Materials Performance

JUN 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Data from the lab experiment comparing lead corrosion in Detroit water (left), Flint water without orthophosphate (middle), and Flint water with orthophosphate (right). Image credit: Flint city-treated water without a corro- sion inhibitor treatment. 4 Tests were conducted over six days to determine the decay of chlorine over time in the Flint city-treated water compared to the DWSD water. The researchers demon- strated that rapid iron corrosion in the Flint city-treated water was consuming the chlo- rine disinfectant and causing much more iron release than the DWSD water. They ex- panded their tests by exposing a steel sam- ple (a 99.99% iron nail) to DWSD water, Flint city-treated water, and Flint city- treated water with orthophosphate added. The water contacting the steel was changed every Monday, Wednesday, and Friday. After a month, the iron samples were photographed and weight loss was mea- sured. The nail exposed to Flint city-treated water exhibited much more surface rust than the nail exposed to the DWSD water. The weight loss measurements of the nails were then used to determine the corrosion rate. For the nail in Flint city-treated water, the corrosion rate was 8.6 times higher than it was for the nail in DWSD water. Even with the added corrosion inhibitor in the Flint city-treated water, the corrosion rate was still 3.5 times higher than in the DWSD water. Metal pipe corrosion can be further accelerated by microbiologically influ- enced corrosion (MIC), Edwards com- ments. Using Biological Activity Reaction Test (BART) kits, the researchers tested the Flint city-treated water for specific MIC- causing bacteria including heterotrophic aerobic bacteria (HAB), acid-producing bacteria (APB), iron-reducing bacteria (IRB), SRB, and slime-forming bacteria (SLYM). They found all of these corrosion- causing bacteria in the Flint city-treated water. According to Edwards, this was probably due to low chlorine, but might also be due to organic matter in the Flint city-treated water, which would provide a food source for the bacteria. When the researchers tested samples of DWSD water, the levels of corrosion-causing bacteria were much lower. Flint Switches Back to Less Corrosive Water On October 16, 2015, the City of Flint switched back to DWSD as the source for the city's drinking water. Because Flint had been using city-treated water from the Flint River for 18 months without corrosion con- trol treatment, the protective scaling on pipes and plumbing formed by the ortho- phosphate corrosion inhibitor in the DWSD water had been destroyed by the more corrosive water. Discussions between the MDEQ and EPA were held to determine the best course of action for obtaining opti- mal corrosion control treatment for the water purchased from DWSD. They decided to add a supplemental dose of orthophosphate to the water to enhance the pipe passivation in Flint since DWSD used a maintenance dose of orthophos- phate in the water. The orthophosphate dose was increased so the distribution sys- tem's phosphate residual was a minimum of 3.1 mg/L. 5 The corrosion control optimi- zation plan also called for a minimum pH of 7.0 to be maintained. Additionally, the EPA and the MDEQ recommended that Flint residents run the water in their homes and businesses to help distribute the orthophosphate in the drinking water system and build-up the protective coating in the pipes. The EPA noted that attention to building a protective coating in pipes does not mean there is any less urgency to remove lead service lines. 6 Bibliography "Flint Water Advisory Task Force—Final Report." March 2016. snyder/FWATF_FINAL_REPORT_ 21March2016_517805_7.pdf. May 17, 2016. References 1 "Optimal Corrosion Control Treatment Evalu- ation Technical Recommendations for Pri- macy Agencies and Public Water Systems," EPA, 816-B-16-003, March 2016. 2 N. Zhu, S. Roy, "The Unintended Conse- quences of Migrating to Flint River Water," Flint Water Study Updates, Aug. 23, 2015, tended-consequences-of-migrating-to-flint- river-water/ (May 17, 2016). 3 "Lead testing results for water sampled by residents," Flint Water Study Updates, http:// idents/results-for-citizen-testing-for-lead- 300-kits/ (May 17, 2016). 4 M. Edwards, "Research Update: Corrosivity of Flint Water to Iron Pipes in the City—A Costly Problem," Flint Water Study Updates, http:// update-corrosivity-of-flint-water-to-iron- pipes-in-the-city-a-costly-problem (May 17, 2016). 5 "Plan for Optimization of Corrosion Control," MDEQ, Taking Action on Flint Water, http:// Plan_for_Optimization_of_Corrosion_Con- trol_514633_7.pdf (May 17, 2016). 6 "EPA, DEQ and City of Flint Recommend Flushing Water to Speed Recovery of System," EPA News Release, 04/16/2016, https:// 61F944BF10B85257F9700491883 (May 17, 2016). 12X Detroit two weeks Flint two weeks Flint +P two weeks 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 Lead Concentration (ppb) 29 NACE INTERNATIONAL: VOL. 55, NO. 6 MATERIALS PERFORMANCE JUNE 2016 Corrosion Caused Lead-Tainted Water in Flint, Michigan

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