Sludge-derived biochar applied in peroxymonosulfate (PMS) activation: Reactive oxygen species (ROS) dominated process and characteristics

Herein, sludge-derived biochar (BS) as an effective peroxymonosulfate (PMS) activator (BS900) was prepared by a simple one-step pyrolysis treatment. The BS900 demonstrated remarkable capability in activating PMS for efficient tetracycline (TC) removal. The existence of zero-valent iron (Fe0), the elevated ratio of Fe2+ to Fe3+, and the elevated percentage content of graphitic N were identified as the main contributors to the high PMS activation performance of BS900. Correspondingly, compared with other BS-derived PMS activators, the lowest charge transfer resistance (Rct) of BS900 was obtained, indicating efficient charge transfer between the PMS molecule and BS900. The generated reactive oxygen species (ROS) including the superoxide radical (O2•-) and singlet oxygen (1O2) were verified by the radical trapping and electron paramagnetic resonance (EPR) tests during the BS-induced PMS activation process. The generated O2•- served as the precursor for 1O2 formation. Whereas, the yields of the OH• and SO4•- were inhibited, suggesting that PMS activation by BS900 was a process dominated by ROS. Furthermore, the evaluation of ecotoxicity showed the TC degradation intermediates exhibit lower developmental toxicity and no mutagenicity. The research offers a novel perspective into the characteristics and mechanism of PMS-based advanced oxidation processes (AOPs) catalyzed by sludge-derived biochar.