| The biological technologies for NOx and SO2 removal in flue gas have the advantages of low cost, mild reaction condition, no secondary pollution, etc. The denitrification process of chemical absorption combined with biological reduction(BioDeNOx) and biological flue gas desulfurization technology(Bio-FGD) as the mature biotechnologies for NO and SO2 removal have received extensive attention of the researchers in recent years. At the same time, a large amount of work was made on sewage treatment by MFC. On the basis of simultaneous desulfurization and denitration by chemical absorption-biological reduction technology we proposed before, this study puts forward a new pathway that combines MFC and the above technology on desulfurization and denitration to realize biotransformation of sulfate produced in Bio-FGD process and Fe(Ⅱ)EDTA-NO/Fe(Ⅲ)EDTA produced in a NOx scrubber liquor during the denitration process in anode and cathode respectively through building a dual-chamber MFC.When sodium acetate(CH3COONa) was used as substrate in the anode chamber, the results of research showed that Fe(Ⅱ)EDTA-NO in cathode was removed more than 90% under the condition of running continuously of MFC, while the reduction efficiency of Fe(Ⅲ)EDTA was about only 30%. The Fe(Ⅲ)EDTA reduction efficiency could reach about 60% when Fe(Ⅲ)EDTA was used as the sole electron acceptor in cayhode. In this system, the insoluble cathode was utilized as the sole electron donor for the Fe(Ⅲ)EDTA reduction, while the process of Fe(Ⅱ)EDTA-NO reduction was more complicated. Microorganism in cathode could capture electrons from cathode electrode directly to reduce Fe(Ⅱ)EDTA-NO, at the same time Fe(Ⅱ)EDTA-NO could be also reduced by microorganism through the process of ferrous-dependent denitrification, in which way Fe(Ⅱ)EDTA was used as electron donor for Fe(Ⅱ)EDTA-NO reduction and microorganism gained energy through oxiding Fe(Ⅱ) to Fe(Ⅲ). So this process with the increase of Fe(Ⅲ) concentration may be an important reason for the low Fe(Ⅲ)EDTA reduction efficiency. In addition, in this coexistence system, Fe(Ⅱ)EDTA-NO and Fe(Ⅲ)EDTA had inhibitory effect on mutual biological reduction and the inhibition of the former to the latter was more obvious than that of the latter to the former. The microbial community of the biocathode was dominated by members of proteobacteria, especially Betaproteobacteria. When the anode was inoculated with microorganisms mixed with sulfate reducing bacteria (SRB) and sulfur oxidizing bacteria (SOB), the sulfate removal efficiency in anode chamber was 56～65% and the reduction efficiency of Fe(Ⅲ)EDTA-NO and Fe(Ⅲ)EDTA in cathode was more than 90% and 36～42% respectively under the continuous operation of MFC. Batch operation test showed that sulfide could act as electron donor for reduction reaction in cathode. In the anode chamber, sulfate was reduced to sulfide by SRB with sodium lactate as substrate firstly, then sulfide was oxidized by the anode through bioelectrochemical process with SOB, the electrons produced in this process were transfered to cathode through external circuit, at last Fe(Ⅱ)EDTA-NO and Fe(Ⅲ)EDTA were reduced by the electrons from cathode. In addition, sodium lactate could also act as electron donor for the reduction process in cathode directly. The oxidation of sulfide was inhibited under the high ratio of substrate/sulfate what results in the sulfide accumulation while the sulfide accumulation did not occur under low ratio of substrate/sulfate. Batch operation tests with a fixed anode potential showed that the oxidation rate of sulfide through bioelectrochemical process had a positive correlation with anode potential. Sulfide oxidation process did not occur when the anode potential was below-600 mV (vs. Ag/AgCl electrode). |
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