Development, modification, and application of low-cost and available biochar derived from corn straw for the removal of vanadium(v) from aqueous solution and real contaminated groundwater

Distinguishing contributions of diverse sediment components to vanadium transport, immobilization and transformation in aquifer

Vanadium (V) occurs in environment naturally and anthropogenically, but little has been understood about its environmental behavior in groundwater aquifer with sediments. This study investigated the pentavalent V [V(V)] transport and transformation under the influence of different sediment components (minerals, organic matter, and microorganisms) through column experiments. All these components played pivotal roles in V immobilization. The synergistic effects of sediment components enhanced V retention compared to individual component. Mineral components, particularly those containing carbonates and metal oxides, predominantly influenced V(V) transport as indicated by XRD analysis. Organic matter, especially under low pH conditions, induced particle aggregation, thereby inhibiting the transport of V(V). The V K-edge X-ray absorption near-edge structure spectroscopy revealed the formation of tetravalent V[V(IV)] in treatments involving organic matter and microorganisms. Notably, organic matter exhibited the capability to directly reduce V(V). The introduction of microorganisms restricted V(V) transfer. V(V) reducing genera (e.g., Brevundimonas, Arenimonas, Xanthobacter) were detected, achieving V(V) reduction to insoluble V(IV). V(V) bioreduction was improved by minerals that promote microbial metabolism with enhanced electron transfer, or by organic matter that increases levels of intracellular nicotinamide adenine dinucleotide and extracellular polymeric substances. This study specifies the contributions of different sediment components to the transportation and transformation of V, deepening our understanding of V biogeochemistry in groundwater aquifer.

Enhanced phytoremediation of vanadium using coffee grounds and fast-growing plants: Integrating machine learning for predictive modeling

Vanadium (V) contamination posed a significant environmental challenge, while phytoremediation offered a sustainable solution. Phytoremediation performance was often limited by the slow growth cycles of traditional plants. A novel approach to enhancing V phytoremediation by integrating coffee grounds with fast-growing plants such as barley grass, wheat grass, and ryegrass was investigated in this study. The innovative use of coffee grounds leveraged not only their nutrient-rich composition but also their ability to reduce oxidative stress in plants, thereby significantly boosting phytoremediation efficiency. Notably, ryegrass achieved 48.7% V5+ removal within 6 d with initial 20 mg/L V5+ (0.338 mg/L·d·g ryegrass). When combined with coffee grounds, V5+ removal by using wheat grass increased substantially, rising from 30.51% to 62.91%. Gradient Boosting and XGBoost models, trained with optimized parameters including a learning rate of 0.1, max depth of 3, and n_estimators of 300, were employed to predict and optimize V5+ concentrations in the phytoremediation process. These models were evaluated using mean squared error (MSE) and coefficient of determination (R2) metrics, achieving high predictive accuracy (R2 = 0.95, MSE = 1.20). Feature importance analysis further identified the initial V5+ concentration and experimental duration as the most significant factors influencing the model's predictions. The addition of coffee grounds not only mitigated the stress of heavy metals on ryegrass, leading to significant reductions in CAT (87.2%), POD (98.8%), and SOD (39.2%) activities in ryegrass roots, but also significantly altered the microbial community abundance in the plant roots. This research provided an innovative enhancement to traditional phytoremediation methods, and established a new paradigm for using machine learning to predict and optimize V5+ remediation outcomes. The effectiveness of this technology in multi-metal polluted environments warrants further investigation in the future.

A review of passive acid mine drainage treatment by PRB and LPB: From design, testing, to construction

An extensive volume of acid mine drainage (AMD) generated throughout the mining process has been widely regarded as one of the most catastrophic environmental problems. Surface water and groundwater impacted by pollution exhibit extreme low pH values and elevated sulfate and metal/metalloid concentrations, posing a serious threat to the production efficiency of enterprises, domestic water safety, and the ecological health of the basin. Over the recent years, a plethora of techniques has been developed to address the issue of AMD, encompassing nanofiltration membranes, lime neutralization, and carrier-microencapsulation. Nonetheless, these approaches often come with substantial financial implications and exhibit restricted long-term sustainability. Among the array of choices, the permeable reactive barrier (PRB) system emerges as a noteworthy passive remediation method for AMD. Distinguished by its modest construction expenses and enduring stability, this approach proves particularly well-suited for addressing the environmental challenges posed by abandoned mines. This study undertook a comprehensive evaluation of the PRB systems utilized in the remediation of AMD. Furthermore, it introduced the concept of low permeability barrier, derived from the realm of site-contaminated groundwater management. The strategies pertaining to the selection of materials, the physicochemical aspects influencing long-term efficacy, the intricacies of design and construction, as well as the challenges and prospects inherent in barrier technology, are elaborated upon in this discourse.

Multiple pathways of vanadate reduction and denitrification mediated by denitrifying bacterium Acidovorax sp. strain BoFeN1

Contamination of aquifers by a combination of vanadate [V(V)] and nitrate (NO3-) is widespread nowadays. Although bioremediation of V(V)- and nitrate-contaminated environments is possible, only a limited number of functional species have been identified to date. The present study demonstrates the effectiveness of V(V) reduction and denitrification by a denitrifying bacterium Acidovorax sp. strain BoFeN1. The V(V) removal efficiency was 76.5 ± 5.41 % during 120 h incubation, with complete removal of NO3- within 48 h. Inhibitor experiments confirmed the involvement of electron transport substances and denitrifying enzymes in the bioreduction of V(V) and NO3-. Cyt c and riboflavin were important for extracellular V(V) reduction, with quinone and EPS more significant for NO3- removal. Intracellular reductive compounds including glutathione and NADH directly reduce V(V) and NO3-. Reverse transcription quantitative PCR confirmed the important roles of nirK and napA genes in regulating V(V) reduction and denitrification. Bioaugmentation by strain BoFeN1 increased V(V) and NO3- removal efficiency by 55.3 % ± 2.78 % and 42.1 % ± 1.04 % for samples from a contaminated aquifer. This study proposes new microbial resources for the bioremediation of V(V) and NO3-contaminated aquifers, and contributes to our understanding of coupled vanadium, nitrogen, and carbon biogeochemical processes.

Pyrrhotite-dependent microbial reduction and magnetic separation for efficient vanadium detoxification and recovery in contaminated aquifer

Microbial reduction under anaerobic condition is a promising method for remediating vanadate [V(V)] contamination in aquifers, while V(V) may be re-generated with redox fluctuations. The inability to remove vanadium after remediation has become a key issue limiting bioremediation. In this study, we proposed the use of pyrrhotite, a natural mineral with magnetic properties, to immobilize V(V) to insoluble V(IV) under microbial action and remove vanadium from the aquifer using a magnetic field, which could avoid the problem of V(V) recontamination under redox fluctuating conditions. Up to 49.0 ± 4.7 % of vanadium could be removed from the aquifer by the applied magnetic field, and the vanadium in the aquifer after the reaction was mainly in the acid-extractable and reducible states. pH had a strong effect on the magnetic recovery of V(V), while the influence of initial V(V) concentration was weak. Microbial community structure analysis showed that Thiobacillus, Proteiniphilum, Fermentimonas, and Desulfurivibrio played key roles for V(V) reduction and pyrrhotite oxidation. Structural equation model indicated the positive correlation between these genera with the magnetic recovery of vanadium. Real time-qPCR confirmed the roles of functional genes of V(V) reduction (napA and nirK) and SO42- reduction (dsrA) in such biological processes. This study provides a novel route to sustainable V(V) remediation in aquifers, with synchronous recovery of vanadium resources without rebound.

An overview of in situ remediation for groundwater co-contaminated with heavy metals and petroleum hydrocarbons

Groundwater is an important component of water resources. Mixed pollutants comprising heavy metals (HMs) and petroleum hydrocarbons (PHs) from industrial activities can contaminate groundwater through such processes as rainfall infiltration, runoff and discharge, which pose direct threats to human health through the food chain or drinking water. In situ remediation of contaminated groundwater is an important way to improve the quality of a water environment, develop water resources and ensure the safety of drinking water. Bioremediation and permeable reactive barriers (PRBs) were discussed in this paper as they were effective and affordable for in situ remediation of complex contaminated groundwater. In addition, media types, technology combinations and factors for the PRBs were highlighted. Finally, insights and outlooks were presented for in situ remediation technologies for complex groundwater contaminated with HMs and PHs. The selection of an in situ remediation technology should be site specific. The remediation of complex contaminated groundwater can be approached from various perspectives, including the development of economical materials, the production of slow-release and encapsulated materials, and a combination of multiple technologies. This review is expected to provide technical guidance and assistance for in situ remediation of complex contaminated groundwater.

Elucidating Multiple Electron-Transfer Pathways for Metavanadate Bioreduction by Actinomycetic Streptomyces microflavus

While microbial reduction has gained widespread recognition for efficiently remediating environments polluted by toxic metavanadate [V(V)], the pool of identified V(V)-reducing strains remains rather limited, with the vast majority belonging to bacteria and fungi. This study is among the first to confirm the V(V) reduction capability of Streptomyces microflavus, a representative member of ubiquitous actinomycetes in environment. A V(V) removal efficiency of 91.0 ± 4.35% was achieved during 12 days of operation, with a maximum specific growth rate of 0.073 d-1. V(V) was bioreduced to insoluble V(IV) precipitates. V(V) reduction took place both intracellularly and extracellularly. Electron transfer was enhanced during V(V) bioreduction with increased electron transporters. The electron-transfer pathways were revealed through transcriptomic, proteomic, and metabolomic analyses. Electrons might flow either through the respiratory chain to reduce intracellular V(V) or to cytochrome c on the outer membrane for extracellular V(V) reduction. Soluble riboflavin and quinone also possibly mediated extracellular V(V) reduction. Glutathione might deliver electrons for intracellular V(V) reduction. Bioaugmentation of the aquifer sediment with S. microflavus accelerated V(V) reduction. The strain could successfully colonize the sediment and foster positive correlations with indigenous microorganisms. This study offers new microbial resources for V(V) bioremediation and improve the understanding of the involved molecular mechanisms.

Nitrogen-rich carbon composite fabricated from waste shrimp shells for highly efficient oxo-vanadate adsorption-coupled reduction

Protein, calcium carbonate, and chitin are abundant in shrimp shells. In this study, chemical treatment followed by hydrothermal carbonization was used to synthesize the nitrogen-rich hydrochar (HSHC) from shrimp shells. The untreated hydrochar exhibited a higher amount of calcium (25.37%) and less amount of nitrogen (2.68%) with alkaline pH (9.1). Interestingly chemical pre-treatment on shrimp shells boosted the nitrogen content to 6.81% and eliminated the calcium while controlling the pH to 6.4, which was beneficial for oxo-vanadate removal. The HSHC achieved vanadium(V) adsorption capacity of 21.20 mg/g at an optimal solution pH of 3.0, whereas the pristine hydrochar performed poorly (0.66 mg/g). The abundance of oxygen and nitrogen-based functional groups that developed through the chemical treatment resulted in improved adsorption coupled reduction performance of HSHC. This study proposed an inexpensive and environmentally friendly method for converting waste shrimp shells into value-added adsorbent.

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.

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.

Effect of ferrous sulfate modified sludge biochar on the mobility, speciation, fractionation and bioaccumulation of vanadium in contaminated soil from a mining area

In contaminated soil, pristine biochar has poor applicability for immobilizing vanadium (V), which mainly exists as oxyanions in soil. To elucidate the immobilization potential and biotic/abiotic stabilizing mechanisms of a ferrous sulfate (FS)-modified sludge biochar in a V-contaminated soil from a mining area, we investigated the effects of biochar addition on the soil characteristics, growth of alfalfa, leachability, bioavailability, speciation, and fractionation of V, and changes in the microbial community structure and metabolic response. The results showed that the water extractable, acid-soluble (F1), and pentavalent fractions of V in soil decreased by up to 99 %, 95 %, and 55 %, respectively, whereas the reducible and (F2) oxidizable (F3) fractions increased by up to 45 % and 76 %, respectively. After the soil was treated with the FS-modified biochar for 90 d, the V concentration in the roots and shoots of alfalfa (Medicago sativa L.) decreased by up to 81.5 % and 96 %, respectively. The changes in the speciation, fractionation, and efficient immobilization of V in the studied soil were due to the combined effects of the biochar-induced decrease in soil pH, adsorption and precipitation by elevated iron concentrations, reduction and complexation due to an increase in the organic matter content, and microbial reduction by Proteobacteria.

Adsorptive removal of heavy metal anions from water by layered double hydroxide: A review

High-valence heavy metals with high ecotoxicity are generally found in water in the form of anions, and this increases heavy metal pollution intensity and treatment difficulty. Recent studies have pointed to the potential efficiency of layered double hydroxides (LDHs) to meet this challenge. In this review, we retrospectively research the development of LDHs using a Java application called CiteSpace. We describe the unique layer structure, highly adjustable chemical properties, and diverse synthesis methods of LDHs, all of which decide the effective adsorption of heavy metal anions by LDHs. Subsequently, we focus on discussing the adsorption mechanism of LDHs on heavy metal anions, as well as the current state of research and future directions for microscopic interaction mechanisms. For practical applications, it is critical to improve the adsorption selectivity and stability. We then recommend solutions to improve the adsorption selectivity and stability after identifying the influencing mechanism. Finally, we provide our perspectives on the future development of LDHs adsorption of heavy metal anions.

Adsorption of vanadium (V) ions from the aqueous solutions on different biomass-derived biochars

The paper presents the results of the studies on the vanadium (V) ions removal from the aqueous solutions in the adsorption process on biochars from different biomass types (cow manure BC1, wet distiller grains BC2, spent mushroom substrates BC3). The adsorbents were characterized by means of the SEM-EDS, FTIR, XRD and XPS techniques. The influence of adsorbent type and basic process parameters, such as pH and metal ion concentration in aqueous phase, adsorbent dose and time of contact of phases on the efficiency of V(V) was determined. Based on the obtained results, the mechanism and kinetics of the adsorption processes occurring on the biochar originating from the wet distiller grains as adsorbents with the greatest affinity for the V(V) ions were characterized, using isotherm models of Langmuir, Freundlich, Temkin and Dubinin-Radushkevich and pseudo-first-order, pseudo-second-order as well as intraparticle diffusion kinetic models. Under the constant process conditions (pH = 3.0; m = 0.5 g; c₀ = 50 mg/L) the order of V(V) ions removal from aqueous solutions was as follows: BC2 > BC1 = BC3. The biochar BC2 exhibited the maximum sorption capacity of 1.61 mg V(V)/g. The experimental kinetic data show the adsorption course according to the pseudo-second order model.

Biochar production with amelioration of microwave-assisted pyrolysis: Current scenario, drawbacks and perspectives

In recent years, biomass has been reported to obtain a wide range of value-added products. Biochar can be obtained by heating biomass, which aids in carbon sinks, soil amendments, resource recovery, and water retention. Microwave technology stands out among various biomass heating technologies not only for its effectiveness in biomass pyrolysis for the production of biochar and biofuel but also for its speed, volumetrics, selectivity, and efficiency. The features of microwave-assisted biomass pyrolysis and biochar are briefly reviewed in this paper. An informative comparison has been drawn between microwave-assisted pyrolysis and conventional pyrolysis. It focuses mainly on technological and economic scenario of biochar production and environmental impacts of using biochar. This source of knowledge would aid in the exploration of new possibilities and scope for employing microwave-assisted pyrolysis technology to produce biochar.

Will Vanadium-Based Electrode Materials Become the Future Choice for Metal-Ion Batteries?

Metal-ion batteries have emerged as promising candidates for energy storage system due to their unlimited resources and competitive price/performance ratio. Vanadium-based compounds have diverse oxidation states rendering various open-frameworks for ions storage. To date, some vanadium-based polyanionic compounds have shown great potential as high-performance electrode materials. However, there has been a growing concern regarding the cost and environmental risk of vanadium. In this Review, all links in the industry chain of vanadium-based electrodes were comprehensively summarized, starting with an analysis of the resources, applications, and price fluctuation of vanadium. The manufacturing processes of the vanadium extraction and recovery technologies were discussed. Moreover, the commercial potentials of some typical electrode materials were critically appraised. Finally, the environmental impact and sustainability of the industry chain were evaluated. This critical Review will provide a clear vision of the prospects and challenges of developing vanadium-based electrode materials.

Biosorption of V(V) onto Lantana camara biochar modified by H3PO4: Characteristics, mechanism, and regenerative capacity

Biochar has been widely recognized as an environmentally efficient adsorbent for removing heavy metals. However, considering the weak adsorption performance of the original biochar to the oxygen-containing anion, the adsorption of vanadium by biochar has rarely been investigated. This study proposes that H₃PO₄ activated biochar made from an invasive plant species growing near mines is a novel material to be investigated for V(V) recovery and reuse. As a noxious, invasive plant, Lantana camara L. (LC) has become widely naturalized around the world. Biochar was prepared from LC by pyrolysis at different conditions (200 °C, 350 °C, 500 °C, and 650 °C). The adsorption effect of biochar with and without P pretreatment on V(V) in aqueous solution was compared. The results show that biochar prepared from LC impregnated with H₃PO₄ (MLBC) had the highest adsorption capacity at 500 °C, and the maximal adsorption capacity fitted by Langmuir model was 77.38 mg g^-1, which was considerably higher than that of untreated biochar (LBC, 5.89 mg g^-1). The adsorption procedure was substantially fitted by the Langmuir isotherm and the pseudo-second-order kinetic. Additionally, the interaction of V(V) on MLBC is pH-dependent, and slightly acidic conditions are more favorable for adsorption. The characterization results indicated that electrostatic interaction, complexation reaction, and redox reaction were the primary mechanisms. After three cycles of adsorption, the final maximal adsorption capacity of MLBC remained at 76.03% of that of the virgin sample, demonstrating that MLBC had a recyclable capability to eliminate and restore V(V) from aqueous solutions.

Optimizing the added ratio of mixed auxiliary packings for enhancing the biological vanadium (V) removal

Developing sustainable and low-cost bio-reduction technologies is essential for vanadium (V) bioremediation in groundwater. With both agricultural waste (wheat stalk) being a solid carbon source and ceramsite and medical stone being auxiliary packings, V(V) removal was confirmed and optimized in this study. The ratio of ceramsite to medical stone was maintained at 1:3 in Group I, which accomplished a V(V) removal efficiency up to 97.5% within 120 h and an average removal rate was around 0.305 mg/(L·h). The dissolution and utilization of carbon and trace elements (Mg, Fe, Mo and Ni) by microbes also contributed to the V(V) bio-reduction enhancement. The main components of DOM (tryptophan and humic acid-like substances) were vital in the V(V) binding and electron transfer processes. This study could promote the current knowledge on the sustainable V(V) bioremediation by using agricultural waste and auxiliary packings.

Comparative efficacy of raw and HNO3-modified biochar derived from rice straw on vanadium transformation and its uptake by rice (Oryza sativa L.): Insights from photosynthesis, antioxidative response, and gene-expression profile

Low concentrations of vanadium (V) are essential for various plant species but it becomes toxic to plants, animals, and humans at high levels. A significant amount of V is currently being emitted into the atmosphere due to intensified industrial processing. Therefore, this study aimed at evaluating the effect of raw (BC) and HNO₃-modified biochar (OBC) derived from rice straw on growth, photosynthetic assimilation, relative chlorophyll content, SPAD index, ion leakage, enzyme activities, hydrogen peroxide (H₂O₂), bioavailability and V uptake by rice in a laboratory-scale experiment. Characterization of OBC and BC by FTIR (Fourier transform infrared spectroscopy), SEM (scan electron microscopy), BET (Brunauer-Emmett-Teller), elemental analysis, and z-potential revealed a substantial difference between both of them. The V-stress significantly reduced the rice plant growth, biomass yield, chlorophyll parameters, root length and surface area. Under V-stress conditions, root accumulated more V than shoots and OBC significantly improved the above-mentioned parameters, while, decreasing hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels in plants. The antioxidant function and gene expression levels induced by V-stress and OBC application further increased the expression profile of three genes (SOD, POD, and CAT) encoding antioxidant enzymes and one metal-tolerant conferring gene (OsFSD1). In summary, these results demonstrated the critical role of OBC in mitigating the detrimental effects of high V-stress on rice growth and enhancing plant defence against V-stress.

Biologically removing vanadium(V) from groundwater by agricultural biomass

Vanadium (V) in groundwater can pose a serious threat on both environment and health. Agricultural biomass contains solid carbon source (SCS) and could be attractive for biologically removing V(V). For this purpose, cypress sawdust, corn cob and wheat straw were selected as SCSs to remove vanadate (NaVO₃). The experiments demonstrated a high efficiency of V(V) up to 98.6%, and the anaerobically biological reduction of V(V) to V(IV) by wheat straw was identified to be the best SCS by the spectrum analysis of XRD and FTIR. Along with increasing the fragment size of wheat straw, the V(V)-removal efficiency decreased, and the fragment size down to 1-3 mm was confirmed to have a significant bio-removal performance on V(V). Based on the analysis of 16s rRNA sequencing, the microbial abundance and diversity increased in the suspension liquid in the end, indicating that the microbial community could tolerate and/or detoxify V(V), besides degrading lignocellulosic materials.

Synergy between pyridine anaerobic mineralization and vanadium (V) oxyanion bio-reduction for aquifer remediation

The co-occurrence of toxic pyridine (Pyr) and vanadium (V) oxyanion [V(V)] in aquifer has been of emerging concern. However, interactions between their biogeochemical fates remain poorly characterized, with absence of efficient route to decontamination of this combined pollution. In this work, microbial-driven Pyr degradation coupled to V(V) reduction was demonstrated for the first time. Removal efficiencies of Pyr and V(V) reached 94.8 ± 1.55% and 51.2 ± 0.20% in 72 h operation. The supplementation of co-substrate (glucose) deteriorated Pyr degradation slightly, but significantly promoted V(V) reduction efficiency to 84.5 ± 0.635%. Pyr was mineralized with NH₄⁺-N accumulation, while insoluble vanadium (IV) was the major product from V(V) bio-reduction. It was observed that Bacillus and Pseudomonas realized synchronous Pyr and V(V) removals independently. Interspecific synergy between Pyr degraders and V(V) reducers also functioned with addition of co-substrate. V(V) was bio-reduced through alternative electron acceptor pathway conducted by gene nirS encoded nitrite reductase, which was evidenced by gene abundance and enzyme activity. Cytochrome c, nicotinamide adenine dinucleotide and extracellular polymeric substances also contributed to the coupled bioprocess. This work provides new insights into biogeochemical activities of Pyr and V(V), and proposes novel strategy for remediation of their co-contaminated aquifer.

Pilot-scale field study for vanadium removal from mining-influenced waters using an iron-based sorbent

This study investigated the removal of vanadium from mining waters at a closed mine site (Mustavaara, Finland) using granular ferric oxyhydroxide (CFH-12) on pilot scale. Two filter systems, pilot A and pilot B, were placed in different streams, where the influent in pilot A contained a higher and very variable vanadium concentration (6.46-99.1 mg/L), while the pilot B treated influent had lower vanadium concentrations (0.443-2.33 mg/L). The operation periods were 51 days for pilot A and 127 days for pilot B. Water quality analyses revealed that vanadium was efficiently captured in the filter system in both pilots. X-ray fluorescence analysis revealed that the filter beds were not fully saturated with vanadium. X-ray photoelectron spectroscopy confirmed that oxidised vanadium (5⁺) existed in the used CFH-12 and the carbon content in the used material had increased due to the adsorbed organic compounds. For comparison, lab-scale coagulation experiments were conducted using ferric sulphate for the influent of pilot A (the sampled batch contained 15.9 mg/L V). The optimum coagulant dosage was 350 mg/L (>93% vanadium removal) at the original pH (7.8-7.9) of the influent, whereas the required coagulant amount decreased when the influent pH was adjusted to 4.6-4.8.

Performance and mechanisms for V(v) bio-reduction by straw: key influencing factors

A high concentration of vanadium [V(v)] in groundwater is extremely harmful for humans. Weak movability and low toxicity after microbial V(v) reduction have attracted remarkable attention, especially for using solid carbon sources. However, the influencing factors remain unclear. In this study, the initial V(v) concentration, inocula amount and straw dosage were examined to ascertain the mechanisms behind them. Increasing the initial V(v) concentration led to the decrease of the V(v) removal efficiency, which was also positively correlated with the straw dosage within a certain range. The initial sludge amount was not a main factor affecting microbial V(v) removal in this study. With the initial amount of 10 mg L-1 V(v), 25 mL initial inocula and 5 g straw, 88.2% of V(v) was removed. According to the dissolved organic matter (DOM) analysis results, microbial activity prevailed in groups with higher V(v) removal efficiency, indicating that the V(v) bio-reduction was attributed to the microbial activity, which was considered a major factor. Functional species as unclassified_f_Enterobacteriaceae presumably contributed to the V(v) bioreduction, with upregulated ABC transporter genes and enzymes.

Novel Pathway for Vanadium(V) Bio-Detoxification by Gram-Positive Lactococcus raffinolactis

Whereas prospects of bioremediation for a vanadium(V) [V(V)]-contaminated environment are widely recognized, reported functional species are extremely limited, with the vast majority of Gram-negative bacteria in Proteobacteria. Herein, the effectiveness of V(V) reduction is proved for the first time by Lactococcus raffinolactis, a Gram-positive bacterium in Firmicutes. The V(V) removal efficiency was 86.5 ± 2.17% during 10-d operation, with an average removal rate of 4.32 ± 0.28 mg/L·d in a citrate-fed system correspondingly. V(V) was bio-reduced to insoluble vanadium(IV) and distributed both inside and outside the cells. Nitrite reductase encoded by gene nirS mainly catalyzed intracellular V(V) reduction, revealing a previously unrecognized pathway. Oxidative stress induced by reactive oxygen species from dissimilatory V(V) reduction was alleviated through strengthened superoxide dismutase and catalase activities. Extracellular polymeric substances with chemically reactive hydroxyl (-OH) and carboxyl (-COO^-) groups also contributed to V(V) binding and reduction as well as ROS scavenging. This study can improve the understanding of Gram-positive bacteria for V(V) bio-detoxification and offer microbial resources for bioremediation of a V(V)-polluted environment.

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.

Microbial vanadate and nitrate reductions coupled with anaerobic methane oxidation in groundwater

Vanadate contaminant in groundwater receives increasing attentions, but little is known on its biogeochemical transformation with gaseous electron donors. This study investigated bio-reduction of vanadate coupled with anaerobic methane oxidation and its relationship with nitrate reduction. Results showed 95.8 ± 3.1% of 1 mM vanadate was removed within 7 days using methane as the sole electron donor. Tetravalent vanadium compounds were the main reduction products, which precipitated naturally in groundwater environment. The introduction of nitrate inhibited vanadate reduction, though both were reduced in parallel. Accumulations of volatile fatty acids (VFAs) were observed from methane oxidation. Preliminary microbial community structure and metabolite analyses indicated that vanadate was likely reduced via Methylomonas coupled with methane oxidation or through synergistic relationships between methane oxidizing bacteria and heterotrophic vanadate reducers with VFAs served as the intermediates.

Preparation of KOH and H3PO4 Modified Biochar and Its Application in Methylene Blue Removal from Aqueous Solution

Improperly treated or directly discharged into the environment, wastewater containing dyes can destroy the quality of water bodies and pollute the ecological environment. The removal of dye wastewater is urgent and essential. In this study, corn stalk was pyrolyzed to pristine biochar (CSBC) in a limited oxygen atmosphere and modified using KOH and H3PO4 (KOH-CSBC, H3PO4-CSBC, respectively). The biochars were characterized by surface area and pore size, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), as well as their behavior in adsorbing methylene blue (MB). Results indicated that the pore structure of CSBC became more developed after modification by KOH. Meanwhile, H3PO4-CSBC contained more functional groups after activation treatment. The pseudo-second-order kinetic and the Langmuir adsorption isotherm represented the adsorption process well. The maximum MB adsorption capacity of CSBC, KOH-CSBC, and H3PO4-CSBC was 43.14 mg g−1, 406.43 mg g−1 and 230.39 mg g−1, respectively. Chemical modification significantly enhanced the adsorption of MB onto biochar, especially for KOH-CSBC. The adsorption mechanism between MB and biochar involved physical interaction, electrostatic interaction, hydrogen bonding and π–π interaction. Hence, modified CSBC (especially KOH-CSBC) has the potential for use as an adsorbent to remove dye from textile wastewater.