AWWA WQTC55209

The City of Chesapeake, Virginia has provided a reliable and safe drinking water to its customers for many years. The City has been providing this drinking water despite a water supply that is extremely high in organics with seasonal outbreaks of chlorides. As a result, the 10-mgd Northwest River Water Treatment Plant receives water that is frequently difficult to treat. This water requires very high coagulant dosages during all times of the year and seasonal reverse osmosis treatment to meet the EPA Stage 1 Disinfection Byproduct (DBP) standard for trihalomethanes (THM) of < 80 ppb and haloacetic acids (HAA) of < 60 ppb. Therefore, to help comply with these regulations as well as reduce sludge generation and overall treatment costs, the City evaluated the magnetic ion exchange resin (MIEX) developed by Orica Watercare. Accordingly, a pilot study was conducted to evaluate the selective DBP precursor removal capability of the MIEX resin in combination with a coagulant. MIEX(R) is a continuous ion exchange process designed to achieve lower THM and HAA standards by removing the TOC fraction that is difficult to remove by conventional water treatment processes. The major conclusions from the trial were as follows: the MIEX(R) resin followed by coagulation provided significantly greater TOC removal (average 80%) compared to the Northwest River WTP (average 63%); significant reductions in the treated water THM and HAA formation potentials can be achieved with MIEX(R) pretreatment; MIEX(R) pretreatment allowed a greater than 75% reduction in the alum dose to meet the plant TOC removal performance, also reducing sludge production by over 75%; and, the resulting downstream savings in treatment costs after MIEX pretreatment will be $0.10/kgal. This savings includes debt service on the capital improvements for the new MIEX treatment system. Includes reference, tables, figures.