Red mud modified sludge biochar for the activation of peroxymonosulfate: Singlet oxygen dominated mechanism and toxicity prediction

In this paper, red mud-sewage sludge derived biochar (RSDBC) was synthesized and employed as the heterogenous activator of peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. With the incorporation of red mud, 82.5% degradation of SMX was achieved by RSDBC/PMS system in a process dominated by 1O2, which was attributed to the participation of oxygen vacancy, ketone groups and graphitic carbon. On the other hand, in the absence of red mud, OH and SO4•- were dominantly accounted for SMX degradation in sewage sludge derived biochar (SDBC)/PMS system. In this case heterogeneous Fe species, ketone groups and graphitic carbon were responsible for PMS activation. Due to the different Reactive Oxygen Species (ROS), effects of reaction conditions including initial pH, common anions and natural organic matter (NOM) were not in full accord. Besides, Fe leaching from RSDBC (0.67 ppm) was much lower than that of SDBC (3.07 ppm), leading to a better reuse ability for RSDBC. Less degradation intermediates were disclosed in RSDBC/PMS system, along with lower residual toxicity. In addition, eco-toxicity of all the intermediates was predicted by ECOSAR program for the further understanding of the detoxification of SMX. Advantages of RSDBC/PMS system as disclosed in this paper further suggest its potential full-scale application of environmental remediation.