This study deals with the treatment and valorization of sludge issued from the municipal wastewater treatment plant of Adrar city (southwest of Algeria). The sludge considered was a complex mixture of substances, essentially organic matters with a rate of 54%. An acute biological activity of the crude substrate was noted (1.67 10(6) germs/1 ml). The diluted sludge with a content of 16 g/l of total solids (TS) was fermented in a digester of one litter capacity under anaerobic conditions during 33 days. The quantity of biogas produced was 280.31 Nml with a yield of 30 Nml of biogas/mg of COD removed. The COD, BOD and TS reduction yields were 88, 90 and 81% respectively, followed by a complete destruction of the pathogenic flora particularly Escherichia coli. This study presented an important energetic opportunity by producing 30,950 KWh. (C) 2011 Published by Elsevier Ltd.