Abstract
Abstract This study assessed the effect of hydraulic retention time (HRT) on biohydrogen production by dark fermentation using an anaerobic fluidized bed reactor fed with cheese whey synthetic wastewater. The reactor of 1.2 L was operated with an approximate carbohydrate concentration of 2800 mg L-1, and HRTs of 6, 4, 2, 1 and 0.5 h. Acetic and butyric acids were the main metabolites produced in the reactor. The hydrogen production increased from 0.039 to 1.43 L-H2 h-1 L-1-reactor as the HRT decreased from 6 to 0.5 h. The best hydrogen yield (HY) (2.73 mol-H2 mol-carbohydrate-1) and carbohydrate consumption (81.02%) were achieved at a HRT of 6 h (12.34 kg-COD m-3 d-1) followed by the HY of 2.43 mol-H2 mol-carbohydrate-1 at a HRT of 0.5h (163.02 kg-COD m-3.d-1). An increase in the influent pH in the operational phase 05 (HRT of 0.5 h) favored hydrogen production despite the reduced carbohydrate conversion compared to phase 01 (HRT of 6 h). In both conditions, the reactor presented the highest amount of acetic acid, indicating that the acetate route favored the hydrogen yield production. The HRT reduction led to an increase in microbial diversity, as evidenced by the Shannon-Wiener coefficient of 2.586, which corresponds to the operational phase with a HRT of 2 h.
Highlights
Hydrogen emerges as a clean energy source since its combustion produces only water, unlike fossil fuels combustion that generates unwanted greenhouse gases (Han et al, 2015)
On account of the above, the aim of this study was to observe the effect of hydraulic retention time (HRT) on biohydrogen production using an anaerobic fluidized bed reactor (AFBR) fed with cheese whey synthetic wastewater and operating at mesophilic temperatures
Since low HRT entails high organic loading rates (OLR), the result indicates that organic matter overloading constricted the carbohydrate conversion
Summary
Hydrogen emerges as a clean energy source since its combustion produces only water, unlike fossil fuels combustion that generates unwanted greenhouse gases (Han et al, 2015). Hydrogen can be produced from non-renewable resources, such as oil, natural gas and coal, or from renewable sources, such as biomass (Tapia-Venegas et al, 2015). Biological processes using biomass waste as substrate are environmentally friendly because they present low energy requirement and contribute to CO2 global reduction (SilvaIllanes et al, 2017). Biological processes to obtain hydrogen encompass the photo-production process (direct or indirect bio-photolysis and photofermentation) or the dark fermentation (Tapia-Venegas et al, 2015). Conversion of the various complex organic wastes to produce hydrogen occurs at high rates via butyric acid-type, propionic acid-type, or ethanol-type fermentation (Liu et al, 2015). The direction of the metabolic pathway is determined by the environmental conditions of the fermentation process. Temperature, pH and the dynamic of the microbial community can affect the fermentation process (Ziara et al, 2018)
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