The Lab-scale Study On Zero-valent Iron-denpendent Denitrification By Microbial Fuel Cell

In this paper,a two-compartment electrochemical reaction system is adopted,izero-valent iron as the anode,carbon brush attached to the biofilm as the cathode,nitrate-containing wastewater as the cathode solution,was used to study the microbial fuel cell（MFC）biological denitrification system based on zero-valent iron.The aim is to solve the dilemma of ammonia/ammonium production by zero-valent iron denitrification.The new technology is promising to improve the efficiency of zero-valent iron dependent biological nitrogen removal,and finally realize the high-efficient autotrophic denitrification based on zero-valent iron in sewage.The main results of this paper are as follows:（1）In this paper,the microbial fuel cell MFC constructed with zero-valent iron as the anode and biofilm-attached carbon brush as the cathode can run continuously for 42 days（6cycles in total）.The nitrate removal rate reaches 91.76%,and the volume removal rate is0.0055 kg·m-3·d-1,but decreases with the aging of the biofilm.The output voltage of the MFC maintained at 540±20 mV in 40 hours,and then linearly reduced to less than 15 mV with nitrate consumption during intermittent operation.The voltammetric charge（q^*）of the MFC cathode decreased by 44%from the first cycle to the sixth cycle,respectively,indicating that the activity of the biological cathode decreased.The Electrochemical impedance spectroscopy test（EIS）results and the power density curve shows that the internal resistance of MFC gradually increased by 27%.The Thauera dominated in the biofilm,which can directly utilize electrode electrons as electron donors.（2）The optimal operating conditions of MFC was obtained,under neutral conditions,with 200 mg/L nitrate and 2 mol/L NaCl as substrate and external resistance of 1000Ω,the MFC worked best.（3）Under optimization conditions,the volumetric nitrate nitrogen removal rate increased to 10 times,and the removal efficiency increased to 2 times comparing with data in the first part.The R_ohm and R_ct values of the MFC significantly reduced to one-tenth,which was conducive to the denitrification process of the reactor.However,the output voltage change trend is consistent with the results in the first part,and there is no significant increase.The variation trend of CV curve and q^*value measured here is also similar to that in the first part.Results of coulombic efficiency test showed that the proportion of electrotrophic denitrification in this experiment gradually increased.