WCW24

A recurring challenge for water treatment systems using surface water sources in Northern Manitoba and Northern Ontario is ensuring that disinfection by-product (DBP) concentrations in treated water are below their Maximum Allowable Concentrations (MACs) as outlined in the provincial and federal guidelines. Two (2) groups of DBPs of interest include trihalomethanes (THMs) and haloacetic acids (HAAs). Dissolved organic carbon (DOC) and total organic carbon (TOC) are known as DBP precursors as they can react with chlorine, a commonly used method to disinfect drinking water, to form DBPs. An effective water treatment system must therefore be able to reliably and consistently remove sufficient DBP precursors to ensure that DBPs are below their respective MACs. The same levels of DOC / TOC in one system may behave differently from the DOC / TOC drawn from another source. Further, concentrations of DOC / TOC can have considerable seasonal variations even from the same water source, underscoring the importance of obtaining as much historical raw water quality data and completing as much site-specific testing as soon as possible, as well as utilizing conservative design practices. Neegan Burnside Ltd., with the help of various water treatment suppliers and laboratories, has recently completed bench-scale and pilot-scale testing programs for several communities in Northern Manitoba and Northern Ontario to inform and support treatment system design. The primary focus of the bench-scale and pilot-scale testing programs was the removal of DOC / TOC and preventing the formation of THMs and HAAs. Simulated distribution system testing was completed to evaluate THM and HAA formation. Several alternative treatment technologies were evaluated including conventional filtration, membrane filtration, slow sand filtration, granular activated carbon (GAC) filtration, ion-exchange as a post-treatment process, and Magnetic Ion Exchange (MIEX®) as a pre-treatment process. In addition to treatment effectiveness, technologies were evaluated against other criteria including capital and operation and maintenance (O&M) cost, ease of operation, and operator familiarity, among others. An important consideration was the lifespan over which filtration media would provide effective treatment, and the process required to restore treatment capability of the media. As an example, GAC filtration has historically been used as an effective post-treatment process to remove organic content in water. Over time, GAC media is exhausted and must be replaced or treatment performance will decline. Rapid small scale column testing (RSSCT) for GAC media was completed to estimate the lifespan of GAC media and the results indicated a short lifespan at some sites, dependent on the other water treatment processes upstream. Information such as this suggests that the required replacement frequency of GAC media to maintain treatment at an acceptable level should be considered using site-specific testing, especially if there is a reliance on the media to remove sufficient DOC / TOC to meet the required guidelines.