Enhanced removal of thioethers from stormwater pipe overflows by coagulation and oxidation treatment: Removal...

The direct discharge of untreated overflow wastewater from the drainage pipes into receiving water bodies can result in water quality deterioration and the formation of black and odorous water bodies. Thioethers, including dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diethyl disulfide (DEDS), and diethyl trisulfide (DETS), are the primary odor-causing substances present in stormwater pipes. This study systematically investigated the removal efficiency of thioethers in overflow wastewater using various coagulation-oxidation processes. Results showed that synchronous PACl/PAM and NaClO (PACl/PAM+NaClO) exhibited superior removal performance with the removal efficiency up to 98.0 % for four types of thioethers in 5 min. Oxidation was identified as the primary thioethers degradation mechanism, while coagulation mainly facilitated sediment removal. In order to assess the impact of background organic matter, humic acid, cysteine, and sucrose, which are commonly found in wastewater, were chosen as model compounds. Humic acid and cysteine reduce the oxidation efficiency of NaClO toward thioethers, likely due to the presence of reactive groups such as carboxyl, phenolic hydroxyl, and carbonyl in humic acid, and the sulfhydryl group in cysteine, which rapidly consume NaClO. In contrast, sucrose enhances thioethers oxidation, possibly through the formation of reactive free radicals or other active intermediates. Additionally, this study identified several thioether oxidation by-products, including ethanesulfonyl chloride, methanesulfonyl chloride, methyl methanethiosulfonate and methyl methanethiosulfinate, and revealed the corresponding degradation pathways. The toxicity of thioethers' oxidation by-products to aquatic organisms significantly decreased. Overall, the PACl/PAM+NaClO process is an effective strategy for controlling thioethers and mitigating ecological risks in overflow wastewater.