Microbial sulfate reduction by Desulfovibrio is an important source of hydrogen sulfide from a large swine finishing facility

There is still a lack of understanding of H2S formation in agricultural waste, which leads to poor odour prevention and control. Microbial sulfate reduction is a major process contributing to sulfide formation in natural and technogenic environments with high sulfate and low oxygen concentration. Agricultural waste can be considered a low-sulfate system with no obvious input of oxidised sulfur compounds. The purpose of this study was to characterise a microbial community participating in H2S production and estimate the microbial sulfate reduction rate (SRR) in manure slurry from a large-scale swine finishing facility in Western Siberia. In a series of manure slurry microcosms, we identified bacterial consortia by 16S rRNA gene profiling and metagenomic analysis and revealed that sulfate-reducing Desulfovibrio were key players responsible for H2S production. The SRR measured with radioactive sulfate in manure slurry was high and comprised 7.25 nmol S cm−3 day−1. Gypsum may be used as a solid-phase electron acceptor for sulfate reduction. Another plausible source of sulfate is a swine diet, which often contains supplements in the form of sulfates, including lysine sulfate. Low-sulfur diet, manure treatment with iron salts, and avoiding gypsum bedding are possible ways to mitigate H2S emissions from swine manure.

Recovery of Metals from Waste Lithium Ion Battery Leachates Using Biogenic Hydrogen Sulfide

Lithium ion battery (LIB) waste is increasing globally and contains an abundance of valuable metals that can be recovered for re-use. This study aimed to evaluate the recovery of metals from LIB waste leachate using hydrogen sulfide generated by a consortium of sulfate-reducing bacteria (SRB) in a lactate-fed fluidised bed reactor (FBR). The microbial community analysis showed Desulfovibrio as the most abundant genus in a dynamic and diverse bioreactor consortium. During periods of biogenic hydrogen sulfide production, the average dissolved sulfide concentration was 507 mg L−1 and the average volumetric sulfate reduction rate was 278 mg L−1 d−1. Over 99% precipitation efficiency was achieved for Al, Ni, Co, and Cu using biogenic sulfide and NaOH, accounting for 96% of the metal value contained in the LIB waste leachate. The purity indices of the precipitates were highest for Co, being above 0.7 for the precipitate at pH 10. However, the process was not selective for individual metals due to simultaneous precipitation and the complexity of the metal content of the LIB waste. Overall, the process facilitated the production of high value mixed metal precipitates, which could be purified further or used as feedstock for other processes, such as the production of steel.

Geochemical processes in compacted clay in contact with an acid landfill leachate: laboratory experiments and modelling results

Clays are commonly used as liners in urban landfills. However, the reactive processes with landfill leachates, and in particular the role of accessory minerals is poorly known. The aim of this work is to evaluate the diffusion of a synthetic urban landfill leachate through compacted natural smectite-illitic clays containing carbonates and sulfates and to predict the functioning of the clay liner for different minor mineral proportions. The leachate, characterized by acidic pH conditions and high organic matter content, is a typical aqueous solution formed in the acetogenic phase of organic matter degradation in urban landfill areas. Medium-scale (11 cm) laboratory diffusion tests were performed over 77 days. Chloride diffusion coefficients, porosity changes, cation exchange constants and the sulfate reduction rate were quantitatively assessed by means of reactive transport modelling. The exchange capacity of the clays is responsible for NH4+retention. However, the presence or absence of gypsum in the initial clay rock controls the functioning of the liner. Gypsum dissolution ensures a high sulfate concentration in the porewater and enhances the acetate consumption via sulfate reduction. Gypsum dissolution and the concomitant calcite precipitation do not significantly alter the porosity of the clay rock.

A UASB bioreactor using silage as a carbon source to reduce sulfate

Low cost-treatment for sulfate removal is required in many areas where potable water is scarce. The biggest challenge in biological treatment is finding an abundant low or no-cost carbon source. This work demonstrated for the first time that leachate from the agricultural byproduct silage can be used in an upflow anaerobic sludge-bed bioreactor to reduce sulfate for on-farm water treatment. The reactor ran continuously for approximately one year with an average silage leachate feed COD concentration of 4,471 ± 857 mg L−1, and sulfate feed concentrations varying from 1,253 to 2,081 mg L−1. The maximum sulfate reduction rate (SRR) of 9.75 ± 0.23 mmol (L day)−1 was achieved at the high sulfate influent concentration and the amount of organics consumed was between 80–90%. Sulfide levels in the UASB bioreactor were consistently high for most of the experiment, averaging 516.6 ± 188.5 mg L−1. Interestingly, during the last month of operation when sulfide concentrations were highest the SRR continued to increase. It was estimated that 36% of the silage leachate carbon was used directly for sulfate reduction.

Diversity, Activity, and Abundance of Sulfate-Reducing Bacteria in Saline and Hypersaline Soda Lakes

ABSTRACT Soda lakes are naturally occurring highly alkaline and saline environments. Although the sulfur cycle is one of the most active element cycles in these lakes, little is known about the sulfate-reducing bacteria (SRB). In this study we investigated the diversity, activity, and abundance of SRB in sediment samples and enrichment cultures from a range of (hyper)saline soda lakes of the Kulunda Steppe in southeastern Siberia in Russia. For this purpose, a polyphasic approach was used, including denaturing gradient gel electrophoresis of dsr gene fragments, sulfate reduction rate measurements, serial dilutions, and quantitative real-time PCR (qPCR). Comparative sequence analysis revealed the presence of several novel clusters of SRB, mostly affiliated with members of the order Desulfovibrionales and family Desulfobacteraceae. We detected sulfate reducers and observed substantial sulfate reducing rates (between 12 and 423 μmol/dm3 day−1) for most lakes, even at a salinity of 475 g/liter. Enrichments were obtained at salt saturating conditions (4 M Na+), using H2 or volatile fatty acids as electron donors, and an extremely halophilic SRB, strain ASO3-1, was isolated. Furthermore, a high dsr gene copy number of 108 cells per ml was detected in a hypersaline lake by qPCR. Our results indicate the presence of diverse and active SRB communities in these extreme ecosystems.

Effect of Low Sulfate Concentrations on Lactate Oxidation and Isotope Fractionation during Sulfate Reduction by Archaeoglobus fulgidus Strain Z†

ABSTRACT The effect of low substrate concentrations on the metabolic pathway and sulfur isotope fractionation during sulfate reduction was investigated for Archaeoglobus fulgidus strain Z. This archaeon was grown in a chemostat with sulfate concentrations between 0.3 mM and 14 mM at 80°C and with lactate as the limiting substrate. During sulfate reduction, lactate was oxidized to acetate, formate, and CO2. This is the first time that the production of formate has been reported for A. fulgidus. The stoichiometry of the catabolic reaction was strongly dependent on the sulfate concentration. At concentrations of more than 300 μM, 1 mol of sulfate was reduced during the consumption of 1 mol of lactate, whereas only 0.6 mol of sulfate was consumed per mol of lactate oxidized at a sulfate concentration of 300 μM. Furthermore, at low sulfate concentrations acetate was the main carbon product, in contrast to the CO2 produced at high concentrations. We suggest different pathways for lactate oxidation by A. fulgidus at high and low sulfate concentrations. At about 300 μM sulfate both the growth yield and the isotope fractionation were limited by sulfate, whereas the sulfate reduction rate was not limited by sulfate. We suggest that the cell channels more energy for sulfate uptake at sulfate concentrations below 300 to 400 μM than it does at higher concentrations. This could explain the shift in the metabolic pathway and the reduced growth yield and isotope fractionation at low sulfate levels.

Salinity Responses of Benthic Microbial Communities in a Solar Saltern (Eilat, Israel)

ABSTRACT The salinity responses of cyanobacteria, anoxygenic phototrophs, sulfate reducers, and methanogens from the laminated endoevaporitic community in the solar salterns of Eilat, Israel, were studied in situ with oxygen microelectrodes and in the laboratory in slurries. The optimum salinity for the sulfate reduction rate in sediment slurries was between 100 and 120‰, and sulfate reduction was strongly inhibited at an in situ salinity of 215‰. Nevertheless, sulfate reduction was an important respiratory process in the crust, and reoxidation of formed sulfide accounted for a major part of the oxygen budget. Methanogens were well adapted to the in situ salinity but contributed little to the anaerobic mineralization in the crust. In slurries with a salinity of 180‰ or less, methanogens were inhibited by increased activity of sulfate-reducing bacteria. Unicellular and filamentous cyanobacteria metabolized at near-optimum rates at the in situ salinity, whereas the optimum salinity for anoxygenic phototrophs was between 100 and 120‰.

Effect of nitrite and nitrate on biogenic sulfide production in sewer biofilms determined by the use of microelectrodes

The effects of O2 and NO3− concentrations on in situ sulfate reduction and sulfide reoxidation in microaerophilic wastewater biofilms grown on rotating disk reactors were investigated by the use of microelectrodes for O2, S2−, NO3−, NO2−, and pH. Microelectrode measurements showed the vertical microzonation of O2 respiration, NO3− respiration, H2S oxidation and SO42− reduction in the biofilms. The microelectrode measurements indicate that sulfate reducing activity was largely restricted to a narrow anaerobic zone located about 500 μm below the biofilm surface. An addition of nitrate forced the sulfate reduction zone deeper in the biofilm and reduced the specific sulfate reduction rate as well. The sulfate reduction zone was consequently separated from the O2 and NO3− respiration zones. Anaerobic H2S oxidation with NO3− was also induced by addition of nitrate to the medium. Measurements of the reduced inorganic sulfur compounds (FeS, FeS2 and S0), total-Mn and total-Fe in the biofilm indicated that the produced H2S became immediately oxidized with O2, NO3− and other oxidants, mainly ferric/ferrous hydrates. On the basis of the present results, it was estimated that of all sulfide produced, 13% of the sulfide was precipitated by metal ions as FeS and S0 just above the sulfate reduction zone, 65% was anaerobically oxidized to SO42− with NO3− as an electron acceptor and 22% was aerobically oxidized within the biofilm incubated in 70 μmol l−1 of DO and 280 μmol l−1 of NO3−.

Diversity of Sulfur Isotope Fractionations by Sulfate-Reducing Prokaryotes

ABSTRACT Batch culture experiments were performed with 32 different sulfate-reducing prokaryotes to explore the diversity in sulfur isotope fractionation during dissimilatory sulfate reduction by pure cultures. The selected strains reflect the phylogenetic and physiologic diversity of presently known sulfate reducers and cover a broad range of natural marine and freshwater habitats. Experimental conditions were designed to achieve optimum growth conditions with respect to electron donors, salinity, temperature, and pH. Under these optimized conditions, experimental fractionation factors ranged from 2.0 to 42.0‰. Salinity, incubation temperature, pH, and phylogeny had no systematic effect on the sulfur isotope fractionation. There was no correlation between isotope fractionation and sulfate reduction rate. The type of dissimilatory bisulfite reductase also had no effect on fractionation. Sulfate reducers that oxidized the carbon source completely to CO2 showed greater fractionations than sulfate reducers that released acetate as the final product of carbon oxidation. Different metabolic pathways and variable regulation of sulfate transport across the cell membrane all potentially affect isotope fractionation. Previous models that explained fractionation only in terms of sulfate reduction rates appear to be oversimplified. The species-specific physiology of each sulfate reducer thus needs to be taken into account to understand the regulation of sulfur isotope fractionation during dissimilatory sulfate reduction.