The aim of this study was to verify the efficiency of a separate hydrolysis step by testing different working temperatures (37-55 degrees C) and hydraulic retention times (two, four and six days) and by evaluating readily biodegradable carbon production. The fermentation products included primarily acetic, propionic and butyric acids. These acids can be easily converted into biogas or can be recovered in a biorefinery approach, for example, to produce polyhydroxyalkanoates. The optimal condition was found by applying an organic loading rate of 17.9 gTVS m(-3) with a four-day retention time at 37 degrees C for an acidification yield of 183.2 gCOD(VFA) kgVS(fed)(1). (C) 2016 Elsevier Ltd. All rights reserved.