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USING ELECTROCHEMICAL MONITORING TO PREDICT METAL RELEASE IN DRINKING WATER DISTRIBUTION SYSTEMS
Title
USING ELECTROCHEMICAL MONITORING TO PREDICT METAL RELEASE IN DRINKING WATER DISTRIBUTION SYSTEMS.
Creator
Vaidya, Rajendra, Taylor, James, University of Central Florida
Abstract / Description
ABSTRACT Corrosion of distribution system piping and home plumbing materials is a major concern in the water community. Iron release adverse affects aesthetic water quality and the release of copper and lead is regulated by the Lead and Copper rule (LCR) and can adversely affect consumer health. Corrosion control is typically done by pH regulation and/or addition of corrosion inhibitors. Monitoring of corrosion control is typically done after the fact by monitoring metal release, functional...
Show moreABSTRACT Corrosion of distribution system piping and home plumbing materials is a major concern in the water community. Iron release adverse affects aesthetic water quality and the release of copper and lead is regulated by the Lead and Copper rule (LCR) and can adversely affect consumer health. Corrosion control is typically done by pH regulation and/or addition of corrosion inhibitors. Monitoring of corrosion control is typically done after the fact by monitoring metal release, functional group concentration of the selected chemical species or water quality. Hence, the associated laboratory analyses create a significant delay prior to the assessment of corrosion in drinking water systems. As corrosion in drinking water systems is fundamentally an electrochemical process, measurement of the electrical phenomena associated with corrosion can be use for real-time corrosion monitoring. This dissertation focuses on using parameters associated with electrochemical corrosion monitoring (EN) measurements in a field facility to predict and control the release of Iron, Copper and Lead in finished waters produced from ground, surface and saline sources with and without usage of corrosion inhibitors. EN data has not been used previously to correlate water quality and metal release; hence the use of EN data for corrosion control in drinking water systems has not been developed or demonstrated. Data was collected over a one year period from a large field facility using finished waters that are distributed to each of the fourteen pilot distribution systems (PDSs), corrosion loops and Nadles each. The PDSs have been built from aged pipes taken from existing distribution systems and contain links of PVC, lined cast Iron, unlined cast Iron and galvanized Steel pipe. The effluent for each PDS was split in two parts. One was delivered to the corrosion loops which are made from coiled copper pipe with lead-tin coupon inserted inside each loop and the other was delivered to the Nadles which housed the EN probes with electrodes for Fe or Cu or Pb-Sn. Finished water quality was monitored in and out of each PDS and total and dissolved Copper and Lead were monitored out of each corrosion loop. Photographs, scanning electron microscope (SEM) micrographs and energy disruptive x-ray spectroscopy (EDAX) conducted on all EN electrodes. EN electrodes showed dark brown to blackish voluminous scales for Fe, and EDAX revealed occurrence of two scales in distinct areas for all Fe electrodes; one comprised of porous, spongy looking structures and scales with more Fe content where the other had denser and more compact scales richer in Ca and P or Si. Cu electrodes had an orange to dark brown thin scale with blue green spots. Small pits were consistently observed mostly in the centre of such blue green spots which were identified as copper carbonates. The Pb electrodes visually showed a thin shiny transparent film with a surface very similar to the unexposed electrodes. Numerous pits were visually for pH controls and not seen for inhibitors; but SEM revealed that all electrodes had pits but the inhibitors reduced number and size of pits compared with pH controls. Thin hexagonal hydrocerussite plates were observed to occur in distinct growth areas and the presence of P or Si inhibitor seemed to increase the occurrence of hydrocerussite. Both Fe & Pb release were mostly in the particulate form while Cu release was mostly in the dissolved form. Total and dissolved Fe, Cu and Pb release models using EN parameters were developed by nonlinear regression. Fe release increased with localized corrosion (PF) and the EN model predicts that Fe release can be effectively controlled to the same degree by pH elevation or inhibitors. Cu release increased with general corrosion (LPRCR) and was also influenced by localized corrosion (ECNCR). However general corrosion was more significant for copper release which was mostly in the dissolved form. Pb release was depended on both general corrosion (LPRCR & HMCR) and localized corrosion (PF). The EN models predict that both Cu and Pb release is highest for pH control and all inhibitors reduced Cu and Pb release, which is consistent with the data. Inhibitors ranked by increasing effectiveness for reducing both Cu and Pb release are pH elevation, Si, ZOP, OP and BOP. EN monitoring is faster and less labor intensive than water quality monitoring and represents a significant advance for controlling metal release in drinking water distribution systems. The EN models were found to be comparable to water quality models developed from this study for metal release, and since EN is a real-time technique it offers a tremendous advantage over traditional water quality sampling techniques. Remote access of EN monitoring equipment is possible and the system requires little to no maintenance with the exception of a power supply or battery. The rapid turn around of corrosion rates from EN can be used to estimate metal release in drinking water proactively and mitigating measures can be implemented before the full adverse impacts are realized.
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Date Issued
2007
Identifier
CFE0001953, ucf:47430
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001953