Energy recovery from lipid-extracted microalgal biomass residues (LMBRs) plays a significant role in the sustainable development of the microalgal biodiesel industry. Different methods were used to pretreat LMBRs to improve their solubilization and anaerobic hydrogen production abilities. The pretreatment methods studied included thermal (100 degrees C and 121 degrees C), alkaline and thermo-alkaline pretreatments (combinations of alkaline and thermal pretreatments). The results showed that thermo-alkaline pretreatments resulted in remarkable improvements of LMBR solubilization, which led to an increase in hydrogen yield. The highest hydrogen yield of 45.54 mL/g-volatile solid (VS) was achieved from LMBRs pretreated by the thermo-alkaline pretreatment at 100 degrees C, which was approximately three-fold higher than the yield from untreated LMBRs. The results of this study proved that thermo-alkaline pretreatment at 100 degrees C is an effective method to improve LMBR solubilization and increase the hydrogen production from LMBRs. Crown Copyright (C) 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.