High-throughput visualization mutation screening technology to enhance the specificity of CadR based whole-cell cadmium biosensor.

As a heavy metal pollutant, Cd2+ often enters the human body through the food chain causing great harm to human health. Whole-cell biosensor is an emerging technology for rapid on-site detection of heavy metals with the advantages of inexpensive, fast to mass-produce, and strong in anti-interference resistance, but suffering from insatisfactory specificity. In this study, a strategy of Adjacent Site Saturation Mutation (ASSM) was designed to improve the specificity of transcription factor CadR, which acted as the recognition element and determined the specificity of whole cell Cd2+ biosensors. A specific saturated library was constructed using the strategy of adjacent mutation. After two rounds of high-throughput visual screening, a whole-cell biosensor with good response to Cd2+, and with significant weakened Hg2+ interference was obtained. The optimized whole-cell biosensor showed a linear dynamic concentration range from 500 nM to 100 µM, a detection limit of 0.079 µM, and has satisfactory specificity and anti-interference. The ASSM strategy proposed in this study can provide a new method for the application of synthetic biology in food safety detection, indicating the importance of whole-cell biosensors for the detection of heavy metals.

Does livestock-Manure-Derived Biochar Suitable for the Stabilization of Cadmium and Zinc in Contaminated Soil?

Both livestock-manure and livestock-manure-derived biochar have been used to remediate heavy metal-contaminated soil. However, direct comparisons of the heavy metal stabilization efficiency of livestock-manure and EQC-manure-biochar (derived from an equal quantity of corresponding livestock-manure) are limited. In the present study, the effect of livestock-manures and EQC-manure-biochars on soil properties and heavy metal bioavailability and leachability were compared using two contrasting soils (Ferralsols and Fluvisols). The results showed that both the livestock-manures and EQC-manure-biochars significantly changed soil pH, available phosphorus, available potassium, alkaline nitrogen and organic matter content (p < 0.05), but the trends were variable. In Ferralsols, the DTPA-extractable Cd and Zn decreased by -0.38%~5.70% and - 3.79%~9.98% with livestock-manure application and by -7.99%~7.23% and - 5.67%~7.17% with EQC-manure-biochars application. In Fluvisols, the DTPA-extractable Cd and Zn decreased by 13.39%~17.41% and - 45.26%~14.24% with livestock-manure application and by 10.76%~16.90% and - 36.38%~16.37% with EQC-manure-biochar application. Furthermore, the change in TCLP-extractable Cd and Zn in both soils was similar to that of DTPA-extractable Cd and Zn. Notably, the Cd and Zn stabilization efficiency of the EQC-manure-biochars was no better than that of the corresponding livestock-manures. These results suggest that the use of livestock-manure-derived biochar is not cost-effective for the remediation of heavy metal-contaminated soil.

Penicillium oxalicum induced phosphate precipitation enhanced cadmium (Cd) immobilization by simultaneously accelerating Cd biosorption and biomineralization.

Soil cadmium (Cd) is immobilized by the progressing biomineralization process as microbial induced phosphate precipitation (MIPP), which is regulated by phosphate (P) solubilizing microorganisms and P sources. However, little attention has been paid to the implications of Cd biosorption during MIPP. In this study, the newly isolated Penicillium oxalicum could immobilize 5.4-12.6 % of Cd2+, while the presence of hydroxyapatite (HAP) considerably enhanced Cd2+ immobilization in P. oxalicum and reached over 99 % Cd2+ immobilization efficiency within 7 days. Compared to P. oxalicum mono inoculation, MIPP dramatically boosted Cd biosorption and biomineralization efficiency by 71 % and 16 % after 96 h cultivation, respectively. P. oxalicum preferred to absorbing Cd2+ and reaching maximum Cd2+ biosorption efficiency of 87.8 % in the presence of HAP. More surface groups in P. oxalicum and HAP mineral involved adsorption which resulted in the formation of Cd-apatite [Ca8Cd2(PO4)6(OH)2] via ion exchange. Intracellular S2-, secreted organic acids and soluble P via HAP solubilization complexed with Cd2+, progressively mineralized into Cd5(PO4)3OH, Cd(H2PO4)2, C4H6CdO4 and CdS. These results suggested that Cd2+ immobilization was enhanced simultaneously by the accelerated biosorption and biomineralization during P. oxalicum induced P precipitation. Our findings revealed new mechanisms of Cd immobilization in MIPP process and offered clues for remediation practices at metal contaminated sites.

The quorum sensing SinI/R system contributes to cadmium immobilization in Ensifer adhaerens NER9 in the cadmium-contaminated solution.

In this study, the cadmium (Cd)-tolerant Ensifer adhaerens strain NER9 with quorum sensing (QS) systems (responsible for N-acyl homoserine lactone (AHL) production) was characterized for QS system-mediated Cd immobilization and the underlying mechanisms involved. Whole-genome sequence analysis revealed that strain NER9 contains the QS SinI/R and TraI/R systems. Strains NER9 and the NER9∆sinI/R, NER9∆traI/R, and NER9∆sinI/R-traI/R mutants were constructed and compared for QS SinI/R and TraI/R system-mediated Cd immobilization in the solution and the mechanisms involved. After 24 h of incubation, strain NER9 significantly decreased the Cd concentration in the Cd-contaminated solution compared with the NER9∆sinI/R, NER9∆traI/R, and NER9∆sinI/R-traI/R mutants. The NER9∆sinI/R mutant had a greater impact on Cd immobilization and a lower impact on the activities of AHLs than did the NER9∆traI/R mutant. The NER9∆sinI/R mutant had significantly greater Cd concentrations and lower cell wall- and exopolysaccharide (EPS)-adsorbed Cd contents than did strain NER9. Furthermore, the NER9∆sinI/R mutant presented a decrease in the number of functional groups interacting with Cd, compared with strain NER9. These results suggested that the SinI/R system in strain NER9 contributed to Cd immobilization by mediating cell wall- and EPS-adsorption in Cd-containing solution.

Effective Removal of Different Heavy Metals Ion (Cu, Pb, and Cd) from Aqueous Solutions by Various Molecular Weight and Salt Types of Poly-γ-Glutamic Acid.

In light of industrial developments, water pollution by heavy metals as hazardous chemicals has garnered attention. Addressing the urgent need for efficient heavy metal removal from aqueous environments, this study delves into using poly-γ-glutamic acid (γ-PGA) for the bioflocculation of heavy metals. Utilizing γ-PGA variants from Bacillus subtilis with different molecular weights and salt forms (Na-bonded and Ca-bonded), the research evaluates their adsorption capacities for copper (Cu), lead (Pb), and cadmium (Cd) ions. It was found that Na-bonded γ-PGA with a high molecular weight showed the highest heavy metal adsorption (92.2-98.3%), particularly at a 0.5% concentration which exhibited the highest adsorption efficiency. Additionally, the study investigated the interaction of γ-PGA in mixed heavy metal environments, and it was discovered that Na-γ-PGA-HM at a 0.5% concentration showed a superior adsorption efficiency for Pb ions (85.4%), highlighting its selectivity as a potential effective biosorbent for wastewater treatment. This research not only enlightens the understanding of γ-PGA's role in heavy metal remediation but also underscores its potential as a biodegradable and non-toxic alternative for environmental cleanup. The findings pave the way for further exploration into the mechanisms and kinetics of γ-PGA's adsorption properties.

Statistical modelling, optimization, and mechanistic exploration of novel ureolytic Enterobacter hormaechei IITISM-SA3 in cadmium immobilization under microbial inclusive and cell-free conditions through microbially induced calcite precipitation.

The study aimed to evaluate the potential of a novel isolated ureolytic Enterobacter hormaechei IITISM-SA3 in cadmium bioremoval through MICP. The optimization and modelling of the biotic and abiotic factors affecting the process of mineralization were also performed. In addition, the underlying mechanism of MICP-driven Cd mineralization under microbial-inclusive and cell-free conditions was revealed and supported through the characterization of the bio-precipitates obtained using various characterization techniques. The results indicated that the isolate could remove 97.18% Cd2+ of 11.4 ppm under optimized conditions of 36.86 h, pH 7.63, and biomass dose of 1.75 ml. Besides, the presence and absence of bacterial cells were found to influence both the morphologies and crystalline structures of precipitates. The precipitates obtained under microbial-inclusive conditions showed typical rhombohedral crystalline structures of the composition comprising CaCO3, CdCO3, and 0.67Ca0.33CdCO3. However, the crystalline nature of the precipitate reduced to a nano-sized granular structure in cell-free media. Unlike the cadmium mineralization process under microbial-inclusive media, where bacterial cells serve as nucleation sites for crystallization, the carbonate precipitation effectively captures Cd2+ through co-precipitation, chemisorption, or alternative mechanisms involving interactions between metal ions and CaCO3 under cell-free conditions. The findings presented suggest that using cell-free culture supernatant enriched with carbonate ions provides an avenue that could be harnessed for sustainable metal remediation.

Chitosan-assisted self-assembly of flower-shaped ε-Fe2O3 nanoparticles on screen-printed carbon electrode for Impedimetric detection of Cd2+, Pb2+, and Hg2+ heavy metal ions in various water samples.

This study focuses on the fabrication of a novel sensing platform on a screen-printed carbon electrode, modified by a combination of hydrothermally synthesized iron dioxide (ε-Fe2O3) nanoparticles and Chitosan (CS) biopolymer. This unique organic-inorganic hybrid material was developed for Electrochemical Impedance Spectroscopy (EIS) sensing, specifically targeting heavy metal ions that include Hg2+, Cd2+, as well as Pb2+. The investigation encompassed a comprehensive analysis of various aspects of the prepared Fe2O3 and CS/ε-Fe2O3 nanocomposites, including phase identification, determination of crystallite size, assessment of surface morphology, etc. CS/ε-Fe2O3 was drop-casted and deposited on the Screen-Printed Electrode (SPE). The resulting sensor exhibited excellent performance in the precise and selective quantification of Hg2+, Cd2+, and Pb2+ ions, with minimal interference from other substances. The fabricated sensor exhibits excellent performance as the detection range for Hg2+, Cd2+, and Pb2+ ions linearity is 2-20 µM, sensitivity, and LOD are 243 Ω/ µM cm2 and 0.191 µM, 191 Ω/µM cm2, and 0.167 µM, 879 Ω/ µM cm2, and 0.177 µM respectively. The stability of the CS/ε-Fe2O3/SPE electrode is demonstrated by checking its conductivity for up to 60 days for Hg2+, Cd2+, and Pb2+ ions. The reusability of the fabricated electrode is 14 scans, 13 scans, and 12 scans for Hg2+, Cd2+, and Pb2+ ions respectively. The findings indicate the successful development of an innovative CS/ε-Fe2O3 electrode for the EIS sensing platform. This platform demonstrates notable potential for addressing the critical need for efficient and sensitive EIS sensors capable of detecting a range of hazardous heavy metal ions, including Hg2+, Cd2+, and Pb2+.

Respective evolution of soil and biochar on competitive adsorption mechanisms for Cd(II), Ni(II), and Cu(II) after 2-year natural ageing.

To reveal the respective evolution of soil and biochar on competitive heavy metal adsorption mechanisms after natural ageing, three soils and two biochars were tested in this study. The soil-biochar interlayer samples were buried in the field for 0.5, 1, and 2 years, for which competitive adsorption characteristics and mechanisms of soils and biochars in four systems (Cd, Cd+Ni, Cd+Cu, and Cd+Ni+Cu) were investigated. Results showed that physicochemical properties, adsorption capacity and mechanisms of soils and biochars all changed the most in the first 0.5 years. The properties and adsorption capacity of biochars gradually weakened with the ageing time, meanwhile, those of soils gradually enhanced. After co-ageing with acidic soil for 0.5 years, the Cd(II) adsorption capacity of modified biochar decreased by 86.59% in the ternary system; meanwhile, that of acidic soil increased by 65.52%. The contributions of mineral mechanisms decreased significantly, while non-mineral mechanisms were slightly affected by ageing. This study highlighted that when using biochar to remediate heavy metal-contaminated soils, biochar should be applied at least half a year in advance before planting crops so that biochar can fully contact and react with the soil.

Bio-sorption capacity of cadmium and zinc by Pseudomonas monteilii with heavy-metal resistance isolated from the compost of pig manure.

The tolerance of Pseudomonas monteilii X1, isolated from pig manure compost, to Cd and Zn, as well as its capacity for biosorption, were investigated. The minimum inhibitory concentrations (MIC) of Cd and Zn for the strain were 550 mg/L and 800 mg/L, respectively. Untargeted metabolomics analysis revealed that organic acids and derivatives, lipids and lipid-like molecules, and organic heterocyclic compounds were the main metabolites. The glyoxylate and dicarboxylate metabolism pathway were significantly enriched under Cd2+ stress. The isothermal adsorption and adsorption kinetics experiments determined that the strain had adsorption capacities of 9.96 mg/g for Cd2+ and 23.4 mg/g for Zn2+. Active groups, such as hydroxyl, carboxyl, and amino groups on the cell surface, were found to participate in metal adsorption. The strain was able to convert Zn2+ into Zn3(PO4)2·4H2O crystal. Overall, this study suggested that Pseudomonas monteilii has potential as a remediation material for heavy metals.

Microwave promoted graft copolymerization of poly(ethylacrylate) onto k-carrageenan for removal of Cd and Ni from aqueous solution.

Microwave promoted graft copolymerization of poly (ethyl acrylate) onto kappa-carrageenan in presence of a redox pair (ascorbic acid and potassium persulfate) led to the formation of a novel copolymer hydrogel, kappa-carrageenan-graft-poly (ethylacrylate). By varying the reaction conditions such as the microwave power, reaction time, concentration of kappa-carrageenan, ascorbic acid and persulfate, copolymers of highest percentage grafting was obtained and characterized by FT-IR, SEM, TGA and XRD. The copolymer was evaluated as an adsorbent for the adsorption of Ni(II) and Cd(II). Various adsorption parameters such as contact time, pH, initial metal ion concentration, temperature, electrolyte strength and adsorbent dosage were varied to obtain the optimum conditions for the adsorption. The adsorption data for Cd(II), fitted better for Langmuir and Ni(II), fitted much better for Freundlich adsorption isotherm model. Maximum adsorption obtained for cadmium ions and nickel ions was 308.6 mg/g-1 and 305.8 mg/g-1 respectively. The adsorption of both metal ions followed pseudo second order kinetic model. The positive ΔH values endorsed the adsorption process to be endothermic in nature. The negative values of ΔG indicate the spontaneity of the adsorption process while the positive ΔS values showed that the adsorption of metal ions proceeded with increased randomness at the surface of the copolymer. High recovery percentage of the metal ions from the adsorbent indicates that the copolymer can be used for more adsorption cycles.

High performance self-assembled sulfidized nanoscale zero-valent iron for the immobilization of cadmium in contaminated sediments: Optimization, microbial response, and mechanisms.

Sulfidized nanoscale zero-valent iron (S-nZVI) showed excellent removal capacity for cadmium (Cd) in aqueous phase. However, the remediation effects of S-nZVI on Cd-contaminated sediment and its interactions with microorganisms in relation to Cd fate remain unclear. The complexity of the external environment posed a challenge for Cd remediation. This study synthesized S-nZVI with different S and Fe precursors to investigate the effect of precursors and applied the optimal material to immobilize Cd in sediments. Characterization analysis revealed that the precursor affected the morphology, Fe0 crystallinity, and the degree of oxidation of the material. Incubation experiments demonstrated that the immobilization efficiency of Cd using S-nZVIFe3++S2- (S/Fe = 0.14) reached the peak value of 99.54%. 1% and 5% dosages of S-nZVI significantly reduced Cd concentration in the overlying water, DTPA-extractable Cd content, and exchangeable (EX) Cd speciation (P < 0.05). Cd leaching in sediment and total iron in the overlying water remained at low levels during 90 d of incubation. Notably, each treatment maintained a high Cd immobilization efficiency under different pH, water/sediment ratio, organic acid, and coexisting ion conditions. Sediment physicochemical properties, functional bacteria, and a range of adsorption, complexation and precipitation of CdS effects dominated Cd immobilization.

Transport and transformations of cadmium in water-biofilm-sediment phases as affected by hydrodynamic conditions.

Hydrodynamic conditions play a crucial role in governing the fate, transport, and risks of metal elements. However, the contribution of hydrodynamic conditions to the fate and transport of heavy metals among water, sediment, and biofilm phases is poorly understood. In our study, we conducted experiments in controlled hydrodynamic conditions using a total of 6 two-phase and 9 three-phase mesocosms consisting of water, biofilm, and sediment. We also measured Cd (cadmium) specification in different phases to assess how hydrodynamic forces control Cd bioavailability. We found that turbulent flow destroyed the surface morphology of the biofilm and significantly decreased the content of extracellular polymeric substances (p < 0.05). This led to a decrease in the biofilm's adsorption capacity for Cd, with the maximum adsorption capacity (0.124 mg/g) being one-tenth of that under static conditions (1.256 mg/g). The Cd chemical forms in the biofilm and sediment were significantly different, with the highest amount of Cd in the biofilm being acid-exchangeable, accounting for up to 95.1% of the total Cd content. Cd was more easily released in the biofilm due to its weak binding state, while Cd in the sediment existed in more stable chemical forms. Hydrodynamic conditions altered the migration behavior and distribution characteristics of Cd in the system by changing the adsorption capacity of the biofilm and sediment for Cd. Cd mobility increased in laminar flow but decreased in turbulent flow. These results enhance our understanding of the underlying mechanisms that control the mobility and bioavailability of metals in aquatic environments with varying hydrodynamic conditions.

Optimization of fenugreek seed mucilage extraction for the synthesis of a novel bio-nano composite for efficient removal of cadmium ions from aqueous environments.

This research investigates the application of an innovative bio-nanocomposite, Fenugreek seed mucilage/silicon carbide (FSM/SiC), as an exceptionally effective adsorbent for eliminating cadmium ions from aqueous solutions. Optimization of fenugreek mucilage extraction involved ultrasonic methods, establishing ideal conditions with a solid-to-solvent ratio of 1:55, 50 °C temperature, 37 kHz frequency, 100 % power, and 30 min processing time. Comprehensive characterization through FTIR spectroscopy, XRD, imaging, DLS, and SEM confirmed the preservation of crucial adsorption-related characteristics. Enhanced adsorption efficiency was achieved by systematically adjusting pH, temperature, adsorbent concentration, pollutant concentration, and contact time, identifying optimal conditions at pH 6, 0.03 g adsorbent dosage, 35 min contact time, and 30 mg/L initial cadmium concentration at 30 °C. Adsorption kinetics followed a pseudo-second-order model, while the Langmuir isotherm fit suggested monolayered adsorption. Thermodynamic analysis indicated exothermic and spontaneous Cd2+ ion adsorption onto FSM/SiC. Remarkably, FSM/SiC demonstrated exceptional regeneration potential, positioning it as a promising solution for water decontamination and environmental remediation. This research showcases FSM/SiC's potential with a maximum adsorption capacity of 41.6 mg/g for cadmium ions, highlighting its significance in addressing cadmium contamination.

Iron-modified biochar effectively mitigates arsenic-cadmium pollution in paddy fields: A meta-analysis.

The escalating problem of compound arsenic (As) and cadmium (Cd) contamination in agricultural soils necessitates the urgency for effective remediation strategies. This is compounded by the opposing geochemical behaviors of As and Cd in soil, and the efficacy of biochar treatment remains unclear. This pioneering study integrated 3780 observation pairs referred from 92 peer-reviewed articles to investigate the impact of iron-modified biochar on As and Cd responses across diverse soil environments. Regarding the treatments, 1) biochar significantly decreased the exchangeable and acid-soluble fraction of As (AsF1, 20.9%) and Cd (CdF1, 24.0%) in paddy fields; 2) iron-modified biochar significantly decreased AsF1 (32.0%) and CdF1 (27.4%); 3) iron-modified biochar in paddy fields contributed to the morphological changes in As and Cd, mainly characterized by a decrease in AsF1 (36.5%) and CdF1 (36.3%) and an increase in the reducible fraction of As (19.7%) and Cd (39.2%); and 4) iron-modified biochar in paddy fields increased As (43.1%) and Cd (53.7%) concentrations in the iron plaque on root surfaces. We conclude that iron-modified biochar treatment of paddy fields is promising in remediating As and Cd contamination by promoting the formation of iron plaque.

Bi(III) Binding Stoichiometry and Domain-Specificity Differences Between Apo and Zn(II)-bound Human Metallothionein 1a.

Bismuth is a xenobiotic metal with a high affinity to sulfur that is used in a variety of therapeutic applications. Bi(III) induces the cysteine-rich metallothionein (MT), a protein known to form two-domain cluster structures with certain metals such as Zn(II), Cd(II), or Cu(I). The binding of Bi(III) to MTs has been previously studied, but there are conflicting reports on the stoichiometry and binding pathway, which appear to be highly dependent on pH and initial metal-loading status of the MT. Additionally, domain specificity has not been thoroughly investigated. In this paper, ESI-MS was used to determine the binding constants of [Bi(EDTA)]- binding to apo-MT1a and its individual αMT fragment. The results were compared to previous experiments using ßMT1a and ßαMT3. Domain specificity was investigated using proteolysis methods and the initial cooperatively formed Bi2MT was found to bind to cysteines that spanned across the traditional metal binding domain regions. Titrations of [Bi(EDTA)]- into Zn7MT were performed and were found to result in a maximum stoichiometry of Bi7MT, contrasting the Bi6MT formed when [Bi(EDTA)]- was added to apo-MT. These results show that the initial structure of the apo-MT determines the stoichiometry of new incoming metals and explains the previously observed differences in stoichiometry.

Zero-valent iron (nZVI) nanoparticles mediate SlERF1 expression to enhance cadmium stress tolerance in tomato.

Cadmium (Cd) pollution threatens plant physiological and biochemical activities and crop production. Significant progress has been made in characterizing how nanoparticles affect Cd stress tolerance; however, the molecular mechanism of nZVI nanoparticles in Cd stress remains largely uncharacterized. Plants treated with nZVI and exposed to Cd had increased antioxidant capacity and reduced Cd accumulation in plant tissues. The nZVI treatment differentially affected the expression of genes involved in plant environmental responses, including those associated with the ERF transcription factor. SlEFR1 was upregulated by Cd stress in nZVI-treated plants when compared with the control and the predicted protein-protein interactions suggested SlERF1 interacts with proteins associated with plant hormone signaling pathway and related to stress. Yeast overexpressing SlEFR1 grew faster after Cd exposure and significantly had higher Cd stress tolerance when compared with empty vector controls. These results suggest that nZVI induces Cd stress tolerance by activating SlERF1 expression to improve plant growth and nutrient accumulation. Our study reveals the molecular mechanism of Cd stress tolerance for improved plant growth and will support new research on overcoming Cd stress and improving vegetable crop production.

Biomass chitosan/sodium alginate colorimetric imprinting hydrogels with integrated capture and visualization detection for cadmium(II).

Due to Cd(II) with highly toxic, persistent and bioaccumulative, the discharge of it into the environment brings serious pollution. Developing strategies that are efficient, low-cost, pollution-free and specific to removing Cd(II) from wastewater is therefore of great urgency and prime importance. A novel chitosan/sodium alginate ionic imprinting(IICA) hydrogels with specific adsorption capacity for Cd(II) was prepared through freeze-thaw and ion imprinting, and finally the colorimetric sensor (IICAS) was prepared via introducing Rhodamine B(RhB) and Victoria blue(VBB) by immersion to achieve visual detection of Cd(II). The IICA hydrogels with imprinted hole structure had higher adsorption capacity and better specific selectivity for Cd(II). As well as internal diffusion, coordination, ion exchange, and hydrogen bonding influenced the adsorption rate. Moreover, the IICAS exhibited good selective detection ability and linearity for Cd(II) with the fitted correlation coefficient (R2) = 0.98, limit of detection (LOD) = 35 nmol/L. Combined with the smartphone platform, portable and quantitative detection of Cd(II) can be achieved, Within the 0-100 mg/L range, R2 remained 0.94, and LOD was 75 nmol/L. This strategy of preparing a novel whole biomass IICAS integrating capture and visual detection provides a new insight into the construction of a promising candidate sensor for the removal and detection of Cd(II).

Low-molecular-weight aromatic acids mediated the adsorption of Cd2+ onto biochars: effects and mechanisms.

Low-molecular-weight aromatic acids (LWMAAs), a ubiquitous organic substance in natural systems, are important in controlling the environmental fate of potentially toxic metals. However, little is known about the effects of LWMAAs on the interactions between biochars and potentially toxic metals. Herein, the influences of three aromatic acids, including benzoic acid (BA), p-hydroxy benzoic acid (PHBA), and syringic acid (SA), on the adsorption of Cd2+ onto biochars generated at three different pyrolysis temperatures under acidic and neutral conditions were examined. Generally, the adsorption ability of biochars for Cd2+ improved with the increase of pyrolysis temperature, which was ascribed to the increased inorganic element contents (e.g., P, S, and Si) and aromaticity, increasing the complexation between mineral anions and metal ions, and the enhanced cation-π interaction. Interestingly, aromatic acids considerably inhibited the adsorption of Cd2+ onto biochars, which was mainly ascribed to multi-mechanisms, including competition of LWMAA molecules and metal ions for adsorption sites, the pore blocking effect, the weakened interaction between mineral anions and Cd2+ induced by the adsorbed aromatic acids, and the formation of water-soluble metal-aromatic acid complexes. Furthermore, the inhibitory effects of LWMAAs on Cd2+ adsorption intensively depended on the aromatic acid type and followed the order of SA > PHBA > BA. This trend was related to the differences in the physicochemical features (e.g., the octanol/water partition coefficient (log Kow) and molecular size) of diverse LMWAAs. The results of this study demonstrate that the effects of coexisting LMWAAs should not be ignored when biochars are applied in soil remediation and wastewater treatment.

Green and effective remediation of heavy metals contaminated water using CaCO3 vaterite synthesized through biomineralization.

Heavy metal pollution has attracted significant attention due to its persistent presence in aquatic environments. A novel vaterite-based calcium carbonate adsorbent, named biogenic CaCO3, was synthesized utilizing a microbially induced carbonate precipitation (MICP) method to remediate heavy metal-contaminated water. The maximum Cd2+ removal capacity of biogenic CaCO3 was 1074.04 mg Cd2+/g CaCO3 with a high Cd2+ removal efficiency greater than 90% (initial Cd2+ concentration 400 mg/L). Furthermore, the biogenic CaCO3 vaterite, induced by microbial-induced calcium carbonate precipitation (MICP) process, demonstrated a prolonged phase transformation to calcite and enhanced stability. This resulted in a sustained high effectiveness (greater than 96%) following six consecutive recycling tests. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the semi-stable vaterite type of biogenic CaCO3 spontaneously underwent dissolution and recrystallization to form thermodynamic stable calcite in aquatic environments. However, the presence of Cd2+ leads to the transformation of vaterite into CdCO3 rather than undergoing direct converting to calcite. This transformation is attributed to the relatively low solubility of CdCO3 compared to calcite. Meanwhile, the biogenic CaCO3 proved to be an efficient and viable method for the removal of Pb2+, Cu2+, Zn2+, Co2+, Ni2+ and Mn2+ from water samples, surpassing the performance of previously reported adsorbents. Overall, the efficient and promising adsorbent demonstrates potential for practical in situ remediation of heavy metals-contaminated water.

Mobility, speciation of cadmium, and bacterial community composition along soil depths during microbial carbonate precipitation under simulated acid rain.

An overexploitation of earth resources results in acid deposition in soil, which adversely impacts soil ecosystems and biodiversity and affects conventional heavy metal remediation using immobilization. A series of column experiments was conducted in this study to compare the cadmium (Cd) retention stability through biotic and abiotic carbonate precipitation impacted by simulated acid rain (SAR), to build a comprehensive understanding of cadmium speciation and distribution along soil depth and to elucidate the biogeochemical bacteria-soil-heavy metal interfaces. The strain of Sporosarcina pasteurii DSM 33 was used to trigger the biotic carbonate precipitation and cultivated throughout the 60-day column incubation. Results of soil pH, electrical conductivity (EC), and quantitative CdCO3/CaCO3 analysis concluded that the combination of biotic and abiotic soil treatment could reinforce soil buffering capacity as a strong defense mechanism against acid rain disturbance. Up to 1.8 ± 0.04 U/mg urease enzyme activity was observed in combination soil from day 10, confirming the sustained effect of urease-mediated microbial carbonate precipitation. Cadmium speciation and distribution analyses provided new insights into the dual stimulation of carbonate-bound and Fe/Mn-bound phases of cadmium immobilization under microbially induced carbonate precipitation (MICP). As confirmed by the microbial community analysis, outsourcing urea triggered diverse microbial metabolic responses, notably carbonate precipitation and dissimilatory iron metabolism, in both oxygen-rich topsoil and oxygen-depleted subsurface layers. The overall investigation suggests the feasibility of applying MICP for soil Cd remediation under harsh environments and stratagem by selecting microbial functionality to overcome environmental challenges.