Decontamination strategies and enzyme dosages for the fermentation of food waste to produce ethanol
Date
2024-03
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Innovative solutions are required to deal with an ever-increasing energy demand and generation of organic waste. Processes where energy or valuable chemicals can be produced from waste, will support the circular economy and a sustainable future. Ethanol production from biomass, such as maize or sugar cane, is a mature technology. However, ethanol production from food waste (FW) is far more challenging, given variable feed composition and microbial contamination. This research aimed to produce ethanol from food waste by evaluating (i) different decontamination strategies, (ii) different yeast strains, namely Saccharomyces cerevisiae Ethanol Red® and S. cerevisiae ER T12, which is an advanced strain engineered to secrete α-amylase, and (iii) increasing solids loading to produce higher ethanol concentrations. Ethanol fermentation using pre- and post-consumer FW was conducted in shake flasks at 30 °C for 72 h. Thermal sterilisation proved effective for post-consumer FW at a low liquefaction temperature of 55 °C with a significant (p < 0.05) increase in ethanol yield of 77.79% compared to 67.29% recorded after fermentation using an unsterilised feed. Similarly, at a liquefaction temperature of 55 °C after thermal sterilisation of pre-consumer FW, an ethanol yield of 92.2% was obtained, substantially higher than the 48.2% yield of the control where the feedstock remained unsterilised. This data suggested that thermal sterilisation effectively served simultaneously as a decontamination and gelatinisation strategy. Substantial decreases in enzyme dosages of up to 33% were achieved by using the consolidated bioprocessing (CBP) yeast S. cerevisiae ER T12 without affecting the ethanol yield of 80.87% ± 1.40 and productivity 1.51 g/L/h compared to 82.56% ± 2.81 and 1.54 g/L/h when using S. cerevisiae strain Ethanol Red as benchmark. The same enzyme reduction of https://scholar.sun.ac.za iii | P a g e 33% was observed for the post-consumer FW. The ethanol concentration of the pre-and postconsumer FW was increased by 96% to 74.11 ± 0.75 g/L and 85% to 48.52 ± 1.32 g/L without a significant effect on the ethanol yield when the solids loading was increased to 20.6% and 21.06% w/v. Although sterilisation proved to be an effective decontamination method, it remains energy intensive, which could affect the process's financial feasibility. Using the CBP yeast can substantially decrease operational costs due to the reduced requirements for commercial enzymes, which is crucialto developing a sustainable FW fermentation process. The CBP yeast strain proved effective even when the solids loading was increased, and the results are promising, showing that the usage of CBP yeasts can further improve the viability of the fermentations.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MEng)--Stellenbosch University, 2024.
Keywords
Food waste; Bioethanol; Decontamination; Consolidated bioprocessing (CBP)