Ion-exchange for trihalomethane control in potable water treatment – a municipal water treatment case study in Rainy River, Ontario, Canada

The objectives of this study were to investigate the ability for ion-exchange (IX) to control trihalomethane (THM) formation, and to act as a potential treatment addition (upgrade) to a conventional treatment plant in Rainy River Ontario, Canada. The primary goal was to investigate the total organic carbon (TOC) and trihalomethane formation potential (THMFP) removal as a function of resin dose; and note the relative improvements over current conventional plant operation. IX resin (DOWEX TAN-1, Purolite 502P and 860, and Amberlite PWA9) removed 68–72% of TOC and 30–40% THMFP from the conventionally filtered water. Fixed-bed fluidized bed contactor was used to investigate the TOC/THMFP breakthrough for the DOWEX TAN-1 resin. Complete resin breakthrough occurred followed by 1,275 and 1,075 bed volumes for TOC and THMFP, respectively. Breakthrough output following 1,000 treated bed volumes was noted as the point at which THMFP levels reach the 0.1 mg L–1 water quality standard threshold required by Canadian regulators. High exchange capacities were recorded for the TAN-1 (3.02 mg mL–1) and PWA9 (2.03 mg mL–1) resins – both of which contain styrene backbones. The results produced in the bench-scale experiments were used very successfully in a full-scale upgrade of the Rainy River water treatment plant.