Semi-coke activated persulfate promotes simultaneous degradation of sulfadiazine and tetracycline in a binary mixture

Semi-coke (SC) is a solid waste of coal chemical process, and the comprehensive utilization of SC is a challenging issue. Based on physicochemical characteristics, SC was firstly utilized as a mineral biochar for activating persulfate (PS) to promote simultaneous degradation of sulfadiazine (SDZ) and tetracycline (TC) in a binary mixture. The influencing parameters were systematically investigated. The dominant reactive oxygen species (ROS) were identified by combination of quenching experiments and electron spin resonance (EPR) analysis. Subsequently, possible activation mechanism and degradation pathways were also proposed. With the evolution of SDZ and TC in SC/PS system, the Vibrio fischeri was used to examine the acute toxicity to explore the detoxification efficiency. The experimental results indicated that in such a binary system, a mutually promoted degradation occurred between SDZ and TC, and at optimized conditions of 0.75 g/L PS, 0.50 g/L SC, pH 3.0 and 30 ℃, the developed SC/PS system had high degradation ability for simultaneous removal of SDZ (97.8%) and TC (97.2%). The polar groups and defects of SC were conducive to the adsorption; the oxygen-containing functional groups, pyridine N and graphite C on SC surface could be used as active sites for activating PS to produce ROS. During the degradation process, both radical (•OH and SO4•−) and non-radical (1O2) pathways coexisted. SC exhibited an excellent reusability, with the degradation efficiency of 84.5% for SDZ and 95.9% for TC after 4 cycles, and high mineralization efficiency of 67.5% after 4 h, demonstrating that such a unique SC/PS system exhibited a great potential for simultaneously efficient removal of different kinds of antibiotics in actual wastewaters.