A four week bench-scale corrosion study was conducted earlier this year by C&E Engineering Partners Inc. on behalf of the Town of Westerly, RI. The town was seeking the Rhode Island Department of Health’s approval of a mixed oxidant disinfectant. The goal of the test was to conduct a head to head comparison of Westerly source water disinfected with either MIOX mixed oxidant solution (MOS) or sodium hypochlorite (bleach) to determine relative rates of corrosion and generation of disinfection byproducts.
Each week, 10 gallons of untreated source water was collected from the same well field for use in the bench scale testing. In order to simulate the treatment conditions of the Westerly municipal distribution system, the pH of the water was adjusted to 8.0 with potassium hydroxide and 1 mg/L polyphosphate corrosion inhibitor was added.
In the corrosion studies, lead and copper coupons, as well as copper coupons partially coated with a 50% tin/50% lead solder, were procured from Alabama Specialty Products. The coupons coated with the solder mixture were used to simulate a soldered copper joint. The coupons were attached to a 2.5 inch plastic holder rod that was securely attached to a 1 liter HDPE plastic jar. The jars were securely covered. Each type of coupon was tested at two different concentrations, 0.2 mg/L and 1.2 mg/L free available chlorine (FAC). In total, 12 jars were used to complete the weekly corrosion studies.
After one week of exposure to the coupon, water was removed and collected for analysis. Once the samples were collected, the jars were refilled with freshly treated source water that had been adjusted to mimic the Westerly water treatment process. The collected water was then tested for total copper, total lead, or in the case of the mixed solder coupon, both copper and lead using EPA method 200.8. Analyses were conducted by an independent analytical laboratory.
