Effect of pH on the Anaerobic Fermentation of Fruit/Vegetables and Disposable Nappies Hydrolysate for Bio-hydrogen Production

Purpose The objective of this work was to optimize the anaerobic fermentation of a mixed waste stream, consisted of fruit and vegetables that have lost their marketing value and a disposable nappies’ hydrolysate. More specifically, the aim was to identify the optimal pH value for maximum hydrogen pr...
Ausführliche Beschreibung

Purpose The objective of this work was to optimize the anaerobic fermentation of a mixed waste stream, consisted of fruit and vegetables that have lost their marketing value and a disposable nappies’ hydrolysate. More specifically, the aim was to identify the optimal pH value for maximum hydrogen production and valuable metabolites such as volatile fatty acids and ethanol. Methods A wide range of pH values was tested (from 4.5 to 7.5 with 0.5 increment) using an automatic controller system, in batch fermentations that took place in mesophilic temperature conditions (37 °C). The first set of experiments was carried out with the fruit and vegetables mixture, diluted with water (2:3 v/v) and subsequent trials followed using the fruit and vegetable mixture with the disposable nappies’ hydrolysate at the same ratio (2:3 v/v). Results The maximum hydrogen volume was produced at pH 6.0 (1.34 L $ H_{2} $/$ L_{Reactor} $) for the fruit/vegetable stream whereas, the maximum concentration of ethanol and volatile fatty acids (15.60 g/L) was reached at pH 6.5 for the same substrate. Regarding the mixed waste stream, both hydrogen production and metabolites concentration reached a maximum at pH 7.5 with 4.09 L $ H_{2} $/$ L_{Reactor} $ and 17.16 g/L respectively. Conclusions Different optimum pH value for bio-hydrogen production was observed between the anaerobic fermentation of the two substrates (fruit/vegetables waste and mixed waste stream). Higher overall yields and concentrations of the metabolic products were obtained with the fermentation of the mixed substrate. Graphic Abstract Ausführliche Beschreibung