Incorporating hydrothermal liquefaction into wastewater treatment – Part III: Aqueous phase characterization and evaluation of on-site treatment

•Hydrothermal decomposition of sludge was not complete at 290 °C-15 min condition.•N-heterocyclic compounds were the most abundant in HTL aqueous phase.•Up to 2.3 g/L gallic acid equivalent phenolics were detected in HTL aqueous.•N-heterocyclics and phenolics were identified as possible inhibitory compounds.•No metal accumulation was detected in sludge-derived HTL aqueous phase.