Evaluation of magnetic ion exchange resin (MIEX®) and alum treatment for formation of disinfection by-products and bacterial regrowth

Four treatment options: (a) alum coagulation without pH adjustment; (b) alum coagulation at pH 6; (c) magnetic ion-exchange (MIEX(R)*) resin; and (d) combined alum/MIEX(R) treatment, were used to compare the removal of dissolved organic carbon (DOC) and treated water quality, particularly the formation of disinfection by-products and bacterial regrowth potential. Improved DOC removal was achieved with the inclusion of MIEX(R) treatment in the process. The DOC remaining after each treatment strategy was different in character. The molecular weight distribution results indicated that MIEX(R) treatment removed a broad range of compounds, whilst alum treatment targetted the removal of high molecular weight compounds. In addition, the DOC remaining after MIEX(R) treatment consisted of compounds with lower specific UV absorbance (SUVA). Including MIEX(R) in the treatment stream provided better DOC and bromide removal thus reducing chlorine decay and trihalomethane (THM) formation. The ability of the water to support bacterial growth as measured by bacterial regrowth potential (BRP) was the lowest after MIEX(R) treatment (option c) compared with the three other treatments (options a, b and d). In summary, laboratory tests show that including MIEX(R) in the treatment process can improve treated water quality. (*MIEX(R) is a registered trademark of Orica Australia Pty Ltd).