Ziyu Song

Performance of a haloalkaliphilic bioreactor and bacterial community shifts under different COD/SO42- ratios and hydraulic retention times

Sulfur dioxide from flue gas was converted into sulfate after the absorption of alkaline solutions. Haloalkaliphilic microorganisms have been used in reducing sulfate to decrease expenses and avoid sulfide inhibition. The effects of different COD/SO4(2-) ratios and hydraulic retention times (HRTs) on the sulfate removal efficiency and bacterial community were investigated in model experiments. Ethanol showed better performance as an electron donor than lactate. The optimum COD/SO4(2-) ratio and HRT were 4.0 and 18 h, respectively, with respective sulfate removal efficiency and rate of 97.8 ± 1.11% and 6.26 ± 0.0710 g/Ld. Sulfide concentrations reached 1,603 ± 3.38 mg/L. Based on denaturing gradient gel electrophoresis analysis of 16S rDNA, the major sulfate-reducing bacterium (SRB) was Desulfonatronovibrio sp., which was only detected at a COD/SO4(2-) ratio of 4.0 using ethanol as an electron donor. Different HRTs had no significant effect on the band corresponding to this species. PCR results show that methane-producing archaea (MPA) were from the acetoclastic methanogenic family Methanosarcinaceae. Quantitative real-time PCR did not demonstrate any significant competition between SRB and MPA. The findings of this study indicate that sulfate reduction, nitrate reduction, and sulfide oxidization may occur in the same bioreactor.

Performance of a haloalkaliphilic bioreactor under different NO3-/SO42- ratios

Effects of NO3(-)/SO4(2-) ratio on denitrification and sulfate removal efficiency were investigated in model experiments applying haloalkaliphilic bioreactor. The reduction of both substrates performed well at different NO3(-)/SO4(2-) ratios ranging from 17.6 to l.5. The removal rates of nitrate and sulfate were 6 and 1.39kgm(-3)d(-1), respectively, at NO3(-)/SO4(2-) ratio 3.0, while sulfide concentration reached up to 703gm(-3). The major sulfate-reducing and denitrifying bacteria were Desulfonatronovibrio sp. and Halomonas campisalis, respectively. Decrease in NO3(-)/SO4(2-) ratio led to obvious changes in bacterial community. Although the sulfate reducers became dominant, the population of denitrifying ones also increased as it was demonstrated by analysis of PCR-amplified 16S rDNA fragments, which suggested that SRB and DB coexisted well in bioreactor.

Dual-phase fermentation enables Actinobacillus succinogenes 130ZT to be a potential role for high-level lactate production from the bioresource.

Initial oxygen aeration enabled Actinobacillus succinogenes 130Z(T) to be regarded as a novel type of lactic-acid-producing strain in subsequent anaerobic cultivation. Lactic acid production increased 32-fold, up to the final titers of 135.6+/-0.14 g L(-1) with an overall yield of 0.96+/-0.09 g g(-1) glucose and 2.94+/-0.03 g L(-1) h(-1) productivity. The metabolites at the end of dual-phase fermentation by 130Z(T) were (in parentheses: the mol end product formed/100 mol glucose) succinic acid (37), acetic acid (69), formic acid (21), and lactic acid (193). Carbon flux distribution shifted toward to lactate in the bi-staged cultivation, where C(3) flux increased and C(4) flux reduced. The enzyme assay revealed that the lactate dehydrogenase (LDH) activity in dual-phase process was nearly 18-fold higher than the values in mono-phase process.

Enhanced sulfate reduction by Citrobacter sp. coated with Fe3O4/SiO2 magnetic nanoparticles

A sulfate-reducing Citrobacter strain was isolated and coated with Fe3O4/SiO2 magnetic nanoparticles (MNPs) to enhance sulfate reduction. Biolog analysis showed that it utilizes a broad range of electron donors. The findings also showed that this bacteria strain is a facultative anaerobe and can completely reduce 12 mM of sulfate to sulfide in 7 days under anaerobic conditions. Moreover, sulfate reduction was enhanced by 79% under optimized conditions. Different SiO2 wrap-ratios of the MNPs attached to the cell surface were studied to optimize the sulfate reduction: the surface of cells coated with 300% silica wrap-ratio MNPs showed the highest stability and increased desulfurization batch time, with a 450% increase in sulfate reduction in comparison with uncoated cells cultivated in anaerobic conditions.

Bio-desulfurization and denitrification by anaerobic-anoxic process for the treatment of wastewater from flue gas washing

For amine-based carbon dioxide capture, nitrogen oxides and sulfur oxides were the main pollutants that had a negative effect on the regeneration of solvent. Before carbon dioxide capture, the sulfur oxides in flue gas should be removed by the method of calcium salt, and then washed by alkaline solution to eliminate the residual nitrogen oxides and sulfur oxides. The washing wastewater containing sulfate and nitrate needs to be treated. In this study, a novel anaerobic-anoxic process was built up for the treatment of this washing wastewater. Nitrate was reduced to nitrogen by denitrifying bacteria. Sulfate was firstly reduced to sulfide by sulfate reducing bacteria, and then selectively oxidized to element sulfur by sulfide oxidizing bacteria. The treated liquid could be reused as absorption after the adjustment of pH value. The performances of this bioprocess were investigated under various pH values and S/N ratios. It was found that the optimal pH value of influent was 6.0, the percentages of denitrification and sulfate reducing could reach 90 and 89%, respectively. Seventy-six percent of sulfate was transformed into element sulfur. Nitrate significantly had a negative effect on sulfate reduction above 10 mM. As 20 mM nitrate, the sulfate reducing percentage would drop to 67%. These results showed that the anaerobic-anoxic process was feasible for the treatment of flue gas washing wastewater. It would be prospectively applied to other wastewater with the higher ratio of SO4(2-)/NO3(-).

A novel up-flow inner-cycle anoxic bioreactor (UIAB) system for the treatment of sulfide wastewater from purification of biogas

An up-flow inner-cycle anoxic bioreactor with a novel three phase separator was designed and implemented for the treatment of sulfide wastewater. The sulfide in wastewater could be converted to elemental sulfur by sulfide oxidizing bacteria, and recovered by simple precipitation. When the oxidation-reduction potential (ORP) was controlled at -100 mV, 91.3% of sulfide could be oxidized to elemental sulfur. To achieve high removal percentage of sulfide and conversion percentage of sulfur, the pH of influent should be controlled in the range from 7.0 to 8.0. The optimal desulfurization process was carried out at 400 mmol L(-1)d(-1) sulfide loading rate and 120 min hydraulic retention time (HRT). The removal percentage of sulfide was approximately 95.2% and elemental sulfur conversion percentage was above 90.3%. These results demonstrated that the novel up-flow in-cycle bioreactor had a potential value for the enhanced treatment of sulfide wastewater from biogas purification.

Inhibition of carbon disulfide on bio-desulfurization in the process of gases purification

Biological desulfurization is a novel technology for the removal of hydrogen sulfide from some biogas or sour gas, in which there are always a certain amounts of carbon disulfide together with much hydrogen sulfide. Nowadays, carbon disulfide is found to have negative effect on the biological desulfurization, but seldom research is afforded to investigate how carbon disulfide inhibits the process of biological desulfurization. In this paper, we investigated the effect of carbon disulfide both on the growth of Thiobacillus thioparus and the resting cells under various concentrations, including 0.01, 0.05, 0.10, 0.15 and 0.20%. In this process, the rate of the cell growth was characterized by the rate of nitrogen consumption in order to solve the problem that the adsorption of cells to sulfur granules have on the accuracy of biomass test. Under the cell density of 23.92 mg N/L, which is lower than the maximum of cell density 36.13 mg N/L, the average rate of thiosulfate oxidation reached the maximum (26.50 S 2 O 3 2- mg/L-h). Carbon disulfide at titers of 0.01% significantly inhibited the growth of cells, but hardly affected the biological desulfurization of resting cells. Although carbon disulfide at titers of 0.05% had negative effect on the biological desulfurization of resting cells, the effect of inhibition could be relieved by the increased density of resting cells. For the resting cells, the parameters of Michaelis-Menten equation were calculated by the method of Lineweaver-Burk. The V max of biological desulfurization was decreased from 27.93 to 14.0 S 2 O 3 2- mg/L-h, and the K m was increased from 0.264 to 0.884 mM, with the concentration of carbon disulfide rising up from 0.0 to 0.1%. These results show that the growth of cells was sensitive to carbon disulfide, and the resting cells had resistance to the low level of carbon disulfide (0.05%). Thus, the inhibition of carbon disulfide to biological desulfurization should be attributed to T. thioparus growth suppression function. Keywords: Carbon disulfide, bio-desulfurization, inhibition, Thiobacillus thioparus , resting cell, gases purification African Journal of Biotechnology , Vol 13(16), 1739-1744