Food waste is a waste stream that is produced globally in huge amounts and therefore constitutes a major environmental concern. Additionally, the growing consumption of fossil fuels sets the need for alternative energy sources. To this end, in this paper, an holistic approach towards bioethanol production from source-separated food waste was studied as an effective strategy to cope with both issues. Source-separated food waste collected from a Greek Municipality was used as raw material. Two fermentation modes, separate hydrolysis and fermentation and simultaneous saccharification and fermentation, were examined in laboratory and pilot scales with varying solids loadings. For separate hydrolysis and fermentation (SHF) trials, the solids loading increase led to a significant ethanol yield reduction from 79 to 55 g/kg food waste, whereas for simultaneous saccharification and fermentation (SSF), the ethanol yield was increased by 77% (from 62 to 110 g/kg food waste) as the solids loading was increased. This is also related to greater ethanol concentrations, which are beneficial in terms of technoeconomics. The lowest bioethanol production cost, 1.57 €/kg ethanol, was estimated for the scenario of SSF with 20% solids loading while for SHF the lowest production cost was achieved (4.40 €/kg ethanol) when 15% solids loading is applied. In most cases, the energy and enzyme costs presented the most pronounced impact on the total bioethanol cost. In conclusion, it was proved that the food waste valorisation towards bioethanol production is technically feasible on a pilot scale. However, further techno-economic factors of the whole value chain must also be taken into consideration while aiming to assess the viability of the process.
The Sustainable Development Goals along with national policies pave the way to a sustainable, circular, and resource efficient development model. The environmental scenario could change with the promotion of biofuels such as bioethanol. Recent research on bioethanol aspires to reduce the costs production, via the optimization of process variables and the increase in ethanol yields. This study presented a stepwise upscaling of bioethanol production from dried source-separated municipal biowaste. Three different scales (250 mL, 4 L, 100 L) were examined applying advanced ethanol production via simultaneous saccharification and fermentation. The bioprocess runs at each of the three scales and produced very similar ethanol yields, indicating excellent scalability. The validated optimum conditions at the pilot scale were 25% solids loading, Spirizyme 40 μL/g starch, NS87014 175 μL/g cellulose, and 2% S. cerevisiae. The results from the pilot trials were very successful and repeatable. Τhe mean ethanol yield was 86.60 ± 4.91%, while the structural component such as starch and cellulose were efficiently hydrolysed. The produced ethanol was recovered and purified meeting the standards of absolute ethanol, rendering it suitable for industrial uses and for biofuel use as well. Energy consumption aspects were discussed as well. Conclusively, all the stages of the value chain for source-separated biowaste valorisation (collection, treatment, added value product recovery) were successfully showcased.
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