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The influence of the applied voltage (Vapp) and the hydraulic retention time (HRT) on hydrogen and methane production and the removal rate for chemical oxygen demand (COD) was studied in a membrane‐less microbial electrolysis cell with a Ni‐based cathode. When a synthetic effluent from a dark‐fermentation process was fed continuously into the anodic chamber, an increase in both the Vapp (from 0.6 to 1.0 V) and HRT (from 8 to 12 h) increased the hydrogen production rate from 0.18 to 1.42 L LA−1 d−1 (liters per liter of anode per day) and the COD elimination rate from 46 to 94%. The influences of Vapp and HRT on hydrogen production and the COD removal rate were found to be interdependent. Whereas acetic and butyric acids were easily degraded, propionic acid exhibited pseudo‐recalcitrant behavior. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 263‐268, 2013

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Digestion of cattle manure collected from a livestock farm together with bedding material (straw) has been studied under mesophilic and thermophilic conditions in batch reactors. The digestion was carried out for a prolonged period with the aim of evaluating the changes undergone by the organic matter. The mesophilic digestion carried out revealed a greater capacity to produce gas and transform organic matter, while a higher conversion rate, but a lower gas yield, was obtained under thermophilic conditions. Degradation of the organic matter was evaluated by means of thermal analysis and (1)H NMR. Stabilisation through anaerobic digestion (either mesophilic or thermophilic) resulted in an increase in the quality of the organic matter, as characterised by an enrichment in thermostable compounds, and an accumulation of long chain aliphatic materials. The experiments performed demonstrated the transformation of organic matter into complex materials under anaerobic conditions with an accumulation of aliphatic components under both types of conditions tested. Degradation through mesophilic digestion, in comparison to the thermophilic process, resulted in a greater destruction of straw particles.