Influence Of Substrates On Microbial Fuel Cells Generating Electricity And Microbial Community Structure

Microbial fuel cell (MFC) is a system utilizing microorganisms as catalysts tomediate direct conversion of chemical energy stored in organic matter into electricalenergy. It can help people with both wastewater treatment and electricity generation,which shows great potential in the field of renewable energy from wastewater. Mostorganics can be used as fuel of MFCs. However, organic wastewater treated in MFCsactually is of great variety. So the study about MFC electricity production usingdifferent substrates and influence of changing substrates on MFCs has an importantguiding significance to MFC practical application on wastewater treatment.The single-chamber air cathode MFCs were used in this study, using lactate assubstrate to setup, and substrates were changed to glucose, acetate and propionateafter stable operation. Later, MFCs were fed with lactate again after four cycles withdifferent substrates. During these three decades, in which the influent COD were alladjusted to500mg/L, electrochemical parameters and biofilm on anode wereinvestigated to analyze the role of microorganism on MFC electricity production. Theresults show that when fed with lactate, maximum voltage of MFC was0.231V, whilepower density was2.33W/m3; internal resistance16Ω, COD removal rate72.27%,coulombic efficiency9.08%. When substrates were changed to glucose, acetate andpropionate, MFCs need500,330and550h respectively for adaptment to achievestable electricity production, and maximum voltage were0.125,0.153and0.189V，while cycle length were120,64,70h; power density were0.77、1.43and1.65W/m3;coulombic efficiency were17.85%,17.91%and29.16%, higher than first decade.When substrates were changed to lactate again in the third decade, it still took sometime for MFCs to produce electricity stably. The adaptation time were193,259and373h respectively, and maximum voltage were0.121,0.11and0.18V, lower thanformer lactate MFCs in first decade. Similarly, power density of MFCs decreased to 0.74,0.97and1.33W/m3,which reflected that switching substrates lowered generatingelectricity ability of MFCs.DGGE graph told us that microbial structure lanes of the three decades in GluMFC are almost the same. But microbial structure in Ace MFC changed a lot aftersubstrate was changed from lactate to acetate, and the diversity index increased from2.48to2.80. As Glu MFC, lanes in Pro MFC were with high similarity. It maybecause that lactate and propionate were similar in structure; so the microbialgathered when organics were degraded.The present study concluded that substrates have great effects on MFC electricitygeneration and microbial community structure on anode biofilm. When substratechanged, it takes some adaption time for MFCs to recover the ability of generatingelectricity. However, switching substrates repeatedly may lower generating electricityability of MFCs. In reality, it is necessary to avoid the negative effects of substrates onMFC.