Overall, in order to reach at least 91% of lipids present in the primary sludge, only three consecutive extraction stages were needed.This extraction efficiency was achieved for 60 min (2:1, 1:1, 1:2,sludge:hexane) as well as for 20 and 40 min (1:2,sludge:hexane). Taking into account the minimization of solvent used, the best operation conditions are 60 min using a 2:1 sludge:hexane ratio. On the other hand, minimizing the extraction time, the best operation conditions area 1:2 sludge:hexane ratio for 20 min of extraction time in each stage.