Characterization of aqueous phase from the hydrothermal liquefaction of Chlorella pyrenoidosa

• Hydrothermal liquefaction of low-lipid microalgae C. pyrenoidosa.
• Response surface method was used to design the whole experiments.
• Interactions of operation conditions on concentration of nutrients of aqueous phase.
• Major chemical compositions of the three aqueous phase samples were determined.

This study investigated the characteristics of aqueous phase from hydrothermal liquefaction of low-lipid microalgae Chlorella pyrenoidosa. The interactions of operating conditions, including reaction temperature, retention time and total solid ratio were evaluated by response surface methodology. The chemical oxygen demand, total nitrogen and total phosphorus were selected as indicators of the property of AP. Results indicated that total solid ratio was found to be the dominant factor affecting the nutrient recovery efficiencies of AP. Based on energy recovery, GC–MS indicated that the AP at two optimized operating conditions (280 °C, 60 min, 35 wt.% and 300 °C, 60 min, 25 wt.%) were observed to have a higher concentration of organic acids (10.35% and 8.34%) while the sample (260 °C, 30 min, 35 wt.%) was observed to have the highest concentration of N&O-heterocyclic compounds (36.16%).