Magnetic Ion Exchange to the Rescue – One Utility’s Journey to Stage 2 Compliance
Authors:
- Cory Hopkins, P.E., Mark Bishop, P.E., Gary Iversen, P.E., Russell Jones, P.E. - Hazen and Sawyer
Many utilities are investigating the use of advanced treatment processes to ensure compliance with the impending Stage 2 Disinfectants/Disinfection Byproducts Rule. Such efforts often follow after exhausting other “low hanging fruit” alternatives such as changes to point of chlorination as well as coagulation and disinfection optimization.
Based on evaluation of the plant and distribution system operations, one such utility, using chloramines as a secondary disinfectant, faces an uphill battle with future regulatory compliance. In a proactive effort to address this concern, two advanced treatment processes, magnetic ion exchange and granular activated carbon adsorption, were piloted to determine their effectiveness for disinfection byproduct (DBP) control as well as their associated capital and operating costs. Results from the piloting effort will be reviewed, revealing ion exchange as the preferential advanced treatment process going forward.
Design and construction challenges of a new 6.75-mgd ion exchange facility will be discussed, including hydraulic considerations and peripheral system design complexities, resulting in modifications and additions to existing plant infrastructure. Existing distribution system operational challenges include high water age, nitrification, and competing disinfectants leading to the decision to divide the existing distribution system into two separate systems. Plant modifications to accommodate this division will be highlighted. An overview of start-up/commissioning of the new process into daily plant operations revealed the need for “on the fly” adjustments to physical and chemical treatment strategies utilized in downstream processes.
Operational data including TOC, UV-254, and DBP levels will be collected on the full-scale effectiveness of the ion exchange process for DBP control. Further, evaluation of chemical usage and residuals treatment practices will highlight impacts to downstream process operating costs.
