Influence of different pretreatment methods applied on anaerobic mixed inoculum was evaluated for selectively enriching the hydrogen (H-2) producing mixed culture using dairy wastewater as substrate. The experimental data showed the feasibility of molecular bio-hydrogen generation utilizing dairy wastewater as primary carbon source through metabolic participation. However, the efficiency of H-2 evolution and substrate removal efficiency were found to be dependent on the type of pretreatment procedure adopted on the parent inoculum. Among the studied pretreatment methods, chemical pretreatment (2-bromoethane sulphonic acid sodium salt (0.2 g/l); 24 h) procedure enabled higher H-2 yield along with concurrent substrate removal efficiency. On the contrary, heat-shock pretreatment (100 degrees C; 1 h) procedure resulted in relatively low H-2 yield. Compared to control experiments all the adopted pretreatment methods documented higher H2 generation efficiency. In the case of combination experiments, integration of pH (pH 3; adjusted with ortho-phosphoric acid; 24 h) and chemical pretreatment evidenced higher H-2 production. Data envelopment analysis (DEA), a frontier analysis technique model was successfully applied to enumerate the relative efficiency of different pretreatment methods studied by considered pretreatment procedures as input and cumulative H-2 production rate and substrate degradation rate as corresponding two outputs. (C) 2006 Elsevier Ltd. All rights reserved.