to environmental guidelines, underscoring the difficulties and limitations of phytoremediation and its potential application in the clean-up of other harmful pollutants. Additionally, we share in-depth experience of safe removing the plants used in phytoremediation-a factor frequently overlooked when choosing plants to remove heavy metals in contaminated conditions.

Investigating immobilization efficiency of Pb in solution and loess soil using bio-inspired carbonate precipitation

Lead (Pb) metal accumulation in surrounding environments can cause serious threats to human health, causing liver and kidney function damage. This work explored the potential of applying the MICP technology to remediate Pb-rich water bodies and Pb-contaminated loess soil sites. In the test tube experiments, the Pb immobilization efficiency of above 85% is attained through PbCO₃ and Pb(CO₃)₂(OH)₂ precipitation. Notwithstanding that, in the loess soil column tests, the Pb immobilization efficiency decreases with the increase in depth and could be as low as approximately 40% in the deep ground. PbCO₃ and Pb(CO₃)₂(OH)₂ precipitation has not been detected as the majority of Pb²⁺ combines with -OH (hydroxyl group) when subjected to 500 mg/kg Pb²⁺. The alkaline front promotes the chemisorption of Pb²⁺ with CO₃^2- reducing the depletion of quartz mineral close to the surface. However, OH^- is in shortage in the deep ground retarding the Pb immobilization. The Pb immobilization efficiency thus decreases with the increase in depth. Quartz and albite minerals, when subjected to 16,000 mg/kg Pb²⁺, appear not to intervene in the chemisorption with Pb²⁺ where the chemisorption of Pb²⁺ with CO₃^2- plays a major role in the Pb immobilization. Compared to the nanoscale urease applied to the enzyme-induced carbonate precipitation (EICP) technology, the micrometer scale ureolytic bacteria penetrate into the deep ground with difficulty. The 'size' issue remains to be addressed in near future.

A review of important heavy metals toxicity with special emphasis on nephrotoxicity and its management in cattle

Toxicity with heavy metals has proven to be a significant hazard with several health problems linked to it. Heavy metals bioaccumulate in living organisms, pollute the food chain, and possibly threaten the health of animals. Many industries, fertilizers, traffic, automobile, paint, groundwater, and animal feed are sources of contamination of heavy metals. Few metals, such as aluminum (Al), may be eliminated by the elimination processes, but other metals like lead (Pb), arsenic (As), and cadmium (Ca) accumulate in the body and food chain, leading to chronic toxicity in animals. Even if these metals have no biological purpose, their toxic effects are still present in some form that is damaging to the animal body and its appropriate functioning. Cadmium (Cd) and Pb have negative impacts on a number of physiological and biochemical processes when exposed to sub-lethal doses. The nephrotoxic effects of Pb, As, and Cd are well known, and high amounts of naturally occurring environmental metals as well as occupational populations with high exposures have an adverse relationship between kidney damage and toxic metal exposure. Metal toxicity is determined by the absorbed dosage, the route of exposure, and the duration of exposure, whether acute or chronic. This can lead to numerous disorders and can also result in excessive damage due to oxidative stress generated by free radical production. Heavy metals concentration can be decreased through various procedures including bioremediation, pyrolysis, phytoremediation, rhizofiltration, biochar, and thermal process. This review discusses few heavy metals, their toxicity mechanisms, and their health impacts on cattle with special emphasis on the kidneys.

Immobilizing lead and copper in aqueous solution using microbial- and enzyme-induced carbonate precipitation

Inappropriate irrigation could trigger migration of heavy metals into surrounding environments, causing their accumulation and a serious threat to human central nervous system. Traditional site remediation technologies are criticized because they are time-consuming and featured with high risk of secondary pollution. In the past few years, the microbial-induced carbonate precipitation (MICP) is considered as an alternative to traditional technologies due to its easy maneuverability. The enzyme-induced carbonate precipitate (EICP) has attracted attention because bacterial cultivation is not required prior to catalyzing urea hydrolysis. This study compared the performance of lead (Pb) and copper (Cu) remediation using MICP and EICP respectively. The effect of the degree of urea hydrolysis, mass and species of carbonate precipitation, and chemical and thermodynamic properties of carbonates on the remediation efficiency was investigated. Results indicated that ammonium ion (NH4+) concentration reduced with the increase in lead ion (Pb2+) or copper ion (Cu2+) concentration, and for a given Pb2+ or Cu2+ concentration, it was much higher under MICP than EICP. Further, the remediation efficiency against Cu2+ is approximately zero, which is way below that against Pb2+ (approximately 100%). The Cu2+ toxicity denatured and even inactivated the urease, reducing the degree of urea hydrolysis and the remediation efficiency. Moreover, the reduction in the remediation efficiency against Pb2+ and Cu2+ appeared to be due to the precipitations of cotunnite and atacamite respectively. Their chemical and thermodynamic properties were not as good as calcite, cerussite, phosgenite, and malachite. The findings shed light on the underlying mechanism affecting the remediation efficiency against Pb2+ and Cu2+.

Immobilizing of lead and copper using chitosan-assisted enzyme-induced carbonate precipitation

Enzyme-induced carbonate precipitation (EICP) is considered as an environmentally friendly method for immobilizing heavy metals (HMs). The fundamental of the EICP method is to catalyze urea hydrolysis using the urease, discharging CO₃^2- and NH₄⁺. CO₃^2- helps to form carbonates that immobilize HMs afterwards. However, HMs can depress urease activity and reduce the degree of urea hydrolysis. Herein, the potential of applying the chitosan-assisted EICP method to Pb and Cu immobilization was explored. The chitosan addition elevated the degree of urea hydrolysis when subjected to the effect of Cu²⁺ toxicity where the protective effect, flocculation and adsorption, and the formation of precipitation, play parts in improving the Cu immobilization efficiency. The use of chitosan addition, however, also causes the side effect (copper-ammonia complex formation). Two calcium source additions, CaCl₂ and Ca(CH₃COO)₂, intervened in the test tube experiments not only to prevent pH from raising to values where Cu²⁺ complexes with NH₃ but also to separate the urease enzyme and Cu²⁺ from each other with the repulsion of charges. The FTIR spectra indicate that the chitosan addition adsorbs Cu²⁺ through its surface hydroxyl and carboxyl groups, while the SEM images distinguish who the mineral are nucleating with. The findings shed light on the potential of applying the chitosan-assisted EICP method to remedy lead- and copper-rich water bodies.

Immobilizing copper in loess soil using microbial-induced carbonate precipitation: Insights from test tube experiments and one-dimensional soil columns

Biomineralization as an alternative to traditional remediation measures has been widely applied to remediate copper (Cu)-contaminated sites due to its environmental-friendly nature. Immobilizing Cu is, however, a challenging task as it inevitably causes inactivation of ureolytic bacteria. In the present work, a series of test tube experiments were conducted to derive the relationships of Cu immobilization efficiency versus pH conditions. The Cu speciation transformation that is invisible in the test tube experiments was investigated via numerical simulations. Apart from that, the one-dimensional soil column tests, accompanied by the X-ray diffraction (XRD) and Raman spectroscopy analysis, mainly aimed not only to investigate the variations of Cu immobilization efficiency with the depth but to reveal the underlying mechanisms affecting the Cu immobilization efficiency. The results of the test tube experiments highlight the necessity of narrowing pH ranges to as close as 7 by introducing an appropriate bacterial inoculation proportion. The coordination adsorption of Cu, while performing the one-dimensional soil column tests, is encouraged by alkaline environments, which differs from the test tube experiments where Cu²⁺ is capsulized by carbonate precipitates to prevent their migration. The findings highlight the potential of applying the microbial-induced carbonate precipitation (MICP) technology to Cu-rich water bodies and Cu-contaminated sites remediation.

Heavy metal bioremediation using microbially induced carbonate precipitation: Key factors and enhancement strategies

With the development of economy, heavy metal (HM) contamination has become an issue of global concern, seriously threating animal and human health. Looking for appropriate methods that decrease their bioavailability in the environment is crucial. Microbially induced carbonate precipitation (MICP) has been proposed as a promising bioremediation method to immobilize contaminating metals in a sustainable, eco-friendly, and energy saving manner. However, its performance is always affected by many factors in practical application, both intrinsic and external. This paper mainly introduced ureolytic bacteria-induced carbonate precipitation and its implements in HM bioremediation. The mechanism of HM immobilization and in-situ application strategies (that is, biostimulation and bioaugmentation) of MICP are briefly discussed. The bacterial strains, culture media, as well as HMs characteristics, pH and temperature, etc. are all critical factors that control the success of MICP in HM bioremediation. The survivability and tolerance of ureolytic bacteria under harsh conditions, especially in HM contaminated areas, have been a bottleneck for an effective application of MICP in bioremediation. The effective strategies for enhancing tolerance of bacteria to HMs and improving the MICP performance were categorized to provide an in-depth overview of various biotechnological approaches. Finally, the technical barriers and future outlook are discussed. This review may provide insights into controlling MICP treatment technique for further field applications, in order to enable better control and performance in the complex and ever-changing environmental systems.

Microbially induced calcium precipitation coupled with medical stone-coated sponges: A targeted strategy for enhanced nitrate and fluoride removal from groundwater

The coexistence of nitrate and fluoride in groundwater is of high concern due to its potential environmental impacts and health risks. Medical stone-coated sponges, as a microbial activity promoter and slow-release calcium source, were introduced into an immobilized bioreactor for enhanced removal of nitrate and fluoride. Under the hydraulic retention time of 3 h, nitrate, fluoride, and calcium contents of 16.5, 3.0, and 100 mg L^-1, the average removal efficiencies of nitrate, fluoride, and calcium reached 99.49%, 74.26%, and 70.43%, respectively. Co-precipitation and chemisorption were the mechanisms for fluoride and calcium removal. Medical stone load improved the competitiveness of dominant bacteria and electron transport activity, accelerated the denitrification process, and stimulated biofilm formation. High fluoride level (5.0 mg L^-1) inhibited the nitrate removal and aromatic protein production. The fluoride content changes altered the carbon source preference of the microbial community, which preferred to use amino acids and carbohydrates under a higher fluoride content. The introduction of medical stones significantly accelerated the fluoride and nitrate removal, providing a new insight for the application of microbially induced calcium precipitation technique in the remediation of low-calcium groundwater.

Enhanced nitrate, fluoride, and phenol removal using polyurethane sponges loaded with rice husk biochar in immobilized bioreactor

Polyurethane sponges loaded with rice husk biochar were prepared to immobilize Aquabacterium sp. CZ3 for intensified removal of nitrate, fluoride (F-), and phenol, with the maximum efficiency of 100 %, 91 %, and 99 %, respectively. The biochar load and increased carbon-to-nitrogen (C:N) ratio (below 3.0) stimulated the secretion of soluble microbial product, improved the electron transport system activity, and promoted denitrification, phenol co-metabolism, and F- and calcium crystallization. The characterization results suggested that F- was removed as fluoride-containing calcium precipitates. According to the microbial community analyses, Aquabacterium was the dominant bacterium. PICRUSt analyses showed that biochar and adequate carbon sources (C:N ratio 3.0) significantly increased the functional abundances of amino acid metabolism, carbohydrate metabolism, energy metabolism, and cell motility. The introduction of biochar reduces the demand for C:N ratio in the system, and expands the application potential of biomineralization technique in the remediation of multiple pollutants contaminated water.

Catalyzing urea hydrolysis using two-step microbial-induced carbonate precipitation for copper immobilization: Perspective of pH regulation

Microbial induced carbonate precipitation (MICP) has recently applied to immobilize heavy metals toward preventing their threats to public health and sustainable development of surrounding environments. However, for copper metallurgy activities higher copper ion concentrations cause the ureolytic bacteria to lose their activity, leading to some difficulty in forming carbonate precipitation for copper immobilization (referred to also as “biomineralization”). A series test tube experiments were conducted in the present work to investigate the effects of bacterial inoculation and pH conditions on the copper immobilization efficiency. The numerical simulations mainly aimed to compare with the experimental results to verify its applicability. The copper immobilization efficiency was attained through azurite precipitation under pH in a 4–6 range, while due to Cu²⁺ migration and diffusion, it reduced to zero under pH below 4. In case pH fell within a 7–9 range, the immobilization efficiency was attained via malachite precipitation. The copper-ammonia complexes formation reduced the immobilization efficiency to zero. The reductions were attributed either to the low degree of urea hydrolysis or to inappropriate pH conditions. The findings shed light on the necessity of securing the urease activity and modifying pH conditions using the two-step biomineralization approach while applying the MICP technology to remedy copper-rich water bodies.

Passivation of heavy metals in copper-nickel tailings by in-situ bio-mineralization: A pilot trial and mechanistic analysis

Metal tailings contain a variety of toxic heavy metals and have potential environmental risks owing to long-term open piling. In the present study, a strain of ureolytic bacteria with bio-mineralization ability, Lysinibacillus fusiformis strain Lf, was isolated from copper-nickel mine tailings in Xinjiang and applied to a pilot trial of tailings solidification under field conditions. The results of the pilot trial (0.5 m³ in scale) showed that strain Lf effectively solidified the tailings. The compressive strength of the solidified tailings increased by 121 ± 9 % and the permeability coefficient decreased by 68 ± 3 %. Compared to the control, the leaching reduction of the solidified tailings of Cu and Ni was >98 %, and that of As was 92.5 ± 1.7 %. Two mechanisms of tailings solidification and heavy metal passivation were proposed based on the findings of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDS) mapping. Biogenic calcite filled the interstices of the tailings particles and cemented the adjacent particles. This improved the mechanical properties and reduced permeability. Moreover, heavy metal colloids were incorporated into large-sized calcite crystals, and heavy metal ions were sequestered within the calcite lattice. This method of using indigenous ureolytic bacteria to solidify tailings was successful in this work and may be replicated to remediate other tailings.

Micro-dynamic process of cadmium removal by microbial induced carbonate precipitation

Microbially induced carbonate precipitation (MICP) is a technique used extensively to address heavy metal pollution but its micro-dynamic process remains rarely explored. In this study, A novel Cd-tolerant ureolytic bacterium DL-1 (Pseudochrobactrum sp.) was used to study the micro-dynamic process. With conditions optimized by response surface methodology, the removal efficiency of Cd²⁺ could achieve 99.89%. Three components were separated and characterized in the reaction mixture of Cd²⁺ removal by MICP. The quantitative-dynamic distribution of Cd²⁺ in different components was revealed. Five synergistic effects for Cd²⁺ removal were found, including co-precipitation, adsorption by precipitation, crystal precipitation on the cell surface, intracellular accumulation and extracellular chemisorption. Importantly, during Cd²⁺ removal by MICP, the phenomenon that crystalline nanoparticles adhere to the cell surface, but without any micrometer-sized precipitation encapsulated bacterial cells was observed. This indicated that the previously studied model of bacterial cells as nucleation sites for metal cation precipitation and crystal growth is oversimplified. Our findings provided valuable insights into the mechanism of heavy metals removal by MICP, and a more straightforward method for studying biomineralization-related dynamic process.

Simultaneous removal of nitrate, tetracycline, and Pb(II) by iron oxidizing strain Zoogloea sp. FY6: Performance and mechanism

Based on the prevalence of combined antibiotics and heavy metals contamination in the aquatic environment, this study utilized a microbial approach to achieve simultaneous removal of nitrate (NO₃^--N), tetracycline (TTC), and Pb(II). Zoogloea sp. FY6 could achieve an optimal NO₃^--N removal efficiency of 91.5% under C/N ratio of 2.0, at a pH of 6.3, and Fe(II) concentration of 20.23 mg L^-1 based on response surface methodology. Additionally, strain FY6 was further found to achieve 89.9 and 81.7% removal of TTC and Pb(II) at 6 h under the optimal conditions. Finally, the results of Fluorescence excitation-emission matrix, X-ray diffraction, Fourier transform infrared spectrometer, and X-ray photoelectron spectroscopy further proved that the biologically formed nanoscale iron oxides and biological action jointly led to the removal of TTC and Pb(II). This study provided a theoretical basis for the application of microbially driven process to remove multi-pollutants in micro-polluted water bodies.

Effect of seepage conditions on the microstructural evolution of loess across north-west China

Loess features metastable microstructure and is deemed susceptible to chemical contaminant permeation. However, studies on the loess permeability evolution under water and chemical environments are remarkably limited. In this study, the response of the loess to the water and sodium sulfate seepages was analyzed using the temporal relationship of cations concentration, X-ray diffraction and fluorescence (XRD and XRF), mercury intrusion porosimetry (MIP), and scanning electron microscope (SEM) tests. The permeability evolution characteristics were identified, and its underlying mechanisms were revealed from aspects of the diffuse double layer (DDL) theory and physiochemical actions. The discharge of Mg²⁺ and precipitation of calcium carbonate, referred also to as the dedolomitization, degraded the macro permeability when subjected to the water seepage test. The salt-induced swelling, induced by the intrusion of Na⁺ into the DDL, caused an increase in the micropore fraction under the sodium sulfate seepage test, thereby increasing the macro permeability.

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The k evolution of the loess under the water and Na₂SO₄ seepages is investigated

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The dedolomitization takes part in the k degradation under the water seepage

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The Na⁺ intrusion into the double layer enhances the k under the Na₂SO₄ seepage

Effects of Bacterial Culture and Calcium Source Addition on Lead and Copper Remediation Using Bioinspired Calcium Carbonate Precipitation

Lead and copper ions from wastewater induced by metallurgical processes are accumulated in soils, threatening plant and human health. The bioinspired calcium carbonate precipitation is proven effective in improving the cementation between soil particles. However, studies on capsulizing heavy metal ions using the bioinspired calcium carbonate precipitation are remarkably limited. The present study conducted a series of test tube experiments to investigate the effects of bacterial culture and calcium source addition on the remediation efficiency against lead and copper ions. The calcium carbonate precipitation was reproduced using the Visual MINTEQ software package to reveal the mechanism affecting the remediation efficiency. The degradation in the remediation efficiency against lead ions relies mainly upon the degree of urea hydrolysis. However, higher degrees of urea hydrolysis cause remediation efficiency against copper ions to reduce to zero. Such high degree of urea hydrolysis turns pH surrounding conditions into highly alkaline environments. Therefore, pursuing higher degrees of urea hydrolysis might not be the most crucial factor while remedying copper ions. The findings shed light on the importance of modifying pH surrounding conditions in capsulizing copper ions using the bioinspired calcium carbonate precipitation.

Effects of the Urease Concentration and Calcium Source on Enzyme-Induced Carbonate Precipitation for Lead Remediation

Heavy metal contamination during the rapid urbanization process in recent decades has notably impacted our fragile environments and threatens human health. However, traditional remediation approaches are considered time-consuming and costly, and the effect sometimes does not meet the requirements expected. The present study conducted test tube experiments to reproduce enzyme-induced carbonate precipitation applied to lead remediation under the effects of urease concentration and a calcium source. Furthermore, the speciation and sequence of the carbonate precipitation were simulated using the Visual MINTEQ software package. The results indicated that higher urease concentrations can assure the availability of CO₃²⁻ during the enzyme-induced carbonate precipitation (EICP) process toward benefiting carbonate precipitation. The calcium source determines the speciation of carbonate precipitation and subsequently the Pb remediation efficiency. The use of CaO results in the dissolution of Pb(OH)₂ and, therefore, discharges Pb ions, causing some difficulty in forming the multi-layer structure of carbonate precipitation and degrading Pb remediation. The findings of this study are useful in widening the horizon of applications of the enzyme-induced carbonate precipitation technology to heavy metal remediation.

Phytoremediation of potentially toxic elements (PTEs) contaminated soils using alfalfa (Medicago sativa L.): A comprehensive review

Soil contamination with potentially toxic elements (PTEs) is an increasing environmental problem, posing serious threats to the living organisms. Phytoremediation is a sustainable and highly accepted technology for remediation of PTE-contaminated soils. Alfalfa has been widely adopted for the phytoremediation of PTE-contaminated soils due to its large biomass productivity, high PTE tolerance, and strong capacity to take up PTEs. However, there are still no literature reviews systematically summarized the potential of alfalfa in the phytoremediation. Therefore, we review the available literatures that present its PTE uptake, phytotoxicity, tolerance mechanisms, and aided techniques improving the phytoremediation efficiency. In this review, alfalfa shows high amounts of PTEs accumulation, especially in their root tissue. Meanwhile, the inner mechanisms of PTE tolerance and accumulation in alfalfa are discussed including: (i) the activation of antioxidant enzyme system, (ii) subcellular localization, (iii) production of glutathione, phytochelatins, and proline, and (iv) regulation of gene expression. Indeed, excessive PTE can overcome the defense system, which causes oxidative damage in alfalfa plants, thereby inhibiting growth and physiological processes and weakening the ability of PTE uptake. Till now, several approaches have been developed to improve the tolerance and/or accumulation of PTE in alfalfa plants as follows: (i) selection of PTE tolerant cultivars, (ii) applying plant growth regulators, (iii) addition of chelating agents, fertilizer, and biochar materials, and (iv) inoculation of soil microbes. Finally, we indicate that the selection of PTE-tolerant cultivars along with inoculation of soil microbes may be an efficient and eco-friendly strategy of the soil PTE phytoremediation.

The Effect of Calcium Source on Pb and Cu Remediation Using Enzyme-Induced Carbonate Precipitation

Heavy metal contamination not only causes threat to human health but also raises sustainable development concerns. The use of traditional methods to remediate heavy metal contamination is however time-consuming, and the remediation efficiency may not meet the requirements as expected. The present study conducted a series of test tube experiments to investigate the effect of calcium source on the lead and copper removals. In addition to the test tube experiments, numerical simulations were performed using Visual MINTEQ software package considering different degrees of urea hydrolysis derived from the experiments. The remediation efficiency degrades when NH4+ and OH− concentrations are not sufficient to precipitate the majority of Pb2+ and Cu2+. It also degrades when CaO turns pH into highly alkaline conditions. The numerical simulations do not take the dissolution of precipitation into account and therefore overestimate the remediation efficiency when subjected to lower Pb(NO3)2 or Cu(NO3)2 concentrations. The findings highlight the potential of applying the enzyme-induced carbonate precipitation to lead and copper remediations.