Ethanol Production from Food Waste at High Solids Content with Vacuum Recovery Technology Haibo Huang, † Nasib Qureshi, ‡ Ming-Hsu Chen, † Wei Liu, † and Vijay Singh* ,† † Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States ‡ Bioenergy Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service (ARS), United States Department of Agriculture (USDA), 1815 North University Street, Peoria, Illinois 61604, United States ABSTRACT: Ethanol production from food wastes does not only solve environmental issues but also provides renewable biofuels. This study investigated the feasibility of producing ethanol from food wastes at high solids content (35%, w/w). A vacuum recovery system was developed and applied to remove ethanol from fermentation broth to reduce yeast ethanol inhibition. A high concentration of ethanol (144 g/L) was produced by the conventional fermentation of food waste without a vacuum recovery system. When the vacuum recovery is applied to the fermentation process, the ethanol concentration in the fermentation broth was controlled below 100 g/L, thus reducing yeast ethanol inhibition. At the end of the conventional fermentation, the residual glucose in the fermentation broth was 5.7 g/L, indicating incomplete utilization of glucose, while the vacuum fermentation allowed for complete utilization of glucose. The ethanol yield for the vacuum fermentation was found to be 358 g/kg of food waste (dry basis), higher than that for the conventional fermentation at 327 g/kg of food waste (dry basis). KEYWORDS: food waste, ethanol, fermentation, vacuum recovery, high solids content ■ INTRODUCTION Over the past few decades, the objectives to establish national energy independence and to reduce the greenhouse gas emissions have led to the development of renewable biofuel technologies based on agricultural materials. Ethanol is by far the most significant biofuel in the United States, accounting for 94% of all biofuel production in 2012. 1 Ethanol is mainly produced from corn in the U.S. and from sugar cane in Brazil. 2 However, corn and sugar cane are also used as food; overuse of corn or sugar cane as feedstock for ethanol production would create “food versus fuel” competition. Furthermore, increasing prices of corn and sugar cane are the main drivers of the high cost of ethanol production. According to the previous studies, corn and sugar cane feedstock costs contributed to 70-90% of the total ethanol production costs. 3-5 Researchers have investigated the production of ethanol from low-cost agricultural residues, such as corn stover, 6,7 wheat straw, 8 sugar cane bagasse, 9 and rice straw. 10 Efficiently releasing sugars from cellulose and hemicellulose is one of the main challenges of using cellulosic biomass. 11 To break cellulose and hemi- cellulose into monosaccharides, the biomass materials have to be processed with a harsh pretreatment process, followed by hydrolysis with the addition of a high dosage of enzymes, which significantly increases the capital and processing costs of the ethanol production. 11,12 Food waste is a complex biomass discharged from house- holds, restaurants, cafeterias, and retail stores and accounts for a considerable portion of municipal solid waste. 13 In the U.S., more than 36 million tons of food waste were generated in 2012 alone. 14 Food waste management raises significant environmental concerns. Disposal of food waste in a landfill is not only costly but also causing potential environmental problems, with direct and indirect emissions of greenhouse gases (CH 4 and CO 2 ). 15,16 Incineration is another way to manage food waste but is banned in different countries because of environmental concerns. Also, energy recovery through incineration may not be feasible, because of the energy loss to evaporate the large water content in food waste. 16 Food waste can be diverted from landfills and incinerators by turning it into compost to improve the soil fertility, but it may cause severe pollution to surface and underground water. 17 On the other hand, food waste contains abundant nutrition (starch, glucose, protein, etc.), making it a good raw material for biofuel production. Until now, most of the research has been focusing on the usage of food waste to produce biogas through anaerobic digestion. 18-20 Food waste can also be used as a low- cost feedstock for producing ethanol, 15,21,22 which is a more valuable fuel compared to biogas. Besides using the low-cost materials, fermentation at higher solids contents can lower the ethanol production costs, because it can reduce the energy and water consumptions as well as the volumes of the processing equipment. 23 However, higher solids fermentation results in a higher ethanol concentration, which inhibits yeast activity, thereby causing reduced ethanol yield and fermentation efficiency. 24 Vacuum stripping, one of the in situ ethanol removal technologies, has been reported to improve the ethanol or butanol fermentations at high solids contents. 23,25-27 In a vacuum fermentation system, the produced ethanol is removed by maintaining the bioreactor under vacuum conditions, so that ethanol boils off at the fermentation temperature and is subsequently recovered by the Received: November 14, 2014 Revised: February 19, 2015 Accepted: February 23, 2015 Published: February 23, 2015 Article pubs.acs.org/JAFC © 2015 American Chemical Society 2760 DOI: 10.1021/jf5054029 J. Agric. Food Chem. 2015, 63, 2760-2766