Bio-crude oil production and valorization of hydrochar as anode material from hydrothermal liquefaction of algae grown on brackish dairy wastewater

Abstract

Hydrothermal liquefaction (HTL) is effective at recovering bioenergy from wet microalgae, which is used for cleaning polluted water body. In this study, a brackish water-grown microalgae polyculture was hydrothermally liquefied into 26.5 wt% bio-crude oil with an energy consumption ratio of 2.4, indicating an energy negative process for bioenergy production. To improve the economic feasibility of wastewater algae-to-bioenergy process, a HTL byproduct, hydrochar, has been recycled to assemble in lithium ion batteries (LIBs) as a renewable anode material. Owing to the organic components produced from HTL and high concentrations of impurities obtained from brackish water, HTL hydrochar needs to be post-treated (CO2 activation and ‘base-acid’ wash) to increase carbon content, leading to better electrochemical performance. By virtue of increased specific surface area (304.06 m2 g−1) and massive mesopores, post-treated hydrochar exhibits reversible discharge-charge capacity of 226 and 223 mAh g−1 at 0.1 A g−1 after 40 cycles. There is no related study to investigate the feasibility of brackish-grown algae-derived hydrochar as green anodes of LIBs. This integration will not only mitigate water pollution (algae treatment for brackish water), produce carbon-neutral alternative to fossil fuel (algae-derived biofuel production), but also valorize solid byproduct for generating clean energy (LIBs anodes synthesis from biomass-derived carbon).