Study On Degradation Of Antibiotic In Photocatalytic Anode Coupled With Simultaneous Denitrification In Biocathode

At present,the main way to remove nitrogen pollution is denitrification,but the core limiting factor in the process is the lack of electron donors.On the other hand,photocatalytic technology has outstanding advantages in the treatment of difficult-to-degrade pollutants,but it also faces practical problems,and needs to solve the problems of photocatalytic fixation and recycling.The photocatalytic electrode coupled with biological electrode can be used to make a microbial photoelectrochemical cell.Thus the microbial photoelectrochemical system is very prominent in combining the advantages of photocatalysis and biodegradation,and related research is rare.In this study,in response to the problem of insufficient denitrification electron donors and photocatalytic fixation,different photocatalytic anodes and biocathodes were coupled.Thus,photocatalytic degradation of sulfadimethoxine（SMT）in anodes driving by low-power LED was achieved,while photogenerated electrons were used for denitrification simultaneously by biocathodes.The surface morphology of electrodes was studied using SEM and TEM.The structural characteristics of anodes were analyzed using XRD and FTIR.The photoelectrochemical performance of the electrodes was discussed by UV-vis DRS,photocurrent test,EIS,etc.The denitrification effect was evaluated according to the test of isotope N₂ and production of greenhouse gas,etc.The distribution and activity of functional microorganisms are revealed by analyzing the microbial community and determining the absolute abundance of denitrifying functional genes.Meanwhile,the differences of pollutant removal effect of different systems were compared,and the degradation effect and operating mechanism were explained.The main research conclusions are as follows:（1）Ti/α-Fe₂O₃（TF）,poly 3-hexylthiophene（P3HT）/α-Fe₂O₃（PF）and P3HT/Ti/α-Fe₂O₃（PTF）photocatalysts（metal-doped,ordinary PN heterojunction and Z-scheme heterojunction,respectively）were stably fixed on stainless steel substrate to make three types of photoanode by using polyvinyl butyral（PVB）as curing stabilizer and graphite as reinforcing conductive agent.Graphite felt was inoculated with denitrifying sludge to form biocathodes.After acclimation and cultivation,three mature experimental systems with different photoanodes were obtained.（2）The SEM images showed that the anode surfaces was granular.The EDS spectra showed the differences of element distribution on photoanodes caused by different photocatalysts,and TEM observed the characteristic lattice spacing of different photocatalysts,which supported that the photocatalysts were successfully loaded.TGA results indicated that each photoanode maintained considerable stability below 200℃.UV-vis DRS results showed that the band gap of PF is 1.58 e V,and the PTF is 1.63 e V,both lower than that of TF（1.96 e V）.Photocurrent and EIS analysis indicated that PTF had stronger charge of separation efficiency and photocatalytic activity.（3）The removal rates of 10 mg/L SMT at 7 days by TF,PF and PTF photoanodes were 41.8%,52.4%,and 56.1%,respectively.The kinetic fitting results were consistent with the quasi-second-order reaction kinetics,with kinetic constants of 0.010 d^-1,0.015d^-1,and 0.018 d^-1,respectively.It was speculated that there may be a fixed number of saturation sites bound to SMT on the surface of the photoanodes.The oxidation ability of PTF was relatively stronger,which was consistent with the analysis of the photocatalytic energy band and the explanation of the electronic transition mechanism.（4）The CV,Tafel curves and EIS analysis results of biocathodes showed that the PF biocathode had a relatively stronger electron transfer efficiency and a higher activity of functional microbial flora.The removal rate of NO₃^--N by PF and PTF biocathode was 100±0%,and 96.56±3.36%by TF.Denitrification of TF biocathode was consistent with zero-order reaction kinetics,and the kinetic constant was 0.133±0.021d^-1.Both of PF and PTF conform to first-order reaction kinetics,with kinetic constants of 0.649±0.161 d^-1 and 0.433±0.115 d^-1,respectively.The PF heterojunction had better electronic separation and long-distance transmission capabilities.The whole denitrification process was thorough,and most of the products was N₂.（5）After domestication,the biodiversity of the biocathode had decreased significantly and the denitrifying genus was obviously dominant.The proportion of five denitrifying bacterial genus of Stenotrophomonas,Denitratisoma,Flavobacterium,Thermomonas and Thauera was 7.9-29.0%,and the enrichment degree in sludge was higher than that in aqueous solution.Nar G,nir S,nir K,and nos Z functional genes had the highest absolute abundance in the PF biocathode,and the different distribution of absolute abundance of functional genes exactly explained the difference of denitrification rate of biocathodes.（6）The monitoring of current confirmed directly that biocathodes accepted photogenerated electrons from anodes.The current efficiency of TF was 83.9%,which was higher than 82.5%of PTF and 76.3%of PF.The system could withstand long-term operation and maintained good stability,and was promising in practical application.