Anaerobic biological fermentation of urine as a strategy to enhance the performance of a microbial electrolysis cell (MEC)

Abstract This study investigated the effect of pre-fermented urine on anode performance of a two-chambered microbial electrolysis cells (MECs) compared to raw urine. Pre-fermentation of urine was performed by anaerobic digestion. The effect of this pre-fermentation on anode performance of a MEC was assessed by measuring the removal of chemical oxygen demand (COD), current density and Coulombic efficiency (CE). The MEC using fermented urine achieved a higher average current density (218 ± 6 mA m −2 ) and a higher CE (17%). Although no significant differences were observed in the COD removal efficiency between both urines, the MEC using fermented urine displayed the highest COD removal rate (0.14 ± 0.02 g L −1  d −1 ). The organic compounds initially found in both urines, as well as the metabolic products associated to the biodegradation of the organic matter were analyzed by proton nuclear magnetic resonance ( 1 H NMR). The main compounds initially identified in the raw urine were urea, creatinine and acetate. In the fermented urine, the main compounds identified were methylamine, acetate and propionic acid demonstrating the effectiveness of the anaerobic fermentation step.