Hydrogen and Methane Production from Anaerobic Co-Digestion of Sorghum and Cow Manure: Effect of pH and Hydraulic Retention Time
Margarita A. Dareioti | Konstantina Tsigkou | Aikaterini I. Vavouraki | Michael Kornaros
The need for alternative energy sources is constantly growing worldwide, while the focus has shifted to the valorization of biomass. The aim of the present study was to determine the optimal pH and hydraulic retention time (HRT) values for treating a mixture of sorghum biomass solution with liquid cow manure (in a ratio 95:5 <i>v</i>/<i>v</i>) through anaerobic digestion, in a two-stage system. Batch tests were initially carried out for the investigation of the pH effect on bio-hydrogen and volatile fatty acids (VFA) production. The highest hydrogen yield of 0.92 mol H<sub>2</sub>/mol carbohydrates<sub>consumed</sub> was obtained at pH 5.0, whereas the maximum degradation of carbohydrates and VFA productivity was observed at pH 6.0. Further investigation of the effect of HRT on hydrogen and methane production was carried out. The maximum yield of 1.68 mol H<sub>2</sub>/mol carbohydrates<sub>consumed</sub> was observed at an HRT of 5 d, with H<sub>2</sub> productivity of 0.13 L/L<sub>R</sub>·d. On the other hand, the highest CH<sub>4</sub> production rate of 0.44 L/L<sub>R</sub>·d was achieved at an HRT of 25 d, with a methane yield of 295.3 mL/g VS<sub>added</sub>, whereas at a reduced HRT of 20 d the process exhibited inhibition and/or overload, as indicated by an accumulation of VFAs and decline in CH<sub>4</sub> productivity.
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