[Effect of permeabilization on sulfate reduction activity of Desulfovibrio vulgaris Hildenborough cells in the presence of different electron donors].

The Desulfovibrio vulgaris Hildenborough (DvH) cells permeabilized with ethanol were used as biocatalysts to enhance hydrogenotrophic sulfate conversion. The effect of permeabilization extent of DvH cells on sulfate reduction was studied in the presence of different electron donors. When hydrogen was used as an electron donor, the highest level of sulfate reduction activity attained in cells treated with 10% ethanol (V/V), followed by 15% -ethanol treated cells. Furthermore, sulfate reduction activity markedly decreased when the ethanol concentration exceeded 15%. However, when lactate was used as the electron donor, the optimum ethanol concentration of the permeabilizing reagent was 20%, followed by 15% and 10%. Even when ethanol concentration reached 25%, DvH cells remained their partial activity with lactate. In a word, sulfate reduction activity of DvH cells responded differently in the presence of different donors. This was because the oxidation process of H2 and lactate occurred at different positions in DvH cells, and consequently intracellular electron transport pathway differed. To ensure the integrity of the electron transport chain between the donor and the accepter was a key factor for determining the permeabilization extent and for the application of cell permeabilization technology.

[Performance of a combined bio-chemical sulfidogenic system and microbial characteristics in the presence of H2].

To study and evaluate the performance of the continuously-operated autohydrogenotrophic sulfate reduction technique enhanced with electrochemical method and to improve the sulfate removal efficiency, a combined bio-electrical sulfidogenic system was developed with a three-dimensional bio-cathode. Sulfate reduction rate was elevated markedly owing to H2 mass transfer enhancement, biomass augmentation and electrical field stimulation. Indeed, when a current of 0.50 mA was applied to the system, the average sulfate removal load was 1.94 g/(L x d) during the stable running status and the maximum removal load was 2.23 g/(L x d). Furthermore, the combined bio-electrical system was comparatively more stable in terms of response to the variation of influx load under the same hydraulic conditions. Results of SEM showed that besides the bacteria attached on the surface of the hollow fiber, large amount of biomass was aggregated on the surface and the inner gridding space of the graphite felt. PCR-DGGE analysis indicated that the diversity of the microbial community structure was slightly reduced resulting in an optimized one. The dominant genera were Desulfovibrio and Desulfomicrobium. Enhanced H2 mass transfer, biomass augmentation, optimized microbial community structure and electrical stimulation were the key important factors for the high sulfate reduction efficiency of the system.

[Bio-electrochemical effect on hydrogenotrophic sulfate reduction stimulated by electrical field in the presence of H2 under atmospheric pressure].

Microbial sulfate reduction rate is limited with H2 as electron donor. In order to improve hydrogenotrophic sulfate reduction under normal atmospheric H2 pressure, a bio-electrochemical system with direct current was designed and performed in this study. Results indicates that sulfate reduction rate (SRR) increases with the augment of current intensity under lower current intensity (I < or = 1.50 mA). When optimum current intensity of 1.50 mA is applied, the SRR is 1.7 to 2.1 times higher than that of the control reactor. The synergistic effect of electrochemistry and microbiology on sulfate reduction varies at different current intensity. Under the condition of I < or = 1.50 mA, the most probable mechanism of SRR increase is that electric or magnetic field stimulates the proliferation of sulfate-reducing bacteria (SRB) and the activity of the enzymes. When I is higher than 1.50 mA, the activity of SRB is inhibited, resulting in lower reduction rate compared with that at lower current. If controlling the cathode potential lower than -0.69 V and H2 partial pressure 1.01 x 10(5) Pa, electro-catalytic sulfate reduction process takes place with H2 as reductant in this bio-electrochemical system. However, the overall reduction rate is still lower than that when I = 1.50 mA is applied, and additionally the energy consumption is much higher. Therefore, electric field of low intensity can enhance hydrogenotrophic sulfate reduction in the presence of H2 under atmospheric pressure.