The treatment of 2,2′,4,4′,6,6′-hexanitrostilbene explosive wastewater by hydrodynamic cavitation combined with chlorine dioxide

Abstract

2,2′,4,4′,6,6′-hexanitrostilbene (HNS) explosive wastewater must be strictly treated before discharge due to its a large number of acute toxic mutagenic nitroaromatic compounds (NACs). This study investigated the degradation effect of HNS explosive wastewater by hydrodynamic cavitation combined with chlorine dioxide oxidation (HC+ClO2). The surface-response model was used to simulate the experiment, and it was established that the surface-response polynomial model had high reliability. After the model simulation and experimental investigation, it was concluded that with pH 4.45, ClO2 concentration 14.86 mg/L and treatment time 120 min, the degradation rate of HNS reaches 64.51% in explosive wastewater. Furthermore, the kinetics of HNS degradation by HC or ClO2 oxidation alone and HC+ClO2 oxidation were examined. Compared with the degradation method alone, the degradation effect of HNS by HC+ClO2 was more significant, and the enhancement factor was 1.33, which indicates that HC greatly enhances the oxidation capacity of ClO2. Based on the detection results of the liquid chromatography–mass spectrometry (LC–MS), the possible degradation pathways of HNS were analyzed: within the attack of •OH, HNS were directly or indirectly decomposed into trinitrophenol, after which continuous denitroso occurred to obtain 1,2,3,5-tetrahydroxy benzene, followed by epoxidation cracking to obtain small organic acids, H2O, CO2, etc.