Long-term continuous production of H2 in a microbial electrolysis cell (MEC) treating saline wastewater

Abstract

A biofilm-based 4L two chamber microbial electrolysis cell (MEC) was continuously fed with acetate under saline conditions (35g/LNaCl) for more than 100days. The MEC produced a biogas highly enriched in H2 (≥90%). Both current (10.6±0.2A/m2Anode or 199.1±4.0A/m3MEC) and H2 production (201.1±7.5LH2/m2Cathode·d or 0.9±0.0m3H2/m3MEC·d) rates were highly significant when considering the saline operating conditions. A microbial analysis revealed an important enrichment in the anodic biofilm with five main bacterial groups: 44% Proteobacteria, 32% Bacteroidetes, 18% Firmicutes and 5% Spirochaetes and 1% Actinobacteria. Of special interest is the emergence within the Proteobacteria phylum of the recently described halophilic anode-respiring bacteria Geoalkalibacter (unk. species), with a relative abundance up to 14%. These results provide for the first time a noteworthy alternative for the treatment of saline effluents and continuous production of H2.