Abstract
Purpose Given that the depletion of fossil fuels is an important issue that should be tackled urgently, alternative routes are being sought for biofuels production. This paper, under this context, studied the potential synergies of co-treatment of two kinds of agro-waste (brewers’ spent grains, BSG and spent coffee grounds, SCG) towards the direction of biodiesel and bioethanol production, alleviating at the same time their treatment and management issues. Methods The technical feasibility of oil extraction and ethanol production was studied and optimized in both laboratory and bench scale. A treatment train including alkaline pretreatment of SCG and dilute acid pretreatment of BSG, neutralization of the solutions by mixing them, enzymatic saccharification and ethanolic fermentation led to the production of bioethanol. Results The co-treatment of BSG and SCG proved beneficial and optimum experimental conditions were defined by setting the bioethanol production cost as optimization parameter. The lowest ethanol production cost (3.9€/kg) was observed for scenario 4 (SCG/BSG mixture, chemical pretreatment (0.5 N, 5 h), enzymatic hydrolysis (400 µL/g cellulose, 16 h)) and scenario 5 (SCG/BSG mixture, chemical pretreatment (0.5 N, 5 h), enzymatic hydrolysis (800 µL/g cellulose, 5 h)). Further upscaling of the process verified the technical feasibility of process units leading to a further increase of ethanol yield and thus a decrease in the production cost. Conclusions Conclusively, it was demonstrated that the recovery and extraction of the oil content of BSG and SCG and the achievement of high ethanol yields is technically feasible. Within this context, an integrated biorefinery was presented, making evident that these substrates could reverse the eminent energy crisis via biofuels production. Graphic Abstract
Highlights
In the concept (“reduce reuse recycle recover”) of circular economy and energy security, waste is considered as a valuable source for further exploitation
Regarding spent coffee grounds (SCG), similar composition for cellulose has been reported by Mussatto et al [32] and Cruz Lopes [33] but with lower hemicellulose fraction (36-39%) and lignin below 10%
It must be noted that approximately the 53% of the brewers’ spent grains (BSG) and the 59% of the SCG consists of carbohydrates with the capacity to be degraded into their monomers and undergo fermentation, while their oil content, especially for SCG indicates their capacity for oil extraction and subsequent biodiesel production
Summary
In the concept (“reduce reuse recycle recover”) of circular economy and energy security, waste is considered as a valuable source for further exploitation. Current industrial activity generates a substantial amount of biomass bioproducts that are left unused, despite their multi-dimensional contribution potential to the development of value-added products. Through the entire food supply chain, from harvesting and processing to the final consumable foodstuff, edible and inedible parts of the original organic materials are discarded. The agro-food industry itself is responsible for the 19% of the overall food waste generated. 17*106 tons of waste are accumulated from the processing and manufacturing of beverages and food products per year in the EU [1]. Taking into account the emerging demand for renewable energies on European level, agro-food wastes have been attracting much attention as potential biomass feedstock for bioenergy and biofuel production
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