Chlorine Reduction Kinetics and its Mass Balance in Copper Premise Plumbing Systems During Corrosion Events.

Ignacio T Vargas,Pablo A Pastén,Javiera M Anguita,Gonzalo E Pizarro

doi:10.3390/ma12223676

Abstract

Hypochlorous acid has been reported as the main oxidant agent responsible for the corrosion of copper plumbing systems in chlorinated water supplies. However, there is little information about chlorine consumption kinetics in a combined system (i.e., with dissolved oxygen (DO) and free chlorine), as well as its complete mass balance within a copper pipe during stagnation. The results of our experiments using copper pipes filled with synthetic drinking water, with a moderate alkalinity (pH = 7.2; dissolved inorganic carbon = 80 mg as CaCO3 /L), and tested under chlorine concentrations from 0 to 8 mg/L, show that chlorine depletion is associated with pipe wall reactions (i.e., copper oxidation and scale formation processes). Free chlorine was depleted after 4 h of stagnation and its kinetic constant depend on the initial concentration, probably due to diffusion processes. Surface analysis including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and total reflection X-ray fluorescence (T-XRF) suggest chlorine precipitation, probably as CuCl. The obtained kinetics of chlorine and DO reduction would be critical for modeling and prediction of corrosion events of copper premise plumbing systems. In addition, our results indicate that the pipe’s surface reactions due to corrosion induces a loss of free chlorine in the bulk water, decreasing chlorine added for disinfection and the subsequent effect on water quality.

Highlights

Chlorination is the most used method for disinfection worldwide [1]
The results of this study have been organized in 3 sections: (1) Water chemistry, including dissolved oxygen (DO)
The estimation of KO2 for Cl2 concentration of 0; 0.2; and 2 mg/L were 0.003 ± 0.001; 0.011 ± 0.004; and 0.017 ± 0.003 L/h, respectively. These results show that chlorine affects DO consumption, probably by an increase in the chemical and electrochemical activity at the pipe wall due to Cu0 and

Summary

Introduction

Chlorination is the most used method for disinfection worldwide [1]. The disinfection is produced by the chlorine oxidative capacity [2]. Typical levels of free chlorine in drinking water range from. To guarantee an adequate disinfection and to maintain a residual chlorine concentration, the actual doses added are usually higher. Health Organization established chlorine concentrations from 0.2 to 5 mg/L at the point of delivery [3]. Chlorine is commonly found as hypochlorous acid (HOCl), a weak acid that does not significantly affect pH [4]. HOCl is a strong oxidizing agent and must be considered in the cathodic half-reaction of metallic copper oxidation [4]

Methods

Results

Conclusion