THE USE OF MICROELECTRODES FOR THE MEASUREMENT OF pH AND DO AT THE WALL OF DRINKING WATER PIPES
This is an investigation of some of the factors affecting copper and iron corrosion in water distribution systems. In this study, microelectrodes were used to measure the dissolved oxygen (DO) concentration and pH of water at a fixed distance (50 ?m) from the pipe wall of new copper as a function of time. Initial pH levels of 6.5 and 8.0, and initial dissolved inorganic carbon (DIC) levels of approximately 2 mg C/L and 100 mg C/L (added as NaHCO 3 ) were studied. DO and pH microelectrode profiles as a function of distance from the wall were also measured using a 100 year old section of 4" diameter cast iron pipe. Overall, although many interesting results were obtained by this study, this set of experiments was insufficient to make confident conclusions because the results were contradictory and not reliably reproducible. Potential reasons for this include lack of complete control over an open system, the over sensitivity of microelectrodes for corrosion applications, especially with new copper pipe, and the inherent spacial variability encountered on a large reactive metal pipe surface. Had the data and experiments been more reproducible, then the data could be more effectively used to better model drinking water systems, to better understand and reduce red water formation, to better understand factors affecting copper release in finished drinking waters, and to provide additional insight into corrosion as it relates to many scientific and industrial applications. Characterizing microenvironments at or near the solid-liquid interface within drinking water pipes is an integral part of understanding the complete oxidation reaction taking place between water and a reactive metal surface. Chemical profiles of this region can be used to more accurately model water distribution networks, allowing prediction of bulk water properties, which can then be used to determine the best means of reducing corrosion. Definitive differences were shown between the bulk water conditions and the pipe wall interface that have not been shown, except in theory, by previous research.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:copper microelectrode drinking water pipes
Date of Publication:01/01/2001