Valorisation of bakery waste via the bioethanol pathway

Abstract

Bakery waste is a stream that is generated in enormous quantities globally and thus poses a significant environmental problem. Furthermore, the increasing use of fossil fuels necessitates the development of alternate energy sources. In an effort to meet the EU circularity goals, in this study, a holistic method to address these issues is proposed; producing bioethanol from bakery waste. Bakery waste that was collected from local bakeries and cafeterias was utilized as feedstock. Two fermentation modes were studied in laboratory scale by applying factorial design; separate hydrolysis and fermentation and simultaneous saccharification and fermentation. For the separate hydrolysis and fermentation trials, the ethanol yield reached was almost 100% for 20 μLgstarch−1 enzyme loading and 20% solid loading at 35°C, whereas the highest ethanol yield for simultaneous saccharification and fermentation was 95% for 20 μLgstarch−1 enzyme loading and 20% solid loading. Even though a small difference in the yield was observed between the two fermentation modes, simultaneous saccharification and fermentation is beneficial in terms of technoeconomics. Furthermore, it was established that the valorisation of bakery waste for the production of bioethanol is technically viable, even at the pilot scale, as 100 gL−1 of ethanol after 31 h in a 200 L bioreactor under the optimum conditions was observed. Nevertheless, to evaluate the process feasibility, other techno-economical factors of the entire value chain must also be taken into account. These include fluctuations in the bakery waste composition, collection of bread residues as well as recovery and purification of ethanol.