Effects of epichlorohydrin-dimethylamine on polytitanium chloride coagulation and membrane fouling in humic-kaolin water treatment: Dosage, dose method and solution pH

This study first investigated the effects of epichlorohydrin-dimethylamine (DAM-ECH) on coagulation performance and floc properties of polytitanium chloride (PTC) in humic acid-kaolin water treatment. The factors including DAM-ECH dosage, dosing sequence of PTC and DAM-ECH and initial solution pH were considered. Results showed that the addition of DAM-ECH could enhance turbidity removal and dissolved organic matter (DOM) removal efficiency of PTC. The larger amount of DAM-ECH did not equal to better performance. The chosen dosage of DAM-ECH was 1.0 mg/L for the consideration of cost and coagulation performance. In addition, dosing sequence and solution pH of PTC and DAM-ECH also significantly affected coagulation behaviour and floc properties. Results indicated that residual turbidity was significantly reduced when pH < 6. Moreover, PTC-1.0DAM-ECH (DAM-ECH was added after PTC) achieved better DOM removal when pH < 6, while 1.0DAM-ECH-PTC (PTC was added after DAM-ECH) achieved better DOM removal efficiency when pH > 6. 1.0DAM-ECH-PTC flocs grew faster and attained a larger size compared with PTC-1.0DAM-ECH. Flocs formed by PTC-1.0DAM-ECH and 1.0DAM-ECH-PTC both were stronger than those formed by PTC when pH < 6. When pH was above 6, floc strength was only enhanced by PTC-1.0DAM-ECH. Meanwhile, floc recovery ability was only improved by PTC-1.0DAM-ECH. In addition, flocs formed by PTC-1.0DAM-ECH were more compact than those formed by PTC, while flocs formed by 1.0DAM-ECH-PTC were looser. Membrane fouling degree was also reduced by the addition of DAM-ECH, especially when DAM-ECH was added before PTC.