Wet Air Oxidation of Hydrothermal Carbonization (HTC) Process Liquid

Abstract

Hydrothermal carbonization (HTC) is a promising thermochemical treatment of wet biomass. The byproduct HTC process liquid often contains a very high total organic carbon (TOC). Various toxic organic compounds (e.g., phenol, furfural, 5-HMF, etc.) can be found in HTC process liquid. As a result, the HTC process liquid often requires further treatment prior to discharge into the environment. In this study, wet air oxidation (WAO) is applied to process liquid produced from HTC of dairy manure and wastewater biosolids. Different oxygen loadings (25 and 50 atm partial pressure) were charged for WAO at 260 °C for 30 min. Furthermore, the oxidation capability of copper oxide (CuO) was evaluated at the same temperature and time. In all cases, the resulting liquid product was clear and has reduced TOC. With an increase in oxygen partial pressure, TOC is reduced up to 60% compared to the control run and 74% compared to the original HTC process liquid. The primary products in the WAO liquid product are short chain organic acids (formic, acetic, succinic, propionic, and glycolic acid), which are not considered as toxic substances.