Research On Reduction Of Fe(Ⅱ)EDTA-NO Using Sulfide And Thiobacillus Denitrificans

Sulfur dioxide and nitrogen oxides are the main atmospheric pollutants in the flue gas. Biological flue gas desulfurization (Bio-FGD) has the advantages of low energy consumption, low cost and no pollution. In this process, firstly, SO2readily dissolves in the water by the form of sulfite (SO32-) or sulfate (SO42-), which can be reduced into sulfide (S2-) by sulfate reducing bacteria (SRB), then sulfide was oxided to sulfur by sulfur-oxidizing bacteria.In the process of metal chelate absorption combined with microbial reduction (BioDeNOx) denitrifying bacteria can reduce Fe(II)EDTA-NO. Therefore, if Bio-FGD is combined with BioDeNOx, the potential reactions of sulfide with Fe(II)EDTA-NO should be taken into account in this combined process.Although the process of Fe(II)EDTA-NO reduction by heterotrophic denitrifying bacteria has been described in detail, thus far, ignoring the process of autotrophic denitrifying bacteria could reduce Fe(II)EDTA-NO. As a part of new process of biological combined with complex absorption simultaneous desulfurization and denitration, the following aspects were researched in this paper:Fe(II)EDTA-NO reduction by sulfide in the anaerobic aqueous phase: stoichiometry and kinetics, the process of Fe(II)EDTA-NO reduction by autotrophic denitrification bacteria and the processes of Fe(II)EDTA-NO reduction by chemical and biological removal. The main results were as follows:1) In the process of the chemical Fe(II)EDTA-NO reduction by sulfide, Fe(II)EDTA-NO was converted into ammonium, and elemental sulfur was the main products of sulfide oxidation. However, the molar ratio of reduced Fe(II)EDTA-NO to the oxidized sulfide was1:3.4-1:3.6, a bit higher than the expected value, suggesting the formation of the polysulfide. Fe(II)EDTA-NO reduction by sulfide was a first-order reaction with respect to Fe(II)EDTA-NO. The reduction rates of Fe(II)EDTA-NO by sulfide went up along with the decrease of the pH values and rise of the reaction temperature. Besides, the reaction order concerning hydrogen ions was approximately0.13. Furthermore, the energy of activation (Ea) and the entropy of activation (S++) were31.1kJ mol-1.2) Thiobacillus denitrificans ATCC25259could conduct ferrous-dependent denitrification. When using ferrous as electron donor, Thiobacillus denitrificans can reduce nitrite rapidly. In the process of Fe(II)EDTA-NO degradation, the bacteria could use Fe(II) itself to reduce NO. When thiosulfate were added, the reduction rate of Fe(Ⅱ)EDTA-NO increased. NiO was the main gaseous products of Fe(II)EDTA-NO reduction, in case of no free Fe(Ⅱ)EDTA, while the bacteria could transform N2O into N2completely in the presence of free Fe(Ⅱ)EDTA.3) Thiobacillus denitrificans ATCC25259could remove nitrite and sulfide simultaneously. With low sulfide concentration could promote nitrite reduction. EDTA and ascorbic acid had slightly effect on the process of ferrous-dependent denitrification. In the process of the abiotic Fe(II)EDTA-NO reduction by sulfide, the rate of Fe(II)EDTA-NO reduction in the inorganic salt medium was faster than in the NaHCO3buffer solutions, mainly due to the influence of pH. In the process of the chemical and biotic Fe(II)EDTA-NO reduction by sulfide, the rates of Fe(II)EDTA-NO reduction and sulfide oxidation were faster than the chemical Fe(II)EDTA-NO reduction by sulfide. Fe(II)EDTA-NO could be deoxygenized through ferrous-dependent denitrification and sulfur autotrophic denitrifying by Thiobacillus denitrificans.