Sorption and recovery of phenolic compounds from aqueous phase of sewage sludge hydrothermal liquefaction using bio-char

Bio-char, a by-product of thermochemical conversion processes, has a great potential in phenolic compounds sorption from the waste aqueous phase produced from the hydrothermal liquefaction (HTL) process while being a low-cost sorbent. This study investigated the effect of temperature, pH, bio-char concentration, and mixing speed on two types of bio-char sorption of phenolic compounds using Taguchi's design of experiment and response surface method. Isothermal kinetics and thermodynamic properties were also evaluated to explain the sorption mechanism. The experimental results were well described by the pseudo-second-order kinetic model for both types of bio-char. The Langmuir isotherm model was found to be more suitable at high sorption temper-atures, while the Freundlich isotherm model was better at low temperatures. Finally, the alkaline desorption and regeneration experiments were examined, and the eluents with phenolic compounds were characterized using a liquid chromatography-mass spectrometer.