| Many industrial wastewaters,containing sulfurous,nitrogenous and organic pollutants at high level,were treated with anaerobic digestion process for removing most organics.The anaerobic digestion effluent,containing a large number of sulfides and nitrogeous compounds,need further removal.Microbial fuel cell?MFC?provide a new approach for wastewater treatment coupled with electricity recovery.Two double-chamber MFCs,a nitrifying sulfide removal MFC?MFC1?and a denitrifying sulfide removal MFC?MFC2?were constructed in this study.MFC1and MFC2 were operated in series to treat ammonium/sulfide-containing wastewater.In this series system,S2-was oxidized to S0 or SO42-in the anodes of both MFCs via electrochemical or microbial reaction.NH4+was firstly oxidated to NO3-in the aerobic cathode of MFC1,and then denitrified to N2 in anoxic cathode of MFC2.After successful start-up of MFC1 and MFC2,the influence of several factors on the performance of series system and the influence of intermediates on MFC2 were studied.The isolation of electroactive denitrifying bacteria was also explored.The main conclusions were as follows.?1?MFC1 and MFC2 were operated in continuous feeding mode and successfully started-up in 28d and 170d,respectively.The cathodes of MFC1 and MFC2 were connected in series and both MFCs were operated in batch mode.The performce of series system reached stable within 15 days.The sulfide removal loading of MFC1 and MFC2 were respectively 0.13±0.0 kgS/m3.d and 0.1±0.0kgS/?m3·d?,with the elemental sulfur deposition effeciencies of 6.6±1%and27.3±0.9%,respectively.Complete nitrification was obtained in MFC1.The total nitrogen removal loading of series system was 10.9±0.2 gN/?m3·d?,51.5±0.4%of which was transformed to gaseous nitrogen.The batch charge of MFC1 and MFC2were 280.1±0.5 C and 193.6±0.6 C,respectively.The anodioc coulombic efficiency were 47.5±0.1%and 55.1±0.3%,respectively,which was significantly higher than that in start-up stage.Scanning electron microscope images revealed that there were aggregated microorganisms in the anode and cathode.?2?With the increase of S/N ratio,the electricity generation of MFC1 and MFC2 increased first and then decreased.The maximal power density of 13.59W/m3 and 5.80 W/m were obtained at a S/N ratio of 3 for MFC1 and MFC2,respectively.The S2-removal loading of MFC1 gradually increased with the the increase of S/N ratio,but that of MFC2 varieded little.The sulfur element deposition efficiencies increased first and then decreased,with maximum levels?33.3±0.9%for MFC1 and 27.4±0.4%for MFC2?at an S/N ratio of 3.The total nitrogen removal loading increased first and then decreased,and showed insignificant difference between the S/N ratio of 2 and 3?18.6±0.4 gN/?m3·d?and 17.1±0.5 gN/?m3·d?,respectively?.The optimal S/N ratio for the series MFC system was deemed as 3.?3?With the increase of temperature,the power generation and pollutant removal performance of both MFCs increased first and then decreased.The optimal performance of the series MFC system was obtained at a temperature of 30°C.The maximum power densities of MFC1 and MFC2 were 13.59 W/m3 and 5.80 W/m3,respectively,and the corresponding S2-removal loading and total nitrogen removal loading were 0.18±0.0 kgS/?m3·d?,0.13±0.0 kgS/?m3·d?and 17.1±0.5 gN/?m3·d?.?4?MFC2 was operation using SO32-,S2O32-,and S2-with same amount of theoretically releasing electrons potentialthe as the anodioc electron donors.The worst performance of denitrification and optimal electricity generation potential were obtained when SO32-was used.But the optimal denitrification performance was achieved when S2-was used,coupled with the highest electron utilization efficiency and the fastest metabolic rate.With the increase of influent NO2-concentration,the maximum power density and sulfide removal performance of MFC2 gradually increased,and the total nitrogen removal loading increased first and then decreased.When same amount of theoretical electron consumption was provided,NO3-was a more competitive electron acceptor than NO2-and more beneficial for electricity generation,but showed slower metabolic rate.?5?Compared to carbon cloth,carbon paper was a suitable electrode material for the isolation of electroactive denitrifying Bacteria.The isolation of electroactive bacteria based on potentiostat driving was beneficial to improve the isolation effect and reduce the adaptation period of isolates cultivation.After six isolations,the relative abundance of Pseudomonas in the microbial community reached 71.36%.Besides,the relative abundances of Leclercia and Enterobacter were 14.64%and6.18%,respectively.Pseudomonas and Leclercia may be the dominant species of electroactive denitrifiers. |
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