Life cycle and economic assessments of biogas production from microalgae biomass with hydrothermal pretreatment via anaerobic digestion

Abstract

Biogas production from microalgae biomass via anaerobic digestion can be enhanced by hydrothermal pretreatment. The process of hydrothermal pretreatment has a significant impact on the energy gain, greenhouse gas emissions, and levelized cost of energy in biogas production from microalgae biomass, which has not been reported until now. In this study, life cycle and economic assessments of biogas production from microalgae biomass with hydrothermal pretreatment and with solar-driven hydrothermal pretreatment were conducted. The results showed that both types of pretreatment methods improved the biogas yield, promoted the energy gain, and reduced the levelized cost of energy. In biogas production through hydrothermal pretreatment, the net energy ratio (Energy input/Energy output), greenhouse gas emissions, and levelized cost of energy were 0.54, −129.94 g CO2-eq/(kWh biogas), and 0.22 $/m3, respectively, whereas in biogas production through solar-driven hydrothermal pretreatment, the corresponding values were 0.69, −166.13 g CO2-eq/(kWh biogas), and 0.17 $/m3, respectively. The biogas yield had the maximum effect on the net energy ratio and economic benefit. The efficiency in nitrogen recovery from the biogas residual had the maximum effect on greenhouse gas emissions. This work provides a theoretical guide to promote the environmental and economic benefits of biogas production from microalgae biomass.