In this paper, the potential of energy recovery from cheese whey in the form of gas biofuels (hydrogen, methane) as well as electricity generation through application of the microbial fuel cell technology are studied.Hydrogen and methane production from cheese whey in a two-stage process has already been studied at a lab scale in a continuous stirred tank reactor (CSTR) of 3 L and a periodic anaerobic baffled reactor of 15 L, respectively. In this work, to scale up the hydrogen production step, the cheese whey fermentation process was studied at a larger scale using a 13.8 L bioreactor of CSTR type. The chemical oxygen demand concentration of the cheese whey fed to the CSTR was 53.3 ( 3.8 g/L. The pH in the bioreactor was maintained at 5.14 ( 0.15 with NaOH addition. The hydrogen produced reached up to 4.8 ( 0.5 L/L/d at an hydraulic retention time of 24 h (corresponding to a yield of 1.3 mol H 2 /mol consumed carbohydrates), approximately twice as much obtained in previous lab-scale experiments in a 3 L bioreactor. In addition, diluted cheese whey at different initial concentrations, was used as feedstock for electricity generation, using a two-chamber microbial fuel cell (MFC). The experiments showed that the MFC performance was not limited by the wastewater strength since the substrate removal efficiency and maximum power output were not affected by the increase of the initial concentration. The time needed for complete substrate degradation increased linearly with the wastewater strength.

Two ceramic stacks, terracotta (t-stack) and mullite (m-stack), were developed to produce energy when fed with neat undiluted urine. Each stack consisted of twelve identical microbial fuel cells (MFCs) which were arranged in cascades and tested under different electrical configurations. Despite voltage reversal, the m-stack produced a maximum power of 800 μW whereas the t-stack produced a maximum of 520 μW after 62.6 h of operation. Moreover, during the operation, both systems were subject to blockage possibly due to struvite. To the Authors' best knowledge, this is the first time that such a phenomenon in ceramic MFC membranes is shown to be the direct result of sub-optimal performance, which confirms the hypothesis that ceramic membranes can continue operating long-term, if the MFCs produce maximum power (high rate of e− transfer). Furthermore, it is shown that once the ceramic membrane is blocked, it may prove difficult to recover in-situ.

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In this study, the use of a dual-chamber microbial fuel cell for the production of bioelectricity from a food residue biomass (FORBI) product was investigated. Food residue biomass was produced by drying and shredding the pre-sorted fermentable fraction of household food waste collected door-to-door in the Municipality of Halandri, Athens, Greece. Different organic loads of food residue biomass expressed as chemical oxygen demand (COD) were examined (0.7, 0.9, 1.4, 2.8, 6 and 14 g COD L, respectively). It was observed that an increase of the initial concentration of the final extract resulted in a corresponding increase in the operating time. The microbial fuel cell potential increased from 33.3 mV to 46 mV as the concentration was increased from 0.7 to 14 g COD L. The best performance in terms of maximum power density (29.6 mW m) corresponding to a current density of 88 mA m was observed for 6 g COD L. Setting the external resistance at its optimal value (R = 2 kΩ) as determined by polarisation experiments, P drastically increased to 13.7 and 17.3 Joule (g FORBI) in two consecutive cycles. The results demonstrate that readily biodegradable substrates, such as food residue biomass, can be effectively used for enhanced bioelectricity harvesting in a microbial fuel cell.

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