A first-of-its-kind study on founding concatenated trio fuels production platform: Biodiesel from lipids, biomethane by anaerobic digestion of defatted biomass, and hydrochar by hydrothermal carbonization of Oscillatoria willei biogas slurry (OWBS)

Abstract

Sustainable production of multiple biofuels from algae/spent algal biomass through a concatenated route imparts a new energy and environmental sustainability platform. Thus, this is a first-of-its-kind study on establishing a novel and integrated trio fuels production platform using a cyanobacterium Oscillatoria willei (O. willei); - (i) production of biodiesel from O. willei (ii) Anaerobic digestion of defatted biomass for biomethane production (iii) Hydrothermal carbonization (HTC) of O. willei biogas slurry (OWBS) for hydrochar production. Initially, a maximum dry weight of 1.63 g/L was obtained from O. willei on the 18th day, and further, it contains 12.86 % lipids, 41.37 % proteins, and 34.21 % carbohydrates. Biodiesel (Bioenergy- I) produced from the test strain was 67.87 % and it contains preferable fatty acids such as C16:0, C16:1, C18:1, C18:2, and C18:3. The defatted biomass was used for anaerobic digestion (AD) for biomethane (Bioenergy- II) production for up to 45 days. The OWBS from the AD process was used as a feedstock in HTC for the production of hydrochar (Bioenergy- III) under different HTC temperatures (200, 220, 240, 260, and 280 °C) and time (60, 90, 120, 150 and 180 min). The highest hydrochar yield from OWBS was estimated to be 41.65 % at 200 °C and 60 min. Further, elemental analysis of hydrochar revealed 37.6, 4.8, 1.7, 0.1, and 28.3 % of C, H, N, S, and O, respectively with 27.5 % ash content. Based on the results, it is concluded that this novel sequence of strategy delivering trio biofuels along with biogas slurry nutrient removal has not been investigated till now to the best of our knowledge, which will lay a road map for the production of multiple bioenergies along with waste management.