Reduction of produced elementary sulfur in denitrifying sulfide removal process

Denitrifying sulfide removal (DSR) processes simultaneously convert sulfide, nitrate, and chemical oxygen demand from industrial wastewater into elemental sulfur, dinitrogen gas, and carbon dioxide, respectively. The failure of a DSR process is signaled by high concentrations of sulfide in reactor effluent. Conventionally, DSR reactor failure is blamed for overcompetition for heterotroph to autotroph communities. This study indicates that the elementary sulfur produced by oxidizing sulfide that is a recoverable resource from sulfide-laden wastewaters can be reduced back to sulfide by sulfur-reducing Methanobacterium sp. The Methanobacterium sp. was stimulated with excess organic carbon (acetate) when nitrite was completely consumed by heterotrophic denitrifiers. Adjusting hydraulic retention time of a DSR reactor when nitrite is completely consumed provides an additional control variable for maximizing DSR performance.     

Functional consortium for denitrifying sulfide removal process

Denitrifying sulfide removal (DSR) process simultaneously converts sulfide, nitrate, and chemical oxygen demand from industrial wastewaters to elemental sulfur, nitrogen gas, and carbon dioxide, respectively. This investigation utilizes a dilution-to-extinction approach at 10⁻² to 10⁻⁶ dilutions to elucidate the correlation between the composition of the microbial community and the DSR performance. In the original suspension and in 10⁻² dilution, the strains Stenotrophomonas sp., Thauera sp., and Azoarcus sp. are the heterotrophic denitrifiers and the strains Paracoccus sp. and Pseudomonas sp. are the sulfide-oxidizing denitrifers. The 10⁻⁴ dilution is identified as the functional consortium for the present DSR system, which comprises two functional strains, Stenotrophomonas sp. strain Paracoccus sp. At 10⁻⁶ dilution, all DSR performance was lost. The functions of the constituent cells in the DSR granules were discussed based on data obtained using the dilution-to-extinction approach.     

Enhancing denitrifying sulfide removal with functional strains under micro-aerobic condition

The biological denitrifying sulfide reaction (DSR) frequently proceeds in anaerobic environments since excess oxygen inhibits the activity of the denitrifiers. This study isolated a consortium H7, comprising two strains, Penibacillus sp. and Aneurinibacillus aneurinilyticus. It indicated that the DSR performance with the H7 in a mixotrophic medium is significantly enhanced at high sulfide concentrations. The H7 was inhibited by adding >200 mg l⁻¹ of S²⁻ under anaerobic conditions. However, when 280 mg ⁻¹ of S²⁻ was added, H7 could still degrade some of the sulfide, nitrate and acetate under micro-aerobic conditions. Micro-aerobic conditions stimulated the activity of sulfide oxidase and increased the removal rate of highly concentrated sulfide, reducing the inhibition of sulfide on denitrifiers and improving DSR performance.     

Rapid acclimation of methanogenic granular sludge into denitrifying sulfide removal granules

Rapid formation of denitrifying sulfide removal granules is of practical interest to start up an expanded granular sludge bed reactor for wastewater treatment. This study demonstrates that methanogenic granules can be easily acclimated into DSR granules in one day, removing all 1.30 kg m⁻³ d⁻¹ sulfide and converting >90% of 0.56 kg-N m⁻³d⁻¹ nitrate into di-nitrogen gas. Under high loadings, reactor performance, however, declined. Under high loading rates, sulfide first inhibited the heterotrophic denitrifier (Caldithrix sp.), thereby accumulating nitrite in the system; the autotrophic denitrifier (Pseudomonas sp. C23) was then inhibited by accumulated nitrite, leading to breakdown of the entire DSR process.     

Reduction of bromate by biogenic sulfide produced during microbial sulfur disproportionation

Bromate (BrO₃ ⁻) is a carcinogenic contaminant formed during ozonation of waters that contain trace amounts of bromide. Previous research shows that bromate can be microbially reduced to bromide using organic (i.e. acetate, glucose, ethanol) and inorganic (H₂) electron-donating substrates. In this study, the reduction of bromate by a mixed microbial culture was investigated using elemental sulfur (S⁰) as an electron donor. In batch bioassays performed at 30°C, bromate (0.30 mM) was completely converted to bromide after 10 days and no accumulation of intermediates occurred. Bromate was also reduced in cultures supplemented with thiosulfate and hydrogen sulfide as electron donor. Our results demonstrated that S⁰-disproportionating microorganisms were responsible for the reduction of bromate in cultures spiked with S⁰ through an indirect mechanism involving microbial formation of sulfide and subsequent abiotic reduction of bromate by the biogenic sulfide. Confirmation of this mechanism is the fact that bromate was shown to undergo rapid chemical reduction by sulfide (but not S⁰ or thiosulfate) in abiotic experiments. Bromate concentrations above 0.30 mM inhibited sulfide formation by S⁰-disproportionating bacteria, leading to a decrease in the rate of bromate reduction. The results suggest that biological formation of sulfide from by S⁰ disproportionation could support the chemical removal of bromate without having to directly use sulfide as a reagent.     

Harvesting biohydrogen from cellobiose from sulfide or nitrite-containing wastewaters using Clostridium sp. R1

Harvesting biohydrogen from inhibiting wastewaters is of practical interest since the toxicity of compounds in a wastewater stream commonly prevents the bioenergy content being recovered. The isolated Clostridium sp. R1 is utilized to degrade cellobiose in sulfide or nitrite-containing medium for biohydrogen production. The strain can effectively degrade cellobiose free of severe inhibitory effects at up to 200 mg l⁻¹ sulfide or to 5 mg l⁻¹ nitrite, yielding hydrogen at >2.0 mol H₂ mol⁻¹ cellobiose. Principal metabolites of cellobiose fermentation are acetate and butyrate, with the concentration of the former increases with increasing sulfide and nitrite concentrations. The isolated strain can yield hydrogen from cellobiose in sulfide-laden wastewaters. However, the present of nitrite significantly limit the efficiency of the biohydrogen harvesting process.     

Kinetic limitations during the simultaneous removal of <Emphasis Type="Italic">p</Emphasis>-cresol and sulfide in a denitrifying process

The aim of this study was to evaluate the capacity of a denitrifying consortium to achieve the simultaneous removal of nitrate, sulfide and p-cresol and elucidate the rate-limiting steps in the mixotrophic process. Nitrite reduction appeared as the most evident rate-limiting step in the denitrifying respiratory process. The nitrite reduction rate achieved was up to 57 times lower than the nitrate reduction rate during the simultaneous removal of sulfide and p-cresol. Negligible accumulation of N₂O occurred in the denitrifying cultures corroborating that nitrite reduction was the main rate-limiting step of the respiratory process. A synergistic effect of nitrate and sulfide is proposed to explain the accumulation of nitrite. The study also points at the oxidation of S⁰ as another rate-limiting step in the denitrifying process. Different respiratory rates were achieved with the distinct electron donors provided (p-cresol and sulfide). The oxidation rate of p-cresol (q_CRES) was generally higher (up to 2.6-fold in terms of reducing equivalents) than the sulfide oxidation rate (q_S2−), except for the experiments performed at 100 mg S²⁻ L⁻¹ in which q_S2− was slightly (~1.4-fold in terms of reducing equivalents) higher than q_CRES. The present study provides kinetic information, which should be considered when designing and operating denitrifying reactors to treat industrial wastewaters containing large amounts of sulfurous, nitrogenous and phenolic contaminants such as those generated from petrochemical refineries.     

Biological breakdown of denitrifying sulfide removal process in high-rate expanded granular bed reactor

This work conducted a denitrifying sulfide removal (DSR) test in an expanded granular sludge bed (EGSB) reactor at sustainable loadings of 6.09 kg m⁻³ day⁻¹ for sulfide, 3.11 kg m⁻³ day⁻¹ for nitrate–nitrogen, and 3.27 kg m⁻¹ day⁻¹ for acetate–carbon with >93% efficiency, which is significantly higher than those reported in literature. Strains Pseudomonas sp., Nitrincola sp., and Azoarcus sp. very likely yield heterotrophs. Strains Thermothrix sp. and Sulfurovum sp. are the autotrophs required for the proposed high-rate EGSB-DSR system. The EGSB-DSR reactor experienced two biological breakdowns, one at loadings of 4.87, 2.13, and 1.82 kg m⁻³ day⁻¹; reactor function was restored by increasing nitrate and acetate loadings. Another breakdown occurred at loadings of up to 8.00, 4.08, and 4.50 kg m⁻¹ day⁻¹; the heterotrophic denitrification pathway declined faster than the autotrophic pathway. The mechanism of DSR breakdown is as follows. High sulfide concentration inhibits heterotrophic denitrifiers, and the system therefore accumulates nitrite. Autotrophic denitrifiers are then inhibited by the accumulated nitrite, thereby leading to breakdown of the DSR process.     

Control of malodorous hydrogen sulfide compounds using microbial fuel cell

In this study, a microbial fuel cell (MFC) was used to control malodorous hydrogen sulfide compounds generated from domestic wastewaters. The electricity production demonstrated a distinct pattern of a two-step increase during 170 h of system run: the first maximum current density was 118.6 ± 7.2 mA m^?2 followed by a rebound of current density increase, reaching the second maximum of 176.8 ± 9.4 mA m^?2. The behaviors of the redox potential and the sulfate level in the anode compartment indicated that the microbial production of hydrogen sulfide compounds was suppressed in the first stage, and the hydrogen sulfide compounds generated from the system were removed effectively as a result of their electrochemical oxidation, which contributed to the additional electricity production in the second stage. This was also directly supported by sulfur deposits formed on the anode surface, which was confirmed by analyses on those solids using a scanning electron microscope equipped with energy dispersive X-ray spectroscopy as well as an elemental analyzer. To this end, the overall reduction efficiencies for HS^? and H₂S_(g) were as high as 67.5 and 96.4 %, respectively. The correlations among current density, redox potential, and sulfate level supported the idea that the electricity signal generated in the MFC can be utilized as a potential indicator of malodor control for the domestic wastewater system.     

Recent advances in microbial capture of hydrogen sulfide from sour gas via sulfur‐oxidizing bacteria

Biological desulfurization offers several remarkably environmental advantages of operation at ambient temperature and atmospheric pressure, no demand of toxic chemicals as well as the formation of biologically re‐usable sulfur (S⁰), which has attracted increasing attention compared to conventionally physicochemical approaches in removing hydrogen sulfide from sour gas. However, the low biomass of SOB, the acidification of process solution, the recovery of SOB, and the selectivity of bio‐S⁰ limit its industrial application. Therefore, more efforts should be made in the improvement of the BDS process for its industrial application via different research perspectives. This review summarized the recent research advances in the microbial capture of hydrogen sulfide from sour gas based on strain modification, absorption enhancement, and bioreactor modification. Several efficient solutions to limitations for the BDS process were proposed, which paved the way for the future development of BDS industrialization.     

Factors affecting the performance of microbial fuel cells for sulfide and vanadium (V) treatment

Sulfide and vanadium (V) are pollutants commonly found in wastewaters. A novel approach has been investigated using microbial fuel cell (MFC) technologies by employing sulfide and V(V) as electron donor and acceptor, respectively. This results in oxidizing sulfide and deoxidizing V(V) simultaneously. A series of operating parameters as initial concentration, conductivity, pH, external resistance were carefully examined. The results showed that these factors greatly affected the performance of the MFCs. The average removal rates of about 82.2 and 26.1% were achieved within 72 h operation for sulfide and V(V), respectively, which were accompanied by the maximum power density of about 614.1 mW m⁻² under all tested conditions. The products generated during MFC operation could be deposited, resulting in removing sulfide and V(V) from wastewaters thoroughly.     

Denitrifying sulfide removal and carbon methanogenesis in a mesophilic, methanogenic culture

The inhibitory effects of 90-189 mg l⁻¹ of sulfide and 25-75 mg-N l⁻¹ of nitrate on methanogenesis were investigated in a mixed methanogenic culture using butyrate as carbon source. In the initial phase of 90 mg l⁻¹ S²⁻ test, autotrophic denitrification of nitrate occurred with sulfide as the electron donor. Then the sulfate-reducing strains converted the produced sulfur back to sulfide via heterotrophic oxidation pathway. Methanogenesis was not markedly inhibited when 90 mg l⁻¹ of sulfide was dosed alone. When 25-75 mg-N l⁻¹ of nitrate was presented, initiation of methanogenesis was seriously delayed. Nitrogen oxides (NO_x), the intermediates for nitrate reduction via denitrification pathway, inhibited methanogenesis. The 90 mg l⁻¹ of sulfide favored heterotrophic dissimilatory nitrate reduction to ammonia (DNRA) pathway for nitrate reduction. Possible ways of maximizing methane production from an organic carbon-rich wastewater with high levels of sulfide and nitrate were discussed.     

Search for polythionates in cultures of Chromatium vinosum after sulfide incubation

Cultures of Chromatium vinosum, devoid of sulfur globules, were supplemented with sulfide and incubated under anoxic conditions in the light. The concentrations of sulfide, polysulfides, thiosulfate, polythionates and elemental sulfur (sulfur rings) were monitored for 3 days by ion-chromatography and reversed-phase HPLC. While sulfide disappeared rapidly, thiosulfate and elemental sulfur (S₆, S₇ S₈ rings) were formed. After sulfide depletion, the concentration of thiosulfate decreased fairly rapidly, but elemental sulfur was oxidized very slowly to sulfate. Neither polysulfides (S _x ^2– ), polythionates (S_nO ₆ ^2– , n=4–6), nor other polysulfur compounds could be detected, which is in accordance with the fact that sulfide-grown cells were able to oxidize polysulfide without lag. The nature of the intracellular sulfur globules is discussed.     

Transformation of iron sulfide to greigite by nitrite produced by oil field bacteria

Nitrate, injected into oil fields, can oxidize sulfide formed by sulfate-reducing bacteria (SRB) through the action of nitrate-reducing sulfide-oxidizing bacteria (NR-SOB). When reservoir rock contains siderite (FeCO₃), the sulfide formed is immobilized as iron sulfide minerals, e.g. mackinawite (FeS). The aim of our study was to determine the extent to which oil field NR-SOB can oxidize or transform FeS. Because no NR-SOB capable of growth with FeS were isolated, the well-characterized oil field isolate Sulfurimonas sp. strain CVO was used. When strain CVO was presented with a mixture of chemically formed FeS and dissolved sulfide (HS⁻), it only oxidized the HS⁻. The FeS remained acid soluble and non-magnetic indicating that it was not transformed. In contrast, when the FeS was formed by adding FeCl₂ to a culture of SRB which gradually produced sulfide, precipitating FeS, and to which strain CVO and nitrate were subsequently added, transformation of the FeS to a magnetic, less acid-soluble form was observed. X-ray diffraction and energy-dispersive spectrometry indicated the transformed mineral to be greigite (Fe₃S₄). Addition of nitrite to cultures of SRB, containing microbially formed FeS, was similarly effective. Nitrite reacts chemically with HS⁻ to form polysulfide and sulfur (S⁰), which then transforms SRB-formed FeS to greigite, possibly via a sulfur addition pathway (3FeS + S⁰ → Fe₃S₄). Further chemical transformation to pyrite (FeS₂) is expected at higher temperatures (>60°C). Hence, nitrate injection into oil fields may lead to NR-SOB-mediated and chemical mineral transformations, increasing the sulfide-binding capacity of reservoir rock. Because of mineral volume decreases, these transformations may also increase reservoir injectivity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effect of sulfide on the blue-green algae of hot springs II. Yellowstone National Park

In the Mammoth Springs (Yellowstone National Park) waters with near neutral pH and soluble sulfide (H₂S, HS^–, S^2–) of over 1–2 mg/liter (30–60M) are characterized by substrate covers of phototrophic bacteria (Chloroflexus and aChlorobium-like unicell) above 50C and by a blue-green alga (Spirulina labyrinthiformis) below this temperature.Synechococcus. Mastigocladus, and other blue-green algae typical of most hot springs of western North America are excluded, apparently by sulfide. The sulfide-adaptedSpirulina photosynthesized at maximum rates at 45C and at approximately 300 to 700Ein/m²/sec of visible radiation. Sulfide (0.6–1.2 mM) severely poisoned photosynthesis of nonadapted populations, but those continuously exposed to over 30M tolerated at least 1 mM without inhibition. A normal¹⁴C-HCO₃ photoincorporation rate was sustained with 0.6–1 mM sulfide in the presence of DCMU (7M) or NH₂OH (0.2 mM), although both of these photosystem II inhibitors prevented photoincorporation without sulfide. Other sulfur-containing compounds (S₂O₃ ^2– SO₃ ^2–, S₂O₄ ^2– thioglycolic acid cysteine) were unable to relieve DCMU inhibition. The lowering of the photoincorporation rate by preferentially irradiating photosystem I was also relieved by sulfide. The most tenable explanation of these results is that sulfide is used as a photo-reductant of CO₂, at least when photosystem II is inhibited. It is suggested that in some blue-green algae photosystem II is poisoned by a low sulfide concentration, thus making these algae sulfidedependent if they are to continue photosynthesizing in a sulfide environment. Presumably a sulfidecytochrome reductase enzyme system must be synthesized for sulfide to be used as a photo-reductant.     

Is hydrogen sulfide a circulating “gasotransmitter” in vertebrate blood?

Hydrogen sulfide (H₂S) is gaining acceptance as a signaling molecule and has been shown to elicit a variety of biological effects at concentrations between 10 and 1000 μmol/l. Dissolved H₂S is a weak acid in equilibrium with HS⁻ and S²⁻ and under physiological conditions these species, collectively referred to as sulfide, exist in the approximate ratio of 20% H₂S, 80% HS⁻ and 0% S²⁻. Numerous analyses over the past 8 years have reported plasma or blood sulfide concentrations also in this range, typically between 30 and 300 μmol/l, thus supporting the biological studies. However, there is some question whether or not these concentrations are physiological. First, many of these values have been obtained from indirect methods using relatively harsh chemical conditions. Second, most studies conducted prior to 2000 failed to find blood sulfide in micromolar concentrations while others showed that radiolabeled ³⁵S-sulfide is rapidly removed from blood and that mammals have a relatively high capacity to metabolize exogenously administered sulfide. Very recent studies using H₂S gas-sensing electrodes to directly measure sulfide in plasma or blood, or HPLC analysis of head-space gas, have also indicated that sulfide does not circulate at micromolar levels and is rapidly consumed by blood or tissues. Third, micromolar concentrations of sulfide in blood or exhaled air should be, but are not, malodorous. Fourth, estimates of dietary sulfur necessary to sustain micromolar levels of plasma sulfide greatly exceed the daily intake. Collectively, these studies imply that many of the biological effects of sulfide are only achieved at supra-physiological concentrations and they question whether circulating sulfide is a physiologically relevant signaling molecule. This review examines the blood/plasma sulfide measurements that have been reported over the past 30 years from the perspective of the analytical methods used and the potential sources of error.     

13C-NMR Study of propionate metabolism by sludges from bioreactors treating sulfate and sulfide rich wastewater

Applications of nuclear magnetic resonance (NMR) to study a variety of physiological and biochemical aspects of bacteria with a role in the sulfur cycle are reviewed. Then, a case-study of high resolution¹³ C-NMR spectroscopy on sludges from bioreactors used for treating sulfate and sulfide rich wastewaters is presented.¹³ C-NMR was used to study the effect of sulfate and butyrate on propionate conversion by mesophilic anaerobic (methanogenic and sulfate reducing) granular sludge and microaerobic (sulfide oxidizing) flocculant sludge. In the presence of sulfate, propionate was degraded via the randomising pathway in all sludge types investigated. This was evidenced by scrambling of [3-¹³C]propionate into [2-¹³C]propionate and the formation of acetate equally labeled in the C₁ and C₂ position. In the absence of sulfate, [3-¹³C]propionate scrambled to a lesser extend without being degraded further. Anaerobic sludges converted [2,3-¹³C]propionate partly into the higher fatty acid 2-methyl[2,3-¹³C]butyrate during the simultaneous degradation of [2,3-¹³C]propionate and butyrate. [4,5-¹³C]valerate was also formed in the methanogenic sludges. Up to 10% of the propionate present was converted via these alternative degradation routes. Labeled butyrate was not detected in the incubations, suggesting that reductive carboxylation of propionate does not occur in the sludges.     

Detoxification of environmental sulfide to sulfane sulfur in the intertidal sipunculid Phascolosoma arcuatum

The capability of Phascolosoma arcuatum to detoxify sulfide in anaerobic conditions was examined. Sulfane sulfur, which underwent cold cyanolysis, was the major excretory end product of sulfide detoxification during anoxia. Thiosulfate was not excreted into the external medium. Instead, it was absorbed by P. arcuatum and its absorption was stimulated by the presence of sodium sulfide (Na₂S) in the incubation medium. The effective formation and excretion of sulfane sulfur by P.␣arcuatum required the presence of both Na₂S and sodium thiosulfate (Na₂S₂O₃). Results obtained indicate that rhodanese might be involved in sulfide detoxification in this sipunculid. Rhodanese could act as a catalyst in the transfer of sulfur atoms from thiosulfate to HS⁻. The body wall and the introvert were the main sites of sulfide detoxification. However, it is unlikely that epibiotic bacteria associated with the outside surface of the worm were involved in the detoxification process. A time-course study on the contents of thiosulfate and sulfane sulfur in the body wall of P. arcuatum incubated anaerobically in the presence of Na₂S + Na₂S₂O₃ verified that thiosulfate absorbed was utilized to detoxify sulfide to sulfane sulfur. Accepted: 24 October 1996     

Synthesis and crystal structure of a highly selective colorimetric and fluorometric sensor for hydrogen sulfide

A novel Cu(II) complex chemosensor for hydrogen sulfide with azo as the colorimetric group has been synthesized. The complex and ligand crystals were obtained and the molecular structures were characterized by X‐ray diffraction and Electrospray ionization High resolution mass spectrometer (ESI‐HRMS). The photophysical and recognition properties were examined. The complex can recognize S^2?, with an obvious color change from yellow to red based on a copper ion complex displacement mechanism. By contrast, no obvious changes were observed in the presence of other anions (AcO^?, H₂PO₄^?, F^?, Cl^?, Br^? and I^?). We present a simple, easily prepared, yet efficient, inorganic reaction‐based sensor for the detection of S^2?. The complex should have many chemical and analytical applications in the sensing of hydrogen sulfide.     

Characterization of elemental sulfur in isolated intact spinach chloroplasts

Incubation of intact spinach (Spinacia oleracea L.) chloroplasts in the presence of ³⁵SO₄²⁻ resulted in the light-dependent formation of a chloroform-soluble sulfur-containing compound distinct from sulfolipid. We have identified this compound as the most stable form (S₈) of elemental sulfur (S⁰, valence state for S = O) by mass spectrometry. It is possible that elemental sulfur (S⁰) was formed by oxidation of bound sulfide, i.e. after the photoreduction of sulfate to sulfide by intact chloroplasts, and released as S₈ under the experimental conditions used for analysis.