Humic acid removal by gas–liquid interface discharge plasma: performance, mechanism and comparison to ozonation

Abstract

The removal of natural organic matter (NOM) is a major objective for drinking water treatment. In this study, a novel advanced oxidation process (AOP) based on plasma in gas–liquid interface discharge was investigated for removing humic acid (HA), and ozonation treatment effect was evaluated as a comparison. Several indexes including UV₂₅₄, dissolved organic carbon (DOC), specific UV absorbance (SUVA), and excitation-emission matrix (EEM) fluorescence spectra were employed to characterize HA transformation. The results showed that typical species including ozone, hydrogen peroxide and HO˙ were produced in the plasma process, which made better removal efficiency than ozonation. Especially, UV₂₅₄ was removed effectively by 96.5% and 90.3% within 15 min by plasma and ozonation, while DOC was 49.2% and 41.1%, respectively. HO˙ radicals were majorly responsible for the degradation of HA in the plasma process, which were mainly generated via reaction of in situ produced ozone and H₂O₂ during the discharge process. UV/vis absorbance and EEM results further showed that HA with the large molecular weight fraction was decomposed to small molecular weight fraction. This study indicates that plasma technology has a significant application prospect as a replacement for ozone in drinking water industry.