Hydrothermal Liquefaction of Chlorella Kessleri: Effects of Algal Growth Stage on Biocrude Production and Characterization

According to a 2017 study by the U.S. Energy Information Administration (EIA), U.S. motor gasoline and diesel fuel consumption accounted 30% of the total U.S. energy-related CO₂ production in the year 2016. Disproportionately high emissions of CO₂ have caused adverse effects on the environment: increasing global temperatures and changing climates. Since 2007, reducing CO₂ emissions in the U.S. economy has been an overarching goal of the U.S. Environmental Protection Agency (EPA), which will require the production of 36 billion gallons of renewable fuel by the year 2022. To help cover this quota, biocrude may be implemented as a renewable replacement for petroleum crude in the synthesis of diesel fuel. The use of biocrude as a feedstock is environmentally beneficial because CO₂ is consumed while cultivating biomass, and the raw materials come from inexhaustible sources. One feasible production route of biocrude is through whole-cell conversion of algae into biocrude. Algae can be cultivated using wastewater treatment, and the bioprocessing of algae would serve the dual purpose of water purification and oil production. The purpose of this study is to demonstrate the optimization of an algae-to-biocrude operation involving the hydrothermal liquefaction of raceway pond algae into high grade biocrude. Algae were inoculated on site under nitrogen-limiting conditions. The nitrogen to phosphorous (N:P) ratio of the growth medium was studied, and algae samples were also collected at each algal growth stage (exponential, transitional, stationary). The production of biocrude was studied in terms of yield and carbon recovery in the biocrude.