Anaerobic Bioreduction Of Sulfate And Fe(Ⅱ)EDTA-NO/Fe(Ⅲ)EDTA

Based on biological flue gas desulfurization technology（Bio-FGD）and chelating absorption-biological regeneration technology（BioDeNOx）,simultaneous desulfurization and denitrification by biological combined with chelating absorption technology was proposed in this study.This technique used the alkaline absorption liquid with Fe（Ⅱ）EDTA to absorb the SO₂ and NO in flue gas.Sulfate(SO₄^2-)and Fe（Ⅱ）EDTA-NO/Fe（Ⅲ）EDTA which are the absorption products were attempted to be removed simultaneously by biological reduction in the anaerobic reactor of this study.The results indicated that:（1）SO₄^2-and Fe（Ⅱ）EDTA-NO average removal efficiencies were 95.16% and 96.61% respectively,when HRT and pH were controlled at 16 h and 7.0 respectively.The reduction products of SO₄^2-were mainly in the form of S₂^-in the liquid phase and hydrogen sulfide（H₂S）in the gas phase,while the reduction product of Fe（Ⅱ）EDTA-NO was N₂.When the ratio of Fe and EDTA was less than 1:2,there was no precioitation of Fe observed in the reactor.When the ratio of Fe and EDTA was 1:2 and HRT were 30 and 23 h,there was also no precioitation of Fe observed and the Fe in the precipitate was dissoluted by EDTA.The reduction of Fe（Ⅲ）EDTA could be achieved at all stages of the operation,but the reduction rate decreased with the reduction of HRT.In the fifth stage,the main sulfate-reducing bacteria（SRB）in the reactor was Desulfomicrobium,the heterotrophic denitrifying bacteria Pseudomonas and two types of the sulfur autotrophic denitrifying bacteria,Sulfurimonas and Sulfurovum,coexisted.Two genera of bacteria that can reduce sulfur,Thermovirga and Mesotoga,were also found.（2）With the increase of the concentration of Fe（Ⅲ）EDTA in the influent,the loss of total iron in each stage increased gradually.The removal rate of Fe（Ⅱ）EDTA-NO decreased slightly to 80% and the removal rate of sulfate decreased significantly to 62%.The oxidation-reduction between Fe（Ⅲ）and sulfide was enhanced,while most Fe（Ⅲ）were reduced and part of the sulfide were converted into elemental sulfur.The increase of the concentration of Fe（Ⅲ）EDTA in the influent had a great influence on the microbial community structure,and the proportion of functional bacteria had obviously decreased.The content of elemental sulfur-reducing bacteria Dethiosulfovibrio was improved greatly.