An integrated energy recovery approach of biohythane-biocrude production from microalgae-sludge through co-digestion and co-liquefaction

Abstract

Higher energy recovery from wet-waste is a challenging task while considering the waste-to-energy approach to tackle the huge wet-waste biomass generated around the globe. This study took the opportunity to explore the combined approach of biohythane (e.g., bioH2 and bioCH4) and biocrude generation using two-stage anaerobic digestion coupled with hydrothermal liquefaction (TSAD-HTL). The finding of this study suggests that the highest biohythane productivity of 268.7 mL/g-VS with energy recovery of 9.95 MJ/kg-VS was produced from sludge-microalgae co-digestion, which was 17% and 205% higher than mono-digestion of microalgae and sludge, respectively. In addition, the highest biocrude yield of 45.4% was obtained from sludge-microalgae-derived digestate. The lighter fraction (<C20) of biocrude was observed at 91.8 % (20 % naphtha, 58 % jet fuel, and 13 % diesel) with an HHV of 35.85 MJ/kg. The higher energy recovery of 81 % and lower energy consumption ratio of 0.25 suggests that the integrated TSAD-HTL is an innovative energy-positive approach for producing biohythane-biocrude from wet wastes as a sustainable concept of zero waste.