Microbial reduction of vanadium (V) in groundwater: Interactions with coexisting common electron acceptors and analysis of microbial community

Unique regulatory network of dragon fruit simultaneously mitigates the effect of vanadium pollutant and environmental factors

Under changing climatic conditions, plants are simultaneously facing conflicting stresses in nature. Plants can sense different stresses, induce systematic ROS signals, and regulate transcriptomic, hormonal, and stomatal responses. We performed transcriptome analysis to reveal the integrative stress response regulatory mechanism underlying heavy metal stress alone or in combination with heat and drought conditions in pitaya (dragon fruit). A total of 70 genes were identified from 31,130 transcripts with conserved differential expression. Furthermore, weighted gene co-expression network analysis (WGCNA) identified trait-associated modules. By integrating information from three modules and protein-protein interaction (PPI) networks, we identified 10 interconnected genes associated with the multifaceted defense mechanism employed by pitaya against co-occurring stresses. To further confirm the reliability of the results, we performed a comparative analysis of 350 genes identified by three trait modules and 70 conserved genes exhibiting their dynamic expression under all treatments. Differential expression pattern of genes and comparative analysis, have proven instrumental in identifying ten putative structural genes. These ten genes were annotated as PLAT/LH2, CAT, MLP, HSP, PB1, PLA, NAC, HMA, and CER1 transcription factors involved in antioxidant activity, defense response, MAPK signaling, detoxification of metals and regulating the crosstalk between the complex pathways. Predictive analysis of putative candidate genes, potentially governing single, double, and multifactorial stress response, by several signaling systems and molecular patterns. These findings represent a valuable resource for pitaya breeding programs, offering the potential to develop resilient "super pitaya" plants.

Efficient reduction of vanadium (V) with biochar and experimental parameters optimized by response surface methodology

Water pollution deteriorates ecosystems and has a great threaten to the environment. The environmental benefits of wastewater treatment are extremely important to minimize pollutants. Here, the biochar purchased from the related industry was used to treat the wastewater which contained high concentration of vanadium (V). The concentration of vanadium was measured by the IC-OES and the results showed that 96.1% vanadium (V) was reduced at selected reaction conditions: the mass ratio of biochar to vanadium of 5.4, reaction temperature of 90 °C, reaction time at 60 min and concentration of H2SO4 of 10 g/L, respectively. Response surface methodology confirmed that all the experimental parameters had positive effect on the reduction of vanadium (V), which could improve the reduction efficiency of vanadium (V) as increased. The influence of each parameter on the reduction process followed the order: A (Concentration of H2SO4) > C (mass ratio of biochar to vanadium) > B (mass ratio of biochar to vanadium). Especially, the mass ratio of biochar to vanadium and concentration of H2SO4 had the greatest influence on the reduction process. This paper provides a versatile strategy for the treatment of wastewater containing vanadium (V) and shows a bright tomorrow for wastewater treatment.

Community assembly and microbial interactions in an alkaline vanadium tailing pond

Intensive development of vanadium-titanium mines leads to an increasing discharge of vanadium (V) into the environment, imposing potential risks to both environmental system and public health. Microorganisms play a key role in the biogeochemical cycling of V, influencing its transformation and distribution. In addition, the characterization of microbial community patterns serves to assess potential threats imposed by elevated V exposure. However, the impact of V on microbial community remains largely unknown in alkaline V tailing areas with a substantial amounts of V accumulation and nutrient-poor conditions. This study aims to explore the characteristics of microbial community in a wet tailing pond nearby a large-scale V mine. The results reveal V contamination in both water (0.60 mg/L) and sediment tailings (340 mg/kg) in the tailing pond. Microbial community diversity shows distinctive pattern between environmental metrices. Genera with the functional potential of metal reduction\resistance, nitrogen metabolism, and carbon fixation have been identified. In this alkaline V tailing pond, V and pH are major drivers to induce community variation, particularly for functional bacteria. Stochastic processes primarily govern the assemblies of microbial community in the water samples, while deterministic process regulate the community assemblies of sediment tailings. Moreover, the co-occurrence network pattern unveils strong selective pattern for sediment tailings communities, where genera form a complex network structure exhibiting strong competition for limited resource. These findings reveal the patterns of microbial adaptions in wet vanadium tailing ponds, providing insightful guidelines to mitigate the negative impact of V tailing and develop sustainable management for mine-waste reservoir.

Vanadium Accumulation and Reduction by Vanadium-Accumulating Bacteria Isolated from the Intestinal Contents of Ciona robusta

The sea squirt Ciona robusta (formerly Ciona intestinalis type A) has been the subject of many interdisciplinary studies. Known as a vanadium-rich ascidian, C. robusta is an ideal model for exploring microbes associated with the ascidian and the roles of these microbes in vanadium accumulation and reduction. In this study, we discovered two bacterial strains that accumulate large amounts of vanadium, CD2-88 and CD2-102, which belong to the genera Pseudoalteromonas and Vibrio, respectively. The growth medium composition impacted vanadium uptake. Furthermore, pH was also an important factor in the accumulation and localization of vanadium. Most of the vanadium(V) accumulated by these bacteria was converted to less toxic vanadium(IV). Our results provide insights into vanadium accumulation and reduction by bacteria isolated from the ascidian C. robusta to further study the relations between ascidians and microbes and their possible applications for bioremediation or biomineralization.

Natural attenuation of BTEX and chlorobenzenes in a formerly contaminated pesticide site in China: Examining kinetics, mechanisms, and isotopes analysis

Groundwater contamination from abandoned pesticide sites is a prevalent issue in China. To address this problem, natural attenuation (NA) of pollutants has been increasingly employed as a management strategy for abandoned pesticide sites. However, limited studies have focused on the long-term NA process of co-existing organic pollutants in abandoned pesticide sites by an integrated approach. In this study, the NA of benzene, toluene, ethylbenzene, and xylene (BTEX), and chlorobenzenes (CBs) in groundwater of a retired industry in China was systematically investigated during the monitoring period from June 2016 to December 2021. The findings revealed that concentrations of BTEX and CBs were effectively reduced, and their NA followed first-order kinetics with different rate constants. The sulfate-reducing bacteria, nitrate-reducing bacteria, fermenting bacteria, aromatic hydrocarbon metabolizing bacteria, and reductive dechlorinating bacteria were detected in groundwater. It was observed that distinct environmental parameters played a role in shaping both overall and key bacterial communities. ORP (14.72%) and BTEX (12.89%) were the main drivers for variations of the whole and key functional microbial community, respectively. Moreover, BTEX accelerated reductive dechlorination. Furthermore, BTEX and CBs exhibited significant enrichment of 13C, ranging from +2.9 to +27.3‰, demonstrating their significance in situ biodegradation. This study provides a scientific basis for site management.

Tidal inundation and plant growth/decay impact redox-sensitive metal geochemistry and fluxes in salt marsh porewater

In dynamic coastal ecosystems, environmental factors can play important roles in the biogeochemical cycle of redox-sensitive metals. This work is focused on the impact of tidal inundation, plant growth and decay on the biogeochemical cycle of redox-sensitive metals (e.g., Fe, Mn, Mo, V and U) in salt marsh wetlands. Samples were collected from the salt marsh wetlands of the Yellow River Estuary under different tidal states and growth stages of plants (Phragmites australis). Compared to the concentration of redox-sensitive metals in the river water and seawater near the study area, Fe, Mn and U were enriched in salt marsh wetland, which might become a potential source of Fe, Mn and U in the coastal sea. Tidal inundation, plant growth and decay can affect redox-sensitive metals through changes in redox conditions; the plant can also affect them directly via root absorption or plant residue decomposition, especially for Mo. Calculations of diffusion flux between sediment porewater and tidal water show that these processes can increase diffusion by at least 16.7 % or decrease it by at least 65.7 %, even reversing the direction of diffusion, which can affect the accumulation of redox-sensitive metals in salt marsh wetlands. The results showed that tidal inundation and the decay of plant residue were not conducive to the accumulation of Fe and Mn but were beneficial to the accumulation of V and U in salt marsh wetlands. The plant growth showed the opposite pattern. The accumulation of Mo in salt marsh wetlands largely depends on ingestion by plants and the decay of plant residue. This research provides a scientific basis for the budget calculation of redox-sensitive metals in salt marsh wetlands.

Soil health implications of some d-block metals in selected agricultural soils in Southeast Nigeria

Soil fertility, soil health and environmental management through the estimation of background concentration of potentially toxic elements is required for environmental safety. This study aims at investigating the concentration, fertility and potential health risks of some d-block metals (Ti, V, Fe, Mn, and Mo) in some agricultural soils, and establishes the relationship between the metals and some soil properties. Eight elevation ranges resulted from the digital elevation models of the study area; two in Ishibori (NG1, NG2), three each in Agoi-Ibami (CG1, CG2, CG3) and Mfamosing (SG1, SG2 and SG3). One soil profile pit was sunk along each of the elevations. Thirty-five composite soil samples were collected at 0-30, 30-60, 60-90, 90-120, 120-150, 150-180 and 180-200 cm depending on soil depth. Only the profile means of Mn (660.82 ± 612.89 mg/kg) and Mo (2.61 ± 0.73 mg/kg) exceeded permissible concentrations and would pose threats to the environment. Also, the concentrations of the d-block metals exceeded permissible values in Ishibori making them prone to toxicity. The metals were irregularly distributed with depth; however, Mn and Fe were concentrated in the subsurface soils. Clay and sand contents correlated positively and negatively, respectively with all the d-block metals at p < 0.05. The linear model was more efficient in estimating V and Mo via soil properties with adjusted R2 of 33 - 67% for the metals. In conclusion, agricultural activities and geology may influence the accumulation of d-block metals, hence the call for environmental monitoring to curtail metals' assimilation by crops. HIGHLIGHTS: • Mn and Mo threaten the environment the most. • Soils in the Southern Guinea Savannah are most prone to d-block metals contamination. • BD, pH, Mg, and CEC are the best predictors of d-block metals in the soils. • The linear model was best performing in the estimation of V and Mo, respectively.

Impact of salinity on anaerobic ceramic membrane bioreactor for textile wastewater treatment: Process performance, membrane fouling and machine learning models

Anaerobic membrane bioreactor (AnMBR) shows great potential for textile wastewater treatment, but high salinity in the influent may undermine its performance. This study evaluated the impact of salinity on the treatment performance of an upflow anaerobic sludge blanket (UASB) configured AnMBR using a flat sheet ceramic membrane. The salinity was stepwise increased (0, 5, 10 and 20 g/L) in four phases of the AnMBR operation. Results indicated that increased salinity jeopardized the COD removal efficiency of AnMBR from 92% to 73%, but had a marginal effect on dye removal efficacy (90-96%). Low salinity (5 g/L) boosted the biogas production whilst high salinity (>10 g/L) had a negative impact. Additionally, the increase of salinity resulted in the soluble microbial production (SMP) concentration soar and membrane fouling rate increase, peaking at a salinity of 10 g/L (Phase III) and recovering back to a lower level at a salinity of 20 g/L (Phase IV). This indicated a transition occurrence at a salinity of 10 g/L (Phase III). The microbial diversity analyses further suggested a transition from salinity-sensitive microbes (Aminiphilus, Caldatribacterium, Mesotoga, Methanobrevibacter, Methanobacterium, Methanosaeta) to salinity-tolerant microbes (Longilinea, Ignavibacterium, Rhodovarius, Bosea and Flexilinea). This transition can be associated with the increase SMP concentration and more severe membrane fouling in Phase III, which were mitigated after a new equilibrium was reached when the microbial consortium acclimatized to the high salinity. Finally, a machine learning model of the Adaboost algorithm was established to predict COD removal under different salinities. Importantly, this study revealed that AnMBR process performance and membrane operation can be maintained for high salinity textile wastewater treatment with a halophilic microbial community growth under high-salinity selection pressure.

Vanadium in the Environment: Biogeochemistry and Bioremediation

Vanadium(V) is a highly toxic multivalent, redox-sensitive element. It is widely distributed in the environment and employed in various industrial applications. Interactions between V and (micro)organisms have recently garnered considerable attention. This Review discusses the biogeochemical cycling of V and its corresponding bioremediation strategies. Anthropogenic activities have resulted in elevated environmental V concentrations compared to natural emissions. The global distributions of V in the atmosphere, soils, water bodies, and sediments are outlined here, with notable prevalence in Europe. Soluble V(V) predominantly exists in the environment and exhibits high mobility and chemical reactivity. The transport of V within environmental media and across food chains is also discussed. Microbially mediated V transformation is evaluated to shed light on the primary mechanisms underlying microbial V(V) reduction, namely electron transfer and enzymatic catalysis. Additionally, this Review highlights bioremediation strategies by exploring their geochemical influences and technical implementation methods. The identified knowledge gaps include the particulate speciation of V and its associated environmental behaviors as well as the biogeochemical processes of V in marine environments. Finally, challenges for future research are reported, including the screening of V hyperaccumulators and V(V)-reducing microbes and field tests for bioremediation approaches.

Soil amendments for vanadium remediation: a review of remediation of vanadium in soil through chemical stabilization and bioremediation

Immobilization of vanadium (V) in soils is one option to prevent groundwater contamination and plant uptake. Phytoremediation, microbial remediation, and chemical stabilization using soil amendments are among the leading environmentally friendly and economically feasible techniques in V remediation. Soil amendments were used to reduce V mobility by immobilizing it in the soil matrix through chemical stabilization, while bioremediation methods such as phytoremediation and microbial remediation were used to remove V from contaminated soils. Vanadium exists in several species and among them V5+ species are the most prevalent, toxic, and soluble form and present as a negatively charged ion (H2VO4- and HVO42-) in oxic soils above pH 4. Amendments used for chemical stabilization can change the physicochemical properties enhancing immobility of V in soil. The pH of the soil environment, point of zero charge of the colloid surface, and redox conditions are some of the most important factors that determine the efficiency of the amendment. Commonly used amendments for chemical stabilization include biochar, zeolites, organic acids, various clay minerals and oxides of elements such as iron, titanium, manganese, and aluminum. For bioremediation, chelating agents and microbial communities are used to mobilize V to enhance phyto-or microbial-extraction procedures. The objectives of this review were to discuss remediation methods of V while considering V speciation and toxicity in soil, and soil amendment application for V removal from soil. The information compiled in this review can guide further research on soil amendments for optimal V remediation in largely contaminated industrial sites.

Transcriptomic and metabolomic perspectives for the growth of alfalfa (Medicago sativa L.) seedlings with the effect of vanadium exposure

Hitherto, the effect of vanadium on higher plant growth remains an open topic. Therefore, nontargeted metabolomic and RNA-Seq profiling were implemented to unravel the possible alteration in alfalfa seedlings subjected to 0.1 mg L^-1 (B group) and 0.5 mg L^-1 (C group) pentavalent vanadium [(V(V)] versus control (A group) in this study. Results revealed that vanadium exposure significantly altered some pivotal transcripts and metabolites. The number of differentially expressed genes (DEGs) markedly up- and down-regulated was 21 and 23 in B_vs_A, 27 and 33 in C_vs_A, and 24 and 43 in C_vs_B, respectively. The number for significantly up- and down-regulated differential metabolites was 17 and 15 in B_vs_A, 43 and 20 in C_vs_A, and 24 and 16 in C_vs_B, respectively. Metabolomics and transcriptomics co-analysis characterized three significantly enriched metabolic pathways in C_vs_A comparing group, viz., α-linolenic acid metabolism, flavonoid biosynthesis, and phenylpropanoid biosynthesis, from which some differentially expressed genes and differential metabolites participated. The metabolite of traumatic acid in α-linolenic acid metabolism and apigenin in flavonoid biosynthesis were markedly upregulated, while phenylalanine in phenylpropanoid biosynthesis was remarkably downregulated. The genes of allene oxide cyclase (AOC) and acetyl-CoA acyltransferase (fadA) in α-linolenic acid metabolism, and chalcone synthase (CHS), flavonoid 3'-monooxygenase (CYP75B1), and flavonol synthase (FLS) in flavonoid biosynthesis, and caffeoyl-CoA O-methyltransferase (CCoAOMT) in phenylpropanoid biosynthesis were significantly downregulated. While shikimate O-hydroxycinnamoyltransferase (HCT) in flavanoid and phenylpropanoid biosynthesis were conspicuously upregulated. Briefly, vanadium exposure induces a readjustment yielding in metabolite and the correlative synthetic precursors (transcripts/unigenes) in some branched metabolic pathways. This study provides a practical and in-depth perspective from transcriptomics and metabolomics in investigating the effects conferred by vanadium on plant growth and development.

Electron transfer routes in nitrate-pentavalent vanadium co-contaminated system of oligotrophic microbiology niche

Microbial techniques have been extensively used for the remediation of nitrate and V(V) co-contaminations, but the mechanisms of electron and substances transport and metabolism of co-contaminations under oligotrophic niche have been largely overlooked. This study quantified the electron transfer and consumption, substance transfer, and metabolic pathways in the nitrate and V(V) co-contamination system under oligotrophic condition to explore the underlying mechanisms by characterizing the products and elucidating conventional cognitive pathways. This study compared the composition of the precipitates under the conditions of sufficient and insufficient carbon sources using energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and discovered the re-oxidation process of the already reduced V(IV). Electronic evidence for the re-oxidation process of V(IV) was also provided by electron transfer and quantitative analysis. Besides, this study found that the electron contribution ratio of NO₃^--N → NO₂^--N and V(V) → V(IV) reduction was 40.2:1. In addition, based on the functional prediction of PICRUSt 2, it was found that the utilization of intracellular reserve carbon source and enzymes in the transport chain were enhanced in oligotrophic microbiology niche. These results provide new insights into the stability of co-contamination reduction in oligotrophic microbiology niche and demonstrate a new mobilization pathway for V(V) in oligotrophic systems.

Performance of a continuous flow reactor on bio-reducing vanadium with straw

Vanadium (V) in groundwater could cause a serious threat to the environment and health. Continuous flow reactors were applied to reduce V(V) with straw being a solid carbon. The reduced efficiency of V(V) in the reactor with straw and inoculated sludge reached to 71.8%-99.9% for two months' operation (after 44 d). However, a long-term operation with only straw was not satisfied, achieving the reduced efficiency of 39.2-66.6%. The SEM images clearly revealed some traces of straw surface by utilized by microbes, which implied that microbes had a stronger capacity to hydrolyze straw. The introducing external microbes were essential to achieve a better bio-reduction performance on V(V). Treponema (5.3%) with metal reduction ability and Prevotellaceae (3.3%) able to specifically degrade complex plant-derived polysaccharides were found to be dominant in the microbial community. Utilizing agricultural biomass can save a lot of normal carbon like acetate, which is of benefit for carbon emissions.

Study on the coordination conduct and kinetic insights within the oxo-vanadate and organic reductive nitrogen and sulfur functionalities during the reduction coupled adsorption processes: Implications in practical applications

Vanadium(V) is arising wastewater contaminant recently. Although bio-reduction of vanadium(V) is effective, the knowledge of electron transfer pathways and coordination nature by cellular organic functionalities is seriously lacking. Herein, the coordination conduct and kinetic modes for the reduction of V(V) by organic nitrogen and sulfur functionalities in working pHs are comprehensively investigated for the first time. The kinetics follow 3 steps; (1) diffusion of V(V) species, (2) reduction of V(V) to V(IV), and (3) adsorption of existing V species. The diffusion of V(V) is controlled by the protonated =NH₂⁺, -SH₂⁺, -CSH⁺ functional groups and oxo-vanadate speciation. The reduction of V(V) to V(IV) was efficient by -SH than =NH, -NH- , because of the higher oxidation potential of sulfur and which acted as the sole electron donor in the process. The coordination of V(V)/V(IV) species interacted with oxygen, nitrogen and sulfur atoms via parallel orientation and leads to multi-docking or single-ionic interactions, revealing the previously unrecognized track. Hence, the system tested in four types of wastewaters with different pHs and resulted the comprehensive practical applicability of the system. This study proposes a novel tactic to design an efficient V(V) wastewater treatment system by considering its water parameters.

The ecology of bacterial communities in groundwater of industrial areas: Diversity, composition, network, and assembly

Groundwater provides freshwater resources necessary for mankind, but its quality is significantly impacted by anthropologic activities. The unique characteristics of groundwater provide a special niche for bacterial colonization. To maintain the sustainability of groundwater ecosystem, a good understanding of the influencing factors and assembly mechanisms for bacterial communities is necessary. Here, we investigated the bacterial communities of groundwater from two industrial zones in Shanghai, a highly industrialized city, during the wet and dry seasons using the high-throughput sequencing technology. Our study uncovered the significant effects of season, geographical location, and industrial type on the diversity and composition of groundwater bacterial communities, particularly, we found that season was the most dominant factor with much stronger influences (give the explanation 17.7%) in comparison with geographical location (8.8%) and industrial type (7.5%). Co-occurrence networks revealed that geographical location explained more variations of bacterial ecological network than season did. Both distance-decay of similarities and variation partitioning analyses indicated that the assembly of groundwater bacterial communities was more governed by environmental filtering compared to spatial-related dispersal. Finally, null model analysis suggested the role of stochastic processes, including dispersal and drift, in shaping the groundwater bacterial communities cannot be ignored. These findings would benefit to improve our understanding of the bacterial communities in groundwater ecosystem and provide a theoretical foundation for groundwater health management.

Vanadate Bio-Detoxification Driven by Pyrrhotite with Secondary Mineral Formation

Vanadium(V) is a redox-sensitive heavy-metal contaminant whose environmental mobility is strongly influenced by pyrrhotite, a widely distributed iron sulfide mineral. However, relatively little is known about microbially mediated vanadate [V(V)] reduction characteristics driven by pyrrhotite and concomitant mineral dynamics in this process. This study demonstrated efficient V(V) bioreduction during 210 d of operation, with a lifespan about 10 times longer than abiotic control, especially in a stable period when the V(V) removal efficiency reached 44.1 ± 13.8%. Pyrrhotite oxidation coupled to V(V) reduction could be achieved by an enriched single autotroph (e.g., Thiobacillus and Thermomonas) independently. Autotrophs (e.g., Sulfurifustis) gained energy from pyrrhotite oxidation to synthesize organic intermediates, which were utilized by the heterotrophic V(V) reducing bacteria such as Anaerolinea, Bacillus, and Pseudomonas to sustain V(V) reduction. V(V) was reduced to insoluble tetravalent V, while pyrrhotite oxidation mainly produced Fe(III) and SO₄^2-. Secondary minerals including mackinawite (FeS) and greigite (Fe₃S₄) were produced synchronously, resulting from further transformations of Fe(III) and SO₄^2- by sulfate reducing bacteria (e.g., Desulfatiglans) and magnetotactic bacteria (e.g., Nitrospira). This study provides new insights into the biogeochemical behavior of V under pyrrhotite effects and reveals the previously overlooked mineralogical dynamics in V(V) reduction bioprocesses driven by Fe(II)-bearing minerals.

Risk assessment and microbial community structure in agricultural soils contaminated by vanadium from stone coal mining

High health risks of vanadium (V) released by the mining of vanadium titanomagnetite (VTM) have been widely recognized, but little is known about the risks and microbial community responses of V pollution as a consequence of the stone coal mining (SCM), another important resource for V mining. In this study, the topsoils and the profile soils were collected from the agricultural soils around a typical SCM in Hunan Province, China, with the investigation of ecological, health risks and microbial community structures. The results showed that ∼97.6% of sampling sites had levels of total V exceeding the Chinese National standard (i.e., 130 mg/kg), and up to 41.1% of V speciation in the topsoils was pentavalent vanadium (V(V)). Meanwhile, the proportions of HQ > 1 and 0.6-1 in the topsoils were ∼8.3% and ∼31.0% respectively, indicating that V might pose a non-carcinogenic risk to children. In addition, the microbial community varied between the topsoils and the profile soils. Both sulfur-oxidizing bacteria (e.g. Thiobacillus, MND1, Ignavibacterium) and sulfate-reducing bacteria (e.g. Desulfatiglans, GOUTB8, GOUTA6) might have been involved in V(V) reductive detoxification. This study helps better understand the pollution and associated risks of V in the soils of SCM and provides a potential strategy for bioremediation of the V-contaminated environment.

Effect of nitrate and sulfate coexistence on hydrogen autotrophic reduction of antimonate (Sb(V)) and microbial community structures

Hydrogen autotrophic bioreduction of antimonate (Sb(V)) to antimonite (Sb(III)) is an alternative approach for removing antimony (Sb) from water. This study investigated Sb(V) reduction kinetics and the effects of various parameters on the Sb(V) removal performance in a hydrogen autotrophic reaction system (HARS). Sb(V) reduction in the HARS was well fitted to the Michaelis-Menten model, showing a positive correlation between the reaction rate and biomass. The maximum specific substrate removal rates were 0.29-4.86 and 6.82-15.87 mg Sb(V)/(g·VSS·h) at initial Sb(V) concentrations of 500 μg/L and 10 mg/L, respectively. Coexisting nitrate significantly inhibited Sb(V) reduction, and the inhibition intensified with increasing nitrate concentration. However, coexisting sulfate had a positive effect on Sb(V) reduction, and the sulfate effectively enhanced total antimony (TSb) removal performance by generating sulfide from sulfate reduction. Illumina high-throughput sequencing technology was used to determine the changes in microbial community structure during different periods in the HARS, revealing the effects of co-existing ions on the dominant Sb(V) reducing bacteria. In the HARS, Longilinea and Terrimonas were the dominant genera in the presence of nitrate, and Longilinea was the dominant genus in the presence of sulfate, at initial Sb(V) concentration of 500 μg/L. When the concentration of Sb(V) was 10 mg/L, Longilinea and Thauera were the dominant genus in the HARS for treating water co-polluted with nitrate and sulfate, respectively. These results provide a theoretical basis of the application of HARS for the bio-remediation of Sb(V) contaminated water.

Synchronous microbial V(V) reduction and denitrification using corn straw as the sole carbon source

The coexistence of nitrate and V(V) in groundwater aquifers poses potential threats to ecological environment and public health. However, much remains to be elucidated about how the complex microbial community coupled nitrate and V(V) simultaneous bio-reduction with carbon source oxidation. For the first time, it was demonstrated that denitrification and V(V) bio-reduction occur by using corn straw as the sole carbon and energy source. Corn straw was proved to have efficient denitrification and V(V) bio-reduction performance in various environments, especially at V(V) concentrations of 100 mg/L for optimal V(V) reduction rate (19.25 mg/L·d) and at pH of 11 with the best nitrate reduction rate (3.12 d^-1). In addition, an interesting phenomenon was found that the release of V(V) occurred when the carbon source was insufficient and the competitive electron acceptor (NO₃^--N) existed. Metagenomic analysis showed that the addition of corn straw increased the abundance of genes related to metal resistance, cytochrome and dimethyl sulfoxide, and increased the abundance of glycolytic process, which may play a vital role in facilitating the reduction of V(V). These findings can provide basic suggestions for improving the mechanism of V(V) reduction pathway and provide guidance for the remediation of groundwater polluted by nitrate and V(V).

Unraveling diverse survival strategies of microorganisms to vanadium stress in aquatic environments

Worldwide vanadium contamination is posing serious risks to ecosystems. Although abilities of microbial communities to cope with vanadium stress using specific survival strategies have been reported, little is known regarding their relative importance and the underlying detoxification/tolerance mechanisms. Herein, we investigated the potential survival strategies of microbial communities and associated pathways in aquatic environments based on geochemistry and molecular biology. High vanadium content was observed for both water (12.6 ± 1.15 mg/L) and sediment (1.18 × 10³ ± 10.4 mg/kg) in the investigated polluted stream. Co-occurrence network investigation implied that microbial communities showed cooperative interactions to adapt to the vanadium-polluted condition. Vanadium was also characterized as one of the vital factors shaping the community structure via redundancy analysis and structural equation models. Based on the metagenomic technology, three survival strategies including denitrification pathway, electron transfer, and metal resistance in innate microbes under the vanadium stress were revealed, with comprehensively summarized vanadium detoxification/tolerance genes. Remarkable role of electron transfer genes and the prevalent existence of resistance genes during detoxifying vanadium were highlighted. Overall, these findings provide novel insights into survival strategies under the vanadium contamination in aquatic environments, which can be of great significance for the identification, isolation, and application of vanadium reducing bacteria in vanadium bioremediation.

An innovative approach for reducing the water and alkali consumption in the lactic acid fermentation via the reuse of pretreated liquid

This study focuses on enhancing lactic acid (LA) production and declining water and alkali consumption by reusing the pretreated liquid (PL) of spent mushroom substance (SMS) in the co-fermentation of food waste (FW) and SMS. First, the compositions of PL are identified, and the effects of the PL inhibitors on enzymatic hydrolysis and fermentation are explored. The PL phenol concentrations exceeded 2 g/L, which affected LA fermentation. Therefore, PL phenols were removed by adjusting the pH value, and the detoxified PL (DPL) phenol concentrations were 70.3% lower than those of PL. Different PL:DPL ratios were established to reuse in the fermentation process, and the LA concentration in the 50% PL + 50% DPL group was the highest (56.7 g/L). Then, pretreated SMS was not water-washed, and a neutralizer was prepared with the PL, LA production remained unchanged. Water and NaOH consumption decreased by 84.6% and 52.0%, respectively, and no wastewater was produced.

A Clean Method for Vanadium (V) Reduction with Oxalic Acid

Water pollution deteriorates ecosystems and is a great threat to the environment. The environmental benefits of wastewater treatment are extremely important to minimize pollutants. Here, the oxalic acid used as reductant was used to treat the wastewater which contained high concentration of vanadium (V). Nearly 100% of vanadium was efficiently reduced at selected reaction conditions. The optimization results simulated by response surface methodology (RSM) analysis indicated the parameters all had significant effects on the reduction process, and followed the order: dosage of oxalic acid > reaction temperature > reaction time > initial pH of vanadium-containing wastewater. The reduction behavior analysis indicated that the pseudo first-order kinetics model could describe well the reduction process with Ea = 42.14 kJ/mol, and was described by the equation as followed: −LnC=K0·[pH]0.1016·[n(O)/n(V)]2.4569·[T]2.2588·exp(−42.14/T)·t.

Dynamics of vertical vanadium migration in soil and interactions with indigenous microorganisms adjacent to tailing reservoir

Severe vanadium pollution in deep soil through surface infiltration during mining activities has been particularly concerned, but little is known about vanadium migration dynamics in vertical soil profile. Indigenous microorganisms widely exist in soil, however, their functions and suffered impacts during vertical vanadium migration have rarely been investigated. In this study, 100 cm height columns were constructed with undisturbed soil around vanadium tailing reservoir were constructed to describe vertical vanadium transport process and corresponding interactions between vanadium and indigenous microorganisms. 91 d continuous leaching with pentavalent vanadium [V(V)] showed that V(V) gradually downward migrated. Soil microorganisms slowed down vertical V(V) migration rate by transferring V(V) to insoluble tetravalent vanadium. Enriched Gemmatimonadaceae and Actinobacteria were identified to contribute to microbial V(V) transformation. Co-existing nitrate weakened the soil's ability to intercept V(V) via electron competition. Microbial communities were reshaped by vanadium during leaching, while enzyme activities increased slightly due to vanadium stimulation. This work advances the understanding of vertical vanadium migration characteristics in soil, which is essential to risk management and effective remediation of vanadium-polluted sites.

The Chironomid Microbiome Plays a Role in Protecting Its Host From Toxicants

Organisms are assemblages of the host and their endogenous bacteria, which are defined as microbiomes. The host and its microbiome undergo a mutual evolutionary process to adapt to changes in the environment. Chironomids (Diptera; Chironomidae), are aquatic insects that grow and survive in polluted environments; however, the mechanisms that protect them under these conditions are not fully understood. Here we present evidence that the chironomids’ microbiome enables them to survival in polluted environments. It has been demonstrated that about 40% of the microbiota that inhabit Chironomus transvaalensis egg masses and larvae has the potential to detoxify different toxicants. Metagenomic analysis of Chironomus ramosus larvae demonstrated the presence of genes in the insects’ microbiome that can help the insects to survive in hostile environments. A set of experiments demonstrated that short exposure of C. transvaalensis larvae to metals significantly changed their microbiota composition in comparison to unexposed larvae. Another experiment, that followed Koch’s postulates, demonstrated that disinfected C. transvaalensis larvae can survive toxic lead and chromium exposure when they are recolonized with bacteria that can detoxify these toxic metals. This accumulating research, points to the conclusion that the chironomid microbiome plays a role in protecting its host from toxicants.

Field study of microbial community structure and dechlorination activity in a multi-solvents co-contaminated site undergoing natural attenuation

BTEX and chlorinated aliphatic hydrocarbons (CAHs) are the common pollutants found at contaminated sites, and natural attenuation (NA) of CAHs was widely observed where they coexist. In this work, the groundwater in a site co-contaminated with BTEX and CAHs was monitored for 1 year. The compositions and activities of the microfloras, especially dechlorinators and their relationships with the contaminants, geochemical properties, seasons and depth were evaluated. The results are consistent with the well-known NA conceptual model where CAHs are not able to stimulate the enrichment of dechlorinators alone, but BTEX does promote dechlorination. The higher temperature, rather than ORP in the deeper groundwater of the wet season became a key factor to promote the abundance of dechlorinators, but only when BTEX was available, indicating that the substrates from the BTEX biodegradation played an important role in the dechlorinator enrichment. The elevated ORP in the shallower groundwater exceeded the optimum conditions for reductive dechlorination and no significant seasonal variation of dechlorinators was found. The co-occurrence network revealed the cooperative interactions among the functional microfloras in which dechlorinators, BTEX degraders, and fermentative bacteria jointly promoted the dechlorination. These findings provided us a further understanding of the NA processes in a commingled plume.

Effect of vanadium on Lactuca sativa L. growth and associated health risk for human due to consumption of the vegetable

Elevated vanadium in the environment adversely affects organisms, including plants, animals, and humans. Plants act as the main conduit for environmental vanadium to enter the food chain, and simultaneously their growth response characteristics reflect vanadium toxicity efficacy for plants. The aim of the present study is to investigate lettuce (Lactuca sativa L.) growth involving morphological change, physiological adjustment, vanadium accumulation under vanadium stress, and the potential health risk (expressed as health risk index (HRI)) of adults and children who consume it. Lettuce was grown in nutrient solution with 0, 0.1, 0.5, 2.0, and 4.0 mg L-1 of pentavalent vanadium [V(V)]. Results showed that 0.1 mg L-1 V did not significantly affect lettuce growth versus control, and marked depression arose at ≥ 0.5 mg L-1 V. Foliar proline increased rapidly at ≥ 0.5 mg L-1 V. No striking change emerged in leaf cell membrane permeability at all treatments. V(V) and total vanadium concentration in plant tissues were ordered as root > stem > leaf, while tetravalent vanadium [V(IV)] was leaf > root > stem. No health risk (HRI < 1) exists for adults and children who consume lettuce at control treatment. However, the health risk occurs (HRI ˃ 1) when they both ingest the seedlings exposed to ≥ 0.1 mg L-1 V, and the risk overall markedly increases with increasing vanadium. Therefore, enough attention needs to be paid to the human health associated with the ingestion of vegetables like lettuce grown in substrata contaminated by vanadium.

The response of bacterial communities to V and Cr and novel reducing bacteria near a vanadium‑titanium magnetite refinery

Soil contamination with multiple heavy metals has always been a pressing issue, but little attention has been given to V and Cr and their chemical fractions' impacts on microorganisms because Cr₂O₃ usually occurs as an associated mineral in vanadium mines. To investigate this issue, samples (N1-N6) less affected by anthropogenic activities were selected for microbial analysis. The area near the refinery was heavily contaminated according to the PLI (pollution load index). Actinobacteriota, Proteobacteria, and Chloroflexi were the dominant phyla in the soil. The diversity of bacteria was positively influenced by V and Cr and negatively influenced by pH, while the abundance was positively correlated with soil nutrients. Interestingly, the influence of heavy metals in the residual fraction on the microbial community structure and functional metabolism was higher than that in the oxidizable fraction, which may be due to the relatively low heavy metal valence of the oxidizable fraction, suggesting that low valence binding forms of multivalence elements have little effect on microorganisms in the soil. Ultimately, two strains with great efficiency in reducing V and Cr were screened, and co-occurrence network characteristics with significant positive interactions suggested that Bacillus can coordinate community structure in the same niche. This research will help to explore the bioavailability of heavy metals and further achieve the bioremediation of heavy metal contamination in soil.

Recent advances in removal techniques of vanadium from water: A comprehensive review

In recent years, with the development of economy and industry, water contaminated with heavy metal has become a global environmental problem. Vanadium (V) is an emerging contaminant reported in wastewater along with the increasing mining, smelting and recovering of vanadium ores and application in many fields as a significant national strategy resource. The increasing attention has been paid to the separations of V from water due to its potential toxic to animals and human beings. In the present study, the most common V removal techniques including adsorption, microbiological treatment, chemical precipitation, solvent extraction, electrokinetic remediation, photocatalysis, coagulation and membrane filtration are presented with discussion of their advantages, limitations and the recent achievements. Several major influencing factors and mechanisms of various processes have been briefly analyzed. Some research perspectives are proposed for improving the capacities to remove V from water. The core objective of this review is to provide comprehensive information or database for the superior approach for V removal.

Effects of different lignocellulosic wastes on alleviating acidification of L-lactic acid production from food waste fermentation

In this study, the effects of different lignocellulosic wastes on alleviating acidification in the fermentation of lactic acid (LA) from food waste (FW) were studied. Amongst three lignocellulosic wastes, spent mushroom substance (SMS) could reach 95.22% lignin removal efficiency through simple NaOH pretreatment. Results showed pretreated SMS was best choice for FW co-fermentation, the maximum LA concentration could reach 46.12 g/L. And the NaOH solution as neutraliser could save 5.69 mL compared with the other two lignocellulosic wastes. The reason for alleviating acidification was 4.71% calcium salt in SMS and the porous structure of SMS. Then, 50% of pretreated liquid (PL) produced in SMS pretreatment was reused in the co-fermentation process. Compared with the group with 0% PL loading, that with 50% PL loading showed an increase in LA concentration and optical purity of L-LA, reaching 50.95 g/L and 96.28%, and NaOH consumption also further decreased by 24.65%.

The role of available phosphorous in vanadate decontamination by soil indigenous microbial consortia

Indigenous microbial consortia are closely associated with soil inherent components including nutrients and minerals. Although indigenous microbial consortia present great prospects for bioremediation of vanadate [V(V)] contaminated soil, influences of some key components, such as available phosphorus (AP), on V(V) biodetoxification are poorly understood. In this study, surface soils sampled from five representative vanadium smelter sites were employed as inocula without pretreatment. V(V) removal efficiency ranged from 81.7 ± 1.4% to 99.5 ± 0.2% in batch experiment, and the maximum V(V) removal rates were positively correlated with AP contents. Long-term V(V) removal was achieved under fluctuant hydrodynamic and hydrochemical conditions in column experiment. Geobacter and Bacillus, which were found in both original soils and bioreactors, catalytically reduced V(V) to insoluble tetravalent vanadium. Phosphate-solubilizing bacterium affiliated to Gemmatimonadaceae were also identified abundantly. Microbial functional characterization indicated the enrichment of phosphate ABC transporter, which could accelerate V(V) transfer into intercellular space for efficient reduction due to the structural similarity of V(V) and phosphate. This study reveals the critical role of AP in microbial V(V) decontamination and provides promising strategy for in situ bioremediation of V(V) polluted soil.

Insights into heterotrophic denitrification diversity in wastewater treatment systems: Progress and future prospects based on different carbon sources

Nitrate, as the most stable form of nitrogen pollution, widely exists in aquatic environment, which has great potential threat to ecological environment and human health. Heterotrophic denitrification, as the most economical and effective method to treat nitrate wastewater, has been widely and deeply studied. From the perspective of heterotrophic denitrification, this review discusses nitrate removal in the aquatic environment, and the behaviors of different carbon source types were classified and summarized to explain the cyclical evolution of carbon and nitrogen in global biochemical processes. In addition, the denitrification process, electron transfer as well as denitrifying and hydrolyzing microorganisms among different carbon sources were analyzed and compared, and the commonness and characteristics of the denitrification process with various carbon sources were revealed. This study provides theoretical support and technical guidance for further improvement of denitrification technologies.

Bacterial community composition of internal circulation reactor at different heights for large-scale brewery wastewater treatment

This study analyzed bacterial community structure for large-scale brewery wastewater treatment at different heights in internal circulation (IC) reactor. Proteobacteria, Bacteroidetes and Chloroflexi were dominant bacteria, which accounted for 64.17%, 64.04%, 59.87% and 55.79% in phylum level, respectively. The unidentified bacteria were accounted for a large proportion in genus level, available data showed that Longilinea, Desulfomicrobium, Caldithrix, Geobacter and Syntrophorhabdus were relatively abundant. Organic fermentation, hydrolysis, and acidification were mainly completed at the bottom, and production of hydrogen and methane were completed in the upper and middle part of reactor. Alpha diversity and cluster distance analysis showed the bacterial community could be divided into bottom, middle and upper part of IC reactor. The IC reactor possessed the COD_Cr removal efficiency of 80% - 84.09%, and BOD₅ of 77.50% - 86% for brewery wastewater. This study would provide bacterial analysis references of IC reactor for industrial wastewater treatment in future.

A Dual Role of Vanadium in Environmental Systems-Beneficial and Detrimental Effects on Terrestrial Plants and Humans

The importance of vanadium (V) in the functioning of land systems is extremely diverse, as this element may exert both positive and harmful effects on terrestrial organisms. It recently become considered an element of beneficial character with a range of applications for human welfare. The health-ameliorative properties of this transition element depend on its degree of oxidation and on optimal concentration in the target cells. It was found that a similar relationship applies to vascular plants. However, excessive amounts of vanadium in the environment contaminate the soil and negatively affect the majority of living organisms. A significantly elevated level of V results in the destabilization of plant physiological balance, slowing down the growth of biomass which significantly reduces yield. In turn, low doses of the appropriate vanadium ions can stimulate plant growth and development, exert cytoprotective effects, and effectively enhance the synthesis of some biologically active compounds. We present the scientific achievements of research teams dealing with such topics. The issues discussed concern the role of vanadium in the environment, particular organisms, and highlight its dualistic influence on plants. Achievements in the field of V bioremediation, with the use of appropriately selected microorganisms and plant species, are emphasized.

Reduction of Vanadium(V) by Iron(II)-Bearing Minerals

Fe(II)-bearing minerals (magnetite, siderite, green rust, etc.) are common products of microbial Fe(III) reduction, and they provide a reservoir of reducing capacity in many subsurface environments that may contribute to the reduction of redox active elements such as vanadium; which can exist as V(V), V(IV), and V(III) under conditions typical of near-surface aquatic and terrestrial environments. To better understand the redox behavior of V under ferrugenic/sulfidogenic conditions, we examined the interactions of V(V) (1 mM) in aqueous suspensions containing 50 mM Fe(II) as magnetite, siderite, vivianite, green rust, or mackinawite, using X-ray absorption spectroscopy at the V K-edge to determine the valence state of V. Two additional systems of increased complexity were also examined, containing either 60 mM Fe(II) as biogenic green rust (BioGR) or 40 mM Fe(II) as a mixture of biogenic siderite, mackinawite, and magnetite (BioSMM). Within 48 h, total solution-phase V concentrations decreased to <20 µM in all but the vivianite and the biogenic BiSMM systems; however, >99.5% of V was removed from solution in the BioSMM and vivianite systems within 7 and 20 months, respectively. The most rapid reduction was observed in the mackinawite system, where V(V) was reduced to V(III) within 48 h. Complete reduction of V(V) to V(III) occurred within 4 months in the green rust system, 7 months in the siderite system, and 20 months in the BioGR system. Vanadium(V) was only partially reduced in the magnetite, vivianite, and BioSMM systems, where within 7 months the average V valence state stabilized at 3.7, 3.7, and 3.4, respectively. The reduction of V(V) in soils and sediments has been largely attributed to microbial activity, presumably involving direct enzymatic reduction of V(V); however the reduction of V(V) by Fe(II)-bearing minerals suggests that abiotic or coupled biotic–abiotic processes may also play a critical role in V redox chemistry, and thus need to be considered in modeling the global biogeochemical cycling of V.

Vanadium in soil-plant system: Source, fate, toxicity, and bioremediation

Vanadium(V) is an important component of industrial activities, while it may pose toxic hazards to plants, animals, and humans at high levels. Owing to its various uses in numerous industrial processes, high amount of V is released into the soil environment. Previous literature has focused on the biogeochemistry and ecotoxicity of V in soil-plant system. Consequently, this overview presents its source, fate, phyto-uptake, phyto-toxicity, detoxification, and bioremediation based on available data, especially published from 2015 to 2020. Vanadium occurs as various chemical forms (primarily as V(V) and V(IV)) in the soil environment, and its biogeochemical behaviour is easily influenced by soil conditions including redox potential, soil pH, organic matter, and microorganisms. Vanadium mainly accumulates in plant roots with very limited translocation to shoots. However, plants such as dog's tail grass and green bean are reported to accumulate high levels of V in aboveground tissues. An insight into the processes and mechanisms that allow plants to absorb and translocate V in soil-plant system is also stressed in this overview. In plants, low levels of V have beneficial effects on plant growth and development. Nevertheless, excessive V provokes numerous deleterious effects including reducing seed germination, inhibiting root and shoot growth, depressing photosynthesis, interfering with nutrients uptake, inducing overgeneration of ROS, and leading to lipid peroxidation. Mechanisms related to detoxification strategies like sequestration in root system, compartmentation in vacuoles and cell wall, and antioxidant defence systems to endure V-induced toxicity in plants are discussed as well. The detailed knowledge of bioremediation involved in the cleanup of V-contaminated soils would immensely help understand and improve the remediation process. Furthermore, this overview outlines several research gaps requiring further investigation in order to advance our understanding of the biogeochemical roles of V in soil-plant systems.

Enriched Co-Treatment of Pharmaceutical and Acidic Metal-Containing Wastewater with Nano Zero-Valent Iron

Among traditional hazardous waste sources, pharmaceutical-containing wastewater and acidic mine drainage need treatment to preserve the expected water supply quality. A nano zero-valent iron (nZVI)-enriched treatment of these two streams is evaluated for simultaneous removal of various heavy metal ions, organic pollutants, sulfates, the efficiency of the treatment system, and separation of reaction products in the fluidized-bed reactor. The reactor packed with silica sand was inoculated with sludge from an anaerobic digester, then 1–3 g/L of nZVI slurry added to cotreat a hospital feed and acid mine wastewater at 5:2 v/v. The biotreatment process is monitored through an oxidation–reduction potential (Eh) for 90 days. The removal pathway for the nZVI used co-precipitation, sorption, and reduction. The removal load for Zn and Mn was approximately 198 mg Zn/g Fe and 207 mg Mn/g Fe, correspondingly; achieving sulfate (removal efficiency of 94% and organic matter i.e., chemical oxygen demand (COD), biological oxygen demand (BOD), dissolved organic carbon (DOC), total dissolved nitrogen (TDN) reduced significantly, but ibuprofen and naproxen achieved 31% and 27% removal, respectively. This enriched cotreatment system exhibited a high reducing condition in the reactor, as confirmed by Eh; hence, the nZVI was dosed only a few times in biotreatment duration, demonstrating a cost-effective system.

Sulfur-based Mixotrophic Vanadium (V) Bio-reduction towards Lower Organic Requirement and Sulfate Accumulation

Although remediation of toxic vanadium (V) [V(V)] pollution can be achieved through either heterotrophic or sulfur-based autotrophic microbial reduction, these processes would require a large amount of organic carbons or generate excessive sulfate. This study reported that by using mixotrophic V(V) bio-reduction with acetate and elemental sulfur [S(0)] as joint electron donors, V(V) removal performance was enhanced due to cooccurrence of heterotrophic and autotrophic activities. Deposited vanadium (IV) was identified as the main reduction product by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Based on 16S rRNA gene amplicon sequencing, qPCR and genus-specific reverse transcription qPCR, it was observed that V(V) was likely detoxified by heterotrophic V(V) reducers (e.g., Syntrophobacter, Spirochaeta and Geobacter). Cytochrome c, intracellular nicotinamide adenine dinucleotide and extracellular polymeric substances were involved in V(V) reduction and binding. Organic metabolites synthesized by autotrophs (e.g., Thioclava) with energy from S(0) oxidation might compensate electron donors for heterotrophic V(V) and sulfate reducers. Less sulfate was accumulated presumably due to activities of sulfur-respiring genera (e.g., Desulfurella). This study demonstrates mixotrophic microbial V(V) reduction can save organic dosage and avoid excessive sulfate accumulation, which will be beneficial to bioremediation of V(V) contamination.

A newly discovered function of nitrate reductase in chemoautotrophic vanadate transformation by natural mackinawite in aquifer

Mackinawite (FeS), a widely-distributed natural reducing mineral, can donate electron for various (bio)processes. However, little is known about mackinawite-driven chemoautotrophic bioreduction of toxic vanadate [V(V)] in aquifer. This study demonstrates that V(V) is successfully bioreduced by mackinawite under anaerobic condition via 150-d operation of constructed aquifer. Complete V(V) removal was achieved at the initial concentration of 10 mg/L and flow rate of 0.125 mL/min. Fluctuant hydrochemistry and hydrodynamics affected V(V) removal performance. Biotic activity was identified as the major contribution to V(V) transformation (76.4 ± 1.01%). Chemoautotrophic genera (e.g., Thiobacillus) could oxidize FeS coupled to direct V(V) reduction independently. Heterotrophic V(V) reducers (e.g., Pseudomonas and Spirochaeta) could also achieve V(V) detoxification by utilizing metabolic intermediates synthesized by autotrophic Fe(II) oxidizers (e.g., Thiobacillus) and S(-II) oxidizing genera (e.g., Sulfuricurvum). Gene abundance and enzymatic activity tests confirmed that nitrate reductase gene napA functioned crucially in chemoautotrophic V(V) reduction by Fe(II) and S(-II) donating electron. V(V) was reduced to insoluble V(IV) while elements in mackinawite were oxidized to Fe(III) and SO₄^2-. This study reveals the coupling of iron, sulfur and vanadium in biogeochemical cycling, and offers a promising strategy for remediation of V(V)-polluted aquifer.

Growth responses, accumulation, translocation and distribution of vanadium in tobacco and its potential in phytoremediation

The metal tolerance mechanism of plants is of great importance to explore the plant-based clean-up of environmental substrata contaminated by heavy metals. Indoor experiment of tobacco (Nicotiana tabacum L.) seedlings growing hydroponically in nutrient solution containing 0, 0.1, 0.5, 2.0, and 4.0 mg L-1 V was conducted. The results indicated that plant overall growth performance was significantly affected at ≥ 2.0 mg L-1 V. Oxidative stress degree as indicated by foliar O2-· and H2O2 content intensified markedly at ≥ 0.5 mg L-1 V treatments. In response, the plant activated its enzyme and non-enzyme protecting mechanism to cope with oxidative stress inflicted by vanadium. The activities of antioxidant enzymes, including SOD, POD, CAT, APX, and the concentration of non-enzyme antioxidants, e.g., AsA and GSH were all conspicuously (p < 0.5 or p < 0.1) enhanced at ≥ 0.5 mg L-1 V treatments. Vanadium accumulated in leaves, stems, and roots increased with increasing vanadium level. The majority of the absorbed vanadium retained in plant root, and minor portions were transferred to aerial parts. Vanadium concentration in plant tissues ordered as root ˃ stem ˃ leaf. Translocation factors (TF) in vanadium-treated tobaccos (TF « 1) were significantly lower than that of control (TF ˃ 1). In conclusion, although vanadium at ≥ 2.0 mg L-1 inhibited plant growth, tobacco exhibited a relatively good vanadium tolerance through self-adaptive regulation and has the potential as a phytostabilizer in decontaminating the environment contaminated by vanadium.

VV Reduction by Polaromonas spp. in Vanadium Mine Tailings

Vanadium (V) is an important metal with critical industrial and medical applications. Elevated V contamination, however, can be a threat to the environment and human health. Microorganisms can reduce the more toxic and mobile V^V to the less toxic and immobile V^IV, which could be a detoxification and energy metabolism strategy adopted by V-reducing bacteria (VRB). The limited understanding of microbial responses to V contamination and the mechanisms for V^V reduction, however, hamper our capability to attenuate V contamination. This study focused on determining the microbial responses to elevated V concentration and the mechanisms of V^V reduction in V tailings. The bacterial communities were characterized and compared between the V tailings and the less contaminated adjacent mineral soils. Further, V^V-reducing enrichments indicated that bacteria associated with Polaromonas, a genus belonging to the family Burkholderiaceae, were potentially responsible for V^V reduction. Retrieved metagenome-assembled genomes (MAGs) suggested that the Polaromonas spp. encoded genes (cymA, omcA, and narG) were responsible for V^V reduction. Additionally, Polaromonas spp. was metabolically versatile and could use both organic and inorganic electron donors. The metabolic versatility of Polaromonas spp. may be important for its ability to flourish in the V tailings.

Microbial vanadate reduction coupled to co-metabolic phenanthrene biodegradation in groundwater

Vanadate [V(V)] and phenanthrene (PHE) commonly coexist in groundwater aquifer, posing potential threats to ecological environment and public health. However, little is known about the complicated biogeochemical processes involving microbial V(V) reduction coupled with co-metabolic PHE biodegradation. Herein we demonstrated that synchronous removal of V(V) and PHE could be realized under anaerobic condition. Complete V(V) removal and PHE degradation efficiency of 82.0 ± 0.8% were achieved in 7-d operation in batch experiment. 250-d continuous column experiment implied that hydrochemical condition affected V(V) and PHE removals. V(V) was reduced to insoluble vanadium (IV) and PHE was degraded into small molecule organics (e.g. salicylic acid). Geobacter and Acetobacterium used methanol and intermediates from PHE degradation as electron donors for V(V) reduction. PHE was decomposed by Mycobacterium and Clostridium with methanol as co-metabolic substrate and V(V) as electron acceptor. Genes encoding proteins for V(V) reduction (omcA, omcB and mtrC) and PHE degradation (phnAc) were upregulated. Cytochrome c and nicotinamide adenine dinucleotide promoted electron transfer for V(V) and PHE detoxification. Extracellular polymeric substances could bind V(V) and improve the bioavailability of PHE. Our findings provide a robust strategy for remediation of V(V) and PHE co-contaminated groundwater.

Spatiotemporal vanadium distribution in soils with microbial community dynamics at vanadium smelting site

Whereas the adverse effects of vanadium released from smelting activities on soil microbial ecology have been widely recognized, little is known about spatiotemporal vanadium distribution and microbial community dynamics in typical contaminated sites. This study describes vanadium contents associated with health risk and microbial responses in both topsoil and subsoil during four consecutive seasons around an ongoing-production smelter in Panzhihua, China. Higher levels of vanadium concentration exceeding soil background value in China (82 mg/kg) were found close to the smelter. Vanadium concentrations decreased generally with the increase in distance to the smelter and depth below surface, as soil vanadium pollution is induced mainly by atmospheric deposition of vanadium bearing dust during smelting. Residual fraction was the predominated vanadium form in soils, with pronounced increase in bioavailable vanadium during rainfall period due to frequent drought-rewetting process. Topsoil close to the smelter exhibited significant contamination, inducing high probability of adverse health effects. Spatiotemporal vanadium distribution creates filtering effects on soil microorganisms, promoting metal tolerant genera in topsoil (e.g. Microvirga) and subsoil (e.g. Bacillus, Geobacter), which is the key in maintaining the community structure by promoting cooperative relation with other taxa. Our results reveal spatiotemporal vanadium distribution in soils at site scale with potential health risk and microbial responses, which is helpful in identifying severe contamination and implementing bioremediation.

Effects of liquid digestate on the valence state of vanadium in plant and soil and microbial community response

Liquid digestate containing high levels of nutrients and humic and fatty acids can affect vanadium species and their plant uptake. To elucidate the effects of liquid digestate on the valence state of vanadium in soil and plant tissue, as well as its effects on the microbial community and soil properties, we grew green bristlegrass (Setaria viridis), a native plant capable of growing in vanadium mining areas, in vanadium-contaminated soils sampled from a mining area and treated it with 5% and 10% liquid digestate for 90 d, respectively. Changes in the concentrations of pentavalent (V[V]) and tetravalent (V[IV]) vanadium in the soils and the shoots and roots of bristlegrass and the soil microbial abundance were measured. The results showed that vanadium existed mainly in the form of V(IV) in the soil but accumulated mainly in the form of V(V) in the bristlegrass. Liquid digestate markedly reduced V(V) concentrations in the soils (by up to 45%) and in the shoots and roots of green bristlegrass (by up to 98%). Liquid digestate enhanced the abundance of Bacteroidetes, which can reduce V(V) to lower valence state. Microbial reduction and phosphorus immobilization were responsible for downregulating V(V) concentrations in the plant and soil. The liquid digestate can be used to enhance in situ bioremediation of vanadium-contaminated soil in mining area.

Temporal dynamics of heavy metal distribution and associated microbial community in ambient aerosols from vanadium smelter

Heavy metals (HMs) such as vanadium (V), zinc (Zn), arsenic (As), chromium (Cr), copper (Cu) and nickel (Ni) are released into atmosphere during V smelting activities, resulting in their co-existence with airborne microbes. However, little is known about HMs distributions and associated microbes in aerosols from such industrial districts. This study reveals seasonal dynamics of HMs and microbes in ambient aerosols from V smelter in Panzhihua, China. Multiple HMs were detected, while V concentration was the highest, maximizing at 228.0 ± 10.3 ng/m³ in Spring. Health risks displayed similar trends to HMs distributions, and children were posed much higher risks than adults due to their more sensitivity to HMs. V and As contributed dramatically to total health risks among all examined HMs. High-throughput 16S rRNA gene sequencing analysis revealed microbes tolerant to V, Zn, As, Cr, Cu and Ni. Acinetobacter widely existed with function of detoxifying V(V) and more species as Bacillus, Gobacter and Thauera tolerating V, Zn, As, Cr, Cu and Ni appeared in Summer. These findings shed light on understandings of HMs dynamics and associated microbial community in aerosols from smelting regions.

Enhanced Microbial Chromate Reduction Using Hydrogen and Methane as Joint Electron Donors

Hydrogen and methane commonly co-exist in aquifer. Either hydrogen or methane has been individually utilized as electron donor for bio-reducing chromate. However, little is known whether microbial chromate reduction would be suppressed or promoted when both hydrogen and methane are simultaneously supplied as joint electron donors. This study for the first time demonstrated microbial chromate reduction rate could be accelerated by both hydrogen and methane donating electrons. The maximum chromate reduction rate (4.70 ± 0.03 mg/L·d) with a volume ratio of hydrogen to methane at 1:1 was significantly higher than that with pure hydrogen (2.53 ± 0.02 mg/L·d) or pure methane (2.01 ± 0.02 mg/L·d) as the sole electron donor (p < 0.01). High-throughput 16S rRNA gene amplicon sequencing detected potential chromate reducers (e.g., Spirochaetaceae, Delftia and Azonexus) and hydrogenotrophic bacteria (e.g., Acetoanaerobium) and methane-metabolizing microorganisms (e.g., Methanobacterium), indicating that these microorganisms might play important roles on microbial chromate reduction using both hydrogen and methane as electron donors. Abundant hupL and mcrA genes responsible for hydrogen oxidation and methane conversion were harbored, together with chrA gene for chromate reduction. More abundant extracellular cytochrome c and intracellular NADH were detected with joint electron donors, suggesting more active electron transfers.

Vanadium contamination and associated health risk of farmland soil near smelters throughout China

Whereas there is broad consensus that smelting causes serious soil contamination during vanadium production, little is known about the vanadium content of soil near smelters and the associated health risk at continental scale. This study is the first to map the distribution of vanadium in farmland soil surrounding smelters throughout mainland China, and assess the associated health risk. Analysis of 76 samples indicated that the average vanadium content in such soil was 115.5 mg/kg - far higher than the 82 mg/kg background content in China (p < 0.05). Southwest China (198.0 mg/kg) and North China (158.3 mg/kg) possessed highest vanadium contents. Vanadium content was strongly related to longitude, altitude, and atmospheric temperature. The reducible fraction accounted for the largest percentages in vanadium speciation. The average Pollution Load Index for all samples was 1.51, denoting significant metal enrichment. The Children's hazard index was higher than unity, indicating elevated health risk. The relative contribution of vanadium to the total health risk ranged from 6.02% to 34.5%, while nickel and chromium were the two main contributors in most regions. This work may serve as a model providing an overview of continental vanadium contamination around smelters, and draw attention to their possible health risks.

Enhanced removal of vanadium(V) from groundwater by layered double hydroxide-supported nanoscale zerovalent iron

To reduce the toxicity of vanadium(V) [V(V)] and inhibit the desorption of adsorbed vanadium in groundwater, we synthesized nanoscale zerovalent iron (nZVI) dispersed on layered double hydroxide (LDH) composites (nZVI@LDH) to remove V(V) from simulated groundwater. We found that nZVI@LDH could reduce high-valence vanadium to low-valence vanadium, then forming vanadium-containing precipitation to reduce the toxicity and inhibiting vanadium from returning to groundwater. SEM and XRD characterizations exhibited the uniform dispersal of nZVI on the surface of LDH. nZVI@LDH with nZVI/LDH at a mass ratio of 1:2 provided the maximum adsorption capacity of 93.7 mg g^-1 at pH 3.0. Coexisting anions and dissolved oxygen in groundwater have little effect on V(V) removal. nZVI@LDH performed well across a wide pH range (3.0-8.0). The surface characterizations and XPS analysis revealed that LDH as supporting materials inhibited the aggregation and passivation of nZVI. The adsorbed V(V) was reduced to V(IV) and V(III) by nZVI and spontaneously transformed into insoluble VO₂ and V₂O₃. The DFT calculations indicated the strong complexation and better stability of the V(IV) and V(III) species with nZVI@LDH than V(V). This work suggests that nZVI@LDH has the potential to serve as an efficient material for the immobilization of V(V) in groundwater.

Soil vanadium(V)-reducing related bacteria drive community response to vanadium pollution from a smelting plant over multiple gradients

The mining and smelting of navajoite has resulted in a serious vanadium pollution in regional geological environments and significant influence on soil microorganisms. However, the core microbiome responsible for adjusting community response to vanadium pollution and the driving pattern have been kept unclear. In this study, a suite of surface and profile soil samples over multiple gradients were collected in four directions and distances of 10-2000 m from a vanadium smelting plant in Panzhihua, China. The indigenous microbial communities and vanadium(V)-reducing related bacteria (VRB) were profiled by 16S rRNA gene high-throughput sequencing technique. Five VRB were detected in the original collected soil samples including Bacillus, Geobacter, Clostridium, Pseudomonas and Comamonadaceae based on high-throughput sequencing data analysis, and their abundances were significantly related with the content of vanadium. Low vanadium concentration promoted the growth of VRB, while high vanadium concentration would inhibit VRB multiplication. The Gaussian equation could be used to quantitatively describe the nonlinear relationship between VRB and vanadium. Network analysis demonstrated that the microbial communities were significantly influenced by VRB assemblage, and 1.32-52.77% of microbes in the community showed a close association with VRB. A laboratory incubation experiment also confirmed the core role of VRB to drive community response to vanadium pressure.

Review of plant-vanadium physiological interactions, bioaccumulation, and bioremediation of vanadium-contaminated sites

Vanadium is a multivalent redox-sensitive metal that is widely distributed in the environment. Low levels of vanadium elevate plant height, root length, and biomass production due to enhanced chlorophyll biosynthesis, seed germination, essential element uptake, and nitrogen assimilation and utilization. However, high vanadium concentrations disrupt energy metabolism and matter cycling; inhibit key enzymes mediating energy production, protein synthesis, ion transportation, and other important physiological processes; and lead to growth retardation, root and shoot abnormalities, and even death of plants. The threshold level of toxicity is highly plant species-specific, and in most cases, the half maximal effective concentration (EC₅₀) of vanadium for plants grown under hydroponic conditions and in soil varies from 1 to 50 mg/L, and from 18 to 510 mg/kg, respectively. Plants such as Chinese green mustard, chickpea, and bunny cactus could accumulate high concentrations of vanadium in their tissues, and thus are suitable for decontaminating and reclaiming of vanadium-polluted soils on a large scale. Soil pH, organic matter, and the contents of iron and aluminum (hydr)oxides, phosphorus, calcium, and other coexisting elements affect the bioavailability, toxicity, and plant uptake of vanadium. Mediation of these conditions or properties in vanadium-contaminated soils could improve plant tolerance, accumulation, or exclusion, thereby enhancing phytoremediation efficiency. Phytoremediation with the assistance of soil amendments and microorganisms is a promising method for decontamination of vanadium polluted soils.

Effects of hydropower dam construction on sulfur distribution and sulfate-reducing prokaryotes assemblage

River damming is significant for hydropower production, but also alters the ecological conditions, and especially affects the microbial community. Sulfate-reducing prokaryotes (SRPs) make vital contributions to biogeochemical sulfur cycle, but the information on the effects of dam construction on the SRPs assemblage are unclear. Here, a comprehensive survey was conducted by collecting water and sediment samples along horizontal and vertical profiles from six sites at the Xiaowan Reservoir on the Lancang River, China. We used 16S rRNA gene amplicon sequencing and qPCR assay with dsrB gene to study the composition and activity of SRPs. The results indicated that river damming accumulated nutrients in the middle layer of the reservoir, and the impoundment provided an anaerobic and high nutrient available environment, which is beneficial for the survival of SRPs. The abundance and diversity of SRPs in water and sediments at the bottom of the reservoir were higher than those in the other sites. The network analyses revealed a synergistic effect between SRPs and other dominant bacteria in water column, which was more complex than in sediments. Moreover, a relatively higher sulfate reduction activity was found in the middle and lower layers of the water profile according to dsrB gene analysis.