Continuous Wet Air Oxidation of the Hydrothermal Liquefaction Aqueous Product from Various Wet Wastes

Abstract

Wet air oxidation (WAO) treats waste streams by converting pollutants into benign substances. It can process the aqueous product from the hydrothermal liquefaction (HTL-AP) of wet wastes. We studied the WAO of HTL-AP from four wet wastes with different chemical oxygen demand (COD) levels, through continuous testing under various conditions. We screened the reaction parameters necessary for substantial COD reduction >90%. Alcohols and ketones in the HTL-AP rapidly oxidized to acetic acid through aldehyde intermediates, while acetic acid, other carboxylic acids, and phenols oxidized relatively slowly. Light N-containing compounds exhibit a change in concentration only after the whole sample reaches an 80% COD reduction, indicating their refractory nature under applied conditions. Energy released in the WAO reaction was calculated. Anaerobic toxicity assay demonstrated that the WAO-treated sample exhibited a 23% enhancement in reaction kinetics, indicating decreased inhibitory effects compared to untreated HTL-AP. These findings provide insights into designing effective WAO processes for valorizing HTL aqueous products, addressing key barriers to HTL process commercialization.