Influence of reactor configuration (biofilm/suspended growth] on fermentative hydrogen (H(2)) production and substrate degradation was evaluated employing anaerobic mixed consortia. Reactors were operated at acidophilic (pH 6.0) condition employing designed synthetic wastewater as substrate at an organic loading rate of 3.4 Kg COD/m(3)-day with a retention time of 24 h at 28 +/- 2 degrees C. Experimental data enumerated the influence of reactor configuration on both H(2) production and wastewater treatment. Biofilm reactor (28.98 mmol H(2)/day; 1.25 Kg COD/m(3)-day) showed relatively efficient performance over the corresponding suspended growth configuration (20.93 mmol H(2)/day; 1.08 Kg COD/m(3)-day). Specific H(2) yields of 6.96 mmol H(2)/g-COD(L)-day (19.32 mmol H(2)/g-COD(R)-day) and 5.03 mmol H(2)/g-COD(L)-day (16.10 mmol H(2)/g-COD(R)-day) were observed during stabilized phase of operation of biofilm and suspended growth reactors respectively. Higher concentration of VFA generation was observed in the biofilm reactor. Both the configurations recorded higher acetate concentration over other soluble metabolites indicating the dominance of acid-forming metabolic pathway during the H(2) production process. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.