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.

Coupling of selenate reduction and pyrrhotite oxidation by indigenous microbial consortium in natural aquifer.

Pyrrhotite is ubiquitously found in natural environment and involved in diverse (bio)processes. However, the pyrrhotite-driven bioreduction of toxic selenate [Se(VI)] remains largely unknown. This study demonstrates that Se(VI) is successfully bioreduced under anaerobic condition with the participation of pyrrhotite for the first time. Completely removal of Se(VI) was achieved at initial concentration of 10 mg/L Se(VI) and 0.56 mL/min flow rate in continuous column experiment with indigenous microbial consortium and pyrrhotite. Variation in hydrochemistry and hydrodynamics affected Se(VI) removal performance. Se(VI) was reduced to insoluble Se(0) while elements in pyrrhotite were oxidized to Fe(III) and SO42-. Breakthrough study indicated that biotic activity contributed 81.4 ± 1.07% to Se(VI) transformation. Microbial community analysis suggested that chemoautotrophic genera (e.g., Thiobacillus) could realize pyrrhotite oxidation and Se(VI) reduction independently, while heterotrophic genera (e.g., Bacillus, Pseudomonas) contributed to Se(VI) detoxification by utilizing metabolic intermediates generated through Fe(II) and S(-II) oxidation, which were further verified by pure culture tests. Metagenomic and qPCR analyses indicated genes encoding enzymes for Se(VI) reduction (e.g., serA, napA and srdBAC), S oxidation (e.g., soxB) and Fe oxidation (e.g., mtrA) were upregulated. The elevated electron transporters (e.g., nicotinamide adenine dinucleotide, cytochrome c) promoted electron transfer from pyrrhotite to Se(VI). This study gains insights into Se biogeochemistry under the effect of Fe(II)-bearing minerals and provides a sustainable strategy for Se(VI) bioremediation in natural aquifer.

Concurrent reductive decontamination of chromium (VI) and uranium (VI) in groundwater by Fe(0)-based autotrophic bioprocess.

The co-presence of chromium (VI) [Cr(VI)] and uranium (VI) [U(VI)] is widely found in groundwater, imposing severe risks on human health. Although zerovalent iron [Fe(0)] supports superb performance for bioreduction of Cr(VI) and U(VI) individually, the biogeochemical process involving their concurrent removal with Fe(0) as electron donor remains unexplored. In the 6-d batch study, 86.1% ± 0.7% of Cr(VI) was preferentially eliminated, while 78.4% ± 0.5% of U(VI) removal was achieved simultaneously. Efficient removal of Cr(VI) (100%) and U(VI) (51.2% ∼ 100%) was also obtained in a continuous 160-d column experiment. As a result, Cr(VI) and U(VI) were reduced to less mobile Cr(III) and insoluble U(IV), respectively. 16 S rRNA sequencing was performed to investigate the dynamics of microbial community. Delftia, Acinetobacter, Pseudomonas and Desulfomicrobium were the major contributors mediating the bioreduction process. The initial Cr(VI) and hydraulic retention time (HRT) incurred pronounced effects on community diversity, which in turn altered the reactor's performance. The enrichment of Cr(VI) resistance (chrA), U(VI) reduction (dsrA) and Fe(II) oxidation (mtrA) genes were observed by reverse transcription qPCR. Cytochrome c, glutathione and NADH as well as VFAs and gas metabolites also involved in the bioprocess. This study demonstrated a promising approach for removing the combined contaminants of Cr(VI) and U(VI) in groundwater.

Independent and synergistic bio-reductions of uranium (VI) driven by zerovalent iron in aquifer.

Zerovalent iron [Fe(0)] can donate electron for bioprocess, but microbial uranium (VI) [U(VI)] reduction driven by Fe(0) is still poorly understood. In this study, Fe(0) supported U(VI) bio-reduction was steadily achieved in the 160-d continuous-flow biological column. The maximum removal efficiency and capacity of U(VI) were 100% and 46.4 ± 0.52 g/(m3·d) respectively, and the longevity of Fe(0) increased by 3.09 times. U(VI) was reduced to solid UO2, while Fe(0) was finally oxidized to Fe(III). Autotrophic Thiobacillus achieved U(VI) reduction coupled to Fe(0) oxidation, verified by pure culture. H2 produced from Fe(0) corrosion was consumed by autotrophic Clostridium for U(VI) reduction. The detected residual organic intermediates were biosynthesized with energy released from Fe(0) oxidation and utilized by heterotrophic Desulfomicrobium, Bacillus and Pseudomonas to reduce U(VI). Metagenomic analysis found the upregulated genes for U(VI) reduction (e.g., dsrA and dsrB) and Fe(II) oxidation (e.g., CYC1 and mtrA). These functional genes were also transcriptionally expressed. Cytochrome c and glutathione responsible for electron transfer also contributed to U(VI) reduction. This study reveals the independent and synergistic pathways for Fe(0)-dependent U(VI) bio-reduction, providing promising remediation strategy for U(VI)-polluted aquifers.

Mechanistic study for mutual interactions of Pb2+ and Trichoderma viride.

Fungi play significant roles in the geochemical processes of heavy metals in the environment. However, the interaction between heavy metals and fungi, especially at the cellular level, is quite complicated and remains unknown. This study explored the mutual interaction mechanism between Pb2+ and Trichoderma viride by combining batch experiments, spectroscopy, and in vitro approaches. Batch experiments revealed that Pb2+ had toxic effect on T. viride, originally causing the biomass of T. viride decreased from 1.3 g in the control group to 0 g in the presence of 200 mg/L Pb2+. The difference in biomass further led to varied pH, even decreasing from 5.7 at the outset to 3.4 due to the acid-production properties of T. viride. Moreover, structural deformation and damage of T. viride mycelium appeared when exposed to Pb2+, and were more evident at a higher dose of Pb2+ exposure. The growth curve exhibited that T. viride gradually adapted to Pb2+ exposure, which related to Pb2+ exposure concentration. Further, intracellular and extracellular secretions of T. viride changed with varying exposure concentrations of Pb2+, indicating that T. viride adapted differently to different concentrations of Pb2+, and MT participated in the detoxification of T. viride. SEM-EDX showed that T. viride could bio-adsorb and bioaccumulate more Pb2+ when exposed to more Pb2+, which was closely related to the content of P. And carbonyl, phosphate, and amino groups of T. viride participated in the Pb2+ biosorption onto T. viride, as evidenced by FT-IR and XPS. Meanwhile, the biomineralization and reduction of Pb2+ by T. viride were observed by XRD and XPS, which might be a possible factor for Pb2+ biosorption and bioaccumulation. CLSM showed that the bio-adsorbed and bioaccumulated Pb2+ were mainly distributed in the membrane of T. viride mycelium.

Interaction behaviors of Cr(VI) at biotite-water interface in the presence of HA: Batch, XRD and XPS investigations.

The interaction behaviors of heavy metals and micaceous minerals are extremely important to understand the environmental behaviors of heavy metals. In this work, the interaction behaviors of Cr(VI) and biotite in the presence and absence of HA were studied combining batch and spectroscopic approaches. Batch experiments showed that biotite had the ability to remove Cr(VI) from the water and the removal markedly increased with decreasing pH. However, sorption of total Cr onto biotite increased with increasing pH (2.0-4.0), whilst quickly decreased above pH âˆ¼ 4.0. It was worth noting that redox process of Cr(VI) to Cr(III), caused by structural Fe(II) on biotite, was another important factor for the high removal of Cr(VI) in a pH range of 2.0-4.0. Ionic strength also influenced Cr(VI) removal that Cr(VI) removal became higher with increasing ion strength. The presence of HA did not show obvious macroscopic effect on Cr(VI) removal, however, HA could cover biotite surface, and promote the sorption of total Cr onto biotite and attenuate the reduction effect caused by Fe(II) on biotite. Spectroscopic approaches, like FT-IR, XRD and XPS further confirmed the existence of Cr(III) on biotite interacting with Cr(VI) and the reduction of Cr(VI) to Cr(III) was drove by the Fe(II) dissolving from biotite to Fe(III). Further, sorption effect and reduction effect competitively contributed to the Cr(VI) removal by biotite, and reduction effect played a more important role at lower pH.

New insights into the sorption of U(VI) on kaolinite and illite in the presence of Aspergillus niger.

The regulation effect of Aspergillus niger to the sorption behavior of U(VI) on kaolinite and illite was studied through investigating the enrichment of U(VI) on kaolinite-Aspergillus niger and illite-Aspergillus niger composites. Kaolinite- or illite-A. niger composites were prepared through co-culturation method. Results showed that U(VI) sorption on kaolinite and illite in different pH ranges could be attributed to ion exchange, outer-sphere complexes (OSCs), and inner-sphere complexes (ISCs), while only the ISCs on the bio-composites. Moreover, micro-spectroscopy tests revealed that U(VI) coordinate with phosphate, amide, and carboxyl groups on illite- and kaolinite- A. niger composites. X-ray photoelectron spectroscopy (XPS) further found that U(VI) was partly reduced to non-crystalline U(IV) by A. niger in the bio-composites, occurring as phosphate coordination polymers or biomass-associated monomers. The findings herein provide further insight into the immobilization and migration of uranium in environments.

Cytotoxic Effect of Graphene Oxide Nanoribbons on Escherichia coli.

The biological and environmental toxicity of graphene and graphene derivatives have attracted great research interest due to their increasing applications. However, the cytotoxic mechanism is poorly understood. Here, we investigated the cytotoxic effect of graphene oxide nanoribbons (GORs) on Escherichia coli (E. coli) in an in vitro method. The fabricated GORs formed long ribbons, 200 nm wide. Based on the results of the MTT assay and plate-culture experiments, GORs significantly inhibited the growth and reproduction of E. coli in a concentration-dependent manner. We found that GORs stimulated E. coli to secrete reactive oxygen species, which then oxidized and damaged the bacterial cell membrane. Moreover, interaction between GORs and E. coli cytomembrane resulted in polysaccharide adsorption by GORs and the release of lactic dehydrogenase. Furthermore, GORs effectively depleted the metal ions as nutrients in the culture medium by adsorption. Notably, mechanical cutting by GORs was not obvious, which is quite different from the case of graphene oxide sheets to E. coli.

Transport behaviors of Cs+ in granite porous media: Effects of mineral composition, HA, and coexisting cations.

The transport of radiocesium (RCs) in granite has attracted great concerns for the consideration of a long-term safety assessment and performance evaluation of the nuclear waste disposal repository. In this study, the transport behaviors of Cs+ in granite were addressed and quantified by column experiments, sequential extraction, and a convection-dispersion equation model. The transport of Cs+ in granite experienced at least two stages including a rapid increase and a slow increase stages. The retardation of Cs+ in granite obviously became higher as biotite content increased. However, a consistent breakthrough plateau and almost overlapped breakthrough curves were observed under different feldspar contents, which suggested that the transport behaviors of Cs+ in granite was quite close to feldspar. Compared to Na+, K+ could effectively inhibit Cs+ adsorption and facilitate the mobility of Cs+ in granite column. In the presence of Sr2+, the transport of Cs+ was provoked in the granite column mainly due to the high competition effects. Humic acid (HA) did not obviously change the transport behaviors of Cs+ in granite column; however, HA could weakly change the adsorption species of Cs+ during Cs+ transport in granitic media. Both sequential extraction and two-site non-equilibrium model suggested that feldspar was the main contributor to the weak adsorption sites and biotite was responsible for the strong affinity sites for Cs+ in Beishan granite. The findings could provide important insights into RCs transport and fate in granitic media.

Exploring the fate of heavy metals from mining and smelting activities in soil-crop system in Baiyin, NW China.

The activity and fate of heavy metals (HMs) from mining and smelting activities in farmland soil is of great significance to effectively prevent the excessive enrichment of HMs in crops. This study focuses on Baiyin area, a typical mining city in northwest China. In this example, the sources, speciation, and fate of HMs in the farmland soil, and the migration and enrichment characteristics of HMs in the different parts of crops planted in different areas were studied in detail combining the chemical sequential extraction and Pb isotope approaches. Results showed that the mean anthropogenic contributions of HMs in farmland soils were approximately 85%, 88%, 76%, and 41% for the ore district (OD), Xidagou sewage irrigation area (XSIA), Dongdagou sewage irrigation area, and the Yellow River irrigation area, respectively, and the risk that HMs were excessively accumulated in crops in OD and XSIA was high. Compared with soil residual fractions, the isotope ratios 206Pb/207Pb in non-residual fractions (1.1304-1.1669) were closer to the values of local ores, suggesting that anthropogenic HMs from mining and smelting activities were mainly enriched in the non-residual fractions. The isotope ratios 206Pb/207Pb in crops (1.1398-1.1686) further confirmed that those anthropogenic HMs were more easily absorbed and concentrated by crops. HMs contents in leaves from OD and XSIA were generally higher than that in roots, suggesting that atmospheric deposition in OD and XSIA had a greater impact on the HMs concentration of crop leaves，while the excess rate of HMs in grain/fruit was the lowest in all parts of crops. The division and classification of crop planting in mining area can effectively help minimize the risk that HMs from anthropogenic source enter the human body through the food chain.

Trichoderma viride involvement in the sorption of Pb(II) on muscovite, biotite and phlogopite: Batch and spectroscopic studies.

In this study, batch and spectroscopic approaches were used to explore the sorption of Pb(II) on micas (i.e., muscovite, biotite and phlogopite) in the presence of Trichoderma viride (T. viride). Batch sorption showed that ion exchange, outer-sphere complexes (OSCs) and inner-sphere complexes (ISCs) contributed to Pb(II) sorption on biotite and phlogopite in the pH range of 2.0-7.4, whereas the ISCs were predominant for Pb(II) sorption on muscovite. X-ray diffraction and Fourier transform infrared (FT-IR) analyses have confirmed the changes of structure and surface properties of micas after co-culturing with T. viride, which could improve the sorption capacity of micas to Pb(II). Scanning electron microscopy revealed the bio-mineralization of Pb(II) on T. viride and mica-T. viride composites forming lead phosphates. Furthermore, FT-IR analysis showed that the groups of Si-OH, Al-OH from micas, and carboxyl, phosphate and amino groups from T. viride were synergistically contributing to Pb(II) sorption on mica-T. viride composite. X-ray photoelectron spectroscopy further confirmed that both OSCs and ISCs formed for Pb(II) sorption on micas; however, in the case of mica-T. viride composites, the synergistic effects of T. viride and micas were contributing to Pb(II) sorption through forming the ISCs and biomineralization.

Ultra-fast enrichment and reduction of As(V)/Se(VI) on three dimensional graphene oxide sheets-oxidized carbon nanotubes hydrogels.

The removals of arsenic and selenium pollutants are always urgent desires for the water security. In this study, both sorption and catalysis strategies were combined for the effective removals of As(V) and Se(VI) over magnetic graphene oxide sheets (GOs)-oxidized carbon nanotubes (OCNTs) hydrogels. The sorption behavior facilitated the operation of catalysis reactions, meanwhile, the catalytic reduction promoted the release of occupied sorption sites and then restarted a new sorption-catalysis cycle. The synergic effect of sorption and catalysis realized 258.2 mg g-1 for As(V) enrichment capacity on MPG2T1, and ultra-fast sorption and catalysis equilibriums were identified within 9 min. In the case of Se(VI), a moderate enrichment performance was observed to be 46.2 mg g-1. Similarly, the ultra-fast sorption and reduction of Se(VI) were realized within 2 min. In the competition experiments, only SO42-, SO32-, and HPO42- showed interference for As(V) and Se(VI) removals. These results testified the superiority of the synergy effect of sorption and catalysis, and the feasibility of 3D magnetic GOs-OCNTs hydrogel in practical implementations.