Dissolved organic matter removal and disinfection byproduct formation control using ion exchange

Three different ion exchange resins were evaluated for their ability to remove dissolved organic matter (DOM) and reduce formation of disinfection byproducts (DBPs) formed during chlorination of surface waters sampled from the Intercoastal Waterway, Myrtle Beach, SC, USA (MB water), and the Tomhannock Reservoir, Troy, NY, USA (TMK water). At resin doses up to 600 mg/L, DOC levels were reduced from 30 to 70%, while total trihalomethane and haloacetic acid formation reactivity (i.e., TTHM/DOC and HAA9/DOC) was reduced from 40 to 70% and 50%, respectively. This suggests that ion exchange, alone or in combination with other processes, holds promise for removing a broad spectrum of DBP precursors. Chloride release was measured to confirm an ion exchange mechanism, but the possibility of physisorption and hydrogen bonding mechanisms was not ruled out. Ion exchange appeared to selectively remove high-specific UV-absorbing (i.e., SUVA254) DOM components from the TMK water; these components also had the highest molecular weights. However, this was not the case for the MB water. The “SUVA254 profile”, the relationship between SUVA254 and DBP formation reactivity (TTHM/DOC and HAA9/DOC), showed significant differences from the patterns observed previously for separation processes (e.g., coagulation and activated carbon adsorption) that rely primarily on hydrophobic interactions as a separation mechanism.