Study On The Characteristics And Mechanism Of Autotrophic Denitrification With Mixed Electron Donors

In this study,bacteria with high efficient nitrate removal characteristics had been isolated and purified from the sediment of Tang Yu reservoir.Subsequently,we had studied the ability,methods,metabolic product characteristics,different factors on nitrate-N removal,and MBR reactor had been established to study on the nitrate-N removal.Suggesting that:(1)Combined with morphological characteristics and 16 S rRNA gene sequence analysis,two strains were identified as Pseudomonas sp.Aiming at the effect of single environmental factors on denitrification,the experiment tested the different Mn(II):Fe(II)ratios(1:9,2:8,3:7,4:6,5:5,6:4,7:3,8:2 and 9:1),temperature(20 o C,25 oC,30 oC and 35 oC),pH(6.0,7.0,8.0 and 9.0),electron donor:electron acceptor ratios(0.5:1,1.54:1 and 3.0:1)and n(NO3--N):n(NO2--N)ratios(0:10,2.5:7.5,5:5 7.5:2.5 and 10:0)on nitrate-N removal.The results suggested that a complete nitrate removal was found at high Mn(II):Fe(II)ratios,30 oC,pH 7.0,and an electron donor/electron acceptor ratio of 3.00.The optimal n(NO3--N):n(NO2--N)ratio on denitrification of strain H-118 were obtained at 5:5,the strain H-117 were obtained at n(NO3--N):n(NO2--N)ratio of 2.5:7.5,this suggested that strain H-117 had a better tolerance on nitrite.(2)The study revealed a complete denitrification mechanism,we had assessed expression of nirS through amplification approaches and demonstrated that N2 was the end product during the denitrification process with a slight N2 O level,this suggested that a complete denitrification process was: NO3--N?NO2--N?NO?N2O?N2.Meanwhile,the end products of Mn(II)and Fe(II)was Fe OOH and MnO2,respectively.(3)Denitrification kinetics study showed that the Monod model could fit thenitrate-N removal profiles reasonably.The Edwards and Aiba models were used to describe denitrification inhibition caused by nitrite,the results suggested that Edwards and Aiba models could fit the nitrate-N removal profiles reasonably.especially the Edwards model.The kinetic parameters determined from Edwards model were rmax of0.242 mg-NO2--N·L-1·h-1,KS of 6.252 mg-NO2--N·L-1,and KI of 23.288 mg-NO2--N·L-1.(4)Biofilm reactor was established,the response surface methodology(RSM)was used to design the experiment,results suggested that the optimal state of the reactor with Yu Long as carrier were Fe(II):Mn(II)ratio of 3.81,electron donor:electron acceptor ratio of 2.62 and hydraulic retention time(HRT)of 10.88 h with the highest removal efficiency of nitrate(100%);the optimal state of the reactor with sand as carrier were Fe(II):Mn(II)ratio of 4.73,electron donor:electron acceptor ratio of 1.92 and hydraulic retention time(HRT)of 11.73 h with the highest removal efficiency of nitrate(100%).Subsequently,kinetic model of autotrophic denitrification was established to describe the nitrate removal,the optimum value of various kinetic parameters,including f 1s1 of 0.53,f 2s1 of 0.03,f 1s0 of 0.31,f 2s0 of 0.20,?max of 0.015,Knitrate-N of 6.33,Knitrite-N of 2.95,KFe of 21 and KMn of 31.33 had a good correlation with the experimental data.Furthermore,high-throughput sequencing was employed to characterize the bacterial diversity in the MBR,the results showed that Pseudomonas sp.H-117 and Pseudomonas sp.H-118 were the dominant contributor for effective removal nitrate in the reactor.(5)Mixed nutrition biofilm reactor was established,the experiment tested the different Cinorganic carbon/Corganic carbon ratios(5:1,2.5:1 and 0.5:1)on nitrate-N removal,the results suggested that NO3--N removal efficiency was increased as the Cinorganic carbon/Corganic carbon ratio decreased,this was due to a higher organic matter could be conducive to denitrification process.In the stable operation,concentration of nitrate in the effluent could be removed completely,TOC value in the effluent could be kept below 1 mg/L,this suggested that the strain could utilized organic matter to take part in the denitrification process.Meanthile,the Pseudomonas sp.were measured in the sample S1,S2 and S3,the relative abundance were increased as the the concentration of organic carbon in the reactor increased,the results also showed that Pseudomonas sp.H-117 and Pseudomonas sp.H-118 were the dominant contributor for effective removal nitrate in the reactor.