The Process And Characteristics Study On Chelating Solution Reduction By Desulfovibrio Sp. CMX For Simultaneous Desulfurization And Denitrification

With the increasing air pollution, development of simultaneous SO2 and NOx removal technology from flue gas is the trend of air pollution control. Biological technology has many advantages, such as high efficiency, low cost, and no secondary pollution etc., so this technology is widely concerned by researchers from the field of SO2 and NOx treatment. The sulfate reducing bacteria (SRB) can reduce sulfate to sulfide, and sulfide can react with Fe(Ⅲ)EDTA and Fe(Ⅱ)EDTA-NO. Moreover, some SRB may reduce Fe(Ⅲ)EDTA and Fe(II)EDTA-NO directly. Thus, based on proposed chelating absorption-biological reduction technology for simultaneous desulfurization and denitrification, reduction process of chelated absorbed NO and SO2 (i.e. sulfate, Fe(Ⅱ)EDTA-NO and Fe(Ⅲ)EDTA) by SRB was studied in this paper. The main results were as follows.In order to provide microbial resources to the research of chelating absorption biological reduction technology for simultaneous desulfurization and denitrification, activated sludge was domesticated in FeEDTA and sulfate solution. A strain CMX, which could reduce sulfate efficiently, was isolated and found to belong to the genus Desulfovibrio by 16S rDNA analysis. It was found that Desulfovibrio sp. CMX could grow well and remove sulfate efficiently when pH was 6-8, lactate was electron donor, and inoculation amount was around 20 mg/L. Its largest sulfate removal amount was about 1.32 g/L. Desulfovibrio sp. CMX could grow and reduce sulfate when the concentration of NaCl was 2%(W/V).Fe(Ⅱ)EDTA could accelerate the sulfate reduction by Desulfovibrio sp. CMX. The enhanced effects of lower Fe(Ⅱ)EDTA concentrations were more obvious than that effects of higher Fe(II)EDTA concentrations (20 mM and 25 mM). Fe(Ⅲ)EDTA could accelerate the sulfate reduction by Desulfovibrio sp. CMX. With the increase of Fe(III)EDTA (0-25 mM), sulfate reduction efficiencies increased. Fe(II)EDTA-NO could inhibit the sulfate reducing capacity of Desulfovibrio sp. CMX, and its inhibitory effect related to Fe(II)EDTA-NO concentration and biomass in the system. The sulfate reducing capacity could recover to its previous level through supplying lactate during reduction process. The Fe(II)EDTA-NO (0.25-4 mM) was removed in 60 h during the sulfate reducing process.Both Fe(Ⅲ)EDTA and Fe(Ⅱ)EDTA-NO could be reduced directly by Desulfovibrio sp. CMX as the electron acceptor under heterotrophic condition. Regardless of the presence or absence of sulfate, reduction efficiencies of Fe(Ⅲ)EDTA and Fe(Ⅱ)EDTA-NO were more than 87%and 97%, respectively. The Fe(Ⅱ)EDTA-NO reduction efficiency was not affected by presence of Fe(III)EDTA and sulfate. As a competitive electron acceptor, Fe(Ⅱ)EDTA-NO reduction rate was affected by presence of Fe(III)EDTA. Fe(Ⅲ)EDTA reduction was inhibited by presence of Fe(Ⅱ)EDTA-NO, and was enhanced by presence of sulfate. When Fe(Ⅱ)EDTA-NO, Fe(Ⅲ)EDTA, and sulfate were presence simultaneously, most of Fe(Ⅲ)EDTA and Fe(II)EDTA-NO were directly reduced by Desulfovibrio sp. CMX. Fe(Ⅱ)EDTA-NO was removed first and then Fe(Ⅲ)EDTA reduction or sulfate reduction occurred when Fe(Ⅱ)EDTA-NO, Fe(Ⅲ)EDTA, and sulfate coexisted.