Hydrothermal oxidation degradation of dioxins in fly ash with water-washing and added Ce–Mn catalyst. (1st September 2022)

• Record Type: Journal Article
• Authors: Zhang, Tong; Yang, Yuchen; Zhou, Kai; Liu, Bo; Tian, Ganpei; Zuo, Wu; Zhou, Haiyun; Bian, Bo
• Is Part Of: Journal of environmental management. Volume 317(2022)
• Publication Date: 2022-09-01
• Subjects: MSWI fly ash -- PCDD/Fs -- Hydrothermal oxidation -- Water-washing; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2022.115430
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: A comprehensive analysis of the effects of the temperature, reaction time, liquid–solid ratio (L/S), and initial pH on the hydrothermal degradation of polychlorinated dibenzo- p -dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) (which are both PCDD/Fs) in municipal solid waste incineration (MSWI) fly ash is presented. Consequently, the hydrothermal degradation reaction is catalyzed using Ce–Mn catalyst under low-temperature conditions to study the effect of the catalyst on the degradation efficiency of PCDD/Fs. The experimental results show that temperature is the most critical factor for the reaction. When the hydrothermal oxidation temperature reaches 280 °C (reaction time = 120 min, original pH = 8.5, L/S = 4 mL/g), the toxicity equivalent (I-TEQ) of PCDD/Fs is only 5.4 ng TEQ/kg, and the degradation efficiency reaches 99.71%. Under these conditions, 2, 3, 4, 7, 8-P5 CDF makes the highest contribution to I-TEQ degradation, reaching 37.4%. There are four main pathways for the reaction of 2, 3, 4, 7, 8-P5 CDF with hydroxyl radicals. A comparison of the PCDD/F concentrations of different products shows that the addition of 0.5%, 1.0%, and 1.5% of the Ce–Mn catalyst reduces the degradation efficiency by 8.79%, 1.40%, and 0.07%, respectively, which indicates that the addition of a small quantity of Ce–Mn catalyst does not facilitate the degradation of PCDD/Fs. The addition of the catalyst significantly decreases the degradation efficiency of low-chlorinated homologs but has a relatively small effect on that of high-chlorinated homologs. Therefore, it is concluded that Ce–Mn catalysts are more likely to promote resynthesis than degradation of PCDD/Fs. Graphical abstract: Image 1 Highlights: The dioxin TEQ of fly ash after hydrothermal oxidation meets the specification. The temperature of hydrothermal oxidation dominates the degradation efficiency. 2, 3, 4, 7, 8-P5 CDF contributes the most to the reduction of TEQ, accounting for 37.4%. Addition of Ce–Mn catalyst promotes the dioxin resynthesis.