Exploring the characteristics and transformation of aromatic halogenated compounds in textile dyeing sludge during Fe-based chemical treatment.

The chemical conditioning of textile dyeing sludge (TDS) is an essential step in its dehydration and treatment. However, the dynamic changes and environmental risks associated with aromatic halogenated compounds (AHCs) during this process remain poorly understood. In this study, representative AHCs in TDS were identified by combining organic matter fractional separation, non-targeted identification (HRMS) and AHCs screening list, and the transformation of these typical AHCs in TDS was systematically explored by using Fe²⁺/peroxysulfate (Fe/PDS) and Fe/HO treatments. This screening approach identified 49-59 aromatic chlorides and 39-48 aromatic bromides in three original TDS samples, with the presence of hazardous compounds like polychlorinated naphthalenes, polychlorinated biphenyls (PCBs), and polychlorinated dibenzo-p-dioxins/furans that may be generated during the secondary treatment of wastewater. The results of TDS oxidation treatment showed that the total organic halogen content initially increased during chemical conditioning but decreased after 30 min. Fe/HO/Cl (140 mM; 1/1) demonstrated superior efficiency in reducing total organic chlorine compared to Fe/PDS/Cl (140 mM; 1/1). However, both treatments triggered the formation of highly halogenated and toxic byproducts, particularly PCBs and hexachlorobenzene-substances banned from use and production. This study provides a theoretical foundation for evaluating the environmental risks associated with TDS chemical conditioning and incomplete incineration processes.