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 degrees C, 60 min, 35 wt.% and 300 degrees C, 60 min, 25 wt.%) were observed to have a higher concentration of organic acids (10.35% and 8.34%) while the sample (260 degrees C, 30 min, 35 wt.%) was observed to have the highest concentration of N&O-heterocyclic compounds (36.16%). (C) 2014 Elsevier Ltd. All rights reserved.