Peroxydisulfate Activation by Pyrolysis Products of Iron Grinding Sludge and Polyethylene Glycol for Methylene Blue Degradation: Mechanism and Performance

The pollution problem of iron grinding sludge (IS) and polyethylene glycol (PEG) threatens the ecosystem and human health. In this study, an iron-rich catalyst (ISPEG) was prepared by co-pyrolysis of grinding sludge and polyethylene glycol and used to activate peroxydisulfate (PDS) for degrading organic wastewater. In the ISPEG/PDS system, methylene blue (MB) was almost completely removed within 60 min with an apparent rate constant (Kobs) of 0.32 min^-1 and a wide range of pH. The effects of IS doping ratio, pyrolysis temperature, catalyst injection, PDS concentration, co-existing ions, and pH on MB removal were investigated. The results showed that ISPEG/PDS had a high removal rate of various organics in the water column. The catalytic mechanism of the ISPEG/PDS system was explored by free radical quenching, electron paramagnetic resonance, and frontier orbital theory studies, in which the main active substance for degrading SDZ was SO₄^•-. Finally, the degradation pathways of MB in the ISPEG/PDS system were analyzed by LC-MS. These results indicate that the ISPEG/PDS system has the potential to treat organic wastewater under the concept of waste control waste.