The production of volatile fatty acids (VFAs) in a continuous process using a synthetic glucose medium as model substrate in the presence of gamma-alumina as promoter is described. The results showed formation of acetic, propionic, isobutyric, butyric, isovaleric and valeric acids, with acetic acid being more than 90% of the total VFAs produced. It is also highlighted that gamma-alumina enhanced the simultaneous production of acetic acid and ethanol, which in some cases was formed at concentrations able to esterify about 85% of the produced VFAs. Since most agro-industrial effluents can be treated by anaerobic acidogenic digestion, while lignocellulosic biomass can be converted to VFAs after hydrolysis, this contribution can lead to a breakthrough in the research of biofuel production from renewable waste sources. (C) 2012 Elsevier Ltd. All rights reserved.