Effect of High Chloride Concentrations on Cast Iron Corrosion and Water Quality in Drinking Water Distribution Systems

Abstract

Chloride can be present in drinking water from various sources including treatment practices for natural organic matter (NOM) removal, saltwater intrusion, run-off from deicing salt, and use of desalinated water. The purpose of this research was to examine the impacts of variable chloride concentrations on disinfection efficacy and microbial regrowth, iron corrosion and its release from iron surfaces, and effectiveness of different corrosion control strategies in chlorinated drinking water distribution systems. Additionally, the characteristics of resulting iron corrosion products and bacterial biofilm communities were investigated. Results showed that elevated chloride concentrations did not have a significant impact on microbial regrowth in terms of bulk or biofilm HPCs, and higher chlorine dosages were required to achieve target free chlorine residuals in high chloride systems. It was observed that in the presence of high chloride concentrations more crystalline and porous scales, which are less protective against corrosion, were formed on the surface of cast iron coupons that promoted the iron corrosion and release. Moreover, larger iron particles were formed, which can resuspend in flowing water and cause water discoloration. Investigations into the effect of variable chloride concentrations on effectiveness of different corrosion control strategies suggested that elevated chloride concentrations interfered with inhibiting action of the corrosion control strategies and reduced their effectiveness. Finally, results showed that bacterial biofilm population decreased with chlorination and increasing chloride concentrations, and were unlikely to contribute to the observed increased corrosion rates in cast iron systems under the conditions tested in this experiment.