Anthraquinones As Electron Mediators Enhanced Bioelectricity Generation And Pollutants Removal In MFC

Microbial fuel cell（MFC）is a novel technology that can use bacteria to convert organic matter into electricity.The anode electron transfer limits the electricity generation efficiency of MFC.The electron mediators（EMs）can accelerate the electron transfer and promote the bioelectricity generation of MFC.Traditional Chinese medicines rich in anthraquinone compounds can be widely found in nature.The redox conversion of hydroquinone and quinone groups of anthraquinone compounds can realize the transfer of electrons.Traditional Chinese medicines rich in anthraquinone compounds are not only environmentally friendly,but also can sustainably release EMs.Therefore,in this study,the electrochemical activity of anthraquinones was explored and used as EMs to investigate electricity generation and pollutants removal performance of MFCs.The main research contents and results of this study are as follows:（1）Cyclic voltammetry（CV）and Ferric-reducing/antioxidant power（FRAP）were used to analyze the electrochemical activity of anthraquinones,and supplemented by Fourier infrared spectroscopy（FTIR）to analyze the changes of functional groups of traditional Chinese medicine before and after the pretreatment to determine the pretreatment method of anthraquinone herbs.The presence of quasi-reversible redox peaks on the CV of anthraquinones indicated its redox-mediating capability.After 2%acid treatment,the ability of traditional Chinese medicine to release electrochemically active substances was significantly enhanced,and 2%acid-treated rhubarb powder had the best electron shuttle ability.（2）With no pre-treated and acid-treated（2%H₂SO₄）Chinese medicine added to MFC,electricity generation of MFC improved,and the Rhubarb-MFC and Madder-MFC always had the best performance.With addition of 0.25 g/L no pre-treated EMs,the duration of voltage in a batch cycle extended,the coulomb efficiency（CE）of Rhubarb-MFC and Madder-MFC increased by 91.62%and67.27%compared to the Blank-group,respectively.Rhubarb-group had the highest maximum power density（20.16 W/m³）and lowest internal resistance（50Ω）among all MFCs.With 0.05 g/L acid-treated（2%H₂SO₄）traditional Chinese medicine as EMs,the electricity generation of Rhubarb-MFC and Madder-MFC was further improved compared to no pre-treated Chinese medicine added to MFC（whether the added concentration was 0.05 g/L or 0.25 g/L）,which CE increased by 125.78%and72.09%compared to Blank-group,respectively;When the EMs concentration was high（0.25g/L）,the voltage of Rhubarb-MFC and Madder-MFC severely fluctuated,but the voltage of systems still maintained a longer duration which exhibited more tolerant to toxic load shock than Alizarin-MFC（pure substance added）.Theoretical analysis indicated that the functional group of anthraquinone compounds in transferring electrons is quinone group,ortho hydroxyl and para hydroxyl.（3）As the microbial community structure sequencing results shown,anode biofilm of Rhubarb-MFC had the highest microbial abundance and diversity,corresponding to its best electricity generation performance,and Aeromonas was the dominant genus of electrogenic bacteria.The addition of EMs had no obvious effect on COD removal of MFC,but the electrochemical transfer of NH₄⁺-N in MFC was strengthened,which gave rise to the increased removal of NH₄⁺-N.（4）The study investigated the MFC operating characteristics with anthraquinone traditional Chinese medicine wastewater as substrate and electron mediators.Based on the concept of“waste controlled by waste”,under the low resistance with high current,the electricity generation of MFC improved significantly（43.03%）.With wastewater rich in anthraquinones as co-matrix,the decolorization efficiency of Reactive red 2 was improved,and high microbial richness and diversity was observed,accompanying Dechloromonas as the most effective decolorizing bacteria.