Abstract
In the current study, a domestic food waste containing more than 50% of carbohydrates was assessed as feedstock to produce second-generation bioethanol. Aiming to the maximum exploitation of the carbohydrate fraction of the waste, its hydrolysis via cellulolytic and amylolytic enzymatic blends was investigated and the saccharification efficiency was assessed in each case. Fermentation experiments were performed using the non-conventional yeast Pichia anomala (Wickerhamomyces anomalus) under both separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) modes to evaluate the conversion efficiencies and ethanol yields for different enzymatic loadings. It was shown that the fermentation efficiency of the yeast was not affected by the fermentation mode and was high for all handlings, reaching 83%, whereas the enzymatic blend containing the highest amount of both cellulolytic and amylolytic enzymes led to almost complete liquefaction of the waste, resulting also in ethanol yields reaching 141.06 ± 6.81 g ethanol/kg waste (0.40 ± 0.03 g ethanol/g consumed carbohydrates). In the sequel, a scale-up fermentation experiment was performed with the highest loading of enzymes in SHF mode, from which the maximum specific growth rate, μmax, and the biomass yield, Yx/s, of the yeast from the hydrolyzed waste were estimated. The ethanol yields that were achieved were similar to those of the respective small scale experiments reaching 138.67 ± 5.69 g ethanol/kg waste (0.40 ± 0.01 g ethanol/g consumed carbohydrates).
Highlights
Biofuels, i.e., fuels that are produced from biomass via biological, thermal, or chemical processes, are regarded among the key renewable energy carriers that can contribute to the sustainable development of economies
The current study investigated the effect of enzymatic hydrolysis via different combinations of enzymatic mixtures, on the saccharification of Domestic food wastes (DFWs) and the subsequent alcoholic fermentation of the waste using the non-conventional yeast
The cellulosic content of FORBI derives from fruit and vegetable residues, as well as from used paper tissue included in the kitchen biowaste that was collected, i.e., wastes containing different types of cellulose with different crystallinity indices [49,50]
Summary
I.e., fuels that are produced from biomass via biological, thermal, or chemical processes, are regarded among the key renewable energy carriers that can contribute to the sustainable development of economies. Sustainable large-scale bioethanol production, can only be assured if based on the bioconversion of biomass types that are abundant, renewable, and low or even zero cost, and preferably biomasses that require minimal pretreatment in order to become exploitable. Domestic food wastes (DFWs) do gather all those characteristics: zero cost and rich in carbohydrates and nutrients that can efficiently support microbial growth and efficient fermentation. They are a universal resource since they are generated throughout the year in huge quantities in both developed and developing countries.
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