Treatment of landfill leachate via two-stage advanced oxidation processes: Photo-electrochemical activation of peroxymonosulfate and percarbonate/ozone/MnO2@carbon

In this study, a two-stage process was used for the treatment of landfill leachate (LL). First, the photo-electrochemical (PE) method was used for peroxymonosulfate (PMS) activation. Under optimum conditions (pH = 3, current density = 20 mA/cm 2 , and PMS = 21 mM), 63.9 % of chemical oxygen demand (COD) was removed. Electrochemical, photochemical, and Fe(II) activations of PMS contributed to the degradation of organic compounds. The LL treated by PE-PMS was introduced into a hybrid process based on ozone (O 3 ) and percarbonate. MnO 2 @activated carbon (C) was synthesized and employed for O 3 and percarbonate (PC) activation (PC/O 3 /MnO 2 @C). Under optimal conditions, 83.5 % of COD was removed from the LL. Overall COD, ammonia, and total organic carbon (TOC) removals for the two-stage process were 94.7, 97.3, and 89.2 %, respectively. The mechanism of ammonia removal was thoroughly evaluated. The results showed that sulfate radicals ( SO 4 • − ), hydroxyl radicals ( • OH), and direct ozonation are the main agents of ammonia degradation. Biodegradability was significantly increased from 0.29 to 0.62, and phytotoxicity results showed that the final effluent is non-toxic for three plant species. This work confirmed that the sequential treatment of the PE-PMS and PC/O 3 /MnO 2 @C system can be an effective strategy for the treatment of LL.