Simultaneous Organics And Nitrate Removal In A Photocatalytic Fuel Cell Using A Biocathode

In China,water contamination is becoming more and more serious as the economy is growing rapidly.At the same time,people face more and more stringent wastewater discharge limit and that brings challenges to traditional wastewater treatments.Photocatalytic fuel cell（PFC）consuming sustainable energy and realizing in simultaneous electric energy harvest from wastewater is a typical green and potential wastewater treatment attracting much attention.In this paper,we redesigned the cathodic half cell reaction specific for a photocatalytic fuel cell by using a biocathode with a denitrifying biofilm in order to utilize the photo-excited electrons more effectively.The denitrification reaction catalyzed by microorganism helps alleviate the accumulation of electrons on the photoanode and the electrons in turn help enhance the degradation of nitrate.The overall PEC could realize simultaneous organics degradation,enhanced nitrate removal and small current generation.The main works fall into following parts:（1）Development of an effective photoanode.Five photoanodes fabricated by sol-gel,anodic oxidation or pulsed ultrasonic wave-assisted anodic oxidation method respectively based on titanium sheet or foam titanium sheet were compared.As for photocatalytic degradation ability,the electrode prepared by ultrasonic-assisted anodic oxidation had best performance of Rhodamine B（RhB）degradation,with a decolourization rate of 60%in 120 min at pH=5.As for anodic potential,the sol-gel made electrode based on titanium sheet had the most negative value which may indicate a largest output voltage when forming a cell with biocathode.In full cell test,sol-gel made electrode also turned out to have the largest open-circuit voltage of 0.84 V and short-circuit current density of 0.019mA·cm^-2,so it was chosen to be photoanode in combined cell.（2）Biocathode preparation.A biofilm electrode reactor was made and the effects of carbon source,C/N ratio,and applied voltage on denitrification were studied.The results showed that methanol was the most suitable carbon source.Almost 100%nitrate removal efficiency were obtained in 12 h,while no more than 50%by using glycine and the highest efficiency was only 7.6%by using urea.The applied voltage was optimized to 0.15 V with a nitrate removal rate of 20.62 mg·L^-1·h^-1,5%improvement on the situation with no applied voltage.Furthermore,the lower the C/N is,the slower the denitrification is but the more significant is about the effect of applied voltage.（3）The combination of photoanode and biocathode to be a PFC.A combined PFC with biofilm cathode was built and simultaneous pollutants removal in two chambers and electricity generation were achieved.The color removal rate of Rhodamine B in anodic half cell and the nitrate removal rate in cathodic half cell during 3 h grew by 15%and 5%respectively compared to open circuit situation.Furthermore,It’s V_oc,J_scc and output power reached 0.51 V,0.217 mA·cm^-2 and 0.026 mW·cm^-2when using 0.05 M Na₂SO₄ and 0.05 M Glucose as fuel.