Integrated Bio-Refinery Approach towards Production of Sustainable Fuel and Chemicals from Algal Bio-Based System

Abstract

Every nation is exploring alternative indigenous energy sources to reduce dependence on fossil fuels or foreign sources, considering the global energy crisis, climate change, and uncertain political turmoil. In this light, biofuels derived from non-edible sources can be a promising option. For this reason, a fast-growing and non-conflicting source such as microalgae is considered a more sustainable biofuel resource. Scenedesmus sp. of microalgae are abundantly found in countries like India, with favorable climate conditions and colossal coastline. The microalgae (Scenedesmums sp.) samples were successively extracted using n-hexane, chloroform, ethyl acetate, acetone, methanol, and water, which were then investigated for their lipid and phytochemicals. The antibacterial and antioxidant activity of these extracts was evaluated with selected test bacteria. Also, the hexane and chloroform extracts contained a high amount of SFA and PUFA, which indicates that the strain is efficient for pharmacological applications and biodiesel production. Furthermore, the lipid extraction was performed in a 15 L capacity hydrodynamic cavitation setup by a process intensification approach at the pilot scale. Further, the defatted biomass was co-pyrolyzed by blending with rice husk (RH). The maximum bio-oil yield of ~16% was obtained at optimized conditions. Further, the thesis presents subcritical water hydrolysis (SCWH) and the hydrothermal liquefaction (HTL) of wet microalgae slurry. SCWH was carried out to extract total reducing sugars (TRS) by varying process parameters such as temperature, 150–250 °C; biomass loading, 3–15%; and retention time, 30–60 min. The process for the HTL of microalgae slurry to produce crude oil was carried out at temperature, 250–350 °C; biomass loading, 3–20%; and retention time, 20–90 min. Furthermore, the whole process was simulated using ASPEN Plus and the mass and energy integration strategies were applied for maximum recovery of nutrients and energy. Finally, the techno-economic analysis of the proposed integrated biorefinery approach was carried out which demonstrates that the integrated production of valuable products like lipids with biofuels can drive the profitability of algal biorefinery. This work could provide critical input on effectively utilizing microalgae for synthesizing biofuel and bio-chemicals using greener techniques.