SPECIAL FOCUS: COLD CLIMATES AND REMOTE LOCATIONS
Community of Windigo Island uses Hollow Fibre Nanofiltration Technology By R.G.Guenther
T
he Windigo Island Community is a part of the Animakee Wa Zhing 37 First Nation and is located within the area known as Lake of the Woods. There are thousands of inhabited and uninhabited islands in this water body, and water quality is fairly consistent throughout the region. From a drinking perspective, the main difficulties in using this lake as a drinking water source are elevated levels of turbidity (<3 by average but >50 NTU during upset events) and dissolved organic carbon (DOC) and colour, which can cause trihalomethane (THM) concerns when chlorinated The 71 residents of Windigo Island live on a small, remote island at the southwest corner of Lake of the Woods. The closest mainland point to Windigo Island is actually in Minnesota. During the summer, most land access to and from Windigo Island is through the cartographic anomaly that is the Northwest Angle or just “The Angle” to locals. In the winter, there are established ice roads through Lake of the Woods, which makes Canadian access to the island more feasible. The island is far enough offshore to make conventional electrical/communication access impractical. There have long been issues with drinking water quality on Windigo Island. At the beginning of the project, the drinking water quality advisory in place was one of the longest in Canadian history. By virtue of its remote location, it was not practical, or reliable, to supply water treatment service and support from the mainland. Conventional treatment solutions, such a simple sand media filtration and/ or traditional small-scale reverse osmosis/nanofiltration treatment skids had proven unreliable and fallen into disuse and abandonment. The residents have historically relied on filtration with a 30 | February 2022
Drinking water treatment challenges included elevated levels of turbidity, dissolved organic carbon and colour, which can cause THM concerns when chlorinated.
sand filter and chlorination to make the lake water potable. The three aspects of the water treatment challenge that most needed to be addressed, primarily to satisfy potability requirements were: • Certified log removal credits for micro-organisms and disinfection credit. • A treatment solution that could minimize the presence of dissolved organic carbon. • Minimal treated water flow rate. Initially, a conventional ultrafiltration (UF) membrane solution was considered. Due to the technology’s references, modular design, and capability of satisfying the requirement for log removal credits, ultrafiltration seemed to be a viable solution. However, after further deliberation, it was unlikely to reduce the elevated levels of DOC/colour in the raw water to a level that would have
made the treated water compliant with THM regulations and sodium hypochlorite dosing. Instead, a dual system technology (e.g., ultrafiltration followed by nanofiltration) would have had to be considered. Along with considering different treatment solutions, the disinfection process was also a point of discussion. Due to the small system and the remote nature of Windigo Island, it made more complicated disinfection solutions, such as chloramination, or carbon dioxide, impractical. Therefore, disinfection by sodium hypochlorite, was the only practical solution. UV disinfection could be added to further extend disinfection log credits if required. What was ultimately proposed was an innovative hollow fibre nanofiltration element. Specifically, one with long, holcontinued overleaf…
Environmental Science & Engineering Magazine
