Microbial fuel cell scale-up options: Performance evaluation of membrane (c-MFC) and membrane-less (s-MFC) systems under different feeding regimes

In recent years, bioelectrochemical systems have advanced towards upscaling applications and tested during field trials, primarily for wastewater treatment. Amongst reported trials, two designs of urine-fed microbial fuel cells (MFCs) were tested successfully on a pilot scale as autonomous sanitation systems for decentralised area. These designs, known as ceramic MFCs (c-MFCs) and self-stratifying MFCs (s-MFC), have never been calibrated under similar conditions. Here, the most advanced versions of both designs were assembled and tested under similar feeding conditions. The performance and efficiency were evaluated under different hydraulic retention times (HRT), through chemical oxygen demand measures and polarisation experiments. Results show that cMFCs displayed constant performance independently from the HRT (32.2 +/- 3.9 W m(-3)) whilst displaying high energy conversion efficiency at longer HRT (NERCOD = 2.092 +/- 0.119 KWh.Kg(COD)(-1), at 24h HRT). The s-MFC showed a correlation between performance and HRT. The highest performance was reached under short HRT (69.7 +/- 0.4 W m(-3) at 3h HRT), but the energy conversion efficiency was constant independently from the HRT (0.338 +/- 0.029 KWh.Kg(COD)(-1)). The c-MFCs and s-MFCs similarly showed the highest volumetric efficiency under long HRT (65h) with NERV of 0.747 +/- 0.010 KWh.m(-3) and 0.825 +/- 0.086 KWh.m 3, respectively. Overall, cMFCs seems more appropriate for longer HRT and s-MFCs for shorter HRT.