Denitrification,Sulfide Removal And Electricity Generation In A Microbial Fuel Cell

A lot of wastewater produced in many industrial production processes contain sulfureous and nitrogeneous compounds,which is usually treated with anaerobic digestion pretreatment to remove most of the organic matter and recover methane.After anaerobic digestion,the digestive effluent still contains nitrogeneous compounds and sulfide that need further removal.The recovered methane contains hydrogen sulfide that need desulfurization before methane utilization.Based on the fact that denitrication from anaerobic digestive effluent and desulfurization from methane exist electronic complementarity,denitrifying desulfurization process could be used for coupling of nitrogen removal from anaerobic digestive effluent and desulfurization from methane.In which desulfurization of methane could make up for the electron donordeficiency in denitrification of digestive effluent.Microbial fuel cell?MFC?is a device that can convert chemical energy contained in wastewater into electrical energy by microbial metabolism,which could realize simultaneous desulfurization,nitrogen removaland electricity generation.A denitrifying and sulfide removal MFC using sulfide as the sole electron donor and nitrate as the electron acceptor was constructed in this study.After successful start-up of denitrifying and sulfideremoval MFC,the effects of influent sulfide concentration,buffer solution type,temperature and hydraulic retention time?HRT?,electrode material on electricity generation and pollutant removal of the MFC were studied.The main conclusions are as follows:?1?A denitrifying and sulfideremoval MFC with continuous feeding mode,using graphite filaments as electrode?named as MFC1?,was successfully started up in 32days.The cell voltage reached 173.7±2.3mV at an external resistance of 100?,with corresponding S^2-removal loading of 0.94±0.026 kg/?m³NC·d?,NO₃^--N removal loading of 1.1±0.43 g/?m³NC·d?and SO₄^2-generation percent of 82%±3.8%.The SEM image of graphite filaments showed that granular sulfur was deposited on the anodic graphite filaments,and obvious rod-shaped bacteria grew on the cathodic graphite filaments.Another MFC using graphite particle as electrode?named as MFC2?was successfully started up in 38 days under the same condition.The maximum power density was near to that of MFC1,and the internal resistance of MFC2?303??was much highthan that of MFC1?192??.?2?With the increase of influent S^2-concentration,the internal resistance decreased gradually.The electricity generation showed a trend of gradual enhancing,but the enhancement increment became small when the influent S^2-concentration exceeded a certain level.The power density increased along with the increase of influent S^2-concentrationat eachexternal resistance.The increase increment of electricity production at high external resistance was smaller than that a slow external resistance.S^2-was almost completely removed at each influent S^2-concentration and external resistance.SO₄^2-generation percent increased slightly with the increase of influent S^2-concentration but decreased with the increase of external resistance.The NO₃^--N removal loading increased with the decrease of external resistance but fluctuated little at different influent S^2-concentration.?3?The components of the buffer solutionshad a little effect on electricity generation performance of the denitrifying and sulfideremoval MFC.It may be related to the buffering capacity of sulfide solution.The internal resistanceof MFC with50mmol/L phosphate buffer solution?PBS?was much lower than that with100mmol/L biocarbonate buffer solution or free buffer solution.The pollutants removal performance of MFC was closely related tobuffer solution pH.?4?Along with HRT being shortened,the maximum power density of denitrifying and sulfide-removal MFC fluctuated at random while the internal resistance decreased gradually with a decreasing increment.The shortening of HRT aslso resulted in an increase in S^2-removal loading and decrease both in SO₄^2-generation percentand NO₃^--N removal loading.?5?With the increase of temperature,the electricity generation performance of denitrifying and sulfide removal MFCwas strengthened and then weakened,while the internal resistance gradually decreased.The increase of temperature had little effect on S^2-removal.When the temperature was increased,the SO₄^2-generation percent increased followed by a decrease,with a maximum level atthe temperature of 30?and the external resistance of 100?.The optimal NO₃^--N removal was obtained at 25?.