Treatment of wastewater from biomass pyrolysis and recovery of its organic compounds with char-assisted drying

This study proposes a new process that treats pyrolytic wastewater (PWW) from biomass pyrolysis with char-assisted drying. It can be operated at two modes: (I) one-stage drying for PWW treatment; and (II) two-stage drying and condensation for both treating PWW and recovering valuable chemicals (e.g., acetic acid). The process is proved via drying the mixture of a char and a synthetic PWW solution containing acetic acid, acetol, furfural, and phenol at different temperatures (60, 80, and 105 °C) and char-to-PWW mass ratios (1.0, 1.5, and 2.0). The results, supported by density functional theory (DFT) calculations, demonstrate that under Mode I, the char captures over 97.1% of the organic compounds in the PWW at 60 °C and a char-to-PWW ratio of 2.0, while evaporating almost all the water. The evaporated stream can be potentially discharged into the atmosphere without condensation or condensed into wastewater with a significantly reduced content of total organic carbon. Under Mode II, the char-PWW mixture is sequentially dried at 60 and 105 °C, with the exhaust gases being separately condensed. This yields a stream of purified acetic acid solution (concentration: ∼76 wt%) concentrated by a factor of ∼6.3 (compared with the PWW), with a recovery rate of ∼29%.