Activation of persulfate by modified drinking water treatment residuals for sulfamethoxazole degradation

In this work, drinking water treatment residuals (WTRs), an iron-rich safety byproducts, was modified via facile reduction calcination and subsequently proved as an effective persulfate (PS) activator for degradation of sulfamethoxazole (SMX). Various parameters affecting SMX degradation efficiency were tested, and the results showed that 80% of SMX (50 mu M) was removed within 60 min in the presence of 2.0 mM PS and 0.2 g L-1 modified WTRs at pH 5.3 under ambient temperature. Radical scavenging and electron spin-resonance spectroscopy tests indicated that sulfate radical was a much more powerful active oxygen specie than hydroxyl radical for the SMX degradation in the WTRs/PS system. To understand the proposed activation mechanism, Xray diffraction and X-ray photoelectron spectroscopy were applied to reveal the change of modified WTRs before and after use. This process confirmed that the activation mechanism was in situ homogenous and heterogeneous reaction simultaneously. Furthermore, liquid chromatography coupled with ion trap time-of-flight mass spectrometry was applied to identify the intermediates of SMX to understand the possible pathway. This work provides a novel value-added reuse approach for WTRs as an efficient and cost-effective heterogeneous activator for PS.