Abiotic aerobic oxidation pathways of stibnite revealed by oxygen and sulfur isotope systematics of sulfate.

The environmental threat posed by stibnite is an important geoenvironmental issue of current concern. To better understand stibnite oxidation pathways, aerobic abiotic batch experiments were conducted in aqueous solution with varying δ18OH2O value at initial neutral pH for different lengths of time (15-300 days). The sulfate oxygen and sulfur isotope compositions as well as concentrations of sulfur and antimony species were determined. The sulfur isotope fractionation factor (Δ34SSO4-stibnite) values decreased from 0.8‰ to -2.1‰ during the first 90 days, and increased to 2.6‰ at the 180 days, indicating the dominated intermediate sulfur species such as S2O32-, S0, and H2S (g) involved in Sb2S3 oxidation processes. The incorporation of O into sulfate derived from O2 (∼100%) indicated that the dissociated O2 was only directly adsorbed on the stibnite-S sites in the initial stage (0-90 days). The proportion of O incorporation into sulfate from water (27%-52%) increased in the late stage (90-300 days), which suggested the oxidation mechanism changed to hydroxyl attack on stibnite-S sites promoted by nearby adsorbed O2 on stibnite-Sb sites. The exchange of oxygen between sulfite and water may also contributed to the increase of water derived O into SO42-. The new insight of stibnite oxidation pathway contributes to the understanding of sulfide oxidation mechanism and helps to interpret field data.

Coupled sulfur and nitrogen cycling at a catchment scale: insights from isotopic and molecular techniques.

The biogeochemical cycles of nitrogen (N) and sulfur (S) play important roles in sustaining the Earth's ecosystem. However, their potential coupling process and underlying mechanisms in the nature remain unclear. Through joint applications of river water's isotopic compositions, isotope-pairing experiments, and molecular techniques, this study revealed the coupled N-S cycling processes at a catchment scale from both geochemical and biological perspectives. The river water's natural abundance isotopic compositions indicated that sulfide oxidation was an important source (67.0 ± 5.5 % in summer and 72.0 ± 5.5 % in winter) of riverine sulfate (SO42-). In addition, sulfide oxidation and NOx reduction (especially denitrification) were tightly coupled in summer but less significantly so in winter. However, the coupling of sulfide oxidation and dissimilatory nitrate reduction to ammonium (DNRA) could not be overlooked in winter. The 15N pairing experiments quantitatively showed that the high sulfide oxidation rates in summer (4.7 ± 2.3 mol/km2/h) were significantly associated with the denitrification. Metagenomics and qPCR analyses of the soils supported the isotopic interpretations, substantiating the metabolic potential and coexistence of bacterial denitrification, DNRA, and sulfide oxidation, which was more prevalent in summer. This study reveals comprehensive evidence that sulfide oxidation and NOx reduction are tightly coupled at the catchment scale, which provides a new perspective towards a better understanding of N-S cycling.

Metagenomics and Stable Isotopes Uncover the Augmented Sulfide-Driven Autotrophic Denitrification in a Seasonally Hypoxic, Sulfate-Abundant Reservoir.

The mechanism governing sulfur cycling in nitrate reduction within sulfate-rich reservoirs during seasonal hypoxic conditions remains poorly understood. This study employs nitrogen and oxygen isotope fractionation in nitrate, along with metagenomic sequencing to elucidate the intricacies of the coupled sulfur oxidation and nitrate reduction process in the water column. In the Aha reservoir, a typical seasonally stratified water body, we observed the coexistence of denitrification, bacterial sulfide oxidation, and bacterial sulfate reduction in hypoxic conditions. This is substantiated by the presence of abundant N/S-related genes (nosZ and aprAB/dsrAB) and fluctuations in N/S species. The lower 15εNO3/18εNO3 ratio (0.60) observed in this study, compared to heterotrophic denitrification, strongly supports the occurrence of sulfur-driven denitrification. Furthermore, we found a robust positive correlation between the metabolic potential of bacterial sulfide oxidation and denitrification (p < 0.05), emphasizing the role of sulfide produced via sulfate reduction in enhancing denitrification. Sulfide-driven denitrification relied on ∑S2- as the primary electron donor preferentially oxidized by denitrification. The pivotal genus, Sulfuritalea, emerged as a central player in both denitrification and sulfide oxidation processes in hypoxic water bodies. Our study provides compelling evidence that sulfides assume a critical role in regulating denitrification in hypoxic water within an ecosystem where their contribution to the overall nitrogen cycle was previously underestimated.

Exploring the Origins and Evolution of Oxygenic and Anoxygenic Photosynthesis in Deeply Branched Cyanobacteriota.

Cyanobacteriota, the sole prokaryotes capable of oxygenic photosynthesis (OxyP), occupy a unique and pivotal role in Earth's history. While the notion that OxyP may have originated from Cyanobacteriota is widely accepted, its early evolution remains elusive. Here, by using both metagenomics and metatranscriptomics, we explore 36 metagenome-assembled genomes from hot spring ecosystems, belonging to two deep-branching cyanobacterial orders: Thermostichales and Gloeomargaritales. Functional investigation reveals that Thermostichales encode the crucial thylakoid membrane biogenesis protein, vesicle-inducing protein in plastids 1 (Vipp1). Based on the phylogenetic results, we infer that the evolution of the thylakoid membrane predates the divergence of Thermostichales from other cyanobacterial groups and that Thermostichales may be the most ancient lineage known to date to have inherited this feature from their common ancestor. Apart from OxyP, both lineages are potentially capable of sulfide-driven AnoxyP by linking sulfide oxidation to the photosynthetic electron transport chain. Unexpectedly, this AnoxyP capacity appears to be an acquired feature, as the key gene sqr was horizontally transferred from later-evolved cyanobacterial lineages. The presence of two D1 protein variants in Thermostichales suggests the functional flexibility of photosystems, ensuring their survival in fluctuating redox environments. Furthermore, all MAGs feature streamlined phycobilisomes with a preference for capturing longer-wavelength light, implying a unique evolutionary trajectory. Collectively, these results reveal the photosynthetic flexibility in these early-diverging cyanobacterial lineages, shedding new light on the early evolution of Cyanobacteriota and their photosynthetic processes.

Nitrite-dependent microbial utilization for simultaneous removal of sulfide and methane in sewers.

Chemicals are commonly dosed in sewer systems to reduce the emission of hydrogen sulfide (H2S) and methane (CH4), incurring high costs and environmental concerns. Nitrite dosing is a promising approach as nitrite can be produced from urine wastewater, which is a feasible integrated water management strategy. However, nitrite dosing usually requires strict conditions, e.g., relatively high nitrite concentration (e.g., ∼200 mg N/L) and acidic environment, to inhibit microorganisms. In contrast to "microbial inhibition", this study proposes "microbial utilization" concept, i.e., utilizing nitrite as a substrate for H2S and CH4 consumption in sewer. In a laboratory-scale sewer reactor, nitrite at a relatively low concentrations of 25-48 mg N/L was continuously dosed. Two nitrite-dependent microbial utilization processes, i.e., nitrite-dependent anaerobic methane oxidation (n-DAMO) and microbial sulfide oxidation, successfully occurred in conjunction with nitrite reduction. The occurrence of both processes achieved a 58 % reduction in dissolved methane and over 90 % sulfide removal in the sewer reactor, with microbial activities measured as 15.6 mg CH4/(L·h) and 29.4 mg S/(L·h), respectively. High copy numbers of n-DAMO bacteria and sulfide-oxidizing bacteria (SOB) were detected in both sewer biofilms and sediments. Mechanism analysis confirmed that the dosed nitrite at a relatively low level did not cause the inhibition of sulfidogenic process due to the downward migration of activity zones in sewer sediments. Therefore, the proposed "microbial utilization" concept offers a new alternative for simultaneous removal of sulfide and methane in sewers.

Storage and Distribution of Organic Carbon and Nutrients in Acidic Soils Developed on Sulfidic Sediments: The Roles of Reactive Iron and Macropores.

In a boreal acidic sulfate-rich subsoil (pH 3-4) developing on sulfidic and organic-rich sediments over the past 70 years, extensive brownish-to-yellowish layers have formed on macropores. Our data reveal that these layers ("macropore surfaces") are strongly enriched in 1 M HCl-extractable reactive iron (2-7% dry weight), largely bound to schwertmannite and 2-line ferrihydrite. These reactive iron phases trap large pools of labile organic matter (OM) and HCl-extractable phosphorus, possibly derived from the cultivated layer. Within soil aggregates, the OM is of a different nature from that on the macropore surfaces but similar to that in the underlying sulfidic sediments (C-horizon). This provides evidence that the sedimentary OM in the bulk subsoil has been largely preserved without significant decomposition and/or fractionation, likely due to physiochemical stabilization by the reactive iron phases that also existed abundantly within the aggregates. These findings not only highlight the important yet underappreciated roles of iron oxyhydroxysulfates in OM/nutrient storage and distribution in acidic sulfate-rich and other similar environments but also suggest that boreal acidic sulfate-rich subsoils and other similar soil systems (existing widely on coastal plains worldwide and being increasingly formed in thawing permafrost) may act as global sinks for OM and nutrients in the short run.

Insight into the effective electrocatalytic sulfide removal from aqueous solutions using surface oxidized stainless-steel anode and its desulfurization mechanism.

The electrochemical oxidation of hydrogen sulfide (H2S) has shown its potential for the real application of H2S emission control in wastewater treatment. In this study, a surface corrosion treatment of stainless steel (SS) was optimized by regulate Ni content in the oxide film on the SS AISI 304 surface for sulfide removal. The X-ray photoelectron spectroscopy and linear sweeping voltammetry results indicated a higher Ni content in the oxide film of surface-oxidized stainless steel (SOSS) attributed to a higher sulfide removal potential. Sulfide removal experiment results showed that SS-150 (with 150 s anodic pretreatment) anodes achieved the highest Ni content of 69% with the best sulfide removal efficiency, i.e., 97% within 48 h, which increased by 20% compared to the untreated SS. This study also demonstrated a strategy for in situ removal of deposited sulfur on the anodes by cathodic treatment at -0.38 V vs. RHE to alleviate the common issue of sulfur passivation. Density functional theory (DFT) calculation revealed that NiOOH was the major active species in SS-150 oxide film for a faster sulfide removal rate. The study developed a SS surface modification process for Ni content regulation that contributed to better sulfide removal efficiency.

Room-temperature sulfur doped NiMoO4 with enhanced conductivity and catalytic activity for efficient hydrogen evolution reaction in alkaline media.

Transition metal oxides have been acknowledged for their exceptional water splitting capabilities in alkaline electrolytes, however, their catalytic activity is limited by low conductivity. The introduction of sulfur (S) into nickel molybdate (NiMoO4) at room temperature leads to the formation of sulfur-doped NiMoO4 (S-NiMoO4), thereby significantly enhancing the conductivity and facilitating electron transfer in NiMoO4. Furthermore, the introduction of S effectively modulates the electron density state of NiMoO4 and facilitates the formation of highly active catalytic sites characterized by a significantly reduced hydrogen absorption Gibbs free energy (ΔGH*) value of -0.09 eV. The electrocatalyst S-NiMoO4 exhibits remarkable catalytic performance in promoting the hydrogen evolution reaction (HER), displaying a significantly reduced overpotential of 84 mV at a current density of 10 mA cm-2 and maintaining excellent durability at 68 mA cm-2 for 10 h (h). Furthermore, by utilizing the anodic sulfide oxidation reaction (SOR) instead of the sluggish oxygen evolution reaction (OER), the assembled electrolyzer employing S-NiMoO4 as both the cathode and anode need merely 0.8 V to achieve 105 mA cm-2, while simultaneously producing hydrogen gas (H2) and S monomer. This work paves the way for improving electron transfer and activating active sites of metal oxides, thereby enhancing their HER activity.

Metabolic and phylogenetic diversity in the phylum Nitrospinota revealed by comparative genome analyses.

The most abundant known nitrite-oxidizing bacteria in the marine water column belong to the phylum Nitrospinota. Despite their importance in marine nitrogen cycling and primary production, there are only few cultured representatives that all belong to the class Nitrospinia. Moreover, although Nitrospinota were traditionally thought to be restricted to marine environments, metagenome-assembled genomes have also been recovered from groundwater. Over the recent years, metagenomic sequencing has led to the discovery of several novel classes of Nitrospinota (UBA9942, UBA7883, 2-12-FULL-45-22, JACRGO01, JADGAW01), which remain uncultivated and have not been analyzed in detail. Here, we analyzed a nonredundant set of 98 Nitrospinota genomes with focus on these understudied Nitrospinota classes and compared their metabolic profiles to get insights into their potential role in biogeochemical element cycling. Based on phylogenomic analysis and average amino acid identities, the highly diverse phylum Nitrospinota could be divided into at least 33 different genera, partly with quite distinct metabolic capacities. Our analysis shows that not all Nitrospinota are nitrite oxidizers and that members of this phylum have the genomic potential to use sulfide and hydrogen for energy conservation. This study expands our knowledge of the phylogeny and potential ecophysiology of the phylum Nitrospinota and offers new avenues for the isolation and cultivation of these elusive bacteria.

Heterostructured WOx/W2C Nanocatalyst for Li2S Oxidation in Lithium-Sulfur Batteries with High-Areal-Capacity.

Lithium-sulfur (Li-S) batteries show extraordinary promise as a next-generation battery technology due to their high theoretical energy density and the cost efficiency of sulfur. However, the sluggish reaction kinetics, uncontrolled growth of lithium sulfide (Li2S), and substantial Li2S oxidation barrier cause low sulfur utilization and limited cycle life. Moreover, these drawbacks get exacerbated at high current densities and high sulfur loadings. Here, a heterostructured WOx/W2C nanocatalyst synthesized via ultrafast Joule heating is reported, and the resulting heterointerfaces contribute to enhance electrocatalytic activity for Li2S oxidation, as well as controlled Li2S deposition. The densely distributed nanoparticles provide abundant binding sites for uniform deposition of Li2S. The continuous heterointerfaces favor efficient adsorption and promote charge transfer, thereby reducing the activation barrier for the delithiation of Li2S. These attributes enable Li-S cells to deliver high-rate performance and high areal capacity. This study provides insights into efficient catalyst design for Li2S oxidation under practical cell conditions.

Using the sulfide-oxidizing bacterium Geobacillus thermodenitrificans to restrict H2S release during chicken manure composting.

Hydrogen sulfide (H2S) is a toxic gas massively released during chicken manure composting. Diminishing its release requires efficient and low cost methods. In recent years, heterotrophic bacteria capable of rapid H2S oxidation have been discovered but their applications in environmental improvement are rarely reported. Herein, we investigated H2S oxidation activity of a heterotrophic thermophilic bacterium Geobacillus thermodenitrificans DSM465, which contains a H2S oxidation pathway composed by sulfide:quinone oxidoreductase (SQR) and persulfide dioxygenase (PDO). This strain rapidly oxidized H2S to sulfane sulfur and thiosulfate. The oxidation rate reached 5.73 µmol min-1·g-1 of cell dry weight. We used G. thermodenitrificans DSM465 to restrict H2S release during chicken manure composting. The H2S emission during composting process reduced by 27.5% and sulfate content in the final compost increased by 34.4%. In addition, this strain prolonged the high temperature phase by 7 days. Thus, using G. thermodenitrificans DSM465 to control H2S release was an efficient and economic method. This study provided a new strategy for making waste composting environmental friendly and shed light on perspective applications of heterotrophic H2S oxidation bacteria in environmental improvements.

Reactive transport modelling of tailings hydrogeochemistry under a composite cover.

Quantitative forecasts of acid mine drainage (AMD) production are important for remediation planning. Reactive transport simulations corresponding to a detailed sampling location at a covered legacy tailings impoundment in northern Ontario, Canada, were conducted to quantitatively assess the predominant hydrogeochemical reactions. The simulations span the period from the end of tailings deposition (circa 1970) to early 2020, 12 years after remediation by a five-layer composite cover. The conceptual model of uncovered tailings weathering and subsequent geochemistry of the covered tailings system was implemented in 1D using the multi-component reactive transport code MIN3P. Transient monthly infiltration, post-cover boundary condition changes, and a dynamic temperature regime were incorporated. The shrinking core model, including parallel O2(aq) and Fe3+ oxidation reactions for the waste rock in the cover and the underlying tailings, was implemented to simulate the oxidation of As-bearing pyrite, chalcopyrite, and sphalerite. Primary carbonate and aluminosilicate host minerals promoted acid-neutralization reactions. Precipitation of secondary phases and sorption/desorption of Cu, Zn, and arsenite were incorporated into the model. The overall agreement between key simulated and field-measured post-cover aqueous geochemical parameters suggests that the conceptual model captured the primary hydrogeochemical processes in the covered tailings. A lack of reliable data on initial tailings mineralogy and pre-cover hydrogeochemistry increased simulation uncertainty. Simulated reaction rates indicate that where intact, the cover decreased sulfide oxidation rates by both O2(aq) and Fe3+ and improved pore-water quality over time. Simulation results indicate that elevated concentrations of Zn and As are likely to persist in the tailings regardless of cover performance, whereas concentrations of Cu and Al are the parameters most sensitive to cover effectiveness.

Elevated arsenic concentrations in groundwater of the Upper Indus Plain of Pakistan across a range of redox conditions.

Groundwater of the Ravi River floodplain is particularly elevated in arsenic (As) on both sides of the Pakistan-India border. To understand this pattern, 14 sites were drilled to 12-30 m depth across floodplains and doabs of Pakistan after testing over 20,000 wells. Drill cuttings were collected at 1.5 m intervals, 132 of which were sand overlain by 77 intervals of clay and/or silt. Radiocarbon dating of clay indicates deposition of the aquifer sands tapped by wells 20-30 kyr ago. Most (85 %) of the sand samples were gray in color, indicating partial reduction to Fe(II) oxides, whereas most (92 %) of the clay and/or silt samples were orange. Associations between groundwater electrical conductivity, dissolved Fe, sulfate, and nitrate suggest that wells can be elevated (>10 µg/L) in As in the region due to either reductive dissolution of Fe oxides, evaporative concentration, or alkali desorption. In the Ravi floodplain, 47 % of 6445 wells tested contain >10 µg/L As compared to only 9 % of 14,165 tested wells in other floodplains and doabs. The As content of aquifer sands in the Ravi floodplain of Pakistan averages 4 ± 4 mg/kg (n = 66) and is higher than the average of 2 ± 2 mg/kg (n = 51) for aquifer sands outside the Ravi. Synchrotron spectroscopy and column-based speciation indicate predominance of As(V) over As(III) in both aquifer sands and groundwater. Whereas multiple processes may be responsible for elevated levels of As in groundwater across the region, spatial heterogeneity in groundwater As concentrations in the Ravi floodplain seems linked to variations in As concentrations in aquifer sands. Regulation by the solid phase may limit variations in groundwater As over time in response to natural and human-induced changes in hydrology. This means spatial heterogeneity could be taken advantage of to lower the exposure across the region with more testing and targeted drilling.

Process conditions affect microbial diversity and activity in a haloalkaline biodesulfurization system.

Biodesulfurization (BD) systems that treat sour gas employ mixtures of haloalkaliphilic sulfur-oxidizing bacteria to convert sulfide to elemental sulfur. In the past years, these systems have seen major technical innovations that have led to changes in microbial community composition. Different studies have identified and discussed the microbial communities in both traditional and improved systems. However, these studies do not identify metabolically active community members and merely focus on members' presence/absence. Therefore, their results cannot confirm the activity and role of certain bacteria in the BD system. To investigate the active community members, we determined the microbial communities of six different runs of a pilot-scale BD system. 16S rRNA gene-based amplicon sequencing was performed using both DNA and RNA. A comparison of the DNA- and RNA-based sequencing results identified the active microbes in the BD system. Statistical analyses indicated that not all the existing microbes were actively involved in the system and that microbial communities continuously evolved during the operation. At the end of the run, strains affiliated with Alkalilimnicola ehrlichii and Thioalkalivibrio sulfidiphilus were confirmed as the most active key bacteria in the BD system. This study determined that microbial communities were shaped predominantly by the combination of hydraulic retention time (HRT) and sulfide concentration in the anoxic reactor and, to a lesser extent, by other operational parameters.IMPORTANCEHaloalkaliphilic sulfur-oxidizing bacteria are integral to biodesulfurization (BD) systems and are responsible for converting sulfide to sulfur. To understand the cause of conversions occurring in the BD systems, knowing which bacteria are present and active in the systems is essential. So far, only a few studies have investigated the BD system's microbial composition, but none have identified the active microbial community. Here, we reveal the metabolically active community, their succession, and their influence on product formation.

Bioremediation of acid mine drainage using sulfate-reducing wetland bioreactor: Filling substrates influence, sulfide oxidation and microbial community.

Two sulfate-reducing wetland bioreactors (SRB-1 filled with lignocellulosic wastes and SRB-2 with river sand) were applied for synthetic acid mine drainage treatment with bio-waste fermentation liquid as electron donor, and the influence of filling substrates on sulfate reduction, sulfur transformation and microbial community was studied. The presence of lignocellulosic wastes (mixture of cow manure, bark, sawdust, peanut shell and straw) in SRB-1 promoted sulfate reduction efficiency (68.9%), sulfate reduction rate (42.1 ± 11 mg S/(L·d)), dissolved sulfide production rate (27.4 ± 7 mg S/(L·d)), and particularly caused high conversion ratio of sulfate reduction into dissolved sulfide (66.4%). In comparison, the relatively low sulfate reduction efficiency (42.9%), sulfate reduction rate (27.0 ± 10 mg S/(L·d)), dissolved sulfide production rate (5.6 ± 3 mg S/(L·d)) and low dissolved sulfide conversion efficiency (21.2%) occurred in SRB-2. Mixed organic substrates including easily assimilated electron donors (in manure) and lignocellulosic matter were effective to promote quick start and long-term microbial sulfate reduction. More than 98% of produced dissolved sulfide was oxidized dominantly by photoautotrophic green sulfur bacteria (genera Chlorobium and Chlorobaculum), of which 64.6% and 54.5% was converted into elemental sulfur for SRB-1 and SRB-2. The oxidation of sulfide into elemental sulfur for potential recovery rather than sulfate is preferred. Diverse sulfate reducing bacteria and sulfide oxidizing bacteria co-existed in the treatment system, which led to a sustainable sulfur transformation. High metal removal efficiency for Fe (99.6%, 92.5%), Cd (99.9%, 99.9%), Zn (99.4%, 98.5%), Cu (94.5%, 94.6%) except for Mn (9.3%, 3.6%) was achieved, and effluent pH increased to 6.5-7.7 and 6.7-7.7 for SRB-1 and SRB-2, respectively. Microbial community was regulated by filling substrates. Synergism between lignocellulosic decomposing bacteria and sulfate reducing bacteria played a vital role in lignocellulosic bioreactor treating AMD, in addition to fermentation liquid serving as effective electron donor.

Atmospheric Gas-Phase Formation of Methanesulfonic Acid.

Despite its impact on the climate, the mechanism of methanesulfonic acid (MSA) formation in the oxidation of dimethyl sulfide (DMS) remains unclear. The DMS + OH reaction is known to form methanesulfinic acid (MSIA), methane sulfenic acid (MSEA), the methylthio radical (CH3S), and hydroperoxymethyl thioformate (HPMTF). Among them, HPMTF reacts further to form SO2 and OCS, while the other three form the CH3SO2 radical. Based on theoretical calculations, we find that the CH3SO2 radical can add O2 to form CH3S(O)2OO, which can react further to form MSA. The branching ratio is highly temperature sensitive, and the MSA yield increases with decreasing temperature. In warmer regions, SO2 is the dominant product of DMS oxidation, while in colder regions, large amounts of MSA can form. Global modeling indicates that the proposed temperature-sensitive MSA formation mechanism leads to a substantial increase in the simulated global atmospheric MSA formation and burden.

Mechanisms of water-rock interaction and implications for remediating flooded mine workings elucidated from environmental tracers, stable isotopes, and rare earth elements.

Contamination from acid mine drainage affects ecosystems and usability of groundwater for domestic and municipal purposes. The Captain Jack Superfund Site outside of Ward, Boulder County, Colorado, USA, hosts a draining mine adit that was remediated through emplacement of a hydraulic bulkhead to preclude acid mine drainage from entering nearby Lefthand Creek. During impoundment of water within the mine workings in 2020, a diverse and novel dataset of stable isotopes of water, sulfate, and carbon (δ2H, δ18OH2O, δ18OSO4, δ34S, δ13CDIC), rare earth elements, and environmental tracers (noble gases and tritium) were collected to understand groundwater recharge and mixing, mechanisms of sulfide oxidation and water-rock interaction, and the influence of remediation on the hydrologic and geochemical system. Water isotopes indicate that groundwater distal from the mine workings has seasonally variable recharge sources whereas water within the workings has a distinctive composition with minimal temporal variability. Sulfate isotopes indicate that sulfide oxidation occurs both within the mine workings and in adjacent igneous dikes, and that sulfide oxidation may occur under suboxic conditions with ferric iron as the oxidant. Carbon isotopes track the neutralization of acidic waters and the carbon mass budget of the system. Rare earth elements corroborate stable isotopes in indicating groundwater compartmentalization, and additionally illustrate enhanced mineral weathering in the mine workings. Environmental tracers indicate mixing of modern and pre-modern groundwater and inform timelines that active remediation may be needed. Together these datasets provide a useful template for similar investigations of abandoned mine sites where physical mixing processes, sources of solute loading, or remediation timeframes are of importance.

Enhancement of bio-S0 recovery and revealing the inhibitory effect on microorganisms under high sulfide loading.

Biodesulfurization is a mature technology, but obtaining biosulfur (S0) that can be easily settled naturally is still a challenge. Increasing the sulfide load is one of the known methods to obtain better settling of S0. However, the inhibitory effect of high levels of sulfide on microbes has also not been well studied. We constructed a high loading sulfide (1.55-10.86 kg S/m3/d) biological removal system. 100% sulfide removal and 0.56-2.53 kg S/m3/d S0 (7.0 ± 0.09-16.4 ± 0.25 µm) recovery were achieved at loads of 1.55-7.75 kg S/m3/d. Under the same load, S0 in the reflux sedimentation tank, which produced larger S0 particles (24.2 ± 0.73-53.8 ± 0.70 µm), increased the natural settling capacity and 45% recovery. For high level sulfide inhibitory effect, we used metagenomics and metatranscriptomics analyses. The increased sulfide load significantly inhibited the expression of flavin cytochrome c sulfide dehydrogenase subunit B (fccB) (Decreased from 615 ± 75 to 30 ± 5 TPM). At this time sulfide quinone reductase (SQR) (324 ± 185-1197 ± 51 TPM) was mainly responsible for sulfide oxidation and S0 production. When the sulfide load reached 2800 mg S/L, the SQR (730 ± 100 TPM) was also suppressed. This resulted in the accumulation of sulfide, causing suppression of carbon sequestration genes (Decreased from 3437 ± 842 to 665 ± 175 TPM). Other inhibitory effects included inhibition of microbial respiration, production of reactive oxygen species, and DNA damage. More sulfide-oxidizing bacteria (SOB) and newly identified potential SOB (99.1%) showed some activity (77.6%) upon sulfide accumulation. The main microorganisms in the sulfide accumulation environment were Thiomicrospiracea and Burkholderiaceae, whose sulfide oxidation capacity and respiration were not significantly inhibited. This study provides a new approach to enhance the natural sedimentation of S0 and describes new microbial mechanisms for the inhibitory effects of sulfide.

Improving the Sulfurophobicity of the NiS-Doping CoS Electrocatalyst Boosts the Low-Energy-Consumption Sulfide Oxidation Reaction Process.

Producing sulfur from a sulfide oxidation reaction (SOR)-based technique using sulfide aqueous solution has attracted considerable attention due to its ecofriendliness. This study demonstrates that NiS-doped cobalt sulfide NiS-CoS-supported NiCo alloy foam can deliver the SOR with superior electrocatalytic activity and robust stability compared to reported non-noble metal-based catalysts. Only 0.34 V vs RHE is required to drive a current density of 100 mA cm-2 for the SOR. According to the experiment, the catalyst exhibits a unique sulfurophobicity feature because of the weak interaction between sulfur and the transition metal sulfide (low affinity for elemental sulfur), preventing electrode corrosion during the SOR process. More impressively, the chain-growth mechanism of the SOR from short- to long-chain polysulfides was revealed by combining electrochemical and spectroscopic in situ methods, such as in situ ultraviolet-visible and Raman. It is also demonstrated that electrons can transfer straight from the sulfion (S2-) to the active site on the anode surface during the low-energy-consumption SOR process. This work provides new insight into simultaneous energy-saving hydrogen production and high-value-added S recovery from sulfide-containing wastewater.

Sulfur disproportionating microbial communities in a dynamic, microoxic-sulfidic karst system.

Biogeochemical sulfur cycling in sulfidic karst systems is largely driven by abiotic and biological sulfide oxidation, but the fate of elemental sulfur (S0 ) that accumulates in these systems is not well understood. The Frasassi Cave system (Italy) is intersected by a sulfidic aquifer that mixes with small quantities of oxygen-rich meteoric water, creating Proterozoic-like conditions and supporting a prolific ecosystem driven by sulfur-based chemolithoautotrophy. To better understand the cycling of S0 in this environment, we examined the geochemistry and microbiology of sediments underlying widespread sulfide-oxidizing mats dominated by Beggiatoa. Sediment populations were dominated by uncultivated relatives of sulfur cycling chemolithoautotrophs related to Sulfurovum, Halothiobacillus, Thiofaba, Thiovirga, Thiobacillus, and Desulfocapsa, as well as diverse uncultivated anaerobic heterotrophs affiliated with Bacteroidota, Anaerolineaceae, Lentimicrobiaceae, and Prolixibacteraceae. Desulfocapsa and Sulfurovum populations accounted for 12%-26% of sediment 16S rRNA amplicon sequences and were closely related to isolates which carry out autotrophic S0 disproportionation in pure culture. Gibbs energy (∆Gr ) calculations revealed that S0 disproportionation under in situ conditions is energy yielding. Microsensor profiles through the mat-sediment interface showed that Beggiatoa mats consume dissolved sulfide and oxygen, but a net increase in acidity was only observed in the sediments below. Together, these findings suggest that disproportionation is an important sink for S0 generated by microbial sulfide oxidation in this oxygen-limited system and may contribute to the weathering of carbonate rocks and sediments in sulfur-rich environments.