Effects of Process Parameters on Hydrothermal Liquefaction of Microalgae Biomass Grown in Municipal Wastewater

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The emerging fuel crisis necessitates a shift in focus towards alternative renewable forms, so that sustainable development can be achieved. Bio-oil is a promising alternative renewable source of energy which is a third generation bio-fuel. Algae are a popular candidate for bio-fuel production due to their high lipid contents, ease of cultivation and rapid growth rate. In this study, Hydrothermal liquefaction of Scenedesmus obliques biomass cultivated in photo-bio-reactor (PBR) from wastewater was studied. The influence of process parameters on the bio-oil yield and bio-oil upgrading was analysed. Different S. obliques biomass to water ratios (0.025, 0.05, 0.075 and 0.1 g/ml) were liquefied at diverse temperatures ranging from 200 to 340°C under 5 MPa N₂ gas atmosphere. The influence of catalyst on bio-oil upgradation was studied at varying catalyst loading of the range 1–5 wt %. Bio-oil was analysed using Gas Chromatography Mass Spectroscopy (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR). Results showed a maximum bio-oil yield of 24.57 wt % at 300°C, 15 g/200 ml biomass load and 2.5 wt % NaOH at 60 min holding time. Also, it was found that the gas generated from liquefaction process contained 22 vol % Hydrogen gas, 18 vol % Carbon dioxide gas, 27 vol % Carbon monoxide gas, 22 vol % of methane gas and a small amount of other gaseous components (H₂S). HTL bio-oil was upgraded and it resulted in 30.15 wt % yield with higher degree of C₇−C₂₁ range hydrocarbons in it.