Combining metal-microbe and microbe-microbe dual direct electron transfer on Fe(0)-cathode of bio-electrochemical system to enhance anaerobic digestion of cellulose wastewater

Considering that cathode of microbial electrochemical system(MES)is a good electrons source for methane production via direct/indirect electron transfer to electroactive microorganisms,and that Fe(0)is also a confirmed electron donor for some electroactive microorganisms through metal-microbe direct electron transfer(DET),Fe(0)-cathode was equipped into an MES digester to enhance cathodic methane production.The results of this study indicated that the potential DET participator,Clostridium possibly obtained electrons directly from Fe(0)-cathode via metal-microbe electrons transfer,then transferred electrons directly to the definite DET participators,Methanosarcina/Methanothrix via microbemicrobe electrons transfer for CH_(4)production.In addition,Methanobacterium is another specially enriched methanogen on Fe(0)-cathode,which might obtain electrons directly from Fe(0)-cathode to produce CH_(4) via metal/electrode-microbe DET.The increment of conductivity of cathodic sludge in Fe(0)-cathode MES digester(R1)further confirmed the enrichment of electroactive microorganisms participating in DET process.As a consequence,a higher CH_(4) production(1205–1508 m L/d)and chemical oxygen demand(COD)removal(79.0%-93.8%)were achieved in R1 compared with graphite-cathode MES digester(R2,720–1090 m L/d and 63.6%-85.6%)and the conventional anaerobic digester(R3,384–428 m L/d and 35.2%-41.0%).In addition,energy efficiency calculated indicated that the output energy of CH_(4) production was 8.16 folds of electricity input in Fe(0)-cathode MES digester.