Examination of protein degradation in continuous flow, microbial electrolysis cells treating fermentation wastewater

• Continuous H2 gas production from fermentation wastewater was examined using MECs.
• Protein was less well removed than other components of the wastewater.
• The use of higher applied voltages increased protein removals but current was erratic.
• A downstream process is needed to achieve higher effluent quality following MECs.

Cellulose fermentation wastewaters (FWWs) contain short chain volatile fatty acids and alcohols, but they also have high concentrations of proteins. Hydrogen gas production from FWW was examined using continuous flow microbial electrolysis cells (MECs), with a focus on fate of the protein. H2 production rates were 0.49 ± 0.05 m3/m3-d for the FWW, compared to 0.63 ± 0.02 m3/m3-d using a synthetic wastewater containing only acetate (applied potential of 0.9 V). Total organic matter removal was 76 ± 6% for the FWW, compared to 87 ± 5% for acetate. The MEC effluent became relatively enriched in protein (69%) compared to that in the original FWW (19%). Protein was completely removed using higher applied voltages (1.0 or 1.2 V), but current generation was erratic due to more positive anode potentials (−113 ± 38 mV, Eap = 1.2 V; −338 ± 38 mV, 1.0 V; −0.426 ± 4 mV, 0.9 V). Bacteria on the anodes with FWW were primarily Deltaproteobacteria, while Archaea were predominantly Methanobacterium.