Activation of peroxymonosulfate by catalysts derived from water treatment plant sludge for the simultaneous removal of Disperse Blue 56 and phosphates

In this study, calcined water treatment plant sludge (C-WTPS) was used as a catalyst for peroxymonosulfate (PMS) activation to simultaneously remove Disperse Blue 56 (DB56) and phosphates. Firstly, the performance of the C-WTPS/PMS system was examined for the degradation of DB56. The results showed that 96.7% of DB56 (400 mg L −1 ) was removed within 60 min in the presence of 4.8 g L −1 PMS and 0.8 g L −1 C-WTPS at pH 3 and 50 °C. Hydroxyl radicals (·OH), sulfate radicals (SO 4· − ), and singlet oxygen ( 1 O 2 ) were generated during the oxidation process, and 1 O 2 was the main active species. The relatively high surface area, proper Fe content, and abundant ketone groups on the catalyst surface were responsible for PMS activation. Furthermore, the possible degradation pathways of DB56 were proposed based on the gas chromatography–mass spectrometry (GC–MS) results. Secondly, the simultaneous removal of DB56 and phosphates by the C-WTPS/PMS system was investigated. Due to the different removal mechanisms, the effects of the initial phosphate concentration and water matrix species on the removal of DB56 and phosphates showed different trends. Reusability tests results showed that C-WTPS had relatively high stability. In addition, the C-WTPS/PMS system exhibited a high decolorization ratio and phosphate removal efficiency in real wastewater tests. This article offers a value-added approach for reusing WTPS as a catalyst for treating organic contaminants and phosphates.