Stillage reflux in food waste ethanol fermentation and its by-product accumulation

•Stillage reflux fermentation used for ethanol production from food waste.•Lactic acid and sodium chloride were accumulated in food waste ethanol fermentation.•Lactic acid affected more on ethanol production than sodium chloride.

Raw materials and pollution control are key issues for the ethanol fermentation industry. To address these concerns, food waste was selected as fermentation substrate, and stillage reflux was carried out in this study. Reflux was used seven times during fermentation. Corresponding ethanol and reducing sugar were detected. Accumulation of by-products, such as organic acid, sodium chloride, and glycerol, was investigated. Lactic acid was observed to accumulate up to 120 g/L, and sodium chloride reached 0.14 mol/L. Other by-products did not accumulate. The first five cycles of reflux increased ethanol concentration, which prolonged fermentation time. Further increases in reflux time negatively influenced ethanol fermentation. Single-factor analysis with lactic acid and sodium chloride demonstrated that both factors affected ethanol fermentation, but lactic acid induced more effects.