Simultaneous Degradation Of Oxytetracycline, Nitrogen Removal And Electricity Generation By Photosynthetic Microbial Fuel Cell

As a bioelectrochemical capacity device,Photosynthetic Microbial Fuel Cell(PMFC)is capable of utilizing photosynthetic microorganisms to enhance the wastewater pollutants degradation while generating electricity,showing a great application potential in wastewater capacity.In this study,simultaneous degradation of oxytetracycline(OTC),nitrogen removal and electricity generation under self-sustaining operation could be achieved by constructing an algal-bactreia biocathode PMFC that follows the algal day/night photosynthetic/respiratory growth rhythm.Continuous nitrification/denitrification(or simultaneous degradation of OTC)could be complied under alternating aerobic/anaerobic conditions that created by algae photosynthetic oxygen production/dark respiration.At the same time,photosynthetic oxygen and nitrate will alternately as cathode electron acceptors to drive anode bioelectrochemical process strengthening OTC degradation and electricity production.Among them,the efficacy of simultaneous OTC degradation,nitrogen removal and electricity generation was focused.Besides,comprehensive testing techniques including biochemical,modern instrument analysis and molecular biology technology will be used to deeply reveal the bioelectrochemistry and microbiology during operation.Final,through cathode modification to enhance PMFC performance was conducted.The main conclusions are as follows:1.During alternate light/ dark,the efficacy and mechanism of algal-bacteria biocathode simultaneous nitrification/denitrification and driving PMFC electricty production under OTC stress were studied.The results shown that PMFC power generation had been significantly increased in all OTC concentration test levels(5-50 mg/L)since the OTC degradation products mediated cathode to oxygen and nitrate electron transfer was enhanced.However,the enhancement of current output level was not proportional as the increasing OTC concentration;The maximum power density can be obtained when the cathode was applied 5 mg/L OTC(illumination)and 20 mg/L OTC(dark),respectively.Corresponding to 1.80 and 7.50 times that of the maximum power density achieved in OTC-free group under the same test conditions.OTC concentration further increased to 50mg/L did not lead to obvious enhancement of power output,indicating the OTC in cathode greatly improved the system power output level,but this strengthening effect was not proportional to the increase of OTC concentration;The nitrate removal can be distinctly accelerated when the OTC concentration was lower 20 mg/L.However,the system power generation and nitrate removal will not continue to be reinforced due to 50 mg/L high OTC stress can pose a toxic effect on the biocathode microbial community;Cathodic bioelectrochemical process was able to promote electrolysis liquid alkalization,further accelerating the photolysis of OTC;In addition to some OTC-resistant bacteria,OTC concentration lower 20 mg/L will stimulate the growth of some dominant bacteria related to biocathode electron transfer,nitrogen removal and OTC degradation,but suppressed at 50mg/L.2.Driving by the algal-bacteria biocathode alternately light/ dark simultaneous nitrification/denitrification and oxygen reduction,the efficacy and mechanism of anode bioelectrochemical enhanced degrading OTC and electricity generation were investigated.The results shown that the OTC-specific removal rate was 61.00% higher than open state under an external resistance of 50 ? since the bioanode electrochemical process can further reinforce the OTC co-metabolism degradation;Cathodic photosynthetic oxygen as high oxidation-reduction potential electron acceptor could continuously drive the anodic electrochemical reaction during illumination,while nitrate as a major electron acceptor during darkness can not achieve this;The anode biofilm electrocatalytic activity can be further strengthened at a high concentration of 50 mg/L OTC;Since the improved electron transfer from microbial to anode,the maximum power density obtained by all OTC test levels(10-50 mg/L)was 1.20,1.76 and 1.80 times that of OTC-free group,respectively;The presence of OTC in the bioanode can selectively enrich a class of OTC-tolerant bacteria,which can degrade complex organic compounds while obtaining electrical energy;The mechanism of ARGs production during OTC bioelectrochemical degradation was more constrained by the anode bacterial community than OTC initial concentration.3.A Graphene Oxide/Cobalt/PolyPyrrole(GO/Co/PPy)modified graphite felt electrode was prepared by a simple one-step electropolymerization method.The resultsshown that the GO/Co/PPy composite modified electrode had better oxygen reduction catalytic activity than Co individually modified and Co/PPy modified electrodes;The maximum power density in the GO/Co/PPy composite modified cathode PMFC can reach4.00 times that of bare biocathode owning to the bioelectrocatalytic activity was greatly improved;Applying 5-50 mg/L OTC in GO/Co/PPy composite modified cathode could further stimulate the system maximum power density to increase by 4.60,3.70,2.90 and1.90 times,respectively;Under 50 mg/L high OTC stress,the synergy of OTC degradation products as cathode electron mediator and GO/Co/PPy composite film could obviously enhance cathodic electrochemical reaction,further stimulating the metabolic activity of related functional bacteria,thus covering the OTC-induced toxic effects;During the whole operation period,the removal rate of nitrate in GO/Co/PPy composite modified cathode was faster than bare biocathode,and all OTC test levels,the specific degradation rate of OTC in GO/Co/PPy composite modified cathode could be increased by 1.36,1.52 and 1.30 times,respectively,thereby intensifing PMFC electricity generation,cathode denitrification and OTC degradation.