A solar-driven continuous hydrothermal pretreatment system for biomethane production from microalgae biomass

Hydrothermal pretreatment is an efficient approach to enhance methane production from microalgae biomass by anaerobic digestion. However, the high energy consumption hinders the development of hydrothermal pretreatment. In this study, a solar-driven hydrothermal pretreatment system was proposed to save energy in hydrothermal pretreatment. In this system, microalgae slurry directly flows through the parabolic trough collector and is hydrolyzed while absorbing solar energy. The effects of operation parameters (i.e., direct normal irradiation, flow rate, mass fraction, and retention time) on the yield of organic matter were also investigated. The maximum yield of carbohydrates (267.3 mg/g total solid) and proteins (265.2 mg/g total solid) from pretreated microalgae biomass was 7.4 and 3.7 times that obtained from the raw microalgae slurry, respectively. In addition, the methane produced from the microalgae biomass pretreated by the solar-driven hydrothermal pretreatment system increased by 57% in anaerobic digestion, compared to that obtained using raw microalgae biomass as a substrate. The solar-driven hydrothermal pretreatment system can be used as an alternative energy saving approach for the hydrothermal pretreatment of microalgae slurry.