Impacts of coagulant types on the treatment efficiency of coal mine wastewater in the ultrafiltration-reverse osmosis process

Abstract

The reverse osmosis (RO) process is commonly employed for coal mine wastewater treatment; however, membrane fouling limits its efficiency and development. This study investigates focusing on impact on membrane fouling and treatment efficacy of three coagulants (polymeric aluminum chloride (PAC), polymeric aluminum ferric chloride (PAFC), and aluminum chloride (AlCl₃)) in the coagulation-ultrafiltration (CUF) process. Results indicate that PAFC outperforms the other coagulants in reducing dissolved organic matter (DOM) and key ions, including calcium, magnesium, and silica. Notably, PAFC exhibited a higher adsorption capacity for aromatic DOM and achieved the highest dissolved organic carbon (DOC) removal rate at lower dosage. In terms of ion removal, PAFC was proved to be the most effective, Silicon concentration was reduced by 58.65 %, calcium by 81.57 %, and magnesium by 71.23 %. The superior performance of PAFC can be attributed to the synergistic interaction between its iron and aluminum ions. Iron ions, with higher charge density and hydrolysis potential, form multinuclear hydroxyl complexes with aluminum ions, enhancing their ability to bridge and adsorb suspended particles and organic pollutants. Additionally, the hydrolysis of PAFC produces more hydroxyl groups, which facilitate chelation with metal ions, improving the removal of ion-organic complexes. The effective pre-treatment using PAFC resulted in the highest subsequent RO flux among the tested coagulants. This study demonstrates that coagulant selection significantly influences both UF flux and RO system performance. PAFC emerges as the most effective and promising coagulant for enhancing CUF process efficiency in coal mine wastewater treatment and extending the operational lifespan of RO membranes.