Evaluation of enhanced coagulation coupled with magnetic ion exchange (MIEX) in natural organic matter and sulfamethoxazole removals: The role of Al-based coagulant characteristic

• Monomeric Al instead of pre-hydrolyzed Al13 attained highest SMX removal.
• Removals of HA with large MW by MIEX and coagulation are comparable.
• SMX removal rate by MIEX is about twice that by coagulation.
• MIEX is best suited to monomeric Al instead of Al13 in organic matter removal.
• MIEX evidently hindered floc aggregation in the subsequent coagulation process.

The removals of humic acid (HA) and a kind of antibiotic compound by enhanced coagulation (EC) employing various Al-based coagulants with, and without MIEX resin pre-treatment were systematically investigated in this study. A range of techniques were used to evaluate the purification behaviors and mechanisms of the coagulation and MIEX adsorption processes. The experimental results indicated that sufficient dose of Al-based coagulants removed 60–70% of HA, while traditional Al2(SO4)3 (AS) coagulant with low dose of 1.0–5.0 mg/L coupled with MIEX contributed to a removal rate of 85%. For sole coagulation, Al13 ([Al13O4(OH)24(H2O)12]7+) only removed 11% to <23% of SMX, while AS and polyaluminum chloride (PACl) contributed to comparable removal of about 40%, indicating charge neutralization was not the major mechanism in SMX removal. The SMX removal could be improved to 68–78% by MIEX pre-treatment. Dynamic floc sizes during coagulation processes were studied using a laser diffraction particle sizing device. The results demonstrated Al13 led to the smallest flocs, while the adsorption and sweep mechanisms in AS and PACl coagulation processes resulted in larger aggregates. Besides, the pretreatment of MIEX could evidently decrease the floc sizes for all the coagulants.

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