Degradation Of Sulfonamides By Microbial Fuel Cells And Its Mechanisms

In this paper,two sulfonamides(SAs)with high usage and detection rate in recent years were selected(sulfamonomethoxine,SMM and sulfadiazine,SDZ).By changing the electrode material,strain conditions,initial concentration of SAs,humic acid content and pH conditions,the degradation efficiency of SAs and electricity generation performance in the MFCs were studied.In order to find out the mechanism of SAs affecting MFCs' electrical production.The main research contents and results are as follows:After 5 days of operation in the MFCs system,the degradation rate of 10 mg/L SMM in MFCs was 58.9%.Under the condition of high temperature inactivation,MFCs had almost no electrochemical activity,and the removal rate of SMM was very low,indicating that the degradation of SMM and the power generation of MFCs electricity were mainly due to the presence of live bacteria in MFCs.The bacterial number of Shewanella putrefaciens was higher than that of Shewanella oneidensis MR-1 under the same time and MFCs operation condition,and the degradation rate of SMM under S.putrefaciens condition was 58.9%,which was higher than that of S.oneidensis MR-1 condition(46.5%).The maximum output power of MFCs under the condition of S.putrefaciens was 31.47 m W/m~2,higher than that under the condition of S.putrefaciens(24.96 m W/m~2).Under three different anode materials,the degradation efficiency of MFCs on SMM were:carbon felt(58.9%),carbon paper(50.3%),and graphite rod(33.6%).The maximum output power of MFCs was 31.47 m W/m~2,followed by carbon paper(26.67 m W/m~2)and graphite rod(10.25 m W/m~2).With the increase of SAs concentration,the output voltage of MFCs decreased significantly.When the SDZ concentration was 10 mg/L,the maximum output voltage of MFCs was 0.4077 V,which was lower than the condition of 10 mg/LSMM.SAs had a negative influence on the electrochemical activity of the anode biofilm.The study of SAs concentration on microbial growth and riboflavin secretion in MFCs solution showed that the bacterial concentration of S.putrefaciens in the blank group reached the highest level on the third day,about 1.35×10~8cells/m L.When 10 mg/L SAs was added,the maximum bacterial concentration significantly decreased.With the increase of SAs concentration,the growth of S.putrefaciens was gradually inhibited.The addition of SAs had a negative effect on the riboflavin concentration in the MFCs solution and inhibited the riboflavin-mediated electron transfer process,and the negative effect of SDZ on the cell growth and riboflavin concentration in the MFCs solution was greater than that in SMM.The degradation efficiency of SMM was 58.9%,30.9%,18.4%and 12.1%when the initial SMM concentration was 10,20,30 and 40 mg/L.The degradation efficiency of SMM gradually decreased with the increase of the initial SMM concentration.The MFCs system has the best electrical performance at pH 6.0 and the best SMM degradation efficiency at pH 7.0.The power density of MFCs at different pH values was in order as follows:pH 6.0>pH 7.0>pH 8.0>pH 5.0>pH 9.0,where the highest was 22.90m W/m~2at pH 6.0.Electrochemical analysis showed that conditions favorable to the protonation of SMM also had a positive effect on the electrical performance of MFCs.When the initial humic acid concentration was 5,15,30 and 60 mg/L,the degradation rates of SMM by MFCs were 69.7%,73.9%,79.9%and 80.9%,respectively.The addition of a certain concentration of humic acid can promote the removal of SMM in MFCs system,but when the initial concentration of humic acid increases from 30 mg/L to 60 mg/L,it has little effect on the removal of SMM.Moreover,the addition of humic acid also benefits the output voltage of MFCs,and the output voltage of MFCs gradually increases with the increase of the concentration of humic acid.Experiment selected N-Acetyl-L-Methionine(Ac Met)and rotenone as electronic inhibitors,in order to study the effects of electron transfer on MFCs generation and SMM degradation.The results showed that two kinds of electron transfer inhibitors added has a negative influence on the degradation of SMM.And the inhibition of MFCs electrochemical activity with rotenone was stronger than Ac Met,these results suggest that adding electron transport inhibitor not only have a negative impact on the efficiency of MFCs degradation SMM,can also affect the production performance of MFCs itself.