Continuous coagulant and alkali dosing enhanced organic separation from hypersaline wastewater in synchronous...

Organic removal from reverse osmosis concentrates (ROC) via oxidation remains challenging due to the high salinity. In this study, a continuous coagulant and alkali dosing synchronous ozonation coagulation (CDSOC) process consisting of two stages was established for actual ROC treatment. In the rapid stirring stage, continuous dosing of coagulant and alkali prolonged the formation of hydrolyzed Al species, which were transformed from monomeric Al_a, medium-polymeric Al_b to high-polymeric and colloidal Al_c, thereby forming primary flocs with smaller size, rougher surface and larger specific surface area. The flocs formed in the CDSOC effectively captured a greater amount of lignin-like CHOS and CHNOS organics, and more coagulable organics were detected in the flocs. In the slow stirring stage, the integration of ozonation and coagulation introduced more active surface hydroxyl groups and adsorbed water onto the flocs, thereby enhancing organic binding and enabling Al(III)Tet. to catalyze ozone decomposition for enhanced hydroxyl (•OH) generation. Notably, intermediate organics with oxygen-containing groups, particularly carboxyl groups, were sustainably captured by flocs in the CDSOC process. The CDSOC process achieved 69.4% DOC removal efficiency for the treatment of actual ROC with coagulation accounting for 71.5% organic removal. FT-ICR MS results demonstrated that the CDSOC process effectively removed sulfur-containing fractions. A larger proportion of low-coagulable organics were effectively eliminated through coagulation in the CDSOC process, indicating a significant improvement in organic removal. This study provides an additional separation pathway for organic removal in a high-salinity environment.