In the case of 100% microalgal biomass (A only), the low methane production from day 0 to 42 may be due to resistance of the cell wall, because pretreatment of the microalgae was not performed in this study. Chen and Oswald (1998) and Keymer et al. (2013) indicated that thermal pretreatment of algal biomass increased methane yield during anaerobic digestion. Also, Keymer et al. (2013) reported algal residue after lipid extraction helped to reduce pretreatment costs. However, costs and energy balances of total anaerobic processes should be considered when pretreating algal biomass. According to Sialve et al. (2009), when algae have a low lipid content (