Preliminary Study on E. coli Microbial Fuel Cell and On-electrode ...

1182 过 程 工 程 学 报 第 8 卷the MFC, anaerobic experiments with E. coli cells wereinitiated in order to pre-adapt bacterial metabolism in ananaerobic environment, then E. coli′s electrochemicalactivity was improved to some extent. So MFC couldrapidly generate electricity and attain stable state.3.2 On-electrode Taming MethodsBiofilm attached to electrode is developed asfollows: bacterial attachment to electrode, earlymaturation and acquisition of biofilm structure, maturebiofilm, and bacterial detachment [22] . The electricitygeneration of MFC is extremely related to the formedmature biofilm attached to the electrode [6,19,20] . However,most of MFC bacterial taming methods usually needrepeatedly scrap biofilm to select and optimize bacteria,but the operation of scraping biofilm can result in theloss of electrochemical activity of biofilm andpostponing the time that biofilm again matures.On-electrode taming method judges the maturation ofbiofilm according to the voltage−ampere curve of MFC,which means that the current density of MFC justattains the plateau phase (reaching the peak currentdensity) when the biofilm has matured [3,6,19,20] , theoperations of on-electrode taming without scraping offof biofilm can simply and rapidly achieve the bacterialselection and optimization.During the experiments, when the MFC attainedthe plateau of current density for the first time, thebiofilm attached to carbon paper had matured, and theelectrochemically activated E. coli biomass wasaccumulated, meantime, the anode solution wasremoved out to eliminate the infection of accumulatedoutgrowth and detached cells in the anode chamber afterthe MFC run for a long time [6,8] , and the anode chamberwas rapidly added with 40 mL medium to anaerobicallyculture the mature E. coli biofilm attached to theelectrode, and the electrochemical activity of E. colibiofilm was conserved. When MFC was again addedwith anolyte to carry out the electrochemical test, itspeak current density was increased, and the time toreach the peak current value was reduced. Successiveanaerobic cultivation and electrochemical test werecarried out to tame of E. coli biofilm and graduallyimprove the electrochemical activity of E. coli biofilm.As shown in Fig.5, after the 4 th taming (n=4), themaximum current density of E. coli MFC and theparental (n=0) E. coli MFC was respectively 612.5 and397.5 mA/m 2 , namely the biofilms attached to theelectrodes had matured. We can see from theexperimental data that the maturation time of tamedbiofilm was obviously reduced to 240 min, quickeningup 1 times compared with that of parental E. coli,meantime, the maximum current density of the tamed E.coli MFC was increased 0.54 times compared with thatof parental E. coli MFC.Current density (mA/m 2 )400650390 (a) Before taming600(b) After the 4th taming380370550360500350450340400330350320200 250 300 350 400 450 500 550300200 250 300 350 400 450 500Time (min)Time (min)Fig.5 Relationship between current density and time in MFCs before and after taming of E. coliFigure 6 shows the relationship of cell voltage andpower density with current density of MFC in thetaming process under n=0, 2, 4. After the 4 thon-electrode taming (n=4), the maximum power densityof tamed E. coli MFC reached 166.67 mW/m 2 ,increasing 64% compared with the maximum powerdensity 101.81 mW/m 2 of the parental E. coli MFC(n=0).As summarized in Fig.7, after the 4 th on-electrodetaming, the electricity generation of tamed E. coli MFCwas remarkably improved compared with the electricityCurret density (mA/m 2 )generation of parental E. coli MFC, the tamed E. coliMFC showed a 54% improvement in peak currentdensity, reaching 612.50 mA/m 2 , a 64% improvement inmaximum power output, reaching166.67 mW/m 2 . Zou etal. [9] reported a parental E. coli MFC, its maximum poweroutput was 70% of that of the MFC in this work, being116 mW/m 2 , and the initial concentration of E. coli inthe literature was 220% of that in this work, being 2.73mg/mL.Because taming of mediator MFC bacteria byserial transfer was not reported in the literature, in the