Investigating organic sulfur in estuarine and offshore environments: A combined field and cultivation approach

Estuarine-offshore sediments accumulate substantial particulate organic matter, containing organic sulfur as a key component. However, the distribution and sources of organic sulfur in such environments remain poorly understood. This study investigated organic sulfur in the Yangtze River Estuary and adjacent East China Sea. Dissolved organic sulfur varied from 0.65 to 1.99 μmol/L (molar S:C 0.006-0.018), while particulate organic sulfur ranged from 0.42 to 2.69 μmol/L (molar S:C 0.007-0.082). Sedimentary organic sulfur exhibited a similar molar S:C ratio (0.014-0.071) to particulate organic sulfur in bottom water, implying that particulate matter deposition is a potential source. Furthermore, sediments exposed to frequent hypoxia harbored significantly higher organic sulfur and S:C values compared to non-hypoxic areas. Laboratory incubation experiments revealed the underlying mechanism: sustained activity of sulfate-reducing bacteria in hypoxic sediments led to a substantial increase in sedimentary organic sulfur (from 15 to 53 μmol/g) within 600 days. This microbially driven sulfurization rendered over 90 % of the organic sulfur resistant to acid hydrolysis. Therefore, this study demonstrates that, alongside particle deposition, microbial sulfurization significantly contributes to organic sulfur enrichment and likely promotes organic matter preservation in estuarine-offshore sediments, particularly under hypoxic conditions. This finding advances our understanding of organic sulfur sources in these vital ecosystems.

Antimony release and volatilization from organic-rich and iron-rich submerged soils

Antimony (Sb) is an poorly understood, increasingly common pollutant, especially in soils susceptible to waterlogging. We investigated the impact of waterlogging on Sb release, methylation, and volatilization from an organic-rich wetland soil and an iron (Fe)-rich floodplain soil in a 27-day microcosm experiment. The release of Sb into the porewaters of the organic-rich soil was environmentally relevant and immediate with waterlogging (3.2 to 3.5 mg L-1), and likely associated with a complex interplay of sulfide precipitation, sorption with organic matter and manganese (Mn) (oxyhydr)oxides in the soil. The release of Sb from the Fe-rich soil was likely associated with Fe-(oxyhydr)oxide reduction and immobilized due to co-precipitation with Fe-sulfides or as Sb-sulfides. Volatile Sb was produced from the soils after waterlogging. The organic-rich soil produced more volatile Sb (409 to 835 ng kgsoil-1), but the Fe-rich soil volatilized Sb more efficiently. The negligible association of Sb volatilization with soil parameters indicates a more complex underlying, potentially microbial, mechanism and that antimony volatilization could be ubiquitous and not dependent on specific soil properties. Future works should investigate the microbial and physiochemical drivers of Sb volatilization in soils as it may be an environmentally relevant part of the biogeochemical cycle.

Enhanced efficiencies on purifying acid mine drainage in constructed wetlands based on synergistic adsorption of attapulgite-soda residue composites and microbial sulfate reduction

Constructed wetlands (CWs) are a promising approach for treating acid mine drainage (AMD). However, the extreme acidity and high loads of heavy metals in AMD can easily lead to the collapse of CWs without proper pre-treatment. Therefore, it is considered essential to maintain efficient and stable performance for AMD treatment in CWs. In this study, pre-prepared attapulgite-soda residue (ASR) composites were used to improve the substrate of CWs. Compared with CWs filled with gravel (CWs-G), the removal efficiencies of sulfate and Fe, Mn, Cu, Zn Cd and Pb in CWs filled with ASR composites (CWs-ASR) were increased by 30% and 10-70%, respectively. These metals were mainly retained in the substrate in stable forms, such as carbonate-, Fe/Mn (oxide)hydroxide-, and sulfide-bound forms. Additionally, higher levels of photosynthetic pigments and antioxidant enzyme activities in plants, along with a richer microbial community, were observed in CWs-ASR than in CWs-G. The application of ASR composites alleviated the adverse effects of AMD stresses on wetland plants and microorganisms. In return, the increased bacteria abundance, particularly SRB genera (e.g., Thermodesulfovibrionia and Desulfobacca), promoted the formation of metal sulfides, enabling the saturated ASR adsorbed with metals to regenerate and continuously capture heavy metals. The synergistic adsorption of ASR composites and microbial sulfate reduction maintained the stable and efficient operation of CWs. This study contributes to the resource utilization of industrial alkaline by-products and promotes the breakthrough of new techniques for low-cost and passive treatment systems such as CWs.

Effective capping of dissolved sulfide generated in Ulva prolifera-rich marine sediments by iron-rich red soil

Bloom-induced macroalgal enrichment on the seafloor can substantially facilitate dissolved sulfide (DS) production through sulfate reduction. The reaction of DS with sedimentary reactive iron (Fe) is the main mechanism of DS consumption, which however usually could not effectively prevent DS accumulation caused by pulsed macroalgal enrichment. Here we used incubations to investigate the performance of Fe-rich red soil for buffering of DS produced from macroalgae (Ulva prolifera)-enriched sediment. Based on our results, a combination of red soil additions (6.8 kg/m2) before and immediately after pulsed macroalgal deposition (455 g/m2) can effectively cap DS within the red soil layer. The effective DS buffering is mainly due to ample Fe-oxide surface sites available for reaction with DS. Only a small loss (4 %) of buffering capacity after 18-d incubation suggests that the red soil is capable of prolonged DS buffering in macroalgae-enriched sediments.

Underlying the inhibition mechanisms of sulfate and lincomycin on long-term anaerobic digestion: Microbial response and antibiotic resistance genes distribution

This study evaluated the resilience of a long-term anaerobic treatment system exposed to sulfate, lincomycin (LCM) and their combined stress. LCM was found to impede anaerobic propionate degradation, while sulfate for restraining methanogenic acetate utilization. The combined stress, with influent LCM of 200 mg/L and sulfate of 1404 mg/L, revealed severer inhibition on anaerobic digestion than individual inhibition, leading to 73.9 % and 38.5 % decrease in methane production and sulfate removal, respectively. Suppression on propionate-oxidizing bacteria like unclassified_f__Anaerolineae and unclassified_f__Syntrophaceae further demonstrated LCM's inhibitory effect on propionate degradation. Besides, the down-regulation of genes encoding dissimilatory sulfate reduction enzymes caused by LCM triggered great inhibition on sulfate reduction. A notable increase in ARGs was detected under sulfate-stressed condition, owing to its obvious enrichment of tetracycline-resistant genes. Genera including unclassified_f__Syntrophaceae, unclassified_f__Geobacteraceae and unclassified_f__Anaerolineaceae were identified as dominant host of ARGs and enriched by sulfate addition. Overall, these results could provide the theoretical basis for further enhancement on anaerobic digestion of pharmaceutical wastewater containing sulfate and lincomycin.

Marsh sediments chronically exposed to nitrogen enrichment contain degraded organic matter that is less vulnerable to decomposition via nitrate reduction

Blue carbon habitats, including salt marshes, can sequester carbon at rates that are an order of magnitude greater than terrestrial forests. This ecosystem service may be under threat from nitrate (NO3-) enrichment, which can shift the microbial community and stimulate decomposition of organic matter. Despite efforts to mitigate nitrogen loading, salt marshes continue to experience chronic NO3- enrichment, however, the long-term consequence of this enrichment on carbon storage remains unclear. To investigate the effect of chronic NO3- exposure on salt marsh organic matter decomposition, we collected sediments from three sites across a range of prior NO3- exposure: a relatively pristine marsh, a marsh enriched to ~70 μmol L-1 NO3- in the flooding seawater for 13 years, and a marsh enriched between 100 and 1000 μmol L-1 for 40 years from wastewater treatment effluent. We collected sediments from 20 to 25 cm depth and determined that sediments from the most chronically enriched site had less bioavailable organic matter and a distinct assemblage of active microbial taxa compared to the other two sites. We also performed a controlled anaerobic decomposition experiment to test whether the legacy of NO3- exposure influenced the functional response to additional NO3-. We found significant changes to microbial community composition resulting from experimental NO3- addition. Experimental NO3- addition also increased microbial respiration in sediments collected from all sites. However, sediments from the most chronically enriched site exhibited the smallest increase, the lowest rates of total NO3- reduction by dissimilatory nitrate reduction to ammonium (DNRA), and the highest DNF:DNRA ratios. Our results suggest that chronic exposure to elevated NO3- may lead to residual pools of organic matter that are less biologically available for decomposition. Thus, it is important to consider the legacy of nutrient exposure when examining the carbon cycle of salt marsh sediments.

Biological upcycling of nickel and sulfate as electrocatalyst from electroplating wastewater

Upcycling nickel (Ni) to useful catalyst is an appealing route to realize low-carbon treatment of electroplating wastewater and simultaneously recovering Ni resource, but has been restricted by the needs for costly membranes or consumption of large amount of chemicals in the existing upcycling processes. Herein, a biological upcycling route for synchronous recovery of Ni and sulfate as electrocatalysts, with certain amount of ferric salt (Fe3+) added to tune the product composition, is proposed. Efficient biosynthesis of bio-NiFeS nanoparticles from electroplating wastewater was achieved by harnessing the sulfate reduction and metal detoxification ability of Desulfovibrio vulgaris. The optimal bio-NiFeS, after further annealing at 300 °C, served as an efficient oxygen evolution electrocatalyst, achieving a current density of 10 mA·cm-1 at an overpotential of 247 mV and a Tafel slope of 60.2 mV·dec-1. It exhibited comparable electrocatalytic activity with the chemically-synthesized counterparts and outperformed the commercial RuO2. The feasibility of the biological upcycling approach for treating real Ni-containing electroplating wastewater was also demonstrated, achieving 99.5 % Ni2+removal and 41.0 % SO42- removal and enabling low-cost fabrication of electrocatalyst. Our work paves a new path for sustainable treatment of Ni-containing wastewater and may inspire technology innovations in recycling/ removal of various metal ions.

Sulfate reduction behavior in response to landfill dynamic pressure changes

During the long-term stabilization process of landfills, the pressure field undergoes constant changes. This study constructed dynamic pressure changes scenarios of high-pressure differentials (0.6 MPa) and low-pressure differentials (0.2 MPa) in the landfill pressure field at 25 °C and 50 °C, and investigated the sulfate reduction behavior in response to landfill dynamic pressure changes. The results showed that the pressurization or depressurization of high-pressure differentials caused more significant differences in sulfate reduction behavior than that of low-pressure differentials. The lowest hydrogen sulfide (H2S) release peak concentration under pressurization was only 29.67% of that under initial pressure condition; under depressurization, the highest peak concentration of H2S was up to 21,828 mg m-3, posing a serious risk of H2S pollution. Microbial community and correlation analysis showed that pressure had a negative impact on the sulfate-reducing bacteria (SRB) community, and the SRB community adjusted its structure to adapt to pressure changes. Specific SRBs were further enriched with pressure changes. Differential H2S release behavior under pressure changes in the 25 °C pressure environments were mediated by Desulfofarcimen (ASV343) and Desulfosporosinus (ASV1336), while Candidatus Desulforudis (ASV24) and Desulfohalotomaculum (ASV94) played a key role at 50 °C. This study is helpful in the formulation of control strategies for the source of odor pollution in landfills.

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.

Microplastic, a possible trigger of landfill sulfate reduction process

The environmental impact of microplastics (MPs) formed from landfill has not been gained enough attention. This research investigated the characteristics of the MPs occurrence in landfills through field sampling. It shows that the MPs abundance in the landfill surface soil and non-landfill areas can reach 3573 items·g-1 and 3041 items·g-1, respectively. The vertical abundance of MPs increases significantly with depth, ranging from 387 to 11,599 items·g-1 with small size (≤10 μm, 65.61 %) and flake or wedge shape (38.48 %). The leachate movement in a longitudinal direction enables MPs to accumulate more easily in the landfill bottom layer with high moisture abundance. The abundance of MPs are significantly correlated with SO42- and S2- content, the two typical metabolic substrate and product of sulfate reduction process. In such heterogeneous environment, this significant correlation is not a random phenomenon in terms of the MPs have known substantial impact on biogeochemical processes. Microplastic is a possible trigger of landfill odor emission related with sulfate reduction. This research could serve as a reference for MPs and odor pollution management in landfills.

The effect of slime accumulated in a long-term operating UASB using crude glycerol to treat S-rich wastewater

An up-flow anaerobic sludge blanket (UASB) reactor targeting sulfate reduction was operated under a constant TOC/S-SO42- ratio of 1.5 ± 0.3 g C/g S for 639 days using crude glycerol as carbon source. A filamentous and fluffy flocculant material, namely slime-like substances (SLS), was gradually accumulated in the bioreactor after the cease of methanogenic activity. The accumulation of SLS was followed by a decrease in the removal efficiencies and a deterioration in the performance. Selected characteristics of SLS were investigated to explore the causes of its formation and the effect of SLS on the UASB performance. Results showed that glycerol fermentation and sulfate reduction processes taking place in the reactor were mainly accomplished in the bottom part of the UASB reactor, as the sludge concentration in the bottom was higher. The accumulation of SLS in the UASB reactor caused sludge flotation that further led to biomass washout, which decreased the sulfate and glycerol removal efficiencies. Batch activity tests performed with granular sludge (GS), slime-covered granular sludge (SCGS) and SLS showed that there was no difference between GS and SLS in the mechanism of glycerol fermentation and sulfate reduction. However, the specific sulfate reduction rate of GS was higher than that of SLS, while SLS showed a higher glycerol fermentation rate than that of GS. The different rates in GS and SLS were attributed to the higher relative abundances of fermentative microorganisms found in SLS and higher relative abundances of sulfate reducing bacteria (SRB) found in GS.

Substrate-dependent strategies to mitigate sulfate inhibition on microbial reductive dechlorination of polychlorinated biphenyls

Sulfate widely co-exists with polychlorinated biphenyls (PCBs) at various concentrations in the subsurface environment. Previous studies have suggested that sulfate often hampers microbial degradation of aliphatic chlorinated solvents such as chloroethenes. However, the impact of sulfate on microbial reductive dechlorination of aromatic PCBs and the underlying mechanisms have received limited attention. Likewise, strategies to mitigate such inhibition remain scarce. Here we found that the mechanisms and mitigation strategies of sulfate inhibition on PCB dechlorination were substrate-dependent. Under electron donor-limiting conditions, even a low concentration of sulfate (2 mM) resulted in a decreased PCB dechlorination rate by 88.7% in a co-culture comprising Dehalococcoides mccartyi CG1 and the sulfate-reducing bacterium Desulfovibrio desulfuricans F1, an inhibition which was attributed to the competition for electron donor between sulfate reduction and PCB dechlorination. As expected, re-amendment of 5 mM lactate effectively re-initiated PCB dechlorination. However, in the presence of a higher concentration of sulfate (5 mM), the PCB dechlorination rate in the co-culture was 77.7% lower than in the control, even with excessive electron donor supply. This inhibition was linked to high concentration of sulfide (∼5 mM) produced from sulfate reduction, as suggested by high availability of electron donor, recovery of dechlorination activity after removal of sulfide, and negligible influence of sulfate on PCB dechlorination in the axenic culture of D. mccartyi CG1. Indeed, sulfide (>5 mM) was found to directly suppress expression of PCB-dechlorinating reductive dehalogenase gene. The highest transcriptional level of pcbA1 was 2.9 ± 0.3 transcripts·cell-1 in the presence of ∼5 mM sulfide, which was increased to 37.4 ± 5.0 transcripts·cell-1 when sulfide was removed. Under this scenario, introduction of ferrous salts (5 mM) efficiently alleviated sulfide inhibition on PCB dechlorination. Interestingly, the augmentation of methanogens in the co-culture was also effective in mitigating sulfide inhibition on PCB dechlorination, offering a new approach to protect Dehalococcoides under sulfide stress. Collectively, these findings deepen our understanding of the influence of sulfate on microbial reductive dechlorination of PCBs and contribute to developing appropriate strategies based on geochemical conditions to alleviate sulfate inhibition during bioremediation of PCB-contaminated sites.

Co-digestion of sulfur-rich vegetable waste with waste activated sludge enhanced phosphorus release and hydrogenotrophic methanogenesis

Anaerobic co-digestion of sulfur-rich vegetable waste (SVW) with waste activated sludge (WAS) and the underlying mechanisms associated with methane production and phosphorus (P) release were investigated. Four types of SVW (Chinese cabbage, cabbage, rapeseed cake, and garlic) were utilized for co-digestion with WAS, and the methane yield increased by 7.3%-35.3%; in the meantime, the P release amount from WAS was enhanced by 9.8%-24.9%. The organic carbon in SVW promoted methane production, while organic sulfur and the formation of FeS facilitated P release. Among the four types of SVW, rapeseed cake was identified as the most suitable co-digestion substrate for enhancing both methane production and P release due to its balanced nutrients and relatively high sulfur content. Syntrophic bacteria working with hydrogenotrophic methanogens, iron-reducing bacteria, sulfate-reducing bacteria, and hydrogenotrophic methanogens were enriched. Metabolic pathways related to sulfate reduction and methanogenesis were facilitated, especially hydrogenotrophic methanogenesis. Enzymes involved in hydrogenotrophic methanogenesis were promoted by 76.05%-407.98% with the addition of Chinese cabbage, cabbage, or rapeseed cake. This study provides an eco-friendly technology for promoting P resource and energy recovery from WAS and an in-depth understanding of the corresponding microbial mechanisms.

Arsenic removal in flue gas through anaerobic denitrification and sulfate reduction cocoupled arsenic oxidation

Arsenic in flue gas from municipal solid waste incineration can damage to human health and ecological environment. A sulfate-nitrate-reducing bioreactor (SNRBR) for flue gas arsenic removal was investigated. Arsenic removal efficiency attained 89.4%. An integrated metagenomic and metaproteomic investigation showed that three nitrate reductases (NapA, NapB and NarG), three sulfate reductases (Sat, AprAB and DsrAB), and arsenite oxidase (ArxA) regulated nitrate reduction, sulfate reduction and bacterial As(III)-oxidation, respectively. Citrobacter and Desulfobulbus could synthetically regulate the expression of arsenite-oxidizing gene, nitrate reductases and sulfate reducatases, which involved in As(III) oxidation, nitrate and sulfate reduction. A bacterial consortium containing Citrobacter, UG_Enterobacteriaceas, Desulfobulbus and Desulfovibrio could capable of simultaneously arsenic oxidation, sulfate reduction and denitrification. Anaerobic denitrification and sulfate reduction were cocoupled to arsenic oxidation. The biofilm was characterized by FTIR, XPS, XRD, EEM, and SEM. XRD and XPS spectra verified the formation of aarsenic species (As(V)) from flue gas As(III) conversion. Arsenic speciation in biofilms of SNRBR consisted of 77% residual arsenic, 15.9% organic matter-bound arsenic, and 4.3% strongly absorbed arsenic. Flue gas arsenic was bio-stabilized in the form of Fe-As-S and As-EPS through biodeposition, biosorption and biocomplexation. This provides a new way of flue gas arsenic removal using the sulfate-nitrate-reducing bioreactor.

Decreasing lactate input for cost-effective sulfidogenic metal removal in sulfate-rich effluents: Mechanistic insights from (bio)chemical kinetics to microbiome response

High material cost is the biggest barrier for the industrial use of low-molecular-weight organics (i.e. lactate) as external carbon and electron source for sulfidogenic metal removal in sulfate-rich effluents. This study aims to provide mechanistic evidence from kinetics to microbiome analysis by batch modeling to support the possibility of decreasing the lactate input to achieve cost-effective application. The results showed that gradient COD/SO42- ratios at a low level had promising treatment performance, reaching neutralized pH with nearly total elimination of COD (91%-99%), SO42- (85%-99%), metals (80%-99%) including Cu, Zn, and Mn. First-order kinetics exhibited the best fit (R2 = 0.81-0.98) to (bio)chemical reactions, and the simulation results revealed that higher COD/SO42- accelerated the reaction rate of SO42- and COD but not suitable to that of metals. On the other hand, we found that the decreasing COD/SO42- ratio increased average path distance but decreased clustering coefficient and heterogeneity in microbial interaction network. Genetic prediction found that the sulfate-reduction-related functions were significantly correlated with the reaction kinetics changed with COD/SO42- ratios. Our study, combining reaction kinetics with microbiome analysis, demonstrates that the use of lactate as a carbon source under low COD/SO42- ratios entails significant efficiency of metal removal in sulfate-rich effluent using SRB-based technology. However, further studies should be carried out, including parameter-driven optimization and life cycle assessments are necessary, for its practical application.

Enhancing sulfate reduction and hydrogen sulfide removal through gas stripping in the acidogenesis phase of a two-phase anaerobic process

This study aims at evaluating two-phase and single-phase reactors for treating sulfate wastewater with low COD/SO₄^2- ratios. Additionally, a new process of gas stripping in an acidogenesis phase is proposed to reduce hydrogen sulfide (H₂S) inhibition and enhance biomethanation. The two-phase performed better than the single-phase in terms of COD removal, CH₄ production and H₂S resistance. After 30 days of stripping, the COD and sulfate degradation rates increased from 85.16% to 91.09% and from 49.39% to 63.07% in the two-phase, respectively. In contrast, without stripping, they were from 79.21% to 64.37% and from 50.26% to 53.15% in the single-phase, respectively. The microbial biodiversity was augmented via stripping, including norank_f__Spirochaetaceae, Petrimonas, Desulfurella and Blvii28_wastewater-sludge_group. Stripping operation enhanced the dissimilatory sulfate reduction, amino acid metabolism and possibly sulfate-dependent anaerobic ammonia oxidation (S-ANAMMOX). This study provides a promising strategy to improve sulfate reduction and reduce H₂S inhibition under a low COD/SO₄^2- ratio.

Fractionation behaviors of Cu, Zn, and S-O isotopes in groundwater contaminated with petroleum and treated by oxidation

Fractionation behaviors of Cu and Zn isotopes have been increasingly studied at the field scale, but those in various redox conditions of groundwater contaminated with petroleum and treated by oxidation have not been assessed. In this study, δ⁶⁵Cu and δ⁶⁶Zn as well as δ³⁴S_SO4 and Δδ¹⁸O_SO4-H2O were assessed in wells undergoing contamination by total petroleum hydrocarbons (TPH) and oxidation using H₂O₂ in 2021 and 2022. High δ³⁴S_SO4 and relevant parameters (e.g., dissolved sulfide and HCO₃^-) indicated the occurrence of sulfate reduction. The plot of δ⁶⁵Cu versus δ³⁴S_SO4 effectively indicated precipitation of Cu sulfides and their reoxidation at oxidation wells. Although the plot of δ⁶⁶Zn versus δ³⁴S_SO4 could also indicate reoxidation of Zn sulfides, the Zn isotopic fingerprint of sulfide precipitation may have been masked by fractionation by sorption. The advantage of using δ⁶⁵Cu in the redox reactions resulted from the wider range of δ⁶⁵Cu owing to the redox behavior of Cu. The plot combining isotopic fractionations of Cu and S can assist in assessing sulfide precipitation and oxidative treatment in TPH-contaminated groundwater.

Simultaneous nitrogen and sulfur removal through synergy of sulfammox, anammox and sulfur-driven autotrophic denitrification in a modified bioreactor enhanced by activated carbon

Anaerobic ammonium (NH₄⁺ - N) oxidation coupled with sulfate (SO₄^2-) reduction (sulfammox) is a new pathway for the autotrophic removal of nitrogen and sulfur from wastewater. Sulfammox was achieved in a modified up-flow anaerobic bioreactor filled with granular activated carbon. After 70 days of operation, the NH₄⁺ - N removal efficiency almost reached 70%, with activated carbon adsorption and biological reaction accounting for 26% and 74%, respectively. Ammonium hydrosulfide (NH₄SH) was found in sulfammox by X-ray diffraction analysis for the first time, which confirmed that hydrogen sulfide (H₂S) was one of the sulfammox products. Microbial results indicated that NH₄⁺ - N oxidation and SO₄^2- reduction in sulfammox were carried out by Crenothrix and Desulfobacterota, respectively, in which activated carbon may operate as electron shuttle. In the ¹⁵NH₄⁺ labeled experiment, ³⁰N₂ were produced at a rate of 34.14 μmol/(g sludge·h) and no ³⁰N₂ was detected in the chemical control group, proving that sulfammox was present and could only be induced by microorganisms. The ¹⁵NO₃^- labeled group produced ³⁰N₂ at a rate of 88.77 μmol/(g sludge·h), demonstrating the presence of sulfur-driven autotrophic denitrification. In the adding ¹⁴NH₄⁺ and ¹⁵NO₃^- group, it was confirmed that NH₄⁺ - N was removed by the synergy of sulfammox, anammox and sulfur-driven autotrophic denitrification, where the main product of sulfammox was nitrite (NO₂^-) and anammox was the main cause of nitrogen loss. The findings showed that SO₄^2- as a non-polluting species to environment may substitute NO₂^- to create a new "anammox" process.

Integration of the sulfate reduction and anammox processes for enhancing sustainable nitrogen removal in granular sludge reactors

The Anammox and Sulfate Reduction Ammonium Oxidation processes were compared in two granular sequencing batch reactors operated for 160 days under anammox conditions. It was hypothesized that increasing the concentration of SO₄^2- may positively influence the rate of N removal under anaerobic conditions and it was tested whether SO₄^2- reduction and anammox occur independently or are related to each other. The cooperation of N-S cycles by increasing the concentration of influent SO₄^2- to 952 mg S/L in the second reactor, a higher ammonium utilization rate and sulfate utilization rate was achieved compared to the first reactor, i.e., 2.1-fold and 15-fold, respectively. Nitrosomonas played the dominant role in the N metabolism, while Thauera - in the S metabolism. This study highlights the benefits of linking the N-S cycles as an effective approach for the treatment of NH₄⁺ and SO₄^2- - rich wastewater, including lower substrate removal cost and reduced energy consumption.

Desulfatitalea alkaliphila sp. nov., an alkalipilic sulfate- and arsenate- reducing bacterium isolated from a terrestrial mud volcano

A novel alkaliphilic sulfate-reducing bacterium, strain M08but^T, was isolated from a salsa lake of terrestrial mud volcano (Taman Peninsula, Russia). Cells were rod-shaped, motile and Gram-stain-negative. The temperature range for growth was 15-42 °C (optimum at 30 °C). The pH range for growth was 7.0-11.0, with an optimum at pH 8.5-9.0 Strain M08but^T used sulfate, thiosulfate, sulfite, dimethyl sulfoxide and arsenate as electron acceptors. Acetate, formate, butyrate, fumarate, succinate, glycerol and pyruvate were utilized as electron donors with sulfate. Fermentative growth was observed with fumarate, pyruvate, crotonate. Strain M08but^T grew chemolithoautotrophically with H₂ and CO₂. The G + C content of the genomic DNA was 60.1%. The fatty acid profile of strain M08but^T was characterized by the presence of anteiso-C_15:0 as the major component (68.8%). The closest phylogenetic relative of strain M08but^T was Desulfatitalea tepidiphila (the order Desulfobacterales) with 96.3% 16S rRNA gene sequence similarity. Based on the phenotypic, genotypic and phylogenetic characteristics of the isolate, strain M08but^T is considered to represent a novel species of the genus Desulfatitalea, with proposed name Desulfatitalea alkaliphila sp. nov. The type strain of Desulfatitalea alkaliphila is M08but^T (= KCTC 25382^T = VKM B-3560^T = DSM 113909^T = JCM 39202^T = UQM 41473^T).

Sulfate reduction behavior in pressure-bearing leachate saturated zone

Attention should be paid to the sulfate reduction behavior in a pressure-bearing leachate saturated zone. In this study, within the relative pressure range of 0-0.6 MPa, the ambient temperature with the highest sulfate reduction rate of 50°C was selected to explore the difference in sulfate reduction behavior in a pressure-bearing leachate saturated zone. The results showed that the sulfate reduction rate might further increase with an increase in pressure; however, owing to the effect of pressure increase, the generated hydrogen sulfide (H₂S) could not be released on time, thereby decreasing its highest concentration by approximately 85%, and the duration extended to about two times that of the atmospheric pressure. Microbial community structure and functional gene abundance analyses showed that the community distribution of sulfate-reducing bacteria was significantly affected by pressure conditions, and there was a negative correlation between disulfide reductase B (dsrB) gene abundance and H₂S release rate. Other sulfate reduction processes that do not require disulfide reductase A (dsrA) and dsrB genes may be the key pathways affecting the sulfate reduction rate in the pressure-bearing leachate saturated zone. This study improves the understanding of sulfate reduction in landfills as well as provides a theoretical basis for the operation and management of landfills.

A novel autotrophic denitrification and nitrification integrated constructed wetland process for marine aquaculture wastewater treatment

We undertook a lab-scale evaluation of a novel autotrophic denitrification and nitrification integrated constructed wetland (ADNI-CW) for improved carbon (C), nitrogen (N), and sulfur (S) cycling to treat mariculture wastewater. The process involved an up-flow autotrophic denitrification constructed wetland unit (AD-CW) for sulfate reduction and autotrophic denitrification, and an autotrophic nitrification constructed wetland unit (AN-CW) for nitrification. The 400-day experiment investigated the performance of the AD-CW, AN-CW, and entire ADNI-CW processes under various hydraulic retention times (HRTs), nitrate concentrations, dissolved oxygen levels, and recirculation ratios. Under various HRTs, the AN-CW achieved a nitrification performance exceeding 92%. Correlation analysis of the chemical oxygen demand (COD) revealed that, on average, approximately 96% of COD was removed by sulfate reduction. Under different HRTs, increases in influent NO₃^--N concentrations caused the amount of sulfide to gradually decrease from sufficient to deficient, and the autotrophic denitrification rate also decreased from 62.18 to 40.93%. In addition, when the NO₃^--N load rate was above 21.53 g N/m²·d, the transformation of organic N by mangrove roots may have increased NO₃^--N in the top effluent of the AD-CW. The coupling of N and S metabolic processes mediated by various functional microorganisms (Proteobacteria, Chloroflexi, Actinobacteria, Bacteroidetes, and unclassified_d__Bacteria) enhanced N removal. We intensively explored the effects of changing inputs as culture species developed on the physical, chemical, and microbial changes of CW to ensure a consistent and effective management of C, N, and S. This study lays the foundation for green and sustainable mariculture development.

The key role of biogenic arsenic sulfides in the removal of soluble arsenic and propagation of arsenic mineralizing communities

Biogeochemical processes govern the transport and availability of arsenic in sediments. However, little is known about the transition from indigenous communities to cultivable consortia when exposed to high arsenic concentrations. Such cultivable communities could be exploited for arsenic bioremediation of waste streams and polluted sites. Thus, it is crucial to understand the dynamics and selective pressures that shape the communities during the development of customized bacterial consortia. First, from the arsenic partitioning of two sediments with high arsenic concentrations, we found that up to 55% of arsenic was bioavailable because it was associated with the soluble, carbonate, and ionically exchangeable fractions. Next, we prepared sediment enrichment cultures under arsenate- and sulfate-reducing conditions to precipitate arsenic sulfide biominerals and analyze the communities. The produced biominerals were used as the inoculum to develop bacterial consortia via successive transfers. Tracking of the 16S rRNA gene in the fresh sediments, sediment enrichments, biogenic minerals, and bacterial consortia revealed differences in the bacterial communities. Removing the sediment caused a substantial decrease in diversity and shifts toward the dominance of the Firmicutes phylum to the detriment of Proteobacteria. In agreement with the 16S rRNA gene results, the sequencing of the arrA gene confirmed the presence of phylotypes closely related to Desulfosporosinus sp. Y5 (100% similarity), highlighting the pivotal role of this genus in the removal of soluble arsenic. Here, we demonstrated for the first time that besides being important as arsenic sinks, the biogenic arsenic sulfide minerals are reservoirs of arsenic resistant/respiring bacteria and can be used to culture them.

Habitability and Biosignature Formation in Simulated Martian Aqueous Environments

Water present on early Mars is often assumed to have been habitable. In this study, experiments were performed to investigate the habitability of well-defined putative martian fluids and to identify the accompanying potential formation of biosignatures. Simulated martian environments were developed by combining martian fluid and regolith simulants based on the chemistry of the Rocknest sand shadow at Gale Crater. The simulated chemical environment was inoculated with terrestrial anoxic sediment from the Pyefleet mudflats (United Kingdom). These enrichments were cultured for 28 days and subsequently subcultured seven times to ensure that the microbial community was solely grown on the defined, simulated chemistry. The impact of the simulated chemistries on the microbial community was assessed by cell counts and sequencing of 16S rRNA gene profiles. Associated changes to the fluid and precipitate chemistries were established by using ICP-OES, IC, FTIR, and NIR. The fluids were confirmed as habitable, with the enriched microbial community showing a reduction in abundance and diversity over multiple subcultures relating to the selection of specific metabolic groups. The final community comprised sulfate-reducing, acetogenic, and other anaerobic and fermentative bacteria. Geochemical characterization and modeling of the simulant and fluid chemistries identified clear differences between the biotic and abiotic experiments. These differences included the elimination of sulfur owing to the presence of sulfate-reducing bacteria and more general changes in pH associated with actively respiring cells that impacted the mineral assemblages formed. This study confirmed that a system simulating the fluid chemistry of Gale Crater could support a microbial community and that variation in chemistries under biotic and abiotic conditions can be used to inform future life-detection missions.

Effect of different carbon sources on sulfate reduction and microbial community structure in bioelectrochemical systems

Microbial electrolysis cells (MECs) have rapidly developed into a promising technology to treat sulfate-rich wastewater that lacks electron donors. Hence, a better understanding of the effect on the microbial community structure caused by different sources in bioelectrochemical systems is required. This study sought to investigate the effect of different carbon sources (NaHCO₃, ethanol, and acetate were employed as sole carbon source respectively) on the performance of sulfate-reducing biocathodes. The sulfate reduction efficiency enhanced by the bioelectrochemical systems was 8.09 - 11.57% higher than that of open-circuit reference experiments. Furthermore, the optimum carbon source was ethanol with a maximum sulfate reduction rate of 170 mg L^-1 d^-1 in the bioelectrochemical systems. The different carbon sources induced significant differences in sulfate reduction efficiency as demonstrated by the application of a micro-electrical field. Microbial community structure and network analysis revealed that all three kinds of carbon source systems enriched large proportions of sulfate-reducing bacteria and electroactive bacteria but were significantly distinct in composition. The dominant sulfate-reducing bacteria that use NaHCO₃ and acetate as carbon sources were Desulfobacter and Desulfobulbus, whereas those that use ethanol as carbon source were Desulfomicrobium and Desulfovibrio. Our results suggest that ethanol is a more suitable carbon source for sulfate reduction in bioelectrochemical systems.

Impacts of the invasive Spartina anglica on C-S-Hg cycles and Hg(II) methylating microbial communities revealed by hgcA gene analysis in intertidal sediment of the Han River estuary, Yellow Sea

We investigated the impact of invasive vegetation on mercury cycles, and identified microorganisms directly related to Hg(II) methylation using hgcA gene in vegetated mud flats (VMF) inhabited by native Suaeda japonica (SJ) and invasive Spartina anglica (SA), and unvegetated mud flats (UMF) in Ganghwa intertidal sediments. Sulfate reduction rate (SRR) and rate constants of Hg(II) methylation (K_m) and methyl-Hg demethylation (K_d) were consistently greater in VMF than in UMF, specifically 1.5, 2 and 11.7 times higher, respectively, for SA. Both K_m and K_d were significantly correlated with SRR and the abundance of sulfate-reducing bacteria. These results indicate that the rhizosphere of invasive SA provides a hotspot for Hg dynamics coupled with sulfate reduction. HgcA gene analysis revealed that Hg(II)-methylators were dominated by Deltaproteobacteria, Chloroflexi and Euryarchaeota, comprising 37.9%, 35.8%, and 6.5% of total hgcA gene sequences, respectively, which implies that coastal sediments harbor diverse Hg(II)-methylating microorganisms that previously underrepresented.

Adaptive response mechanisms of granular and flocculent sulfate-reducing sludge toward acidic multi-metal-laden wastewater

Dissimilatory sulfate reduction-based processes have long been a viable option for treating acidic metal-laden wastewater (AMW). Such processes can be optimized through enhancing sulfidogenic activity and the microbial consortia's resilience against a harsh environment. This study investigated how granular and flocculent sulfate-reducing bacteria (SRB) sludge respond to AMW as well as the mechanisms through which they adapt to the wastewater, with particular focuses on the stability of the sulfidogenic activities, metal removal, and the bacteria's resistance over the long-term: the flocculent SRB lost more than 50% of their treatment capacity after 35 days of treating AMW with the presence of Cd²⁺, Cu²⁺, Zn²⁺, and Ni²⁺ at 30 mg/L each, under pH = 4.5. In contrast, the granular SRB maintained its metal removal rate at 91% throughout the 161-day trial. Despite the SRB abundance remaining at approximate 40%, organics-partial oxidizing genera (Desulfobulbus and Desulfobacter) began to dominate due to their kinetic advantage. The extracellular glycosyl compositions were revealed to be critical for the stability of the granular structure and microbial activity as the extracellular proteins disintegrated irreversible. Usage the molecular dynamic simulation, the mobility of the metal ions in the SRB granular system was suppressed by the presence of a more diverse glycosyl composition compared with the flocculent system (10-50% diffusion coefficients differences). All of the identified glycosyls (especially xylose and rhamnose) exhibited strong interactions with Cu²⁺ (-470 kJ mol^-1), while the maximum binding strength of Cd²⁺ to glycosyls was greater than -40 kJ mol^-1, suggesting a low Cd²⁺complexation efficiency. The findings of this study shed light on the defensive mechanisms of SRB granules against multi-metal stress, and provide clues for efficient AMW treatment.

Antimony release and volatilization from rice paddy soils: Field and microcosm study

The fate of antimony (Sb) in submerged soils and the impact of common agricultural practices (e.g., manuring) on Sb release and volatilization is understudied. We investigated porewater Sb release and volatilization in the field and laboratory for three rice paddy soils. In the field study, the porewater Sb concentration (up to 107.1 μg L^-1) was associated with iron (Fe) at two sites, and with pH, Fe, manganese (Mn), and sulfate (SO₄^2-) at one site. The surface water Sb concentrations (up to 495.3 ± 113.7 μg L^-1) were up to 99 times higher than the regulatory values indicating a potential risk to aquaculture and rice agriculture. For the first time, volatile Sb was detected in rice paddy fields using a validated quantitative method (18.1 ± 5.2 to 217.9 ± 160.7 mg ha^-1 y^-1). We also investigated the influence of two common rice agriculture practices (flooding and manuring) on Sb release and volatilization in a 56-day microcosm experiment using the same soils from the field campaign. Flooding induced an immediate, but temporary, Sb release into the porewater that declined with SO₄^2-, indicating that SO₄^2- reduction may reduce porewater Sb concentrations. A secondary Sb release, corresponding to Fe reduction in the porewater, was observed in some of the microcosms. Our results suggest flooding-induced Sb release into rice paddy porewaters is temporary but relevant. Manuring the soils did not impact the porewater Sb concentration but did enhance Sb volatilization. Volatile Sb (159.6 ± 108.4 to 2237.5 ± 679.7 ng kg^-1 y^-1) was detected in most of the treatments and was correlated with the surface water Sb concentration. Our study indicates that Sb volatilization could be occurring at the soil-water interface or directly in the surface water and highlights that future works should investigate this potentially relevant mechanism.

Biological selenate and selenite reduction by waste activated sludge using hydrogen as electron donor

Biological reduction of selenium oxyanions is widely used for selenium removal from wastewater. The process is, however, limited by the availability of a suitable, efficient and low cost electron donor. In this study, selenite and selenate reduction by waste activated sludge using hydrogen as the electron donor was investigated. Both selenite and selenate (80 mg/L) were completely removed using H₂ within 8 days of incubation. In the presence of sulfate in the medium, the Se removal efficiency decreased to 77.8-95.4% (for selenite) and 88.2-99.4% (for selenate) at different temperatures and initial sulfate concentrations. Thermophilic conditions (50 °C) were better suited for both selenite and selenate reduction using H₂ as electron donor with a 0.8-13.5% increase in overall Se removal. Similarly, sulfate reduction also increased from 69.1- 88% at 30 °C to 72-94.6% at 50 °C. Most of the H₂ utilized was diverted towards Se and sulfate reduction with minimal production of byproducts such as methane (<0.32 mM) or volatile fatty acids (<0.92 mg/L). The elemental Se produced from selenite and selenate reduction ranged between 33.9 and 52.1 mg/L. The elemental selenium nanoparticles produced as a result of selenite and selenate reduction were characterized using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and dynamic light scattering (DLS) spectroscopy. Furthermore, characterization of the biomass using Fourier-transform infrared spectroscopy (FTIR) and excitation emission matrix (EEM) spectra of the extracellular polymeric substances (EPS) produced by the waste activated sludge were performed to elucidate the mechanism of selenium oxyanion reduction to elemental selenium nanoparticles.

Low pe+pH induces inhibition of cadmium sulfide precipitation by methanogenesis in paddy soil

Soil flooding is associated with the formation of cadmium (Cd)-sulfide, which is known to decrease Cd solubility and extractability. However, the threshold for Cd-sulfide precipitation is largely unknown, particularly because carbon can capture electrons for methanogenesis during sulfate reduction in highly reducing soil conditions. Using soil microcosms with different water regimens applied, we analyzed the electrochemical and spectroscopic properties and revealed a key mechanism controlling Cd stabilization that is dependent on pe+pH (a comprehensive indicator of soil redox status). The extent of Cd-sulfide precipitation was limited, with the proportion decreasing from 58.5% to 49.6% under flooding conditions (corresponding to a decrease in pe+pH from 3.28 to 2.82). Our data suggest that the increase in Cd mobilization in highly reducing soil is due to methanogenesis outcompeting sulfate reduction for available electrons. Although glucose supply could reduce the competition between oxidized carbon and sulfur in the soil for seizing electrons, the role of glucose as an electron donor/shuttle became weaker when soil was more anaerobic. The optimal soil reductive environment for maximum Cd-sulfide precipitation was observed when pe+pH was between 4.45 and 6.58. Overall, this study provides a quantitative and mechanistic understanding of how redox status (pe+pH), sulfate reduction, and methanogenesis are coupled with Cd remobilization in over-reductive paddy soil.

The influence of shellfish farming on sedimentary organic carbon mineralization: A case study in a coastal scallop farming area of Yantai, China

This study quantified the rate and relative contribution of each sedimentary organic carbon (OC) mineralization pathway in the Yantai coastal area. The results showed that scallop farming activities with raft-breeding facilities led to increased accumulation of OC and reactive Fe(III), which in turn promoted OC aerobic mineralization, Fe reduction, and competitively inhibited sulfate reduction. In the scallop farming area (SFA), O₂ reduction, dissimilatory Fe reduction, and sulfate reduction contributed 32.17 %, 27.77 %, and 30.18 % of the total OC mineralization, 1.6 times, 1.2 times, and 0.6 times those of the non-farming area, respectively. Nevertheless, scallop harvesting and resuspension by water currents will increase the short-term risk of dissolved inorganic carbon accumulation in the water column. The OC budget showed that the Yantai coastal area exhibited more OC mineralization than storage, with only 5.0-7.2 % of the net settled OC being permanently buried in the sediment.

Roles of Fe-C amendment on sulfate-containing pharmaceutical wastewater anaerobic treatment: Microbial community and sulfur metabolism

The effects of multiple two-phase anaerobic treatment involving acidification coupling Fe-C on sulfate-containing chemical synthesis-based pharmaceutical wastewater treatment were investigated. Fe-C was added as a filler with 25% vol. to acidogenic reactors for semi-continuous operation. The results suggested that Fe-C amendment promoted sulfate removal efficiency by 47.5% and shortened the reaction time by 50% in the acidogenic phase. With mitigation of sulfate inhibition, SCOD removal efficiency and methane production were further increased by 24.6% and 398% compared to direct raw wastewater anaerobic digestion, respectively, in methanogenic phase. The results of sulfate removal kinetics confirmed a 150% increase of removal rate in acidogenic phase. However, the apparent kinetic microbial sulfate removal constant without Fe-C amendment was maintained at approximately 0.06 h^-1. The Fe-C amendment not only increased the relative abundance of Methanothrix and Desulfovibrio for sulfate reduction but also enriched unclassified_p__Chloroflexi and unclassified_c__Deltaproteobacteria for acidification. Metagenomic results indicated that Fe-C enhanced dissimilatory sulfate reduction and PAPS synthesis of assimilatory step. The hydrogen sulfide production through the 3-mercaptopyruvate to pyruvate pathways was also enhanced. Butyrate-oxidizing genes were increased synchronously to convert butyrate to acetate.

Insights into the microbial response mechanisms to ciprofloxacin during sulfur-mediated biological wastewater treatment using a metagenomics approach

The fate and removal of ciprofloxacin, a class of fluoroquinolone antibiotic, during sulfur-mediated biological wastewater treatment has been recently well documented. However, little is known regarding the genetic response of microorganisms to ciprofloxacin. Here, a lab-scale anaerobic sulfate-reducing bioreactor was continuously operated over a long term for ciprofloxacin-contaminated wastewater treatment to investigate the response of the microorganisms to ciprofloxacin by adopting a metagenomics approach. It was found that total organic carbon (TOC) removal and sulfate reduction were promoted by approximately 10% under ciprofloxacin stress, along with the enrichment of functional genera (e.g., Desulfobacter, Geobacter) involved in carbon and sulfur metabolism. The metagenomic analytical results demonstrated that ciprofloxacin triggered the microbial SOS response, as demonstrated by the up-regulation of the multidrug efflux pump genes (8-125-fold higher than that of the control) and ciprofloxacin-degrading genes (4-33-fold higher than that of the control). Moreover, the contents of ATP, NADH, and cytochrome C, as well as related functional genes (including genes involved in energy generation, electron transport, carbon metabolism, and sulfur metabolism) were markedly increased under ciprofloxacin stress. This demonstrated that the carbon and sulfur metabolisms were enhanced for energy (ATP) generation and electron transport in response to ciprofloxacin-induced stress. Interestingly, the microbes tended to cooperate while being subjected exposure to exogenous ciprofloxacin according to the reconstructed metabolic network using the NetSeed model. Particularly, the species with higher complementarity indices played more pivotal roles in strengthening microbial metabolism and the SOS response under long-term ciprofloxacin stress. This study characterized the response mechanisms of microorganisms to ciprofloxacin at the genetic level in sulfur-mediated biological wastewater treatment. These new understandings will contribute the scientific basis for improving and optimizing the sulfur-mediated bioprocess for antibiotics-laden wastewater treatment.

Influence of iron species on the simultaneous nitrate and sulfate removal in constructed wetlands under low/high COD concentrations

Nitrate and sulfate are crucial factors of eutrophication and black and odorous water in the surface water and thus have raised increasing environmental concerns. Constructed wetlands (CWs) are the last ecological barrier before effluent enters the natural water body. To explore the simultaneous removal of nitrate and sulfate, the CW microcosms of CW-Con (with quartz sand), CW-ZVI (quartz sand and zero-valent iron), CW-Mag (quartz sand and magnetite), CW-ZVI + Mag (quartz sand, ZVI and magnetite) groups were set up under the low (100 mg/L)/high (300 mg/L) chemical oxygen demand (COD) concentration. Under the high COD condition, CW-ZVI group showed the best performance in nitrate (97.1%) and sulfate (96.9%) removal. Under the low COD concentration, the removal content of nitrate and sulfate in CW-ZVI group was better than CW-Mag group. The reason for this result was that zero-valent iron (ZVI) could be the electron donor for nitrate and sulfate reduction. Meanwhile, ZVI promoted chemical denitrification under high COD concentration according to PCA analysis. In addition, the produced sulfides inhibited the relative abundance of denitrifying bacteria, resulting in the lowest nitrate removal rate in CW-Mag group with sufficient electron donors. This study provided an alternative method to enhance simultaneous sulfate and nitrate removal in CWs.

Insights into the role of biochar on the acidogenic process and microbial pathways in a granular sulfate-reducing up-flow sludge bed reactor

In this study, the effect of biochar on sulfate reduction and anaerobic acidogenic process was explored in a granular sulfate-reducing up-flow sludge bed reactor in both long-term operation and batch tests. Both bioreactors had a high sulfate reduction efficiency of over 95% during the long-term operation, while the reactor with biochar addition showed higher sulfate reduction efficiency and stronger robustness against volatile fatty acids accumulation with a higher organic loading and sulfate loading rate. Batch tests showed that adding biochar significantly lessened the lag phase of the sulfate-reducing process, accelerated the adaption of acidogens, and facilitated both production and utilization of volatile fatty acids. The microbial pathways proved that biochar could regulate the acidification fermentation pathway and facilitate the enrichment of assimilative desulfurization bacteria. Overall, this study revealed that the acidogenic sulfate-reducing metabolic pathway could be enhanced by biochar, offering a potential application for effective sulfate-laden wastewater treatment.

Oxytetracycline co-metabolism with denitrification/desulfurization in SRB mediated system

Aquaculture wastewater contained a high remnant of oxytetracycline (OTC) and nitrate. In this study, OTC co-metabolized with denitrification/desulfurization was investigated in terms of kinetic analysis, pathway, microbial communities and produces analysis in sulfate-reducing bacteria (SRB) mediated system. Long-term acclimatization with sulfate (300 mg-S/L) could markedly accelerate the removed rate of OTC from 0.9 to 1.4 mg/g-SS/d, with the kinetic constants increasing from 0.2760 to 0.5232 d^-1, mainly via enzymes including adenosine-5'-phos-phosulfate reductase and cytochrome P450, and non-enzymatic process related to intermediates (adenosine-5'-phos-phosulfate and S⁰). Furthermore, OTC was likely detoxified by SRB enriched sludge mainly via hydrolysis, dehydration, oxidation and reduction. The denitrification process would postpone the OTC degradation via outcompeting electron donors with the desulfurization process. Redundancy analysis suggested that sulfur-oxidizing bacteria (Acidithiobacillus, Ochrobactrum) were highly related to OTC degradation processes. This study provides deep insight and a new opportunity for the treatment of aquaculture wastewater containing OTC, sulfate and nitrate by SRB sludge.

Impacts of molybdate and ferric chloride on biohythane production through two-stage anaerobic digestion of sulfate-rich hydrolyzed tofu processing residue

Biohythane production through one-stage anaerobic digestion of sulfate-rich hydrolyzed tofu processing residue has been hampered by high H₂S production. Herein, two-stage anaerobic digestion was investigated with the addition of molybdate (MoO₄^2-; 0.24-3.63 g/L) and ferric chloride (FeCl₃; 0.025-5.4 g/L) to the dark fermentation stage (DF) to improve biohythane production. DF supplemented with 1.21 g/L MoO₄^2- increased hydrogen yield by 14.6% over the control (68.39 ml/g-VS_fed), while FeCl₃ had no effect. Furthermore, the maximum methane yields of methanogenic fermentation were 524.8 and 521.6 ml/g-VS_fed with 3.63 g/L MoO₄^2- and 0.6 g/L FeCl₃ compared to 466.07 ml/g-VS_fed of the control. The maximum yields of biohythane and energy were 796.7 ml/g-VS_fed and 21.8 MJ/kg-VS_fed with 0.6 g/L FeCl₃ when the sulfate removal efficiency was 66.7%, and H₂S content was limited at 0.08%. Therefore, adding 0.6 g/L FeCl₃ is the most beneficial in improving energy recovery and sulfate removal with low H₂S content.

Carbon‑sulfur coupling in a seasonally hypoxic, high-sulfate reservoir in SW China: Evidence from stable CS isotopes and sulfate-reducing bacteria

Anthropogenic input of sulfate (SO₄^2-) in reservoirs may enhance bacterial sulfate reduction (BSR) under seasonally hypoxic conditions in the water column. However, factors that control BSR and its coupling to organic carbon (OC) mineralization in seasonally hypoxic reservoirs remain unclear. The present study elucidates the coupling processes by analyzing the concentrations and isotopic composition of dissolved inorganic carbon (DIC) and sulfur (SO₄^2-, sulfide) species, and the microbial community in water of the Aha reservoir, SW China, which has high SO₄^2- concentration due to the inputs from acid mine drainage about twenty years ago. The water column at two sites in July and October revealed significant thermal stratification. In the hypoxic bottom water, the δ¹³C-DIC decreased while the δ³⁴S-SO₄^2- increased, implying organic carbon mineralization due to BSR. The magnitude of S isotope fractionation (Δ³⁴S, obtained from δ³⁴S_sulfate-δ³⁴S_sulfide) during the process of BSR fell in the range of 3.4‰ to 27.0‰ in July and 21.6‰ to 31.8‰ in October, suggesting a change in the community of sulfate-reducing bacteria (SRB). The relatively low water column stability in October compared to that in July weakened the difference of water chemistry and ultimately affected the SRB diversity. The production of DIC (ΔDIC) scaled a strong positive relationship with the Δ³⁴S in July (p < 0.01), indicating that high OC availability favored the survival of incomplete oxidizers of SRB. However, in October, Δ¹³C-DIC was correlated with the Δ³⁴S in the bottom hypoxic water (p < 0.01), implying that newly degraded OC depleted in ¹³C could favor the dominance of complete oxidizers of SRB which caused greater S isotope fractionation. Moreover, the sulfide supplied by BSR might stimulate the reductive dissolution of Fe and Mn oxides (Fe(O)OH and MnO₂). The present study helps to understand the coupling of C and S in seasonally hypoxic reservoirs characterized by high SO₄^2- concentration.

High rate production of concentrated sulfides from metal bearing wastewater in an expanded bed hydrogenotrophic sulfate reducing bioreactor

Metallurgical wastewaters contain high concentrations of sulfate, up to 15 g L^-1. Sulfate-reducing bioreactors are employed to treat these wastewaters, reducing sulfates to sulfides which subsequently co-precipitate metals. Sulfate loading and reduction rates are typically restricted by the total H₂S concentration. Sulfide stripping, sulfide precipitation and dilution are the main strategies employed to minimize inhibition by H₂S, but can be adversely compromised by suboptimal sulfate reduction, clogging and additional energy costs. Here, metallurgical wastewater was treated for over 250 days using two hydrogenotrophic granular activated carbon expanded bed bioreactors without additional removal of sulfides. H₂S toxicity was minimized by operating at pH 8 ± 0.15, resulting in an average sulfate removal of 7.08 ± 0.08 g L^-1, sulfide concentrations of 2.1 ± 0.2 g L^-1 and peaks up to 2.3 ± 0.2 g L^-1. A sulfate reduction rate of 20.6 ± 0.9 g L^-1 d^-1 was achieved, with maxima up to 27.2 g L^-1 d^-1, which is among the highest reported considering a literature review of 39 studies. The rates reported here are 6-8 times higher than those reported for other reactors without active sulfide removal and the only reported for expanded bed sulfate-reducing bioreactors using H₂. By increasing the influent sulfate concentration and maintaining high sulfide concentrations, sulfate reducers were promoted while fermenters and methanogens were suppressed. Industrial wastewater containing 4.4 g L^-1 sulfate, 0.036 g L^-1 nitrate and various metals (As, Fe, Tl, Zn, Ni, Sb, Co and Cd) was successfully treated with all metal(loid)s, nitrates and sulfates removed below discharge limits.

Sulfate concentrations affect sulfate reduction pathways and methane consumption in coastal wetlands

Coastal wetlands are an important source of methane emissions, and understanding the mechanisms that control methane emissions from coastal wetlands is of great significance to global warming. Anaerobic oxidation of methane driven by sulfate is an important process to prevent methane emissions from coastal wetlands. The effects of environmental changes on this process and the function of the sulfate-methane transition zone (SMTZ) are poorly understood. In this study, spatiotemporal variations in pore-water geochemistry (concentrations of SO₄^2-, CH₄ and DIC as well as δ¹³C-DIC and δ¹³C-CH₄) in the Beidagang wetland, Tianjin, China, were investigated to unravel factors controlling the role of anaerobic oxidation of methane in coastal wetlands. Results show that the geochemical profile of pore-water is characterized by significant spatial and temporal variability, which may be related to changes in sulfate concentration, temperature and dissolved oxygen. The carbon isotope fractionation factors (ε_C) during methane oxidation range from 8.9‰ to 12.5‰, indicating that the sulfate-driven anaerobic oxidation of methane (S-AOM) dominates the methane oxidation in the Beidagang coastal wetland in both winter and summer, in both high and low salinity wetlands, and in both open water and littoral areas. However, sulfate concentration has a strong influence on the sulfate reduction pathways and methane consumption. The consumption of methane and sulfate by S-AOM is more significant in coastal wetlands with high sulfate concentrations, with S-AOM consuming nearly all of the upward-diffusing methane (96%) and downward-diffusing sulfate (96%). In addition, the dissolved inorganic carbon (DIC) produced in the pore-water mainly comes from methanogenesis, accounting for more than 80% of the total DIC pool, but in the areas with high sulfate concentrations in water column, the contribution of S-AOM to the DIC pool is greater, although only a small fraction of the total DIC pool (9%). The depth and width of the SMTZ show a clear spatial and temporal pattern, with active methanogenesis activity and upward high methane flux shoaling the SMTZ and increasing the risk of high methane emissions from coastal wetlands with low sulfate concentrations. Our findings highlight the importance of sulfate-driven anaerobic oxidation of methane in coastal wetlands and the effect of sulfate concentration on it. It contributes to our understanding of the mechanism of methane production and emissions from the coastal wetland system, particularly in light of the increased demand for coastal wetland restoration under global warming.

Enhancing the resistance to H2S toxicity during anaerobic digestion of low-strength wastewater through granular activated carbon (GAC) addition

Low-strength wastewater was treated using two laboratory-scale up-flow anaerobic sludge blankets (UASB) for 130 days under sulfate-reducing conditions. Granular activated carbon (GAC) was added to one of the reactors. The GAC addition increased the total chemical oxygen demand removal by 21-28% and total methane production by 32-78%. The sludge from the GAC-amended UASB showed higher specific methanogenic activities (SMA) and higher activities in the presence of H₂S, indicating that the GAC addition enhanced the resistance of methanogens to H₂S toxicity. Further, the microbial communities showed that the GAC addition shifted microbial communities. A robust syntrophic partnership between bacteria (i.e., Bacteroidetes_vadinHA17 and Trichococcus) and methanogens was established in the GAC-amended UASB. Sulfate-reducing bacteria (SRB) were enriched in the GAC biofilm, indicating the coexistence of competition and cooperation between SRB and methanogens. These findings provide significant insights regarding microbial community dynamics, especially SRB and methanogens, in a GAC-amended anaerobic digestion process under sulfate-reducing conditions.

Conversion and speculated pathway of methane anaerobic oxidation co-driven by nitrite and sulfate

Anaerobic sludge from sewage treatment was employed to derive a microbial colony that is capable of anaerobic oxidation of methane coupled with sulfate reduction and denitrification. Investigations revealed that methane can be oxidized with sulfate reduction and denitrification. When sulfate and nitrite acted as electron acceptors together, the rates and amount of methane conversion were higher than that when sulfate or nitrite alone was employed as an electron acceptor. The oxidation rate and amount of methane conversion reached 1.9 mg/(d•gVSS) and 22.24 mg, respectively. Methanotrophic bacteria, such as M. oxyfera, and Methylocystis sp., sulfate-reducing bacteria (SRB), e.g. Desulfosporosinus sp., and Desulfuromonas sp.; and denitrification bacteria, such as Hyphomicrobium sp., and Diaphorobacter sp., presented in the bacterial community. Anaerobic methanotrophic archaea (ANME), including Methanosaeta sp. and Methanobacterium sp. were found in the archaeal community. These findings indicate the coexistence of ANME, SRB and denitrification bacteria in the system. Nitrite reduction coupled with methane oxidation was performed independently by M. oxyfera during which limited oxygen generated. The oxygen released may be utilized by methanotrophic bacteria to produce organics, which could be used by denitrifying bacteria to reduce nitrite. Methanotrophic archaea could also oxidize methane to carbon dioxide or organics by reverse methanogenesis whereas sulfate was reduced to sulfide by SRB. This study opens possibility for biotechnological process of sulfate reduction and denitrification with methane as electron donor and provides a method for the synergistic treatment of wastewater containing sulfate/nitrite and waste gas containing methane.

Sulfate-reduction behavior in waste-leachate transition zones of landfill sites

The sulfate reduction behavior of the waste-leachate transition zone of landfill was investigated at different temperatures and moisture contents. Marked differences in the sulfate reduction behavior were observed in the waste-leachate transition zone. The highest H₂S concentration was observed when the solid-to-liquid ratio was 1:3 at both temperatures. Although more leachate led to higher H₂S concentrations, the solid-to-liquid ratio was likely of subordinate significance compared with temperature. The microbial community was more unstable at 50 °C and more extensive mutualistic interactions among bacteria were observed, resulting in SRB showing a more violent response to changes in the solid-to-liquid ratio. At 25 °C, it's the opposite. A temperature of 25 °C was suitable for most SRB (such as Desulfomicrobium and Desulfobulbus), while some specific SRB that did not contain the functional genes (such as Dethiobacter and Anaerolinea) played a pivotal role in the significant differences in sulfate reduction behavior observed at 50 °C. This study provides a theoretical basis for controlling the release of H₂S from landfill.

Effects of cadmium sulfide nanoparticles on sulfate bioreduction and oxidative stress in Desulfovibrio desulfuricans

Sulfate-containing wastewater has a serious threat to the environment and human health. Microbial technology has great potential for the treatment of sulfate-containing wastewater. It was found that nano-photocatalysts could be used as extracellular electron donors to promote the growth and metabolic activity of non-photosynthetic microorganisms. However, nano-photocatalysts could also induce oxidative stress and damage cells. Therefore, the interaction mechanism between photosynthetic nanocatalysts and non-photosynthetic microorganisms is crucial to determine the regulatory strategies for microbial wastewater treatment technologies. In this paper, the mechanism and regulation strategy of cadmium sulfide nanoparticles (CdS NPs) on the growth of sulfate-reducing bacteria and the sulfate reduction process were investigated. The results showed that the sulfate reduction efficiency could be increased by 6.4% through CdS NPs under light conditions. However, the growth of Desulfovibrio desulfuricans C09 was seriously inhibited by 55% due to the oxidative stress induced by CdS NPs on cells. The biomass and sulfate reduction efficiency could be enhanced by 6.8% and 5.9%, respectively, through external addition of humic acid (HA). At the same time, the mechanism of the CdS NPs strengthening the sulfate reduction process by sulfate bacteria was also studied which can provide important theoretical guidance and technical support for the development of microbial technology combined with extracellular electron transfer (EET) for the treatment of sulfate-containing wastewater.

Evolution of sulfate reduction behavior in leachate saturated zones in landfills

The sulfate reduction behavior of the landfill leachate saturated zone under different temperatures was investigated. The results showed that temperature had significant effects on sulfate reduction behavior. The sulfate reduction efficiency was the highest at high temperatures (55 °C and 45 °C), followed by mesophilic temperature (35 °C). Normal temperature 25 °C was far less effective than 55 °C, 45 °C and 35 °C. High abundances of aprA and dsrA genes were distributed under high temperatures. Through indicator species analysis and functional comparison, some key taxa were identified as putative key genera for sulfate reduction. Under high temperature, Paenibacillus could effectively degrade dimethyl sulfide. DsrAB is present in the genome of Tissierella. Gordonia, Syntrophomonas, and Lysinibacillus under mesophilic temperature indicates the potential of these organisms to degrade heterogenous biomass, environmental pollutants or other natural polymers with slow biodegradation. This microbial function is similar to that of the putative key genera under normal (25 °C) temperature. Most of the putative key genera belong to Firmicutes, Proteobacteria and Myxococcota. This study provides theoretical support for the control of hydrogen sulfide release from landfills.

Sulfate-reducing and methanogenic microbial community responses during anaerobic digestion of tannery effluent

Microbial communities were monitored in terms of structure, function and response to physicochemical variables during anaerobic digestion of tannery and associated slaughterhouse effluent in: (i) 2 L biochemical methane potential batch reactors at different inoculum to substrate ratios (2-5) and initial sulfate concentrations (665-2000 mg/L), and (ii) 20 L anaerobic sequencing batch reactors with different mixing regimes (continuous vs. intermittent). Methanogenic and sulfidogenic community compositions in the 2 L reactors evolved initially, but stabilised after the start of biogas generation, although significant (ANOSIM p < 0.05) changes in the physicochemical parameters indicated continued metabolic activity. Both hydrogenotrophic and acetoclastic archaeal genera were present in high relative abundances. Continuous stirring preferentially selected the metabolically versatile genus Methanosarcina, suggesting that higher specific methane generation in the continuously stirred system (168 vs. 19.5 mL methane per gram volatile solids per week) was related to the metabolic activities of members of this genus.

The core root microbiome of Spartina alterniflora is predominated by sulfur-oxidizing and sulfate-reducing bacteria in Georgia salt marshes, USA

BACKGROUND

Salt marshes are dominated by the smooth cordgrass Spartina alterniflora on the US Atlantic and Gulf of Mexico coastlines. Although soil microorganisms are well known to mediate important biogeochemical cycles in salt marshes, little is known about the role of root microbiomes in supporting the health and productivity of marsh plant hosts. Leveraging in situ gradients in aboveground plant biomass as a natural laboratory, we investigated the relationships between S. alterniflora primary productivity, sediment redox potential, and the physiological ecology of bulk sediment, rhizosphere, and root microbial communities at two Georgia barrier islands over two growing seasons.

RESULTS

A marked decrease in prokaryotic alpha diversity with high abundance and increased phylogenetic dispersion was found in the S. alterniflora root microbiome. Significantly higher rates of enzymatic organic matter decomposition, as well as the relative abundances of putative sulfur (S)-oxidizing, sulfate-reducing, and nitrifying prokaryotes correlated with plant productivity. Moreover, these functional guilds were overrepresented in the S. alterniflora rhizosphere and root core microbiomes. Core microbiome bacteria from the Candidatus Thiodiazotropha genus, with the metabolic potential to couple S oxidation with C and N fixation, were shown to be highly abundant in the root and rhizosphere of S. alterniflora.

CONCLUSIONS

The S. alterniflora root microbiome is dominated by highly active and competitive species taking advantage of available carbon substrates in the oxidized root zone. Two microbially mediated mechanisms are proposed to stimulate S. alterniflora primary productivity: (i) enhanced microbial activity replenishes nutrients and terminal electron acceptors in higher biomass stands, and (ii) coupling of chemolithotrophic S oxidation with carbon (C) and nitrogen (N) fixation by root- and rhizosphere-associated prokaryotes detoxifies sulfide in the root zone while potentially transferring fixed C and N to the host plant. Video Abstract.

Dynamic anaerobic membrane bioreactor coupled with sulfate reduction (SrDMBR) for saline wastewater treatment

This study investigated organic removal performance, characteristics of the membrane dynamics, membrane fouling and the effects of biological sulfate reduction during high-salinity (1.0%) and high-sulfate (150 mgSO₄^2--S/L) wastewater treatment using a laboratory-scale upflow anaerobic sludge bed reactor integrated with cross-flow dynamic membrane modules. Throughout the operational period, dynamic membrane was formed rapidly (within 5-10 min) following each backwashing cycle (21-16 days), and the permeate turbidity of <5-7 NTU was achieved with relatively high specific organic conversion (70-100 gTOC/kgVSS·d) and specific sulfate reduction (50-70 gSO₄^2--S/kgVSS·d) rates. The sulfide from sulfate reduction can be reused for downstream autotrophic denitrification. 16S rRNA gene amplicon sequencing revealed that the microbial communities enriched in the sludge were different than those accumulated on the dynamic layer. Overall, this study demonstrates that the anaerobic dynamic membrane bioreactor coupled with sulfate reduction (SrDMBR) shows promising applicability in saline wastewater treatment.

Increasing sulfate concentration and sedimentary decaying cyanobacteria co-affect organic carbon mineralization in eutrophic lake sediments

Sulfate (SO₄^2-) concentrations in eutrophic lakes are continuously increasing; however, the effect of increasing SO₄^2- concentrations on organic carbon mineralization, especially the greenhouse gas emissions of sediments, remains unclear. Here, we constructed a series of microcosms with initial SO₄^2- concentrations of 0, 30, 60, 90, 120, 150, and 180 mg/L to study the effects of increased SO₄^2- concentrations, coupled with cyanobacterial blooms, on organic carbon mineralization in Lake Taihu. Cyanobacterial blooms promoted sulfate reduction and released a large amount of inorganic carbon. The SO₄^2- concentrations in cyanobacteria treatments significantly decreased and eventually reached close to 0. As the initial SO₄^2- concentration increased, the sulfate reduction rates significantly increased, with maximum values of 9.39, 9.44, 28.02, 30.89, 39.68, and 54.28 mg/L∙d for 30, 60, 90, 120, 150, and 180 mg/L SO₄^2-, respectively. The total organic carbon content in sediments (51.16-52.70 g/kg) decreased with the initial SO₄^2- concentration (R² = 0.97), and the total inorganic carbon content in overlying water (159.97-182.73 mg/L) showed the opposite pattern (R² = 0.91). The initial SO₄^2- concentration was positively correlated with carbon dioxide (CO₂) emissions (R² = 0.68) and negatively correlated with methane (CH₄) emissions (R² = 0.96). The highest CO₂ concentration and lowest CH₄ concentration in the 180 mg/L SO₄^2- treatment were 1688.78 and 1903 μmol/L, respectively. These biogeochemical processes were related to competition for organic carbon sources between sulfate reduction bacteria (SRB) and methane production archaea (MPA) in sediments. The abundance of SRB was positively correlated with the initial SO₄^2- concentration and ranged from 6.65 × 10⁷ to 2.98 × 10⁸ copies/g; the abundance of MPA showed the opposite pattern and ranged from 1.99 × 10⁸ to 3.35 × 10⁸copies/g. These findings enhance our understanding of the effect of increasing SO₄^2- concentrations on organic carbon mineralization and could enhance the accuracy of assessments of greenhouse gas emissions in eutrophic lakes.

Roles of granular activated carbon (GAC) and operational factors on active microbiome development in anaerobic reactors

Ambient temperature municipal sewage was treated using two laboratory-scale up-flow anaerobic sludge blanket reactors for 225 days. Granular activated carbon (GAC) was added to one reactor to facilitate the development of direct interspecies electron transfer (DIET). The GAC addition increased total chemical oxygen demand removal by 5% - 18%. In addition to assessing the relative abundance of active amplicon sequence variants (ASVs), the mass balance model, the Mantel test, and the generalized linear models were applied to evaluate the dynamics of the active ASVs and the key operational factors controlling the bioreactor microbial community. These results demonstrated that, in addition to the GAC addition, extrinsic engineering operational factors played important roles in controlling (active) microbial communities. This study underlines the importance of taking a wholistic approach to assess microbial population dynamics. Reactor design and performance prediction should consider key engineering parameters when using DIET-based AD reactors in the future.