Study On The Characteristics Of Autotrophic Denitrification With Sulfurous Iron Ore As Substrate

Nitrate is a common pollutant both in the natural water body and the sewage.Nitrate pollution may not only lead to eutrophication of water,but also poses a serious threat to drinking water safety.Denitrification is the main method to remove nitrate in water,especially autotrophic denitrification reaction with sulfurous iron ore as substrate.In this study,ferrous sulfide and pyrite were utilized as the substrate to explore the process and characteristics of autotrophic denitrification.The main findings are as follows:（1）The process of autotrophic denitrificans conducted by Thiobacillus denitrificans ATCC 25259 with ferrous sulfide or pyrite as substrate was studied by batch experiment.The results exhibited that Strain T.denitrificans had the ability to conduct autotrophic denitrification reaction with FeS as the only electronic donor,and almost no autotrophic denitrification reaction took place when pyrite(30 g·L^-1)as the only electronic donor.When utilizing FeS as the sole electron donor,NO₃^--N(30 mg·L^-1)was finally reduced to N₂ by T.denitrificans utilizing FeS as the sole electron donor,with NO₂^-and without N₂O accumulated as intermediates.The elemental sulphur in FeS was converted to SO₄^2-via autotrophic denitrification,wheras the elemental iron was precipitated with PO₄^-as the form of Fe₃（PO₄）₂·8H₂O.Besides,according to the fitted curves,this autotrophic denitrification process was demonstrated to accord with the zero-order kinetics（R²>0.93）.As the rising amount of FeS,both the reduction rates of NO₂^-and NO₃^-increased,and the maximum accumulation concentration of NO₂^-was improved.The appropriately lower initial pH facilitated the denitrification reaction in the current study.When the amount of FeS was 20g·L^-1,the strain T.denitrifican was able to completely reduce NO₃^--N with an initial concentration of 50 mg·L^-1,but little NO₂^-was not completely reduced.When the initial concentration of NO₃^--N was increased to 100 mg·L^-1,neither NO₃^-nor NO₂^-was completely reduced.（2）The performance of the reactor with different sulfurous iron ore as substrates was investigated by column reactor experiments,and the microbial community structure in the reactors was analyzed.Activated sludge was acclimated with different substrates and inoculated,respectively,in sulfur autotrophic denitrification（SAD）reactor,pyrite autotrophic denitrification（PAD）reactor and ferrous sulfide autotrophic denitrification（FSAD）reactor.The results showed that the average removal rates of NO₃^-in SAD,PAD and FSAD reactors were 99.5%,70.0%and 96.9%,respectively,when HRT was 21.6 h and the influent NO₃-N concentration was 50.45 mg·L^-1.The analysis of the by-products of the reactor indicated that NH₄⁺was present in the effluent of the SAD and FSAD reactors,and the effluent of the PAD reactor was almost free of NH₄⁺;the effluent SO₄^2-accumulation of the SAD reactor was the most and the effluent contained S^2-,the amount of effluent SO₄^2-accumulated in the PAD and FSAD reactors were lesser and no S^2-was detected.In the SAD and PAD reactors,the most abundant microorganisms at the genus level were Thiobacillus which has ability of autotrophic denitrification,respectively,accounting for 17.44%and 22.68%;Thiobacillus accounted for 11.2%in the FSAD system,and Azoarcus which has ability to reduce nitrate couple with oxidize sulfide accounted for 7.39%.