Characteristics of coagulation-flocculation of humic acid with effective performance of polymeric flocculant and inorganic coagulant

Ferric chloride and aluminium sulphate as coagulants and positive charged flocculants PDDMAC ((PDDMAC = poly (diallyldimethylammonium chloride) were used for pre-treatment of water and wastewater for removing humic substance prior to RO membrane filtration. It was found that a combination of flocculant and coagulant enhanced the coagulation-flocculation process and humic acid removal. The optimum conditions of coagulation-flocculation were established in reference to the ratio of humic acid and coagulant. Zeta potential and the ratio of E-4/E-6 were investigated to explore the possible micro-mechanisms of coagulation-flocculation. The ratios of E-4/E-6 show the molecular size variations using different coagulants and flocculants, which are expected to benefit membrane-fouling control.