Effects of epichlorohydrin-dimethylamine on coagulation and membrane performance of ferric chloride in coagulation-ultrafiltration hybrid process

Cationic polymer epichlorohydrin-dimethylamine (DAM-ECH) was applied as coagulation aid of ferric chloride (FC) in treatment of humic acid-kaolin (HA-Kaolin) simulated water in this study. Impacts of DAM-ECH on coagulation performance, flocs characteristics and membrane fouling of FC in coagulation-ultrafiltration (C-UF) process were investigated under different pH conditions. Results showed that the removal rates of UV₂₅₄ (ultraviolet adsorption at 254nm) and DOC (dissolved organic carbon) of FC/DAM-ECH was much better than that of FC at same dosage. The optimum coagulation condition was FC at 10mg/L with FC/DAM-ECH mass ratio (MR) of 3:1 based on the consideration of treatment cost and performance. Moreover, turbidity, UV₂₅₄ and DOC removal rates increased when pH increased from 4 to 6 and then decreased as pH grew from 7 to 10. Thus, the optimum pH for coagulation was also determined to be 6 accordingly. Addition of DAM-ECH also increased sizes of produced flocs and made them looser in structure comparing with FC-HA flocs. Meanwhile, results obtained from ultrafiltration experiments showed that membrane fouling would be reduced by introducing DAM-ECH in coagulation treatment; the optimum membrane performance was given by FC/DAM-ECH under pH 6. In conclusion, proper dose of FC/DAM-ECH under pH 6 could ensure an ideal HA removal rate and meanwhile increase operating duration of C-UF system by restricting membrane fouling.