Valorisation of source-separated food waste to bioethanol: pilot-scale demonstration

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 euro/kg ethanol, was estimated for the scenario of SSF with 20% solids loading while for SHF the lowest production cost was achieved (4.40 euro/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.