Microbial electrolysis cell performance using non-buffered and low conductivity wastewaters

• MEC performance is evaluated with non-buffered and/or low-conductivity media.
• Cathodic overpotentials increased with lack of buffer in single-chamber MEC.
• Anodic failure is caused by non-buffered medium in two-chamber MEC.
• Lowering conductivity did not have a relevant role at such low current intensities.

Microbial electrolysis cells (MEC) are a novel technology aiming at producing hydrogen from wastewater. MEC performance gives successful results in lab-scale experiments with well buffered media and synthetically-increased conductivity, thus preventing operational problems and reducing the internal resistance of the cell. This is especially important in two-chamber configuration where membranes cause potential losses associated to the pH gradients across them. However, domestic and many industrial wastewaters have a limited buffer capacity and low conductivity. In this study, the performance of an MEC with a culture medium more like a real wastewater, in terms of buffer capacity and conductivity, was assessed in both single-chamber and two-chamber configurations and compared to that of a well-buffered cell. Single-chamber MEC tests demonstrated that the lack of buffer affected both the overpotentials of the anode and the cathode, although the overpotential of the latter was significantly higher. In two-chamber configuration, the non-buffered cell failed as a result of a high pH drop in the anode, which harmed the anodic biofilm. The conductivity increase from low (4 mS/cm) to high values (13 mS/cm) did not improve significantly any configuration tested.

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