November:2007
11/6/07
9:08 PM
Page 30
Groundwater
Iron, manganese, 1,4-dioxane, hydrogen peroxide, and fines - A tale of multi-stage processing By Ryan Steckly, Leigh McDermott, Elia Edwards, and Donna Serrati n 2004, the Regional Municipality of Waterloo (Region) discovered 1,4-dioxane in groundwater feeding the Greenbrook Water Supply System in Kitchener, Ontario. At the time, the plant was slated to be upgraded with replacement iron and manganese pressure filters. These plans were put on hold, however, while the Region developed a strategy for treating the 1,4-dioxane. The approach for solving the issue involved investigating a number of different advanced oxidation technologies and quenching techniques. Ultimately, the project team settled on a multistaged process that allowed for 1,4-dioxane treatment as well as the filter upgrades the Region had planned. Greenbrook Water Supply System The Greenbrook Water Supply System (WSS) consisted of pressure filters for iron and manganese removal, 9,500 m3 of on-site storage, and a high-lift pumping system. Five groundwater wells supply the facility at a permitted capacity of 189 L/s. When concentrations of 1,4dioxane up to 285 µg/L were found in one of these wells, and concentrations of up to 30 µg/L in the blended treated water, the plant was temporarily shut down. Although the Greenbrook system only contributes approximately 5 percent
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of the total supply to the Region’s Integrated Urban Supply system, any shutdown causes a ripple effect of problems. That 5 percent reduces the burden on other supplies in the system and provides additional water during higher demand periods. When the plant was shut down, various drinking water standards existed in Ontario, but none regulated 1,4-dioxane. To determine the realistic limit for 1,4dioxane at the plant, the Region consulted with Stantec Consulting, the Ontario Ministry of Environment, and toxicologists. The group defined an appropriate 1,4-dioxane treatment objective for this plant to be 10 µg/L, or as low as reasonably achievable. Through the Class Environmental Assessment (Class EA) process - including public consultation - and a number of studies, the team decided on several upgrades to the plant, including installing an advanced oxidation system to destroy 1,4-dioxane and return the Greenbrook WSS back into service as soon as possible. Treatability study A treatability study was initiated concurrent to the Class EA to investigate the treatment requirements to remove the 1,4-dioxane and to investigate the func-
tionality and performance of the various advanced oxidation technologies that were available. The technologies included ozone/peroxide, UV/peroxide, and UV/titanium dioxide. The treatability study included a literature review, bench-scale testing, and small-scale piloting of the technologies. Issues that were determined early in the study included potential bromate formation with the ozone/peroxide technology as concentrations of bromide were present in the water supply; the reliance of the UV/peroxide efficiency on UVT percentage; and potential hydroxyl radical scavenging from various water quality compounds such as chloride, sulphates, and hardness, for which Greenbrook WSS had a history of elevated concentrations. During piloting, each of the technologies was tested on a range of water quality from two of the wells; Well K2 was characteristic of the highest 1,4dioxane concentration, and Well K4B was characteristic of high iron and lower percent UVT. Each of the piloted advanced oxidation technologies was capable of reducing the 1,4-dioxane concentrations in excess of 1.0 log removal (90-percent recontinued overleaf...
Figure 1. Primary and secondary control sectors. 30 | November 2007
Environmental Science & Engineering Magazine