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.

Monitoring stratification of anode biofilms in bioelectrochemical laminar flow reactors using flow cytometry

A laminar flow bioelectrochemical systems(BES)was designed and benchmarked using microbial anodes dominated with Geobacter spp.The reactor architecture was based on modeled flow fields,the resulting structure was 3D printed and used for BES manufacturing.Stratification of the substrate availability within the reactor channels led to heterogeneous biomass distribution,with the maximum biomass found mainly in the initial/middle channels.The anode performance was assessed for different hydraulic retention times while coulombic efficiencies of up to 100%(including also hydrogen recycling from the cathode)and current densities of up to 75 μA cm^(-2) at an anode surface to volume ratio of 1770 cm^(2) L^(-1) after 35 days were achieved.This low current density can be clearly attributed to the heterogeneous distributions of biomass and the stratification of the microbial community structure.Further,it was shown that time and space resolved analysis of the reactor microbiomes per channel is feasible using flow cytometry.

Direct ammonium oxidation to nitrogen gas (Dirammox) in Alcaligenes strain HO-1: The electrode role

It has been recently suggested that Alcaligenes use a previously unknown pathway to convert ammonium into dinitrogen gas(Dirammox)via hydroxylamine(NH2OH).This fact alone already implies a significant decrease in the aeration requirements for the process,but the process would still be dependent on external aeration.This work studied the potential use of a polarised electrode as an electron acceptor for ammonium oxidation using the recently described Alcaligenes strain HO-1 as a model heterotrophic nitrifier.Results indicated that Alcaligenes strain HO-1 requires aeration for metabolism,a requirement that cannot be replaced for a polarised electrode alone.However,concomitant elimination of succinate and ammonium was observed when operating a previously grown Alcaligenes strain HO-1 culture in the presence of a polarised electrode and without aeration.The usage of a polarised electrode together with aeration did not increase the succinate nor the nitrogen removal rates observed with aeration alone.However,current density generation was observed along a feeding batch test representing an electron share of 3%of the ammonium removed in the presence of aeration and 16%without aeration.Additional tests suggested that hydroxylamine oxidation to dinitrogen gas could have a relevant role in the electron discharge onto the anode.Therefore,the presence of a polarised electrode supported the metabolic functions of Alcaligenes strain HO-1 on the simultaneous oxidation of succinate and ammonium.