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Abstract: A two-stage process to produce hydrogen and methane from lipid-extracted microalgal biomass residues (LMBRs) was developed. The biogas production and energy efficiency were compared between one- and two-stage processes. The two-stage process generated 46 ± 2.4 mL H2/g-volatile solid (VS), and 393.6 ± 19.5 mL CH4/g-VS. The methane yield was 22% higher than the one in the one-stage process. Energy efficiency increased from 51% in the one-stage process to 65% in the two-stage process. Additionally, it was found that repeated batch cultivation was a useful method to cultivate the cultures to improve the methane production rate and reduce the fermentation time. In the repeated batch cultivation, the methane yield slightly decreased if the ammonia levels rose, suggesting that the accumulation of ammonia could affect methane production. [Copyright &y& Elsevier]

Abstract: 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 °C and 121 °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 °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 °C is an effective method to improve LMBR solubilization and increase the hydrogen production from LMBRs. [ABSTRACT FROM AUTHOR]