<P><B>Abstract</B></P> <P>Anaerobic digestion of biodegradable substrates is a proven biological-based technology that recovers energy in the form of biogas for use in combined heat and power plants. In this respect, hydrogen production during the acidogenic phase can improve process efficiency. The purpose of this study is to evaluate energy recovery from the production of hydrogen and methane by using food waste as substrate. The primary energy saving obtained by different users of biogas was calculated considering the specific gas production evaluated through pilot tests carried out in semi-continuous mode. The physical separation of the traditional anaerobic digestion in two-phase anaerobic process was demonstrated to be beneficial for the methanogenic phase in terms of gas production increase but not efficient in terms of overall energy performance. Although specific methane production increased in semi-continuous mode respect to batch tests, H<SUB>2</SUB> production decreased and hydrogen concentration dropped from 45% to 22.9%. Therefore, bio-hydrogen production in semi-continuous conditions results to be not sufficient to balance out adding energy consumption due to heating of dark fermentation digester.</P>