Oxidation of hydrogen sulfide by Thiobacillus denitrificans: desulfurization of natural gas

It has been demonstrated that Thiobacillus denitrificans may be readily cultivated anaerobically in batch reactors on H(2)S (g) under sulfide-limiting conditions. Under these conditions sulfide concentrations in the culture medium were less than 1 muM, resulting in very low concentrations of H(2)S in the reactor outlet gas. The stoichiometry of the reaction was determined, and stable reactor operation was demonstrated at reactor loadings as high as 4-5 mmol H(2)S oxidized/h g biomass. Maximum loading was estimated at 5.4-7.6 mmol H(2)S/h g biomass under the conditions employed in this study. Indicators of reactor upset were determined and recovery from upset conditions demonstrated. Barotolerance of T. denitrificans to 12.5 MPa as well as a relative insensitivity to pressurization-depressurization cycles were also demonstrated. T. denitrificans was observed to be very sensitive to CH(3)SH but relatively tolerant of CS(2), COS, and CH(3)SCH(3).     

脱氮硫杆菌的脱硫特性及其处理恶臭物质硫化氢的应用

污水和污泥的处理过程中会产生大量的恶臭气体硫化氢(H2S)。脱氮硫杆菌是氧化H2S和其他硫化物的重要的脱硫工程菌。本文阐述了脱氮硫杆菌的生物学特性和氧化H2S的两种途径。分析了反应体系中的硫化物负荷、硝酸盐和亚硝酸盐的浓度、氧含量以及pH值等因素对氧化效果、反应速率、氧化途径及产物形式的影响。介绍了脱氮硫杆菌在恶臭污染治理中的应用及其在同步处理含氮含硫恶臭物质方面的发展趋势。     

Anaerobic oxidation of thiosulfate and elemental sulfur in Thiobacillus denitrificans

Thiobacillus denitrificans strain RT could be grown anaerobically in batch culture on thiosulfate but not on other reduced sulfur compounds like sulfide, elemental sulfur, thiocyanate, polythionates or sulfite. During growth on thiosulfate the assimilated cell sulfur was derived totally from the outer or sulfane sulfur. Thiosulfate oxidation started with a rhodanese type cleavage between sulfane and sulfone sulfur leading to elemental sulfur and sulfite. As long as thiosulfate was present elemental sulfur was transiently accumulated within the cells in a form that could be shown to be more reactive than elemental sulfur present in a hydrophilic sulfur sol, however, less reactive than sulfane sulfur of polythionates or organic and inorganic polysulfides. When thiosulfate had been completely consumed, intracellular elemental sulfur was rapidly oxidized to sulfate with a specific rate of 45 natom S°/min·mg protein. Extracellularly offered elemental sulfur was not oxidized under anaerobic conditions.     

Effect of acetylene on nitrous oxide reduction and sulfide oxidation in batch and gradient cultures of Thiobacillus denitrificans.

Anaerobic enrichment cultures with H2S and N2O as substrates which were inoculated with a biofilm sample showed rapid growth and gas formation after 2 to 3 days at 27 degrees C. By using the deep-agar dilution technique, a pure culture was obtained. The strain was tentatively identified as Thiobacillus denitrificans. The isolate was used for batch and gradient culture studies under denitrifying conditions, oxidizing H2S with concomitant reduction of N2O to N2. In batch culture, oxidation of H2S was stepwise, with transient accumulation of elemental sulfur; the final oxidation product was SO4(2-). In gradient culture, there was no notable accumulation of elemental sulfur and microsensor measurements of H2S and N2O showed that H2S was oxidized directly to SO4(2-). In the presence of C2H2, however, oxidation of H2S stopped at the level of elemental sulfur and no SO4(2-) was produced in either batch or gradient cultures. This is a hitherto unknown inhibitory effect of C2H2. The inhibition is suggested to occur at the level of sulfite reductase, which catalyzes the oxidation of elemental sulfur to SO3(2-) in T. denitrificans. However, reduction of N2O in this strain was, surprisingly, not affected by C2H2. The isolate is the first chemolithoautotrophic organism shown to reduce N2O in the presence of C2H2. Denitrification in natural ecosystems is often quantified as N2O accumulation after C2H2 addition. However, the presence of large numbers of similar organisms with C2H2-insensitive N2O reduction could lead to underestimation of in situ rates.     

Effect of acetylene on nitrous oxide reduction and sulfide oxidation in batch and gradient cultures of Thiobacillus denitrificans.

Anaerobic enrichment cultures with H2S and N2O as substrates which were inoculated with a biofilm sample showed rapid growth and gas formation after 2 to 3 days at 27 degrees C. By using the deep-agar dilution technique, a pure culture was obtained. The strain was tentatively identified as Thiobacillus denitrificans. The isolate was used for batch and gradient culture studies under denitrifying conditions, oxidizing H2S with concomitant reduction of N2O to N2. In batch culture, oxidation of H2S was stepwise, with transient accumulation of elemental sulfur; the final oxidation product was SO4(2-). In gradient culture, there was no notable accumulation of elemental sulfur and microsensor measurements of H2S and N2O showed that H2S was oxidized directly to SO4(2-). In the presence of C2H2, however, oxidation of H2S stopped at the level of elemental sulfur and no SO4(2-) was produced in either batch or gradient cultures. This is a hitherto unknown inhibitory effect of C2H2. The inhibition is suggested to occur at the level of sulfite reductase, which catalyzes the oxidation of elemental sulfur to SO3(2-) in T. denitrificans. However, reduction of N2O in this strain was, surprisingly, not affected by C2H2. The isolate is the first chemolithoautotrophic organism shown to reduce N2O in the presence of C2H2. Denitrification in natural ecosystems is often quantified as N2O accumulation after C2H2 addition. However, the presence of large numbers of similar organisms with C2H2-insensitive N2O reduction could lead to underestimation of in situ rates.     

Mathematical model for microbial oxidation of pure lead sulfide by Thiobacillus ferrooxidans

A shrinking-core mathematical model describing bioleaching of lead sulfide is developed considering the deposition of insoluble bio-oxidation products on metal sulfide particle surfaces. Variations in particle size are considered as it affects diffusion limitations.     

Oxidation of hydrogen sulfide by flocculated Thiobaccillus denitrificans in a continuous culture

In a continuous fermentation, significant advantages may be gained by immobilization of microbial cells. Immobilization allows cells to be retained in the fermenter or to be readily recovered and recycled. Therefore, the hydraulic retention time and the biomass retention time are decoupled. A novel cell immobilization has been developed for the immobilization of autotrophic bacteria by coculture with floc-forming heterotrophic bacteria with growth of the latter limited by the availability of organic carbon. The result is an immobilization matrix which grows along with the immobilized autotroph. We have previously demonstrated the utility of this approach by immobilizing the chemoautotroph Thiobacillus denitrificans in macroscopic floc by coculture with floc-forming heterotrophs from an activated sludge treatment facility. Floc with excellent settling characteristics were produced. These floc have now been used to remove H(2)S from a gas stream bubbled through continuous cultures. The stoichiometry and kinetics of H(2)S oxidation by immobilized T. denitrificans were comparable to that reported previously for free-cell cultures. Oxygen uptake measurements indicated the growth of both T. denitrificans and the heterotrophs although the medium contained no added organic carbon. Continuous cultures with total biomass recycle were maintained for up to four months indicating the long-term stability of the commensal relationship between the immobilized autotroph and the heterotrophs which composed the immobilization matrix. It was observed that at any given H(2)S loading the biomass concentration reached a maximum and leveled out. The ultimate biomass concentration was dependent upon the H(2)S feed rate.     

Removal of dimethyl sulfide,methyl mercaptan,and hydrogen sulfide by immobilized Thiobacillus thioparus TK-m

Cells of Thiobacillus thioparus TK-m were immobilized on cylindrical porous polypropylene pellets (5 mmφ × 5 mm) which were packed in an acrylic cylinder of 50 mm inner diameter up to the height of 800 mm. When a sulfur-containing malodorous gas was charged to this packed tower at the superficial velocity of 0.1 m/s, maximum loading capacity (mmol/l·d) for a malodorous gas to attain the removal rate of 95% or more was: 3.65 for dimethyl sulfide, 8.74 for methyl mercaptan, and 17.36 for hydrogen sulfide. At this time, the inlet concentration (μl/l) of the malodorous compound was: 7.44 for dimethyl sulfide, 17.8 for methyl mercaptan, and 35.4 for hydrogen sulfide. For every compound, higher loading resulted in greater removal quantities. The removal rate of dimethyl sulfide was not overly affected by the presence of a large amount of easily decomposable hydrogen sulfide.     

Sulfur metabolism in Thiobacillus denitrificans

The relatively high specific sulfite reductase activity of 25 mU/mg protein was found in extracts from Thiobacillus denitrificans. The absorption spectrum of the partially purified enzyme was similar to the siroheme containing sulfite reductases from other sources. It is suggested that the T. denitrificans sulfite reductase may function during the oxidation of reduced sulfur compounds.     

Physiology and kinetics of autotrophic denitrification by Thiobacillus denitrificans

Summary A strain of Thiobacillus denitrificans was isolated after enrichment under anaerobic conditions by the continuous culture technique using thiosulfate as energy source and nitrate as electron acceptor and nitrogen source. The isolate was an active denitrifyer, the optimal conditions being 30°C and pH 7.5–8.0. Denitrification was inhibited by sulfate (the reaction product) above 5 g SO ₄ ⁼ /l, whereas high concentrations of the substrates nitrate and thiosulfate were less harmful; nitrite affected denitrification above 0.2 g NO ₂ ^– /l. During the time course of denitrification in a batch culture growth and substrate consumption slowed down already after only half the substrate was utilized due to product inhibition. The following parameters were determined in continuous culture under nitrate limitation: _max=0.11 h^–1, K _S=0.2 mg NO ₃ ^– /l, maximum denitrification rate=0.78 g NO ₃ ^– /g cells·h, g cells/g NO ₃ ^– , g cells/g S₂O ₃ ⁼ . Nitrite did not accumulate during steady state denitrification; the denitrification gas was almost pure N₂. The concentrations of N₂O and NO were below 1 ppm.     

Anaerobic, nitrate-dependent oxidation of U(IV) oxide minerals by the chemolithoautotrophic bacterium Thiobacillus denitrificans

Under anaerobic conditions and at circumneutral pH, cells of the widely distributed, obligate chemolithoautotrophic bacterium Thiobacillus denitrificans oxidatively dissolved synthetic and biogenic U(IV) oxides (uraninite) in nitrate-dependent fashion: U(IV) oxidation required the presence of nitrate and was strongly correlated with nitrate consumption. This is the first report of anaerobic U(IV) oxidation by an autotrophic bacterium.     

Cell yield and bioenergetics of Thiomicrospira denitrificans compared with Thiobacillus denitrificans

From cell yields of Thiomicrospira denitrificans grown in the chemostat at different growth rates under anaerobic conditions a value of 1.4mm S₂O _inf3 ^sup= per g dry wt and per h could be calculated for maintenance energy requirements, and of 5.65 g dry wt per mole S₂O _inf3 ^sup= for the true growth yield.Cell yields of Thiomicrospira denitrificans appeared to be almost half of those of Thiobacillus denitrificans. Though in Thiobacillus denitrificans at D=0.03 h^-1 under anaerobic conditions a value was found of 11.60 g dry wt per mole of thiosulphate used for energetic purposes, a value of 5.72 g dry wt per mole of thiosulphate was found under comparable conditions in Thiomicrospira denitrificans. Under aerobic conditions at D=0.03 h^-1 values of 18.54 g dry wt per mole of thiosulphate were found in Thiobacillus denitrificans whereas Thiomicrospira denitrificans yielded only 9.38 g dry wt per mole of thiosulphate.As in Thiobacillus denitrificans anaerobic cell yields on sulphide were comparable to those on thiosulphate.Calculations have been made which indicate that the biosynthetic efficiency of Thiomicrospira denitrificans is lower than that of Thiobacillus denitrificans. This can only partly be explained by the absence of adenosine-phosphosulphate (APS) reductase.