| The worldwide energy crisis and environmental pollution problems have beencreating a demand to develop more sustainable technologies for energy recovery aswell as waste disposal. Microbial Fuel Cell (MFC) is considered to be a promisingand sustainable technology to effectively solve problems of current water pollutionand energy shortage. It can make full use of different kinds of organic matters inwastewater, which can simultaneously realize electricity recovery and wastewatertreatment. The denitrifying MFC is a new concept of biological wastewater treatmenttechnology, which can be used to drive electricity generation and simultaneousnitrogen and carbon removal.Phosphate buffer solution (PBS) has been widely used in MFC studies tomaintain a suitable pH for electrogens and to increase the solution conductivity.However, addition of a high concentration of PBS in MFC is expensive, especiallyfor the application in wastewater treatment. Moreover, the phosphate can contributeto eutrophication of water bodies if the effluents are discharged without beingremoved. Therefore, it is urgent to find alternative buffer solutions for MFC. In thisstudy, with a boric acid-borate buffer solution, the start-up, effect of temperature,external resistance, influent COD concentration, mixing intensity and buffer solutionconcentration on electricity generation and pollutant removal of denitrifying MFCwere studied in order to optimize the operational conditions and to enhance itsperformance. The main conclusions are as follows:(1) Denitrifying MFC with boric acid-borate buffer solution was started upsuccessfully in51days under continuous feeding condition. the maximum powerdensity of6.46W/m3NC and internal resistance of63.9were obtained according totheoretical approach of electrochemistry. When the external resistance was set at50,the stable cell voltage, COD and nitrate removal rate were respectively205.1±1.96mV,0.85±0.020kg/(m3NC.d) and6.17±1.906mg/(m3NC.d). While theaccumulation of NO-2-N in cathode effluent was only0.092±0.034mg/L. The SEM image of biofilm on the anode and cathode showed that the bacteria growing on theanode appeared to be similar to a larva and appeared to have a uniform morphology,while the bacteria growing on the cathode were smaller and fewer than those on theanode.(2) As the temperature was increased from15to35℃, the maximum powerdensity of denitrifying MFC increased along with the decrease of internal resistance.the maximum power density and corresponding internal resistances were respectively5.61,6.86,7.89,8.23,8.76W/m3NC and82.7、60.1、50.9、49.0、47.9at thetemperature of15,20,25,30,35℃. The temperature posed little effect on CODremoval, COD removal loading maintained at about0.89kg/(m3NC·d). but theincrease of temperature benefited nitrogen removal in cathode. The nitrate removalrate was up to7.54±0.204mg/(m3NC.d) at an external resistance of4andtemperature of25℃.(3) Within a certain range, the capacity of electricity production increased withthe increase of organic loding rate. the maximum power density of10.01W/m3NCand minimum internal resistance of38.1were both occurred at the the CODconcentration of400mg/L. The dependence of power density on initial CODconcentration exhibited “saturation effect”, which could be described and explainedwith traditional Monod equation. The higest anodic coulombic efficiency of44.3±2.84%was obtained at the inflent COD concentration of300mg/L and externalresistance of5. The maximum COD and NO-3-N removal loading were repectively1.180±0.017kg/(m3NC.d) and9.57±0.834mg/(m3NC.d) obtained at the externalresistance of5and inflent COD concentration of400mg/L.(4) Recirculation was found to have a substantial impact on electrochemicalperformance. With the increase of mixing intensity, the capacity of electricityproduction showed a rapid increase followed by a slow increase while the internalresistance showed a rapid decrease followed by a gradual increase. the maximumpower density of8.24W/m3NC and minimum internal resistance of48.0were bothoccurred at a recirculation rate of20mL/min. The optimal COD removal wasobtained at a recirculation rate of10mL/min because of the optimal flow state, withthe effluent COD of3.59±0.35mg/L. And the maximum NO-3-N removal loading15.65±0.402mg/(m3NC.d) was occurred at free mixing. Because free mixing hindered the dissloved oxygen penetration into biofilm.(5) Buffering solution played an important role in maintaining pH within a stablelevel. Increasing ion strength could result in a decrease of internal resistance as wellas an increase of power density. the maximum power density of8.27W/m3NC andminimum internal resistance of48.0were both occurred at a buffer solutionconcentration of100mmol/L. The concentration of buffer solution posed little effecton COD removal, but increasing the concentration of buffer solution can decrease theeffluent pH of cathode and promote the nitrogen removal performance. |
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