As depicted in Fig. 1, primary sludge after lipid liquid–liquid extraction was subjected to anaerobic digestion directly and after residual solvent evaporation. The residual hexane was removed using a rotary evaporator at 40 °C under vacuum at 50 mbar. The sludge was anaerobically digested at 33 °C under mesophilic conditions [11]. Lipid-extracted sludge (LES) and evaporated lipid-extracted sludge (ELES) were digested in order to evaluate the impact of the remaining solvent on biogas production. Anaerobic digestion test was conducted in 120 mL serum bottles in triplicate. Digested sludge was used as inoculum and, although acclimation is not strictly required, an anaerobic semi-continuous plant was set to adapt inoculum to a more stable temperature, 33 °C. The optimal digestion conditions were assured with anaerobic basic medium addition [11]