In this study, fermentation of a thermally treated simulated organic solid waste into hydrogen (H-2) was examined using a pretreated anaerobic mixed culture. The culture was fed a steam exploded food waste plus paper-cardboard waste blend liquor with and without linoleic acid (LA). The individual and interaction effects of the initial pH, LA concentration and the initial chemical oxygen demand (COD) concentration on H-2 and methane (CH4) production was assessed using a Box-Behnken design (BBD). The BBD model predicted a maximum H-2 yield of 87 mL g(-1) COD or 98 mL H-2 g(-1) VS with 1.6 g L-1 LA, an initial pH of 5.93 and an initial COD of 9.34 g COD L-1. The major microbial populations detected in cultures at pH 5.5 with and without LA included Clostridium sp., Enterococcus asini, Enterococcus faecalis, and Lactobacillus gallinarum. The dendrogram for the 16S rRNA gene T-RFs profiles showed four major groups with a similarity index of 72-75% for Clade III. The major H-2-producing populations were grouped in Cade I with a similarity index range of 55-75%. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.