Anaerobic acidogenesis in an up-flow non-woven biofilm reactor was investigated to convert chemical oxygen demand (COD) into volatile fatty acids (VFAs) as carbon source in the subsequent nitrogen removal process in synthetic domestic sewage pretreatment. A specifically designed non-woven padding inserted vertically into the reactor proved very favorable for acidogenic bacterial attachment. The characterization of the microorganisms was performed using scanning electron microscopy and fluorescent in situ hybridization. Multiple factors, including hydraulic retention time (HRT), pH, and influent COD and NH4+-N concentrations, played comprehensive roles in acidogenesis. Based on the Taguchi orthogonal array, the ordering sequence of the influential factors for VFAs production was influent NH4+-N (R = 41.4) > pH (R = 37.3) > influent COD (R = 20.2) > HRT (R = 14.8). The suitable conditions were HRT = 1.5 h, pH = 8.5, influent COD = 100 mg L-1, and influent NH4+-N = 30 mg L-1. Moreover, acetic acid, propionic acid, and n-butyric acid prevailed over other VFAs. Finally, the most influential factor for each VFA was demonstrated. (C) 2013 Elsevier B.V. All rights reserved.