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

•A 4 L microbial electrolysis cell was used to continuously treat saline wastewater.•A biogas stream highly enriched in H2 (ca. 90%) was produced for more than 100 days.•Scanning electron microscopy showed the formation of uniform biofilm.•Within the biofilm the high enrichment of Geoalkalibacter (unk. species) took place.•We provide a noteworthy biological treatment of saline effluents and H2 production.

A biofilm-based 4 L two chamber microbial electrolysis cell (MEC) was continuously fed with acetate under saline conditions (35 g/L NaCl) for more than 100 days. The MEC produced a biogas highly enriched in H2 (≥90%). Both current (10.6 ± 0.2 A/m2Anode or 199.1 ± 4.0 A/m3MEC) and H2 production (201.1 ± 7.5 LH2/m2Cathode·d or 0.9 ± 0.0 m3H2/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.

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