Performance And Mechanism Of Electricity Generation And Oily Sludge Degradation In MFC Enhanced By Rhamnolipid

The research on the mechanism and application of Microbial fuel cells(MFC)is now in the ascendant.extracellular electron transfer(EET)is the most complex and important process in MFC.In recent years,studies on the mechanism of EET have focused on pure cultures exoelectrogens.However,MFCs with mixed bacteria inoculation have higher power output and widly applicable range.This study combined the electrochemical and metagenomic analysis method to explore the mechanism and limited factors of EET.Based on the obtained result,this study added rhamnolipid into MFCs to enhance the electricity generation of MFC and degration of dewatered oily sludge.The results showed that during the start-up process of single-chamber air cathode MFC with glucose as substrate,the anodic process was the limiting process of MFC power generation.From start-up to steady state of MFC,the power density increased from 1.51 W/m3 to 4.12 A/m3,the equilibrium potential of anode decreased from-0.349 V vs.Ag/Ag Cl to-0.457 V vs.Ag/Ag Cl,the exchange current as well as the exchange coefficient increaed from 2.36×10-5 A to 4.37×10-4 A and 0.06 to 0.15,respectively,the biofilm content in the anode biofilm increased from 0.13 ± 0.04 mg/cm3 to 0.48 ± 0.06 mg/cm3.These results proved that the enhancement of the electircity generation and biofilm formation during the operation.Metagenomic analysis of anode biofilm indicated that Geobacter sulfurreducens(23.07%),Tolumonas osonensis(15.50%),Desulfovibrio desulfuricans(12.03%)and Methanosaeta concilii(9.44%)were the dominant bacteria,and genes belongs to signal transduction play an important role in EET.To enhance the electricity generation of MFC,rhamnolipids were added into the anode.The adsorption of rhamnolipids on anode will cause the Frumkin effect under nonfaradaic process,resulting in the increase of anode capacitance from 15.12 F/m2 to 19.39 F/m2,and the decrease of the open circuit potential from 0.19 V vs.Ag/Ag Cl to 0.12 V vs.Ag/Ag Cl.It was found the power density of MFC increased by 33%,the coulombic efficiency increased by 43%,and and the total protein content of anodic biofilm increased by 52% with 40 mg/L rhamnilipids addition at the 7th day after initiation.The Frumkin effect caused by rhamnolipid adsorption can accelerate the anodic electron transfer,resulting in the decrease of equilibrium potential(30.23%),exchange current density(71.32%),and the increase of symmetry coefficient(0.36 to 0.50).The "power overshoot" phenomenon weakened after rhamnolipids addition.The variation of the inn Helomholtz plane potential may be the main reason for "power overshoot".This study proved that rhamnolipid addition can significantly increase the abundance of signal transduction related genes in the biofilm.Moreover,the relative abundance of Aeromonas?Klebsiella,Desulfovibrio,Tolumonas and Methanosaeta varied greatly with rhamnolipid addition.The relative abundance of the signal transduction related genes in Geobacter,Aeromonas and Desulfovibrio was higher than others.In addition,Methanosaeta can only gain energy through methane metabolism,and competing with exoelectrogens for electron donors,which is not conducive to the electricity generation of MFC.In order to verify the effect of rhamnolipid on complex substrates,MFCs with dewatered oily sludge as anodic substrate were constructed in this study.To enhance the electricity generation and the degradation of dehydrated oily sludge,rhamnolipids were added into the anode substrate.It was shown that the addition of rhamnolipid could increase the total cell voltage and maximum power density of MFC by 40% and 125%,respectively,and increase the coulombic efficiency.The addition of rhamnolipid can significantly enhance the biodegradation of dewatered oily sludge as well as the hydrolysis and fermentation process,resulting in the enhancment of TOC,TCOD and TPH remvoal and the increase content of SCOD and VFAs.The addition of rhamnolipid enhanced the relative abundance of Desulfosalsimonas and Sulfuricurvum in dewatered oily sludge by 6.38 and 28.44 times,reflecting the enhanced sulfate/sulfide cycle in dehydrated oily sludge.The research proved that rhamnolipids can effectively promote the degradation and conversion of high solids content organic pollutants in MFC,which have certain guiding significance to engineering applications.This article was firstly discovered Frumkin effect can accelerate electron transfer and proved the importance of signal transduction related genes in EET,which play an important role in promoting the EET mechanisms.The research also proved that rhamnolipid can effectively promote the degradation and conversion of high solids content organic pollutants in MFC and the electricity generation of MFC,guiding significance to the engineering application of MFC.