Life cycle assessment of deep-eutectic-solvent-assisted hydrothermal disintegration of microalgae for biodiesel and biogas co-production

A life-cycle assessment was carried out to evaluate the industrial feasibility of deep eutectic solvents (DES) for microalgae pretreatment. The effects of DES on hydrothermal disintegration (HTD) of microalgae for biodiesel and biogas co-production was assessed in terms of net energy ratio (NER, Energy input/Energy output) and greenhouse gas (GHG) emissions. Although the addition of DES during HTD increased the energy output by 36.33 %, the NER increased from 0.65 to 0.83 due to the larger increase in energy input. The increase in energy input is because DES synthesis consumed a lot of energy, accounting for 45.93 % of the total energy input. The addition of DES also increased the net GHG emissions from −25.53 g CO2-eq MJ−1 to 26.04 g CO2-eq MJ−1. It is essential to reduce the GHG emissions and energy consumption via DES recovery for commercial applications. When DES was recovered by a combined method of membrane filtration and recrystallization, a low NER of 0.58 along with negative net GHG emissions were achieved for microalgal biofuel production via DES-HTD.