Electron Donor For Sulfate Reduction Research Articles

Desulfofustis limnaeus sp. nov., a freshwater sulfate-reducing bacterium isolated from marsh soil.

A novel sulfate-reducing bacterium, strain PPLLT, was isolated from marsh soil. Cells of strain PPLLT were rod-shaped with length of 1.5μm and width of 0.7μm. Growth was observed at 22-37°C (optimum 35°C) and pH 6.8-8.4 (optimum 7.3). Lactate, succinate, fumarate, formate and malate were utilized as electron donors for sulfate reduction. Fermentative growth was not observed on tested organic acids. Besides sulfate, sulfite, thiosulfate and elemental sulfur were utilized as electron acceptors. Hydrogen is used only in the presence acetate or yeast extract. The major fatty acid was C16:0. The complete genome of strain PPLLT was composed of a circular chromosome with length of 4.2 Mbp and G + C content of 57.7mol%. Sequence analysis of the 16S rRNA gene showed that strain PPLLT was affiliated with the genus Desulfofustis in the family Desulfocapsaceae. On the basis of differences in the phylogenetic and phenotypic properties between the strain and the type strain of the genus Desulfofustis, strain PPLLT (DSM 110475T = JCM 39161T) is proposed as the type strain of a new species, with name of Desulfofustis limnaeus sp. nov.

Comparison of different small molecular weight alcohols for sustaining sulfidogenic bioreactors maintained at moderately low pH.

Sulfate-reducing bacteria (SRB) catalyse the dissimilatory reduction of sulfate to hydrogen sulfide using a wide range of small molecular weight organic compounds, and hydrogen, as electron donors. Here we report the effects of different combinations of small molecular weight alcohols on the performance and bacterial composition of a moderately low pH sulfidogenic bioreactor (pH 4.0–5.5) operated at 35°C in continuous flow mode. Ethanol alone and methanol or ethanol used in combination with glycerol were evaluated based on their equivalent amounts of carbon. Although evidenced that methanol was utilised as electron donor to fuel sulfidogenesis at pH 5.5, rates of sulfate reduction/sulfide production were negatively impacted when this alcohol was first introduced to the system, though these rates increased in subsequent phases as a result of adaptation of the microbial community. Further increased dosage of methanol again caused rates of sulfidogenesis to decrease. Methanol addition resulted in perturbations of the bioreactor microbial community, and species not previously detected were present in relatively large abundance, including the sulfate-reducer Desulfovibrio desulfuricans. Ethanol utilization was evidenced by the increase in rates of sulfidogenesis as the dosage of ethanol increased, with rates being highest when the bioreactor was fed with ethanol alone. Concentrations of acetate in the effluent liquor also increased (up to 8 mM) as a result of incomplete oxidation of ethanol. This alcohol continued to be used as the electron donor for sulfate reduction when the bioreactor pH was decreased incrementally (to pH 4.0), but rates of sulfidogenesis decreased. The relative abundance of Dv. desulfuricans diminished as the bioreactor pH was lowered, while that of the acidophilic Firmicute Desulfosporosinus acididurans increased. This study has shown that all three alcohols can be used to fuel microbial sulfidogenesis in moderately acidic liquors, though the cost-effectiveness, availability and toxicity to the microbial community will dictate the choice of substrate.

Desulfosporosinus metallidurans sp. nov., an acidophilic, metal-resistant sulfate-reducing bacterium from acid mine drainage.

A novel, spore-forming, acidophilic and metal-resistant sulfate-reducing bacterium, strain OLT, was isolated from a microbial mat in a tailing dam at a gold ore mining site. Cells were slightly curved immotile rods, 0.5 µm in diameter and 2.0-3.0 µm long. Cells were stained Gram-negative, despite the Gram-positive cell structure revealed by electron microscopy of ultrathin layers. OLT grew at pH 4.0-7.0 with an optimum at 5.5. OLT utilised H2, lactate, pyruvate, malate, formate, propionate, ethanol, glycerol, glucose, fructose, sucrose, peptone and tryptone as electron donors for sulfate reduction. Sulfate, sulfite, thiosulfate, nitrate and fumarate were used as electron acceptors in the presence of lactate. Elemental sulfur, iron (III), and arsenate did not serve as electron acceptors. The major cellular fatty acids were C16:1ω7c (39.0 %) and C16 : 0 (12.1 %). The draft genome of OLT was 5.29 Mb in size and contained 4909 protein-coding genes. The 16S rRNA gene sequence placed OLT within the phylum Firmicutes, class Clostridia, family Peptococcaceae, genus Desulfosporosinus. Desulfosporosinus nitroreducens 59.4BT was the closest relative with 97.6 % sequence similarity. On the basis of phenotypic and phylogenetic characteristics, strain OLT represents a novel species within the genus Desulfosporosinus, for which we propose the name Desulfosporosinus metallidurans sp. nov. with the type strain OLT (=DSM 104464T=VKM В-3021T).

Biological Sulfate Reduction Using Gaseous Substrates To Treat Acid Mine Drainage

Acid mine drainage (AMD) is a serious environmental problem due to its high sulfate and heavy metal content. In comparison with the conventionally used physico-chemical methods, biological methods involving sulfate-reducing bacteria (SRB) offer a green and sustainable way to treat AMD. Biological sulfate reduction requires an efficient and low-cost electron donor. This paper overviews different gaseous substrates as electron donor that can be used for sulfate reduction to treat AMD. The use of gaseous substrates as electron donor for sulfate reduction is advantageous as it avoids dilution of wastewater and avoids secondary pollution problems arising from unutilized electron donor. Among the different gaseous substrates for sulfate reduction, hydrogen (H2) is more energetically favourable to the sulfate-reducing microorganisms. Carbon monoxide (CO) is a low-cost waste gas substrate for sulfate reduction, but its toxicity limits its applications. Only a limited number of specialized slow-growing microorganisms can utilize methane (CH4) coupled to sulfate reduction under anaerobic conditions. Different gases (H2, CO and CH4) are evaluated as potential electron donor for biological sulfate reduction to treat AMD. Several bacterial and archaeal species can use these gases as the sole electron donor for reducing sulfate to sulfide. Heavy metals present in the AMD can be removed by sulfidic precipitation although high concentrations of heavy metals can inhibit SRB activity, thus reducing the process efficiency. In addition, proper choice of the bioreactor system has a great influence on the AMD treatment efficiency by biological sulfate reduction using gaseous substrates.

Sulfate and metals removal from acid mine drainage in a horizontal anaerobic immobilized biomass (HAIB) reactor

The acid mine drainage (AMD) can causes negative impacts to the environment. Physico-chemical methods to treat AMD can have high operational costs. Through passive biological methods, such as anaerobic reactors, sulfate reduction, and recovery of metals are promoted. This study evaluated the performance of a horizontal anaerobic immobilized biomass (HAIB) reactor for the treatment of synthetic AMD using polyurethane foam as support material, and anaerobic sludge as inoculum. Ethanol was used as an electron donor for sulfate reduction, resulting in an influent chemical oxygen demand (COD) in the range of 500–1,500 mg/L and COD/sulfate ratio at 1. A gradual increase of sulfate and COD concentration was applied that resulted in COD removal efficiencies higher than 78%, and sulfate removal efficiencies of 80%. Higher sulfate and COD concentrations associated with higher hydraulic retention times (36 h) proved to be a better strategy for sulfate removal. The HAIB reactor was able to accommodate an increase in the SLR up to 2.25 g SO42−/L d−1 which achieved the greatest performance on the entire process. Moreover, the reactor proved a suitable alternative for reaching high levels of metal removal (86.95 for Zn, 98.79% for Fe, and 99.59% for Cu).

Influence of Organic Carbon Sources on Metal Removal from Mine Impacted Water Using Sulfate-Reducing Bacteria Bioreactors in Cold Climates

Acid mine drainage (AMD) is a major environmental challenge for the mining industry in northern climates. Laboratory-scale experiments were conducted to test various simple and complex carbon sources available in the Yukon as electron donors for sulfate reduction to allow the subsequent removal of Cd and Zn from a Yukon AMD. The 1 L capacity bioreactors were monitored biweekly at 5 °C. After 162 days, a diminution of both total organic carbon and sulfate concentrations was observed in all bioreactors. A long adaptation period was necessary before consumption of the carbon source started, which might be due to the cold temperature. Simple organic sources of carbon (methanol and ethylene glycol) and complex organic sources of carbon (potato oil, brewery residue, peat, and straw) were used to support SRB growth. Methanol and ethylene glycol led to a diminution of sulfate concentrations of 71.2 and 36.9%, respectively, while the decrease of sulfate concentrations was limited to 13.8 and 5.3% when using peat and straw, respectively.

Impact of light oil toxicity on sulfide production by acetate-oxidizing, sulfate-reducing bacteria

Souring, the reduction of sulfate to sulfide by sulfate-reducing bacteria (SRB) is a serious problem for the oil and gas industry. Produced waters from oil fields, injected with seawater, often contain high concentrations of acetate and sulfate, indicating a lack of activity of SRB using acetate as electron donor for sulfate reduction. Experiments with an enrichment of lactate- and sulfate-utilizing SRB from a shale oil field, indicated oxidation of lactate to acetate and subsequent oxidation of acetate in the absence of added shale oil. However, acetate was not oxidized in the presence of shale oil. In view of these results we hypothesized that acetate-utilizing SRB were inhibited by low molecular weight components present in the light shale oil, which had an American Petroleum Institute gravity (API_G) of 38°. Low molecular weight components decrease in concentration with decreasing API_G of the oil. We therefore tested the effects of diluent (83° API_G, consisting predominantly of C5-C7 alkanes), light oils (38, 41 and 46° API_G) and heavy oil (16° API_G), as well as of selected light oil components (toluene, pentane and heptane). Acetate-dependent sulfate reduction by a pure culture of Desulfobacter postgatei at 30 °C was inhibited by diluent and light oils, but not by heavy oil. Similar results were obtained with a shale gas field source water enrichment (SWE), which contained Desulfotomaculum and Desulfoarculus as the most prominent acetate-utilizing SRB. Use of dilutions of oils in heptamethylnonane indicated that diluent inhibited acetate-utilizing SRB in SWE more strongly than light oils. Use of pure oil components indicated toluene to be more inhibitory than either pentane or heptane. GC-MS analysis confirmed that diluent had the highest concentrations of these low molecular weight components, explaining its strong inhibitory effect. Inhibition of acetate-utilizing SRB by light oil components, causing acetate accumulation in produced waters, may contribute to souring control and should be incorporated in souring control models.

Microbial Sulfate Reduction Potential in Coal-Bearing Sediments Down to ~2.5 km below the Seafloor off Shimokita Peninsula, Japan.

Sulfate reduction is the predominant anaerobic microbial process of organic matter mineralization in marine sediments, with recent studies revealing that sulfate reduction not only occurs in sulfate-rich sediments, but even extends to deeper, methanogenic sediments at very low background concentrations of sulfate. Using samples retrieved off the Shimokita Peninsula, Japan, during the Integrated Ocean Drilling Program (IODP) Expedition 337, we measured potential sulfate reduction rates by slurry incubations with 35S-labeled sulfate in deep methanogenic sediments between 1276.75 and 2456.75 meters below the seafloor. Potential sulfate reduction rates were generally extremely low (mostly below 0.1 pmol cm−3 d−1) but showed elevated values (up to 1.8 pmol cm−3 d−1) in a coal-bearing interval (Unit III). A measured increase in hydrogenase activity in the coal-bearing horizons coincided with this local increase in potential sulfate reduction rates. This paired enzymatic response suggests that hydrogen is a potentially important electron donor for sulfate reduction in the deep coalbed biosphere. By contrast, no stimulation of sulfate reduction rates was observed in treatments where methane was added as an electron donor. In the deep coalbeds, small amounts of sulfate might be provided by a cryptic sulfur cycle. The isotopically very heavy pyrites (δ34S = +43‰) found in this horizon is consistent with its formation via microbial sulfate reduction that has been continuously utilizing a small, increasingly 34S-enriched sulfate reservoir over geologic time scales. Although our results do not represent in-situ activity, and the sulfate reducers might only have persisted in a dormant, spore-like state, our findings show that organisms capable of sulfate reduction have survived in deep methanogenic sediments over more than 20 Ma. This highlights the ability of sulfate-reducers to persist over geological timespans even in sulfate-depleted environments. Our study moreover represents the deepest evidence of a potential for sulfate reduction in marine sediments to date.

Promotion of Ni2+ removal by masking toxicity to sulfate-reducing bacteria: addition of citrate.

The sulfate-reducing bioprocess is a promising technology for the treatment of heavy metal-containing wastewater. This work was conducted to investigate the possibility of promoting heavy metal removal by the addition of citrate to mask Ni2+ toxicity to sulfate-reducing bacteria (SRB) in batch reactors. SRB growth was completely inhibited in Ni2+-containing medium (1 mM) when lactate served as the sole carbon resource, leading to no sulfate reduction and Ni2+ removal. However, after the addition of citrate, SRB grew well, and sulfate was quickly reduced to sulfide. Simultaneously, the Ni-citrate complex was biodegraded to Ni2+ and acetate. The NiS precipitate was then formed, and Ni2+ was completely removed from the solution. It was suggested that the addition of citrate greatly alleviates Ni2+ toxicity to SRB and improves the removal of Ni2+, which was confirmed by quantitative real-time PCR targeting dissimilatory sulfite reductase (dsrAB) genes. Analysis of the carbon metabolism indicated that lactate instead of acetate served as the electron donor for sulfate reduction. This study offers a potential approach to increase the removal of heavy metals from wastewater in the single stage SRB-based bioprocess.

Reclassification of Desulfobacterium anilini as Desulfatiglans anilini comb. nov. within Desulfatiglans gen. nov., and description of a 4-chlorophenol-degrading sulfate-reducing bacterium, Desulfatiglans parachlorophenolica sp. nov.

A strictly anaerobic, mesophilic, sulfate-reducing bacterial strain (DS(T)), isolated from river sediment contaminated with volatile organic compounds, was characterized phenotypically and phylogenetically. Cells were Gram-reaction-negative, non-motile short rods. For growth, optimum NaCl concentration was 0.9 g l(-1), optimum temperature was 30 °C and optimum pH was 7.2. Strain DS(T) utilized phenol, benzoate, 4-hydroxybenzoate, 4-methylphenol, 4-chlorophenol, acetate, butyrate and pyruvate as electron donors for sulfate reduction. Electron donors were completely oxidized. Strain DS(T) did not utilize sulfite, thiosulfate or nitrate as electron acceptors. The genomic DNA G+C content of strain DS(T) was 58.9 mol%. Major cellular fatty acids were iso-C14 : 0, anteiso-C15 : 0 and C18 : 1ω7c. Phylogenetic analyses based on the 16S rRNA gene indicated its closest relatives were strains of Desulfobacterium anilini (about 98-99 % sequence similarity) but the DNA-DNA hybridization value with Desulfobacterium anilini Ani1(T) was around 40 %. Although strain DS(T) and its relatives shared most phenotypic and chemotaxonomic characteristics, the utilization of 4-chlorophenol, the range of electron acceptors and the optimum growth conditions differed. Strain DS(T) is closely related to strains of Desulfobacterium anilini, but constitutes a different species within the genus. Based on phylogeny, phenotypic characteristics and chemotaxonomic characteristics, strain DS(T) and Desulfobacterium anilini were clearly different from strains of other species of the genus Desulfobacterium. We thus propose the reclassification of Desulfobacterium anilini within a new genus, Desulfatiglans gen. nov., as Desulfatiglans anilini comb. nov. We also propose Desulfatiglans parachlorophenolica sp. nov. to accommodate strain DS(T). The type strain is DS(T) ( = JCM 19179(T) = DSM 27197(T)).

The role of acetogens in microbially influenced corrosion of steel.

Microbially influenced corrosion (MIC) of iron (Fe0) by sulfate-reducing bacteria (SRB) has been studied extensively. Through a mechanism, that is still poorly understood, electrons or hydrogen (H2) molecules are removed from the metal surface and used as electron donor for sulfate reduction. The resulting ferrous ions precipitate in part with the sulfide produced, forming characteristic black iron sulfide. Hydrogenotrophic methanogens can also contribute to MIC. Incubation of pipeline water samples, containing bicarbonate and some sulfate, in serum bottles with steel coupons and a headspace of 10% (vol/vol) CO2 and 90% N2, indicated formation of acetate and methane. Incubation of these samples in serum bottles, containing medium with coupons and bicarbonate but no sulfate, also indicated that formation of acetate preceded the formation of methane. Microbial community analyses of these enrichments indicated the presence of Acetobacterium, as well as of hydrogenotrophic and acetotrophic methanogens. The formation of acetate by homoacetogens, such as Acetobacterium woodii from H2 (or Fe0) and CO2, is potentially important, because acetate is a required carbon source for many SRB growing with H2 and sulfate. A consortium of the SRB Desulfovibrio vulgaris Hildenborough and A. woodii was able to grow in defined medium with H2, CO2, and sulfate, because A. woodii provides the acetate, needed by D. vulgaris under these conditions. Likewise, general corrosion rates of metal coupons incubated with D. vulgaris in the presence of acetate or in the presence of A. woodii were higher than in the absence of acetate or A. woodii, respectively. An extended MIC model capturing these results is presented.

Abiotic and biotic factors influencing the mobility of arsenic in groundwater of a through-flow island in the Okavango Delta, Botswana

Summary The Okavango Delta of Botswana is a large arid-zone wetland comprising 20,000 km2 of permanent and seasonal floodplains and over 100,000 islands. It has been shown that island groundwater can have very high dissolved arsenic (As) concentration, but the abiotic and biotic controls on As mobility are not well understood in this setting. At New Island, an island located in the seasonal swamp, dissolved As concentration increased from below detection limits in the surface water to 180 μg/L in groundwater, present as As(III) species. We investigated the relative importance of hydrologic, geochemical, and geomicrobial processes, as well as influences of recent extreme flooding events, in mobilizing and sequestering As in the shallow groundwater system under this island. Our results suggest that evapotranspiration and through-flow conditions control the location of the high arsenic zone. A combination of processes is hypothesized to control elevated As in the concentration zone of New Island: high evapotranspiration rates concentrate As and other solutes, more alkaline pH leads to desorption of arsenic or dissolution of arsenic sulfides, and formation of thioarsenic complexes acts to keep arsenic in solution. Evidence from X-ray absorption near-edge structure spectroscopy (XANES) and sulfate reducing bacteria (SRB) measurements further suggests that SRBs influence arsenic sequestration as orpiment (As2S3). Although dissolved organic matter (DOM) was not significantly correlated to dissolved As in the groundwater, our results suggest that DOM may serve as an electron donor for sulfate reduction or other microbial reactions that influence redox state and As mobility. These results have important implications for water management in the region and in other large wetland environments. The processes evaluated in this study are also relevant for arsenic removal in subsurface constructed wetland systems that may exhibit rapidly changing processes over small spatial scales.

Acetate Production from Oil under Sulfate-Reducing Conditions in Bioreactors Injected with Sulfate and Nitrate

Oil production by water injection can cause souring in which sulfate in the injection water is reduced to sulfide by resident sulfate-reducing bacteria (SRB). Sulfate (2 mM) in medium injected at a rate of 1 pore volume per day into upflow bioreactors containing residual heavy oil from the Medicine Hat Glauconitic C field was nearly completely reduced to sulfide, and this was associated with the generation of 3 to 4 mM acetate. Inclusion of 4 mM nitrate inhibited souring for 60 days, after which complete sulfate reduction and associated acetate production were once again observed. Sulfate reduction was permanently inhibited when 100 mM nitrate was injected by the nitrite formed under these conditions. Pulsed injection of 4 or 100 mM nitrate inhibited sulfate reduction temporarily. Sulfate reduction resumed once nitrate injection was stopped and was associated with the production of acetate in all cases. The stoichiometry of acetate formation (3 to 4 mM formed per 2 mM sulfate reduced) is consistent with a mechanism in which oil alkanes and water are metabolized to acetate and hydrogen by fermentative and syntrophic bacteria (K. Zengler et al., Nature 401:266-269, 1999), with the hydrogen being used by SRB to reduce sulfate to sulfide. In support of this model, microbial community analyses by pyrosequencing indicated SRB of the genus Desulfovibrio, which use hydrogen but not acetate as an electron donor for sulfate reduction, to be a major community component. The model explains the high concentrations of acetate that are sometimes found in waters produced from water-injected oil fields.

Temperature and feed strategy effects on sulfate and organic matter removal in an AnSBB

The objective of this work was to analyze the interaction effects between temperature, feed strategy and COD/[SO 4 2−] levels, maintaining the same ratio, on sulfate and organic matter removal efficiency from a synthetic wastewater. This work is thus a continuation of Archilha et al. (2010) who studied the effect of feed strategy at 30 °C using different COD/[SO 4 2−] ratios and levels. A 3.7-L anaerobic sequencing batch reactor with recirculation of the liquid phase and which contained immobilized biomass on polyurethane foam (AnSBBR) was used to treat 2.0 L synthetic wastewater in 8 h cycles. The temperatures of 15, 22.5 and 30 °C with two feed strategies were assessed: (a) batch and (b) batch followed by fed-batch. In strategy (a) the reactor was fed in 10 min with 2 L wastewater containing sulfate and carbon sources. In strategy (b) 1.2 L wastewater (containing only the sulfate source) was fed during the first 10 min of the cycle and the remaining 0.8 L (containing only the carbon source) in 240 min. Based on COD/[SO 4 2−] = 1 and on the organic matter (0.5 and 1.5 gCOD/L) and sulfate (0.5 and 1.5 gSO 4 2−/L) concentrations, the sulfate and organic matter loading rates applied were 1.5 and 4.5 g/L.d, i.e., same COD/[SO 4 2−] ratio (=1) but different levels (1.5/1.5 and 4.5/4.5 gCOD/gSO 4 2−). When reactor feed was 1.5 gCOD/L.d and 1.5 gSO 4 2−/L.d, gradual feeding (strategy b) showed to favor sulfate and organic matter removal in the investigated temperature range, indicating improved utilization of the electron donor for sulfate reduction. Sulfate removal efficiencies were 87.9; 86.3 and 84.4%, and organic matter removal efficiencies 95.2; 86.5 and 80.8% at operation temperatures of 30; 22.5 and 15 °C, respectively. On the other hand, when feeding was 4.5 gCOD/L.d and 4.5 gSO 4 2−/L.d, gradual feeding did not favor sulfate removal, indicating that gradual feeding of the electron donor did not improve sulfate reduction.

Full-scale anaerobic sequencing batch biofilm reactor for sulfate-rich wastewater treatment

This paper describes the performance and biofilm characteristics of a full-scale anaerobic sequencing batch biofilm reactor (ASBBR; 20 m3) containing biomass immobilized on an inert support (mineral coal) for the treatment of industrial wastewater containing a high sulfate concentration. The AS-BBR reactor was operated during 110 cycles (48 h each) at sulfate loading rates ranging from 6.9 to 62.4 kgSO2- 4/cycle corresponding to sulfate concentrations of 0.58–5.2 kgSO2- 4/L. Domestic sewage and ethanol were utilized as electron donors for sulfate reduction. After 71 cycles the mean sulfate removal efficiency was 99%, demonstrating a high potential for biological sulfate reduction. The biofilm formed in the reactor occurred in two different patterns, one at the beginning of the colonization and the other of a mature biofilm. These different colonization paterns are due to the low adhesion of the microorganisms on the inert support in the start-up period. The biofilm population is mainly made up of syntrophic consortia among sulfate-reducing bacteria and methanogenic archaea such as Methanosaeta spp.

Desulfovibrio butyratiphilus sp. nov., a Gram-negative, butyrate-oxidizing, sulfate-reducing bacterium isolated from an anaerobic municipal sewage sludge digester

Strictly anaerobic, mesophilic, sulfate-reducing bacterial strains were isolated from two anaerobic municipal sewage sludge digesters. One representative strain (BSY(T)) was characterized phenotypically and phylogenetically. Cells were Gram-negative, motile by means of a single polar flagellum, non-spore-forming, curved rods. Cells had desulfoviridin and cytochrome type c. Catalase and oxidase activities were not detected. The optimum NaCl concentration for growth was 0.5 % (w/v). The optimum temperature was 35 degrees C and the optimum pH was 7.1. Strain BSY(T) utilized butyrate, 2-methylbutyrate, valerate, pyruvate, lactate, ethanol, 1-propanol, butanol and H(2) as electron donors for sulfate reduction. This strain grew lithoautotrophically with H(2)/CO(2) under sulfate-reducing conditions. Most organic electron donors were incompletely oxidized to mainly acetate, whereas 2-methylbutyrate and valerate were oxidized to equivalent amounts of acetate and propionate. Strain BSY(T) utilized thiosulfate as an electron acceptor, and grew with pyruvate in the absence of electron acceptors. The genomic DNA G+C content of strain BSY(T) was 63.3 mol%. Menaquinone MK-6(H(2)) was the major respiratory quinone. Major cellular fatty acids were C(14 : 0), C(16 : 0), C(16 : 1) omega7 and C(18 : 1)omega7. Phylogenetic analyses based on 16S rRNA and dissimilatory sulfite-reductase beta-subunit gene sequences assigned strain BSY(T) to the genus Desulfovibrio in the family Desulfovibrionaceae within the class Deltaproteobacteria . Its closest recognized relative based on 16S rRNA gene sequences was the type strain of Desulfovibrio putealis (95.3 % similarity). On the basis of significant differences in 16S rRNA gene sequences and phenotypic characteristics, the sewage sludge strains are considered to represent a single novel species of the genus Desulfovibrio, for which the name Desulfovibrio butyratiphilus sp. nov. is proposed. The type strain is BSY(T) (=JCM 15519(T)=DSM 21556(T)).

Biotechnological aspects of sulfate reduction with methane as electron donor

Biological sulfate reduction can be used for the removal and recovery of oxidized sulfur compounds and metals from waste streams. However, the costs of conventional electron donors, like hydrogen and ethanol, limit the application possibilities. Methane from natural gas or biogas would be a more attractive electron donor. Sulfate reduction with methane as electron donor prevails in marine sediments. Recently, several authors succeeded in cultivating the responsible microorganisms in vitro. In addition, the process has been studied in bioreactors. These studies have opened up the possibility to use methane as electron donor for sulfate reduction in wastewater and gas treatment. However, the obtained growth rates of the responsible microorganisms are extremely low, which would be a major limitation for applications. Therefore, further research should focus on novel cultivation techniques.

The treatment of sulfate-rich wastewater using an anaerobic sequencing batch biofilm pilot-scale reactor

This paper presents the results from 92 cycles of an anaerobic sequencing batch biofilm reactor containing biomass immobilized on inert support (mineral coal) applied for the treatment of an industrial wastewater containing high sulfate concentration. The pilot-scale reactor, with a total volume of 1.2 m 3 , was operated at sulfate loading rates ranging from 0.15 to 1.90 kgSO 4 2− /cycle (48 h — cycle) corresponding to sulfate concentrations of 0.25 to 3.0 gSO 4 2− l − 1 . Domestic sewage and ethanol were utilized as electron donors for sulfate reduction. Influent sulfate concentrations were increased in order to evaluate the minimum COD/sulfate ratio at which high reactor performance could be maintained. The mean sulfate removal efficiency remained between the range of 88 to 92% at several sulfate concentrations. Temporal profiles along the 48 h cycles were carried out under stable operation at sulfate concentrations of 1.0, 2.0 and 3.0 gSO 4 2− l − 1 . Sulfate removal reached 99% for cycle times of 15, 25, and 30 h, and the effluents sulfate concentrations were lower than 8 mgSO 4 2− l − 1 . The results demonstrate the potential applicability of the anaerobic configuration for the biological treatment of sulfate-rich wastewaters.

Effect of the sulfide concentration on zinc bio-precipitation in a single stage sulfidogenic bioreactor at pH 5.5

Dissolved zinc is present in natural waters and process streams generated by the mining and metallurgical industry. These streams usually have a low pH. By using sulfate reducing bacteria, sulfide can be produced that precipitates with zinc as zinc sulfide (sphalerite), which can be easily separated from the wastewater and even reused as zinc concentrate. In this study, a sulfate reducing gas-lift bioreactor was operated at pH 5.5 using hydrogen as electron donor for sulfate reduction. We demonstrate effective zinc removal (7.2 mmol L −1 d −1) with low zinc effluent concentrations (0.65–8.8 μM) in a system combining sulfide generation by sulfate reducing bacteria (7.2–10.6 mmol SO 4 2− L −1 d −1) at low pH (5.5) with the bio-precipitation of crystalline sphalerite. To investigate the effect of the sulfide excess on the settling properties of the sphalerite precipitates, the sulfide excess concentration was varied about two orders of magnitude (0.008–2.2 mM). The results show that crystalline sphalerite was formed in all cases, but larger particles with better settling properties were formed at lower sulfide concentrations.

Citric acid wastewater as electron donor for biological sulfate reduction

Citrate-containing wastewater is used as electron donor for sulfate reduction in a biological treatment plant for the removal of sulfate. The pathway of citrate conversion coupled to sulfate reduction and the microorganisms involved were investigated. Citrate was not a direct electron donor for the sulfate-reducing bacteria. Instead, citrate was fermented to mainly acetate and formate. These fermentation products served as electron donors for the sulfate-reducing bacteria. Sulfate reduction activities of the reactor biomass with acetate and formate were sufficiently high to explain the sulfate reduction rates that are required for the process. Two citrate-fermenting bacteria were isolated. Strain R210 was closest related to Trichococcus pasteurii (99.5% ribosomal RNA (rRNA) gene sequence similarity). The closest relative of strain S101 was Veillonella montepellierensis with an rRNA gene sequence similarity of 96.7%. Both strains had a complementary substrate range.