Household food waste (HFW) a complex biomass containing soluble sugars, lipids, proteins, cellulose, was used for bioethanol production at high substrate concentration and low enzyme loadings. HFW was subjected to microwave digestion (121 °C, 15 min) at 20 % (w/v) substrate concentration in the presence or absence of dilute sulfuric acid. The whole slurry was hydrolyzed and simultaneously saccharified and fermented using 5 and 10 FPU/g dry HFW. Enzymatic hydrolysis resulted in glucose yields in the range of 44–47 % of the theoretical (based on potential glucose content in the HFW) for both enzyme loadings tested, indicating that enzyme loadings lower than 10 FPU/g HFW could be used. During SSF tests the highest ethanol production (23.12 g/L) was obtained from the pretreated in the presence of dilute sulfuric acid HFW at 10 FPU/g HFW. In an attempt to protect the soluble fraction from possible decomposition and increase ethanol concentration, hot water treatment and higher substrate concentrations were examined. At optimal pretreatment conditions (100 °C, 60 min), glucose yields of 54.69 and 58.39 % (of the theoretical based on potential glucose content in the HFW) were achieved at 30 and 50 % w/v substrate concentration, respectively, which corresponds to an ethanol production of 17.44 and 31.03 g/L, respectively. In order to overcome the technical difficulties due to high initial viscosity of the material, when operating hydrolysis and fermentation at high initial substrate concentrations, a non-isothermal simultaneous saccharification and fermentation process operating in fed-batch mode was applied at 40 % (w/v) final substrate concentration, resulting in 42.66 g/L (or 107 g/kg HFW) ethanol production.
