Heavy Metal Remediation Research Articles

Genomic characterization of Enterobacter sp. PGRG2 and Achromobacter insolitus PGRG5: bacterial strains isolated from soil present near electronics manufacture industry for heavy metal remediation.

This article reports the whole-genome sequence of PGRG5 and the draft genome sequence of PGRG2. These strains were isolated from electronic waste contaminated soil. According to microbial identification, strain PGRG2 was identified as Enterobacter sp. (unclassified) with a size of ~4.4 Mbp and PGRG5 as Achromobacter insolitus with a size of ~6.2 Mbp.

Isolation and Identification of Mercury-Resistant Fungi as Bioremediation Agents from Gold Mining

To overcome the pollution problem due to the accumulation of heavy metal Hg, a clean-up or remediation effort is needed from the former landfill for hazardous and toxic waste. In this research, bioremediation experiments will be conducted by inoculating fungi culture that is already known to have the potential to absorb heavy metals Hg. Samples of soil contaminated with heavy metals Hg taken from the tailings of gold mining owned by the people in Kertajaya Village, Simpenan District, Sukabumi Regency. The stages of this study consisted of isolation of fungi, purification and morphology of fungi isolate, screening of fungi isolate, qualitative screening of fungi for ligninolytic activity (laccase), and molecular identification of the isolated fungi. The results of the screening showed that three isolates of potential fungi coded M.2, M.10, and M.13 were able to grow with a mercury concentration of 350 ppm, while one isolate coded R4.28 reached a concentration of 1000 ppm. In addition, isolate M.2 was selected as the best strain compared to isolates M.10, M.13, and R4.28 for the qualitative test of laccase production in ligninolytic enzymes. Based on the molecular analysis of the 18S rRNA gene, M.2 isolates were similar to Trichoderma yunnanense, which was strengthened by a similarity value of 99.66%. Isolate R4.28 was similar to Penicillium soli, which was strengthened by a similarity value of 99.32%.

Adsorption mechanism and remediation of heavy metals from soil amended with hyperthermophilic composting products: Exploration of waste utilization

Due to high humification, hyperthermophilic composting products (HP) show potential for remediating heavy metal pollution. However, the interaction between HP and heavy metals remains unclear. This study investigated the adsorption mechanism and soil remediation effect of HP on heavy metals. The results showed that the maximum adsorption capacity of HP increased by an average of 30.74 % compared to conventional composting products. HP transformed 34.87 % of copper, 42.55 % of zinc, and 35.63 % of lead from exchangeable and reducible forms into residual and oxidizable forms, thus reducing the soil risk level. In conclusion, HP significantly enhanced the adsorption of heavy metals and their transformation from unstable to stable forms, primarily due to the higher content of hydroxyl and carboxyl groups. This study aims to demonstrate the effectiveness of HP for remediating heavy metal pollution and to enhance the understanding of the underlying mechanism, which lays a foundation for waste utilization.

Fungal Peptidomelanin: A Novel Biopolymer for the Chelation of Heavy Metals.

Melanin is an amorphous, highly heterogeneous polymer found across all kingdoms of life. Although the properties of melanin can greatly vary, most forms are insoluble and strongly absorb light, appearing dark brown to black. Here, we describe a water-soluble form of melanin (peptidomelanin) secreted by the spores of Aspergillus niger (strain: melanoliber) during germination. Peptidomelanin is composed of an insoluble L-DOPA core polymer that is solubilized via short, copolymerized heterogeneous peptide chains forming a "corona" with a mean amino acid length of 2.6 ± 2.3. Based on in vitro experiments, we propose a biochemical copolymerization mechanism involving the hydroxylation of tyrosynylated peptides. Peptidomelanin is capable of chelating heavy metals such as lead, mercury, and uranium (as uranyl) in large quantities. Preliminary data indicates that peptidomelanin may have applications for the remediation of heavy metals in situ, including in agricultural settings.

Utilization and Characterization of Microbes for Heavy Metal Remediation

Utilization and Characterization of Microbes for Heavy Metal Remediation

Pectin-nano zero valent iron nanocomposites for efficient heavy metal removal and bactericidal action against waterborne pathogens — Innovative green solution towards environmental sustainability

This study investigated the effectiveness of a pectin-nano zero-valent iron-based nanocomposite in adsorbing heavy metals in bimetallic form (chromium‑lead mixture), along with assessing its antibacterial properties. The nanocomposite was synthesized using a straightforward dispersion method, employing eco-friendly components like biocompatible pectin sourced from banana peels and nano-scale zero-valent iron. Analytical characterization confirmed the formation of stable, nano-crystalline particles with active interactions between the functional groups of pectin and nano iron. Batch adsorption experiments optimized various parameters such as pH, adsorbent dosage, contact time, metal ion concentration, and temperature to enhance bimetal removal from water. The optimal conditions were determined as pH 8.0, a temperature of 40 °C, 1.0 g/L adsorbent dosage, 75 mg/l initial bimetal concentration, and a contact time of 30 min. Further assessments revealed that the nanocomposite did not induce phytotoxic or ecotoxic effects, confirming its non-toxicity and environmental safety. Biocompatibility studies conducted using zebrafish models showed no adverse effects on hatching, survival, or heart rate. These findings underscore the potential of the nanocomposite as a sustainable and efficient solution for heavy metal remediation in water treatment process.

Biomimetic mineralization of hydrated magnesium carbonate for hydrogel reinforcement and heavy metal adsorption

With excessive Mn(Ⅱ) and Cu(Ⅱ) pollution in aquatic environments posing potential health risks to inhabitants, the emergence of carbon capture, utilization and storage (CCUS) technology has promoted the improvement of heavy metal remediation technologies. Using hydrothermal sediment as a crystal seed, rhamnolipid was used to mediate biomimetic mineralization to prepare hydrated magnesium carbonate (HMC) composites to enhance the Mn(Ⅱ)/Cu(Ⅱ) adsorption performance of alginate hydrogels. Hydrothermal sediment is beneficial for accelerating biomimetic mineralization, while rhamnolipid can induce a crystalline phase transformation from dypingite to nesquehonite. The addition of sediment significantly enhanced the compressive mechanical properties and thermal stability of the hydrogels. The adsorption performances of the nesquehonite and dypingite hydrogels were better for Mn(II) and Cu(II), respectively. An increase in the amount of sediment improved the adsorption of Cu(II) by the hydrogels appropriately, resulting in stronger selectivity for Cu(II). The adsorption of Mn(II) and Cu(II) on the hydrogel beads was thermodynamically spontaneous. The inhibitory effects of sodium dodecyl benzene sulfonate (SDBS), fulvic acid (FA) and alginate on Cu(II) adsorption were more obvious than those of bovine serum albumin (BSA). Both the complexation of functional groups on alginate and mineralization by HMC participated in the adsorption of Mn(II) and Cu(II).

Different calcium sources affect the products and sites of mineralized Cr(VI) by microbially induced carbonate precipitation

Microbially induced carbonate precipitation (MICP) is a common biomineralization method, which is often used for remediation of heavy metal pollution such as hexavalent chromium (Cr(VI)) in recent years. Calcium sources are essential for the MICP process. This study investigated the potential of MICP technology for Cr(VI) remediation under the influence of three calcium sources (CaCl2, Ca(CH3COO)2, Ca(C6H11O7)2). The results indicated that CaCl2 was the most efficient in the mineralization of Cr(VI), and Ca(C6H11O7)2 could significantly promote Cr(VI) reduction. The addition of different calcium sources all promoted the urease activity of Sporosarcina saromensis W5, in which the CaCl2 group showed higher urease activity at the same Ca2+ concentration. Besides, with CaCl2, Ca(CH3COO)2 and Ca(C6H11O7)2 treatments, the final fraction of Cr species (Cr(VI), reduced Cr(III) and organic Cr(III)-complexes) were mainly converted to the carbonate-bound, cytoplasm and cell membrane state, respectively. Furthermore, the characterization results revealed that three calcium sources could co-precipitate with Cr species to produce Ca10Cr6O24(CO3), and calcite and vaterite were present in the CaCl2 and Ca(CH3COO)2 groups, while only calcite was present in the Ca(C6H11O7)2 group. Overall, this study contributes to the optimization of MICP-mediated remediation of heavy metal contaminated soil. CaCl2 was the more suitable calcium source than the other two for the application of MICP technology in the Cr(VI) reduction and mineralization.

An Enzyme-Induced Carbonate Precipitation Method for Zn2+, Ni2+, and Cr(VI) Remediation: An Experimental and Simulation Study

Heavy metal contamination has long been a tough challenge. Recently, enzyme-induced carbonate precipitation (EICP) has been proposed to handle this problem. This paper aims to explore the efficacy, process, and mechanisms of EICP using crude sword bean urease extracts to remediate Zn2+, Ni2+, and Cr(VI) contamination. A series of liquid batch tests and geochemical simulations, as well as microscopic analyses, were conducted. The liquid batch test results show that Zn2+, Ni2+, and Cr(VI) can be effectively immobilized by the EICP method, and the highest immobilization percentage was observed for Zn2+, reaching up to 99%. Ni2+ and Cr(VI) were immobilized at 62.4% and 24.4%, respectively. Additionally, the immobilization percentage of heavy metals increased with the concentration of added Ca2+. The simulation results and XRD results reveal that the organic molecules in crude sword bean urease can promote ZnCO3, Zn(OH)2, Zn5(CO3)2(OH)6, and NiCO3 precipitation. The FTIR and SEM-EDS results provide evidence for heavy metal adsorption by the functional groups in crude urease and calcium carbonate. The liquid batch test results, as well as the simulation results and the microscopic analysis results, indicate that the mechanism of EICP in heavy metal remediation can be summarized as biomineralization to form heavy metal carbonate precipitates and metal hydroxide precipitates, adsorption by calcium carbonate, and adsorption or complexation or promoting nucleation by organic molecules.

A Review of the Electrochemical Coupled Leaching Technique: An Effective Solution for Remediation of Heavy Metal Contaminated Soils

A Review of the Electrochemical Coupled Leaching Technique: An Effective Solution for Remediation of Heavy Metal Contaminated Soils

A critical review on hydrothermal liquefaction screening using Microalgae as a two-way approach to sewage water treatment and biofuel production

<p>Hydrothermal liquefaction (HTL) is involved in concurrently treating both sewage water and generating biofuels. It involves the analysis of various operating parameters, such as pressure, catalyst temperature, and reaction time, to determine the productivity and physiochemical properties of the resulting bio-oil. The critical assessment of over 100 algal strains, compared on the basis of their growth kinetics in different wastewater environments and their HTL-based yields, identified Auxenochlorella pyrenoidosa and Microchaete spirulina strains as the most suitable ones for optimised municipal wastewater treatment. Additionally, other strains like Chlorella sorokiniana, Tetradesmus obliquus, and Desmodesmus abundance are found to be effective for heavy metal remediation in municipal wastewater due to their high biosorption capacities. Furthermore, certain microalgal strains, namely Auxenochlorella pyrenoidosa, Botryococcus braunii, Microchloropsis gaditana, and Microchaete spirulina, were described as promising microalgae in the production of high crude oil yields through the HTL technique. The current review highlights the integrated approach of sustainable and economical HTL techniques using the best microalgal strains as a technologically and environmentally feasible solution selected through a systematic protocol for sewage water treatment and biofuel production.</p>

High sulfur-to-iron ratios enhance thallium(I) sequestration by sulfidated zero-valent iron

Sulfidated zero-valent iron (SZVI) has been recognized for its enhanced reactivity in heavy metal remediation, yet its efficacies and mechanisms for sequestering thallium (Tl) from wastewater are not well understood. This study aimed to address this knowledge gap by synthesizing SZVI through one-step (OS) and two-step (TS) methods, using varying sulfur-to-iron (S/Fe) molar ratios. Results revealed that high S/Fe ratios in the OS method yielded SZVI with low crystallinity and irregular morphology, whereas the TS method produced SZVI with more crystalline and core-shell structure. Both OS and TS methods, particularly at high S/Fe ratios (2.0 for OS and 3.0 for TS), demonstrated high Tl removal capacities—645.16 mg/g for OS-2.0 and 510.20 mg/g for TS-3.0, respectively. These formulations effectively reduced Tl(I) concentrations in simulated wastewater containing complex matrixes and in industrial wastewater with intricate metal(loid) pollutants. Spectroscopic analyses, including X-ray photoelectron and 57Fe Mössbauer spectroscopy, identified three primary mechanisms for Tl sequestration: chemical precipitation facilitated by various sulfidized iron species (FeSx) as Tl2S, surface complexation through iron oxyhydroxide and FeSx, and electrostatic attraction to the negatively charged SZVI surface. The study confirmed that SZVI, when synthesized at high S/Fe ratios with elevated sulfides content, served as an efficient medium for remediating Tl-contaminated wastewater.

Investigation of Eucalyptus camaldulensis and Tamarix aphylla species' capacities for methylene blue removal in wastewater and heavy metal remediation in soil.

In the contemporary landscape, the reuse of wastewater holds paramount significance. Concurrently, wastewater carries an array of pollutants encompassing chemical dyes and heavy metals. This study delves into the potential of Tamarix aphylla (TA) and Eucalyptus camaldulensis (EC) species for mitigating heavy metals in soil and eliminating methylene blue dye (MB) from wastewater. The research begins with assessing the dye adsorption process, considering pivotal factors such as initial pH, adsorbent dosage, initial dye concentration, and contact time. Outcomes reveal EC's superiority in dye removal compared to TA. As a bioremediation agent, EC exhibits a 90.46% removal efficacy for MB within 15 min, with pH 7.0 as the operative condition. Equilibrium analysis employs Temkin (T), Freundlich (F), and Langmuir (L) isotherms, revealing an excellent fit with the L isotherm model. The study delves further by probing surface adsorption kinetics through pseudo-first-order (PFO) and pseudo-second-order (PSO) models. Furthermore, to discern the divergent impacts of EC and TA on soil heavy metal reduction, soil samples were collected from three distinct zones: an untouched control area, alongside areas where EC and TA were cultivated at the Yazd wastewater site in Iran. Heavy metal levels in the soil were meticulously assessed through rigorous measurement and statistical scrutiny. The findings spotlight TA-cultivated soil as having the highest levels across all examined factors. Ultimately, EC emerges as the superior contender, proficiently excelling in both MB eliminations from wastewater and heavy metal amelioration in the soil, positioning it as the preferred phytoremediation agent.

Enhancing high-efficient cadmium biosorption of Escherichia coli via cell surface displaying metallothionien CUP1

ABSTRACT Cadmium (Cd) is one of the common heavy metal pollutants in soil, which can induce various diseases and pose a serious threat to human health. Metallothioneins (MTs) are well-known for their excellent metal binding ability due to a high content of cysteine, which has great potential for heavy metal chelation. In this study, we used the Escherichia coli (E. coli) surface display system LPP-OmpA to construct a recombinant plasmid pBSD-LCF encoding LPP-OmpA-CUP1-Flag fusion protein. Then we displayed the metallothionein CUP1 from Saccharomyces cerevisiae on E. coli DH5α surface for Cd removing. The feasibility of surface display of metallothionein CUP1 in recombinant E. coli DH5α (pBSD-LCF) by Lpp-OmpA system was proved by flow cytometry and western blot analysis, and the specificity of the fusion protein in the recombinant strain was also verified. The results showed that the Cd2+ resistance capacity of DH5α (pBSD-LCF) was highly enhanced by about 200%. Fourier-transform infrared spectroscopy showed that sulfhydryl and sulfonyl groups were involved in Cd2+ binding to cell surface of DH5α (pBSD-LCF). Meanwhile, Cd removal rate by DH5α (pBSD-LCF) was promoted to 95.2%. Thus, the recombinant strain E. coli DH5α (pBSD-LCF) can effectively chelate environmental metals, and the cell surface expression of metallothionein on E. coli can provide new ideas and directions for heavy metals remediation.

Experimental study on unfrozen water content of loess polluted by heavy metals

Currently, there are very few investigations on the unfrozen water content of contaminated soil due to heavy metals. This will have an impact on the efficacy and use of freezing technology in the remediation of heavy metal-contaminated soil. Thus, the purpose of this research is to determine the unfrozen water content and contributing factors of heavy metal-contaminated loess. As a result, Lanzhou loess was employed as an experimental material to produce contaminated soil with varied initial water content and heavy metal concentrations. Additionally, Zn, Ni, Cu, Cr, Cd, and Pb were used as pollution elements. The findings indicate that: 1) Unfrozen water content of loess with heavy metal ions underwent three processes: severe phase transition, transition stage, and freezing stage; 2) Effects of different heavy metal ions on the amount of unfrozen water in loess are as follows: Cu > Cr > Pb > Cd > Ni > Zn when levels are low. Effects of different heavy metal ions on the amount of unfrozen water in loess are as follows: Cu > Zn > Cr > Ni > Pb > Cd when levels are high; 3) The prediction model of unfrozen water content in the loess polluted by heavy metals was established as follows: wu = aT–b. This will help the remediation and management of heavy metals in urban contaminated soil in the future by freezing technology.

Optimizing Copper Adsorption from Aqueous Solutions with Modified Rice Straw Using Response Surface Methodology

Heavy metal contamination poses an impulsive threat to human and aquatic life and ecosystem health. To ensure safe and sustainable water accessibility, biosorption with low-cost adsorbents is acknowledged as a promising approach for the remediation of noxious pollutants. The current study was oriented to appraise the performance of modified rice straw for copper adsorption in hand with the optimization of its operational parameters. RSM-based Box-Behnken design was employed to optimize the operational variables encircling temperature, pH, and adsorbent dose. The results elucidated that the generated model exhibited an R-squared of 0.98, reflecting its validity in describing the experimental data well. The optimized conditions for attaining maximum copper adsorption were marked to be a temperature of 37.71 oC, a solution pH of 5.7, and an adsorbent dose of 11.26 g L-1. Under these optimized conditions, the adsorption efficiency was marked to be 86.65 %. The experimental adsorption efficiency under these conditions was noted to be approximately 86.43 %, reflecting the suitability of the RSM-based Box-Behnken design. Conclusively, it can be inferred that acid modified rice straw offers a promising low cost adsorbent for remediation of heavy metals in accordance with the principles of green chemistry.

Predicting and refining acid modifications of biochar based on machine learning and bibliometric analysis: Specific surface area, average pore size, and total pore volume

Acid-modified biochar is a modified biochar material with convenient preparation, high specific surface area, and rich pore structure. It has great potential for application in the heavy metal remediation, soil amendments, and carrying catalysts. Specific surface area (SSA), average pore size (APS), and total pore volume (TPV) are the key properties that determine its adsorption capacity, reactivity, and water holding capacity, and an intensive study of these properties is essential to optimize the performance of biochar. But the complex interactions among the preparation conditions obstruct finding the optimal modification strategy. This study collected dataset through bibliometric analysis and used four typical machine learning models to predict the SSA, APS, and TPV of acid-modified biochar. The results showed that the extreme gradient boosting (XGB) was optimal for the test results (SSA R2 = 0.92, APS R2 = 0.87, TPV R2 = 0.96). The model interpretation revealed that the modification conditions were the major factors affecting SSA and TPV, and the pyrolysis conditions were the major factors affecting APS. Based on the XGB model, the modification conditions of biochar were optimized, which revealed the ideal preparation conditions for producing the optimal biochar (SSA = 727.02 m2/g, APS = 5.34 nm, TPV = 0.68 cm3/g). Moreover, the biochar produced under specific conditions verified the generalization ability of the XGB model (R2 = 0.99, RMSE = 12.355). This study provides guidance for optimizing the preparation strategy of acid-modified biochar and promotes its potentiality for industrial application.

Preparation of electrospun cellulose acetate/chitosan membranes for efficient sorption of heavy metals from aqueous solutions

Guided by efficient utilization of natural abundant cellulose and chitosan as separation materials, it is desired to tailor the composition of electrospun cellulose acetate/chitosan (CL/CS) membranes to achieve their optimal application in the management of aquatic heavy metal pollution. In this work, CL/CS membranes with enhanced surface area of 11.3–38.6 m2/g were successfully fabricated via electrospinning technique by dissolving cellulose acetate and chitosan into the environmental-friendly electrospinning solvent of LiOH/thiourea/H2O. Electrospun CL/CS membranes allowed the efficient sorption of Cr(VI), Pb(II) and Cu(II) with favorable kinetics (8.0 h), and excellent capacities (127.6 mg/g for Cr(VI), 66.2 mg/g for Pb(II), 46.7 mg/g for Cu(II) at pH 5.0, T 298 K). Meanwhile, they presented favorable efficiencies in the removal of these multiple heavy metals from acid simulated wastewaters. The spectroscopic analysis results indicated that the sorption mechanism should be dominant by the surface complexation of heavy metals with hydroxyl O-/amino N-species, the electrostatic attraction (protonated NH3+ with negatively charged HCrO4-, deprotonated O- with positively charged Pb(II) and Cu(II)), as well as the reduction of Cr(VI) to Cr(III) by surface reductive N-species. This work demonstrated the feasibility of electrospun CL/CS membranes as a promising choice for the remediation of aquatic heavy metals.

Remediation of Pb, Cd, and Cu contaminated soil with Mg‐Fe‐Al layered double hydroxides (LDHs) synthesized from waste red mud

AbstractSoils contaminated with multiple heavy metals pose a significant threat to human health and ecosystem functionality. Following a “treat pollution with waste” strategy, we synthesized Mg‐Fe‐Al ternary layered double hydroxides (LDHs) from waste Bayer red mud for the remediation of heavy metal contaminated soils. Characterization using XRD, FTIR, SEM and EDS methods revealed a characteristic layered structure rich in functional groups, offering reaction sites for heavy metal passivation. Passivation experiments showed that the application of Mg‐Fe‐Al LDHs (2.5 wt.%) reduced the availability of Pb (29.7%), Cd (64.1%) and Cu (66.0%) in contaminated soil from a sulphide iron ore area in southern Sichuan Province. Simulated acid rain experiments showed leachate concentrations of Pb, Cd, and Cu reduced by 43.3%, 72.7% and 42.4%, respectively. This work provides a reference for the development of high‐performance and environmentally friendly adsorption‐stabilizing materials for green remediation.

Effects of enzyme-induced carbonate precipitation technique on multiple heavy metals immobilization and unconfined compressive strength improvement of contaminated sand

Enzyme-induced carbonate precipitation (EICP) has been studied in remediation of heavy metal contaminated water or soil in recent years. This paper aims to investigate the immobilization mechanism of Zn2+, Ni2+, and Cr(VI) in contaminated sand, as well as strength enhancement of sand specimens by using EICP method with crude sword bean urease extracts. A series of liquid batch tests and artificially contaminated sand remediation experiments were conducted to explore the heavy metal immobilization efficacy and mechanisms. Results showed that the urea hydrolysis completion efficiency decreased as the Ca2+ concentration increased and the heavy metal immobilization percentage increased with the concentration of Ca2+ and treatment cycles in contaminated sand. After four treatment cycles with 0.5 mol/L Ca2+ added, the immobilization percentage of Zn2+, Ni2+, and Cr(VI) were 99.99 %, 86.38 %, and 75.18 %, respectively. The microscale analysis results presented that carbonate precipitates and metallic oxide such as CaCO3, ZnCO3, NiCO3, Zn(OH)2, and CrO(OH) were generated in liquid batch tests and sand remediation experiments. The SEM-EDS and FTIR results also showed that organic molecules and CaCO3 may adsorb or complex heavy metal ions. Thus, the immobilization mechanism of EICP method with crude sword bean urease can be considered as biomineralization, as well as adsorption and complexation by organic matter and calcium carbonate. The unconfined compressive strength of EICP-treated contaminated sand specimens demonstrated a positive correlation with the increased generation of carbonate precipitates, being up to 306 kPa after four treatment cycles with shear failure mode. Crude sword bean urease with 0.5 mol/L Ca2+ added is recommended to immobilize multiple heavy metal ions and enhance soil strength.