Bio-oil from hydrothermal liquefaction (HTL) represents a promising fuel source due to large higher heating values and compatibility with current energy infrastructure. For bio-oil production to become commercially viable, novel methods of co-product recycling must be explored.
The aims of this study were to culture Chlorella vulgaris, a common HTL feedstock, in various concentrations of the effluent wastewater produced from a novel method of hydrothermal liquefaction. This process, known as nutrient recycling, was used to explore the possibility of improving net efficiency by reducing fertilizer and water inputs while simultaneously investigating the toxicity of the effluent wastewater. Results indicated that C. vulgaris was able to grow in all concentrations of the wastewater, though growth was partially stunted if no prior dilution occurred. Growth of C. vulgaris was optimized between 25% and 50% concentration of the effluent wastewater compared to a growth media control. With no dilution of the wastewater, C. vulgaris was able to reach a biomass concentration of 1,100,000 cells/mL suggesting that a partially closed-loop reactor in a commercial setting is plausible. Further research is needed to determine whether this process is scalable.