Molecular transformation of dissolved organic matter in reverse osmosis concentrated leachate during a tight-ultrafiltration membrane combined with an O3/GAC system

Abstract

The dissolved organic matter (DOM) composition in reverse osmosis concentrated landfill leachate (ROCL) is very complex and difficult to treat. In this study, tight ultrafiltration (TU) combined with the O3/granular activated carbon (GAC) catalytic oxidation system was used to treat DOM in ROCL. The treatment effect and mechanism of TU combined with the O3/GAC catalytic oxidation system were carefully studied using ESI FT-ICR MS. The results show that DOM in ROCL mainly has Ali and UnPh-like structures, showing the characteristics of reduction and unsaturation. In the membrane treatment link (i.e., TU and deamination system), the DOM with LO-UnPh-like structures can be effectively intercepted and removed, and the DOM in the effluent mainly has Ali and LO-UnPh-like structures, showing the characteristics of reduction and unsaturation. In the process of the O3/GAC system, DOM with HO-UnPh-like structures was further removed through catalytic oxidation, which not only destroys the aromatic structure of DOM but also forms daughter products with a higher degree of saturation, fewer aromatic properties, fewer carbon atoms, and more oxygen-containing functional groups. The action intensity of •OH in the O3/GAC catalytic oxidation system was verified, and the reaction mechanism of GAC catalytic O3 was analyzed according to the surface properties of GAC. Finally, the GAC after use was treated with several regeneration methods; the results showed that the morphology and structure of the deactivated GAC could be restored by the method of washing–microwave irradiation. This study provides a promising method for the proper treatment of ROCL.