| Antibiotics in wastewater usually coexist with nitrogen-containing pollutants.Nitrogencontaining compounds have biological toxicity,and antibiotics could exert selective pressure on environmental microorganisms even at extremely low concentration which leads to the generation of resistant bacteria and resistant genes.Consequently,ecological system and human health were faced with huge threat.Physicochemical technology is easy-operated to antibiotic removal and denitrification,but the high cost of equipment and large energy consumption make it difficult to apply to real life.Biological treatment is regarded as an environmentally friendly technology,which has high economic benefits,but at the same time has the disadvantages of high energy consumption and slow metabolic efficiency,even the produced gas is difficult to use which may cause the greenhouse effect.In this study,a photosynthetic bioelectrochemical system(PMFC)was established based on the circadian laws of algae photosynthesis and respiration.The system created the conditions for the denitrification of the cathode by the cooperation of algae and bacteria,and nitrate and nitrite alternately used as cathode electron receptor to promote degradation of antibiotics in anode,thereby achieving PMFC self-sustaining synchronization of wastewater antibiotic degradation,denitrification and electricity production.Compared with traditional physicochemical and biological treatment technology,PMFC is applied by using solar energy and bioenergy to remove pollutants in wastewater without the need for additional artificial energy input,which is a new sustainable wastewater treatment technology,and can eventually achieve self-sustaining simultaneous wastewater degradation,nitrogen removal and power generation.In addition,considering that the PMFC cathode lacks high redox potential electron acceptor at night and cannot effectively drive bioelectrochemical reactions in cathode and anode.Therefore,the photovoltaic solar capacitor is further integrated with the PMFC,and In order to enhance the bioelectrochemical reaction of PMFC,solar cells are used to charge the capacitance in the daytime and discharge the capacitance at night,eventually achieving all-weather PMFC anode bioelectrochemical degradation of antibiotics and cathode denitrification.The above-mentioned operational characteristics and mechanism provide theoretical basis and technical parameters for the construction of a self-sustaining highefficiency wastewater treatment system based on algal bacteria bioelectrochemistry.The main conclusions are as follows:1.Effect and mechanism of Florfenicol(FLO)degradation and nitrogen removal by algal bacteria(PMFC)were studied under the condition of day night alternate light / dark operation.The results shown that 100 mg / L of ammonia nitrogen was completely removed from the cathode in 90 hours,which was mainly attributed to the photosynthetic oxygen production of Chlorella to promote the nitrification of ammonia nitrogen,while the acceleration of denitrification in bioelectrochemistry was due to the nitration of nitrate and nitrite as the cathode electron acceptor,and the residual concentration of nitrate and nitrite were 72% and 60% lower than that of the open circuit control.The degradation rate of FLO by PMFC anode is 1.63 times higher than that of open circuit.The intermediates formed during FLO degradation were identified by LC–MS,the bioelectrochemical degradation of FLO in the anode of the generated ten intermediate degradation products(corresponding to 165,200,225,228,278,386,302,320,354 and 369 in M/Z).Basically,two halogen groups,Cl and F,have been removed,and halogen group is the key group with antibacterial property in FLO molecule.Therefore,it can be concluded that the bioelectrochemically enhanced co-metabolic reductive dehalogenation was mainly responsible for the FLO removal in the anode of the PMFC.Cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)were used to determine the electrochemical properties of the membrane.The results showed that the activity of the membrane was not in direct proportion to the concentration of FLO.The activity of the membrane increased with the addition of FLO 0.5-1mg/l,but the activity of the membrane with 3 mg / L FLO was lower than that with 0.5-1mg/l FLO.It can be seen that the addition of FLO to the anode has both positive and negative effects on the electrochemical process of the anode,depending on the concentration of FLO added.Phylogeneticanalysis of 16 S r RNA was performed to investigate the effect of FLO feeding on anodic bacterial community and transmembrane diffusion of FLO from the anode to the cathode on cathodic bacterial community.compared to the FLO-free anodic biofilm,the results showed that,the 0.5 mg/L FLO feeding resulted in 0.64,7.43 and 37.78-fold increases in the abundance of phylum Proteobacteria,Actinobacteria and Fimicutes,respectively,but 86.98% decreases in the abundance of phylum Bacteroidetes,while the phylum Planctomycetes and Ignavibacteriae had almost completely disappeared.When 0.5 mg/L FLO was fed to the anode,the dominant genera were reduced to six species,including Pseudomonas(38.38%),Achromobacter(27.02%),Petrimonas(3.13%),Stenotrophomonas(2.86%),Methylobacterium(2.44%)and Rhodococcus(2.18%).Among them,the exoelectrogen Pseudomonas exhibited the greatest abundance indicating that FLO at this concentration level stimulated the growth of Pseudomonas,which coincided with enhanced power output of the PMFC by feeding 0.5 mg/L FLO to the anode.The feeding of 5 mg/L FLO to the anode and the transmembrane diffusion of FLO from the anode to the cathode resulted in significant changes in the bacterial community structure within the cathodic biofilm.The abundances of genus Simplicispira,Pseudomonas and Aquamicrobium significantly increased whereas the abundances of genus Nitrosomonas,Ignavibacterium and Thermomonas decreased in response to FLO feeding in the anode.Moreover,transmembrane diffusion of FLO from the anode to the cathode also stimulated the growth of the genus Acidovorax which has been reported to catalyze the oxidation of ferrous iron coupled to nitrate reduction.Based on these results,it can be concluded that FLO crossover from the anode to the cathode might exert a selection pressure to cathodic bacterial community,thereby affecting the nitrogen removal performance of the cathode.2.Effect and mechanism of different capacity capacitors in daytime solar cell charging and nighttime discharge to enhance the anode degradation FLO and cathode denitrification of PMFC were investigated by connecting solar photovoltaic capacitors into PMFC,the experimental results show that the anode FLO removal and cathode denitrification was Significant enhanced by capacitance discharging at night under Bioelectrochemical system of algae of light/dark cycle.Capacitance discharging with 3.3 F,10 F and 100 f capacitors,that the degradation rate of FLO on the anode of hotosynthetic bioelectrochemical system of algae was increased 44%,89% and 582% and the removal rate of ammonia nitrogen on the cathode was increased 20.4%,39.8% and 55.6% and the accumulated nitrate was decreased 70.0%,86.5% and 93.3%,and the accumulated nitrite was decreased 48.6%,45.7% and 87.1%,respectively.Anode potential was raised and cathode potential was reduced by capacitance discharging,and promoted the enrichment of functional bacteria in anode that has ability to degrade complex organics and extracellular electron transfer and also promoted the enrichment of autotrophic denitrifiers and multifunctional denitrifiers with the ability of extracellular electron transfer in the cathode.At the same time,the electrochemical activity of anode and cathode biofilm was enhanced,which further enhanced FLO removal of anode and denitrification of cathode. |
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