Abstract
In this study, the feasibility of hydrogen and methane production from grass and leaves via hyperthermophilic anaerobic digestion was investigated. The hyperthermophilic treatment of grass at 70 °C resulted in the highest concentrations of volatile fatty acids (TVFA) and reducing sugars in the supernatant of over 21 and 6.5 g/L reported on day 3 and 4 of the experiment. In contrast, hydrolysis and acidification of leaves performed slower and with lower efficiency, as the peak concentrations of TVFA and reducing sugars were observed at the end of the process. However, the highest cumulative hydrogen and methane yields of 69.64 mLH2/gVS and 38.63 mLCH4/gVS were reported for leaves digested at 70 °C, whereas the corresponding maximum productions observed for grass were 50 mLH2/gVS and 1.98 mLCH4/gVS, respectively. A temperature increase to 80 °C hampered hydrogen and methane production and also resulted in lower yields of volatile fatty acids, reducing sugars and ammonia as compared to the corresponding values reported for 70 °C.
Highlights
Waste is considered as an attribute of modern civilization
The aim of this research was to assess if hyperthermophilic anaerobic treatment could efficiently hydrolyze grass and leaves, and whether it is accompanied by the production of hydrogen or methane
The experiments in flasks were carried out in order to assess the dynamics of hyperthermophilic treatment based on metabolic products released to the supernatant, including the highest concentrations of volatile fatty acids (TVFA), reducing sugars, and ammonium nitrogen
Summary
Waste is considered as an attribute of modern civilization. Global demand and energy consumption are increasing at a rate of 2–3% per year. Renewable energy sources include biofuels produced from biomass and organic waste, of which biomethane and biohydrogen are of great importance [2]. Grass and leaves represent biomass, which is cheap, available and quickly regenerates. Huge amounts of these wastes originate from grassy areas, parks, municipal forests as well as individual households [3]. An alternative approach could be the use of grass and leaves for the production of biogas (methane and hydrogen) via anaerobic digestion [4]. These materials are composed of lignocellulosic structures, in which cellulose and hemicelluloses are surrounded by a lignin coating. From an economic point of view, the use of hyperthermophilic pretreatment (70–80 ◦ C)
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