Study On Photoelectric Combined Enhanced Biofilm To Remove Nitrogen,phosphorus,antibiotics And Accumulate High Value-added Products

The discharge of wastewater containing high concentrations of nitrogen（N）and phosphorus（P）can lead to eutrophication of water bodies,disrupting the balance of aquatic systems and thus putting enormous pressure on water sanitation and environmental management.These N-and P-containing wastewater often contain antibiotics,which can pose a serious risk to ecological safety and human health.Microorganisms can degrade or utilize pollutants through assimilation,and they can use wastewater to produce high-Value products such as lipid and protein.In this study,a mixotrophic photo-electrochemical biofilm reactor（MPEBR）was constructed by introducing solid electrodes as electron acceptors for mixed microorganisms,and the rate of extracellular electron extraction was controlled by simultaneously adjusting the light intensity（3000 lux,8000 lux and 23000 lux）and Varying the applied potential（-0.3 V,0 V,0.3 V）to enhance the photoelectron-active biofilm to remove N,P,sulfadiazine（SDZ）and accumulation of lipid and protein,with the following findings:（1）Photoelectric combination significantly enhanced the removal of N,P and SDZ by photoelectron-active biofilm.When the initial concentrations of NH₄⁺-N,PO₄^3--P and SDZ were 125mg/L,15mg/L and 1mg/L,respectively,under-0.3 V/high light intensity（23000lux）condition,MPEBR showed the best removal of NH₄⁺-N,PO₄^3--P and SDZ,reaching65.91%for NH₄⁺-N and 95.87%for PO₄^3--P within 72 h,respectively,and 52%for SDZ within 12 h.（2）NH₄⁺-N and PO₄^3--P were mainly removed by photoelectron-active biofilm absorption.Bioelectric degradation accounted for 86.64%of the SDZ removal pathway and was the main removal pathway.（3）Photoelectric combination significantly promoted the accumulation of lipid and protein by photoelectron-active biofilm.0.3 V/low light intensity（3000 lux）accumulated the highest amount of lipid（409.28 mg/g）and 0 V/low light intensity accumulated the highest amount of protein（362.29 mg/g）.The three-dimensional fluorescence spectra（3D-EEM）showed that different light intensities combined with the applied potential could promote the secretion of fluorescent active protein,and the main fluorescent active protein substances were aromatic and tryptophan-like protein.The 3D distribution of lipid and protein on the biofilm was observed by confocal laser scanning microscopy（CLSM）.Lipid was distributed in a punctiform manner and protein was distributed in a lamellar manner.The lipid and protein of the biofilm were distributed in an interspersed pattern under low light（3000 lux）and medium light intensities（8000 lux）with applied potential.The protein of the biofilm was distributed in the inner layer near the working electrode and the lipid was distributed in the outer side under high light intensity with applied potential（4）The coulomb efficiency showed a positive correlation with the current density,and the coulomb efficiency decreased with increasing potential for the same light intensity.The maximum biocurrent（3.385 m A）was obtained at-0.3 V/high light intensity,with a converted extracellular electron extraction efficiency of 9.65%and was accompanied by the best NH₄⁺-N,PO₄^3--P and SDZ removal efficiencies.A significant positive correlation between the three pollutants removal efficiencies,light intensity and applied potential.Compared with no applied potential under high light intensity,the removal efficiencies of NH₄⁺-N,PO₄^3--P and SDZ were all improved under the applied potential condition,indicating that using the electrode as an extracellular electron acceptor to extract intracellular electrons from microorganisms can effectively alleviate the photoinhibition of microorganisms under high light intensity.The cyclic voltammetric curve（CV）diagram with large redox peak currents at high light intensity with applied potential also indicated the good electron extraction ability under this condition.（5）Photoelectric combination led to selective enrichment of specific functional microorganisms by MPEBR.High throughput sequencing results showed that the biofilm grown under low light intensity with applied potential was dominated by the photosynthetic bacterium Chlorobium,which can absorb and assimilate NH₄⁺-N and PO₄^3--P and produce large amounts of lipid and protein;five typical electroactive microorganisms,Bacteroidetes,Erysipelotrichaceae,Tissierella,Desulfoviibrio and Rhodocyclaceae,were significantly enriched in MPEBR at medium and high light intensities with applied potential,all of which have been shown to be able to assimilate NH₄⁺-N and PO₄^3--P and have the ability to degrade complex organic pollutants,and in which electroactive photosynthetic bacteria such as Rhodocyclaceae played an important role.