Acetogenic bacteria utilize the Wood-Ljungdahl pathway to convert hydrogen, carbon dioxide, carbon monoxide, and a wide range of sugars to volatile fatty acids and alcohols, especially acetate and ethanol. Acetate production using hydrogen gas (H2) as electron donor has been widely reported; however, H2 hydrophobicity has limited the success of this process. The Membrane Biofilm Reactor (MBfR) is a unique technology that delivers H2 gas directly to microorganisms that live as a biofilm on the outer surface of gas-transfer membranes. Direct transfer to the biofilm overcomes interfacial gas-liquid mass-transfer limitations. We operated a 120-cm3 glass MBfR with 110-cm2 of composite hollow fibers (polyurethane-polyethylene) and a hydraulic retention time of 24 h, tracked gas production/consumption by gas chromatography, and measured acetate concentrations by high performance liquid chromatography. We also sequenced the 16S ribosomal RNA gene in biofilm samples and performed qPCR to assay total 16S ribosomal RNA gene, mcrA gene for methanogens, and the FTHFS gene for homoacetogens. H2 pressure inside the membrane was increased stepwise from 2 psig to 15 psig (giving maximum H2 delivery capacities of 1.2 to 3.8 g H2/m2-d) by 2-3 psig increments after each condition reached steady state. Although general bacteria decreased from about 8x1010 to 5x108 gen copies/cm2 and methanogens decreased from 106 to undetectable, acetogens increased from about 104 to 108 gen copies/cm2. This situation is desired, since the biofilm became substantially enriched with acetogenic bacteria. The genus Acetobacterium became the most important phylotype, increasing to a relative abundance of 56% of the sequenced 16S rRNA genes in the biofilm with the highest H2-delivery capacity. The highest H2 delivery achieved an acetate concentration up to 55 mM when using 150 mM of bicarbonate as the carbon source, and the acetate production rate was ~6.4 mg acetate/cm2-d. Thus, the H2-based MBfR provides a good platform for acetate production and enrichment of acetogens in a biofilm.

Acetate production by anaerobic, autotrophic bacteria in a H2-based membrane biofilm reactor

254th National Meeting (2017)

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