Treatment of wastewater containing 2-methoxyphenol by persulfate with thermal and alkali synergistic activation: Kinetics and mechanism

Both thermal and alkali are effective means of persulfate (PS) activation, and the synergistic effect of them should achieve a great degradation result. It is evaluated for treating coal chemistry industry wastewater because the by-product produced in the process is sulfate, which is pre-existing in the wastewater. With thermal and alkali synergistic activation, the application of the response surface method revealed the effects of temperature, pH and concentration of persulfate on the degradation ratio of 2-methoxyphenol (MOP, a typical contaminant in coal chemical industry wastewater) and their interactions. The results showed that the degradation rate of the contaminant was temperature and pH dependent, while chloride (Cl-) and sulfate (SO42-) ions had no obvious negative effect. The degradation ratio could be enhanced with higher activation temperature and pH (7-12). The faster degradation could be achieved by thermal-alkali synergistic activation, and the degradation ratio of 88.4% and 93.8% could be achieved at pH = 12 within 10 min and 20 min, respectively. Electron spin resonance (ESR) spectra and free radical scavenging experiments indicated that MOP degradation was achieved by the oxidation of both sulfate radical (SO4 center dot-) and hydroxyl radical (center dot OH) at pH = 6, and only by (center dot OH) at pH = 12. In addition, the radical reaction was intense under thermal-alkali synergistic activation of PS, while the quenching reaction was ineffective.