Valorization of process wastes from soft-wheat processing industry through biofuel production

A substantial amount of process waste is generated during the manufacture of soft-wheat products (SWPs), such as biscuits/cookies, crackers, wafers, and cakes. A small portion of waste is reused in specific biscuits, whereas the rest is usually discarded. This study aimed to investigate the suitability of this waste for the co-production of bioethanol and fatty acid methyl esters (FAMEs or biodiesel). Two groups of waste generated in the SWP industry were included in the study: (a) the waste of low-moisture (<10%) biscuits, crackers, and wafer sheets with no fillings and/or coatings, and (b) the waste of high-moisture (>10%) biscuits, crackers, wafers, and cakes with fillings and/or coatings. The study involved extracting each sample with hexane, and the recovered fat was converted to the FAME through alkali-catalyzed transesterification. The remaining carbohydrate-rich fraction was then converted to bioethanol through amylolytic hydrolysis and yeast fermentation. A great portion (92.42%-93.17%) of the fat was extracted from the wastes and converted to the FAME with adequate yields (13.81-14.55 g FAME/g waste, dm) and acceptable conversion efficiencies (85.19%-89.04%). However, bioethanol production from the defatted carbohydrate-rich fractions proceeded rather slowly, yielding only 16.54-18.02 (g ethanol per g of waste, dm), corresponding to fermentation efficiencies ranging from 43.32% to 48.29%. Upon the co-production of FAME and ethanol, a considerable amount (50.93%-53.08%) of waste solids remained in the residue fraction. These findings indicated that production of the FAME with adequate yields and conversion efficiencies is viable from the SWP industry wastes; however, bioethanol yields and fermentation efficiencies are rather limited, which warrants further investigation. PRACTICAL APPLICATION: The soft-wheat processing industry generates 1%-5% of total production as waste. The waste was studied to produce FAME and bioethanol. The fat was extracted from the waste and converted to FAME. Bioethanol yields and fermentation efficiencies are limited due to dough modifiers and antimicrobial additives used in SWP production. Further research is required to improve ethanol yield.