Treatment of organics in reverse osmosis concentrate from a municipal wastewater reclamation plant: Feasibility test of advanced oxidation processes with/without pretreatment

Four simple advanced oxidation processes (AOPs), i.e. heterogeneous photocatalytic oxidation (PCO), sonolysis (US), ozonation (O3) and H2O2 oxidation, as well as their combinations were investigated in bench-scale for removing the organics present in the reverse osmosis (RO) concentrate from a municipal wastewater reclamation plant. It was observed that the degradation efficiencies reached a plateau after 1h of reaction, with varying removals of dissolved organic carbon (DOC) up to 52%. The O3-based AOPs exhibited relative high efficiencies in treating the organics present in the raw RO concentrate. Ferric chloride (FeCl3) coagulation was preferred over activated carbon adsorption as pretreatment process to improve the subsequent AOP treatments of the RO concentrate. Coupling pretreatment with coagulation, the various AOPs could efficiently remove the organics, resulting in an overall DOC removal of 34–68%, a significant improvement in biodegradability (7–20 times), and a decrease of ecotoxicity. Analyses of molecular weight (MW) distribution of the treated RO concentrate revealed that coagulation could remove large MW organics that were AOP-resistant, while AOP treatments could effectively decompose the complex organics into small molecular organics. The results also demonstrated that a simple integrated method, FeCl3 coagulation+photocatalysis (UVC/TiO2), could finally achieve 95% of the organics removal from the RO concentrate within 6h.