Domestication of Acidithiobacillus Ferroxidans and Its Application to Bio-desulfuration of Coal
|School||Nanjing Agricultural College|
|Keywords||Acidithiobacillus ferrooxidans Pyrite Domestication Extracellular polymeric substance Coal desulfurization Conditions optimization|
As one of the most important energy resources, coal occupies a critical position in the energy structure of China. China consume huge amount of coal every year, of which 90% is used for combusting directly. Consequently, China has become the country which discharges the largest amount of SO2 in the world since 1998 and acid deposition accounts for 40% of its land. So we study the bio-desulfurizing of coal, not only to avoid the acid rain caused by emission of SO2 at root, but also to get to know the mechanism of the bio-desulfurizing of the coal in theory, which can provide theoric basis to the industrialization and scalization of bio-desulfurizing.In this study, Acidithiobacillus ferrooxidans LX5 was cultured in 9K medium with pyrite and ferrous sulfate as the substrate, respectively. Biomass was enhanced by the presence of ferrous sulfate, for example, the LX5 number was 3.0×107cell/mL cultured for 20d in the presence of pyrite, and 108cell/mL cultured for 48h in presence of ferrous sulfate. After A. ferrooxidans LX5 acclimated by pyrite, the isoelectric point of A.ferrooxidans LX5 was bigger than that of A. ferrooxidans LX5 acclimated by ferrous sulfate, more easy to adhere to the surface of the pyrite. Compared the different of A.ferrooxidans LX5 acclimated by pyrite and ferrous sulfate as the substrates, the results showed that concentration of SO42-were 2241.6mg/Land 516.2mg/L more than that of the the A. ferrooxidans LX5 acclimated by FeSO4, indicating the oxidation activity of A.ferrooxidans LX5 in pyrite was stronger than it in ferrous sulfate.Incubation experiments under shaking conditions were used to investigate the response of A. ferrooxidans LX5 to additions of pyrite and ferrous sulfate, two substrates that might be expected to influence EPS in amount and configuration. It was found that the EPS generation rate of pyrite was 2973.2μg/1010 cells and was as three times as that of ferrous sulfate. With pyrite and ferrous sulfate as substrates, the polysaccharides and proteins in EPS were 46.6% and 34.6%, and 44.6% and 36.2%, respectively. It was presented that the composition of the EPS was almost same by the FTIR spectra, for example, either of EPS containing -OH、-NH2 and -COOH functional groups, respectively. The increase rate of SO42- in the flasks with A. ferrooxidans LX5 and EPS were markedly higher than those in the flasks with A. ferrooxidans LX5 only throughout the incubation. The EPS played a key role on the oxidation activity of LX5 during the desulfurization of coal.500-mL conical flasks containing freely suspended biomass were shaken with a high-strength coal liquors to determine the desulfurization rates at various initial pH, inoculation of LX5 and sulfur loadings. In view of desulfurization rate, an intermittent mode, with initial pH 2.5, additions of 10% bacterial suspension and 10% high-sulfur coal, showed the best results, and the coal desulfurization rate was up to 72.4% after bioleaching for 13d. Under these optimal conditions, a maximum coal desulfurization rate of 69.2% was achieved in a laboratory-scale continuously stirred tank reactor (5.0-L working volume) after the inoculation lasting 15 days, indicating great potential of A. ferrooxidans LX5 for future full-scale applications.