In this study, the feasibility of acidogenic fermentation in synthetic soft drink wastewater (SDW) was evaluated. Batch experiments were conducted using a mixed microbial culture (anaerobic sludge inoculum) without any external sources of inhibition for methanogenic bacteria and with no pH control. Three food-to-microorganism (F/M) ratios (1.6,4.0 and 6.4 gCOD/gVSS) and different initial alkalinity values (in the range 1.0-2.5 gCaCO(3)/L) were tested. After six days of fermentation, accumulation of volatile fatty acids (VFA) was observed in all assays, indicating that SDW can serve as a substrate for VFA production. After 21 days of fermentation, the maximum degree of acidification achieved was 70.3+/-0.4%, and it was obtained at an F/M of 4.0 gCOD/gVSS and an initial alkalinity of 2.0 gCaCO(3)/L. The predominant VFA generated in all mixtures were butyrate and acetate. Additionally, a substantial percentage of propionate (approximately 10%) was observed when operating at pH values close to 7. In this study, the F/M ratio was the critical parameter for maintaining acidogenic conditions by inhibiting methanogenic bacteria (and other VFA consuming bacteria). (C) 2015 Elsevier Ltd. All rights reserved.