A comparison of mono- and multi-valent ions as stack feed solutions in microbial reverse-electrodialysis electrolysis cells and their effects on hydrogen generation

• The effects of multivalent ions on MREC performances was investigated.
• The presence of multivalent ions in MREC system reduces maximum cell current from 4.2 mA to 3.7 mA.
• The presence of multivalent ions in the MREC system reduces the hydrogen production and rates 32 and 35%, respectively.

Microbial reverse-electrodialysis cells (MRECs) are an emerging technology combining microbial electrolysis cells (MEC) with reverse electrodialysis (RED) for the production of hydrogen gas. In this study, the MREC system used monovalent ions (Na+ and Cl−) and a mixture of mono- and multi-valent ions (Mg2+ and SO42−) as stack feed solutions, which were compared to determine the effect of the presence of multivalent ions on MREC performance. The MREC system operated under batch conditions using acetate as a substrate while the RED stack operated under continuous flow conditions using pure NaCl and a mixture with a 10% molar fraction of multivalent ions and a 90% molar fraction of monovalent ions as stack feed solutions (flow rate = 1.2 mL min−1). When using 10% of MgSO4 as a stack feed solution, the maximum current achieved for the MREC system decreased from 4.2 to 3.7 mA compared to the pure NaCl. Moreover, the quantity of hydrogen produced, the production rate, and yield also decreased by approximately 32, 35, and 23%, respectively. The results obtained from this study demonstrated that the presence of multivalent ions had an adverse effect on MREC performance.