Investigating Elimination Processes Of Triclosan And 1,4-dioxane In Bioelectric System

Persistent and mobile organic compounds(PMOCs)are a class of compounds with relatively high persistence and mobility in water,allowing fast migration in surface water and participate in water cycle,and eventually occur in groundwater and drinking water sources.The traditional water treatment processes are not efficient to eliminate PMOCs,and other shortcomings are possible secondary contamination and high maintainance costs.Microbial fuel cells(MFCs)are a device that converts the chemical energy of organic matter into electrical energy via the catalysis of microorganisms.MFC is an efficient and low-cost water treatment technology,which could handle power generation and removal of pollutants simultaneously.Compound-specific isotope analysis(CSIA)technology is applied to determine stable isotopic composition of a certain element in specific organic compounds,therefore becoming a valuable tool to differentiate multiple sources as well as to elucidate organic compounds underlying transformation processes.In this paper,triclosan(TCS)and 1,4-dioxane,two PMOC substances,are chosen as model compounds to investigate their electricity-generation performance and removal efficiency in MFC system.Also,transformation processes of the two pollutants in the microbial electrochemical system were studied by applying carbon CSIA.In the experiment of electricity generation,a two-chamber MFC was established,and activated sludge from a sewage treatment plant was used for microbial inoculation.The MFC was first domesticated with sodium acetate as the anode substrate,and potassium ferricyanide was used as the cathode electron acceptor.After stablelizing electricity generation,lg/L sodium acetate together with TCS at different concentrations(i.e.10mg/L,50mg/L,100mg/L),and lg/L sodium acetate with 1,4-dioxane at different concentrations(i.e.10mg/L,20mg/L,40mg/L)are added as the fuel materials of MFC,respectively.The output voltage of MFC is monitored online by using data collector.The results show that under the external resistance of 1000Ω,when TCS or 1,4-dioxane is used as sole fuel,MFC is not alble to generate electricity,but under mixing feeding of sodium acetate and TCS,100mg/L TCS could generate the maximum voltages of 0.58V(i.e.experiment with lg/L NaAc+10mg/L TCS),0.45 V(i.e.experiment with lg/L NaAc+50mg/L TCS)and 0.25 V(i.e.experiment with lg/L NaAc+100mg/L TCS).The corresponding internal resistance of MFC are 231.88Ω,246.13Ω,and 289.28Ω,respectively.By adding sodium acetate and 1,4-dioxane as the fuel of MFC,the maximum voltage of 0.45V were obtained(i.e.experiment with lg/L NaAc+10mg/L 1,4-dioxane),the maximum voltage of 0.4V were obtained for the experiment by adding lg/L NaAc and 20mg/L 1,4-dioxane,and the maximum voltage of 0.25V by adding lg/L NaAc and 40mg/L 1,4-dioxane,respectively.The experimental results indicate that TCS and 1,4-dioxane could significantly affect the activity of biofilm in MFCs.Concerning removal efficiency of the two model compounds,TCS was successfully removed in MFC.About 95%of TCS in the water were removed within 48 hours.Our results imply that adsorption of TCS occurred on the inner wall of the reactor as well as on the anode electrode with the corresponding sorptive mass contribution of 21.73%and 19.92%,respectively.The reactor containing a anode electrode brush resulted in a stronger adsorption for TCS compared with the reactor without anode electrodes.In addition,we found that pH values did not influence the adsorption.The stable carbon isotope ratios were also measured in order to identify transformation processes.Our results showed that after 48 hours of reaction,a smaller extent of TCS carbon isotope fractionation(about 1‰)was observed in the microbial experiment.The carbon isotope enrichment factors were also evaluated according to Rayleigh model,where εC values of-0.887±0.162 ‰ and-0.152±0.291 ‰ were obtained,respectively.These results indicate that eleimination of TCS in MFC is mainly caused by both physical adsorption and microbial degradation.In summary,the microbial electrochemical system(i.e.MFC)was established for the treatment of TCS and 1,4-dioxane in water.When sodium acetate is used as a co-substrate,at higher concentration of TCS or 1,4-dioxane,lower the maximum voltage output of the MFC were obtained.TCS could be removed in MFC,and the contribution of adsorption is dominant,which mainly occurs on the surface of anode carbon brush.In addition,compound-specific carbon isotope analysis has been successfully used to track biotransformation process of TCS,where stable carbon isotope fractionation of TCS was observed.