Study On The Microbial Community And Denitrification Performance Of MFC With Simultaneous Nitrification And Denitrification

Microbial fuel cell(MFC)have gained widespread attention due to their ability to generate electricity while treating wastewater.In this study,the synthetic wastewater(480mg/L NH4+-N,300 mg/L COD)was pumped into the anode chamber,then the effluent was pumped into the cathode chamber for nitrogen removal.The influence of dissolved oxygen(DO)on the performance of denitrification and predominant species has been investigated.The main results are as follows:(1)The DO concentration was controled in 0.5–1 mg/L through intermittent aeration.After long-term operation,the process of short-cut nitrification and denitrification was successfully achieved in the cathode chamber.The nitrification in the cathode chamber was strengthened and the nitrification rate was up to 63%.Denitrification reactions included heterotrophic denitrification and electrode denitrification,the total.nitrogen removal was up to 30%.(2)The DO concentration was controled in 3–4.2 mg/L through continuous aeration.After long-term operation,the process of simultaneous nitrification and denitrification was successfully achieved in the cathode chamber.With the increase of temperature and DO,autotrophic nitrifying bacteria were gradually replaced by thermophilic aerobic denitrifying bacteria,which resulted in the rise of voltage and coulomb efficiency,meanwhile,the removal efficiency of nitrogen decreased.This demonstrated electrode denitrification by aerobic denitrifying bacterium(ADB)is beneficial for achieving a higher voltage of the MFC,while traditional heterotrophic denitrification is conducive to higher total nitrogen(TN)removal.Moreover,the performance of MFC was investigated under different external resistance.The nitrous oxide production and TN removal efficiency were higher with a 50 ?external resistance than with a 100 ? resistance,which demonstrated that the electrode denitrification by ADB occurred in the cathode of the MFC.It was inferred that sufficient electrons were provided by the electrode to allow ADB survival at low carbon:nitrogen ratios(C/N<1).(3)The predominant species in two phases was studied by PCR-DGGE.Results showedthat increasing the DO resulted in a change of the predominant species from thermophilic autotrophic nitrifiers and facultative heterotrophic denitrifiers at low DO concentrations to thermophilic ADB at high DO concentrations.In the phase of short-cut nitrification and denitrification(low DO,0.5–1.0 mg/L),it was speculated that possible reactions in the cathode were anaerobic fermentation,anaerobic denitrification.In the phase of simultaneous nitrification and denitrification(high DO,3.0–4.2 mg/L),it was speculated that possible reactions in the cathode were aerobic nitrification and denitrification.SND in the aeration cathode of the MFC may be beneficial for the growth of ADB.