Chloride levels are increasing in some water supplies around the country due to use of road salts and seawater intrusion, which can increase the chloride-to-sulfate mass ratio (CSMR) and trigger serious water lead contamination from galvanic lead solder: copper pipe corrosion. Previous attempts to control this problem through simple water chemistry modifications were unsuccessful, but in this work a combination of zinc orthophosphate and moderate alkalinity mitigated lead release in testing at two utilities. Either zinc alone or phosphate alone were irrelatively ineffective, but the combination of zinc orthophosphate reduced lead leaching by 54-99% (compared to the control without inhibitors) if alkalinity was above about 55 mg/L as CaCO3. These results may help mitigate future lead in water contamination events. / MS / Chloride levels are increasing in some water supplies around the country due to use of road salts and seawater intrusion, which can increase the chloride-to-sulfate mass ratio (CSMR) and trigger serious water lead contamination from galvanic lead solder: copper pipe corrosion. Previous attempts to control this problem through simple water chemistry modifications were unsuccessful, but in this work a combination of zinc orthophosphate and moderate alkalinity mitigated lead release in testing at two utilities. Bench-scale experiments were completed with water from two utilities to look at the effectiveness of zinc orthophosphate, orthophosphate and zinc alone to reduce lead leaching in copper pipes with lead solder. Either zinc alone or phosphate alone were irrelatively ineffective, but the combination of zinc orthophosphate reduced lead leaching by 54-99% (compared to the control without inhibitors) if alkalinity was above about 55 mg/L as CaCO₃. These results may help mitigate future lead in water contamination events.

Premise plumbing can contain copper and lead bearing fixtures, and although copper is considered primarily an aesthetic issue, the neurotoxic effects of lead present a significant public health concern. Utilities approach corrosion control in low alkalinity water by increasing the pH (>9) or adding a phosphate inhibitor at neutral pH. Phosphate inhibitors, pH and chlorine are known to affect lead and copper release through their direct action as corrosion inhibitors or oxidizing agents or through an indirect action via microbial growth. Biofilms are often an implied cause of premise plumbing corrosion, although little is known about their community structure or ability to store metals. The central hypothesis of this thesis is that biofilm contributes to lead and copper release in premise plumbing. This thesis addresses a unique gap in corrosion literature by integrating traditional corrosion chemistry methods with microbiological and molecular biology techniques. The experiments used three distinct approaches: (i). electrochemical cell experiments to determine the key factors in decreasing lead and copper corrosion in galvanically coupled systems while maintaining microbial control (ii). galvanic macrocells using premise plumbing components to examine the unintended consequences of adding a phosphate based corrosion inhibitor and (iii). an annular reactor study to examine the impacts of two commonly applied corrosion control strategies. In the electrochemical cell experiments, the pH 9.2 with zinc orthophosphate and chlorine treatment achieved both goals: decreased lead and copper release and limited microbial growth. In galvanic macrocells experiments with premise plumbing components, zinc orthophosphate addition was shown to be positively correlated with increased bulk water bacteria, biofilm growth and biofilm community structure as measured by DGGE. Biofilm was also observed to sorb 3-29% of lead and 3-16% of copper from the bulk water. The comparison of the two corrosion control strategies showed that the majority of lead released was in the particulate form, and the results further alluded to the potentially significant role lead particles play in biofilm formation.

The objective of this study was to evaluate galvanic corrosion potential under various pH conditions, buffering capacities, and corrosion inhibitors including zinc orthophosphate (ZOP) and orthophosphate (OP). Bench-scale dump-and-fill experiments evaluated metals release from a lead and copper couple under stagnant conditions. Key findings from this study were that increasing DIC from 3 to 7 or 17 mg CaCO3/L significantly reduced lead release with or without corrosion inhibitor; however, the lowest lead concentrations were observed in water conditions with corrosion inhibitor addition. However, addition of 20 mg PO4/L as OP exacerbated lead release in some cases; though dissolved lead release was always below 28 µg/L, particulate lead was as much as 4 times greater compared to no corrosion inhibitor. Overall, this study demonstrated the potential of high dose ZOP and OP for lead corrosion control in drinking water, however, overdosing OP can lead to exacerbated particulate concentrations.

This dissertation consists of four papers concerning impacts of zinc orthophosphate (ZOP) inhibitor on iron, copper and lead release in a changing water quality environment. The mechanism of zinc orthophosphate corrosion inhibition in drinking water municipal and home distribution systems and the role of zinc were investigated. Fourteen pilot distribution systems (PDSs) which were identical and consisted of increments of PVC, lined cast iron, unlined cast iron and galvanized steel pipes were used in this study. Changing quarterly blends of finished ground, surface and desalinated waters were fed into the pilot distribution systems over a one year period. Zinc orthophosphate inhibitor at three different doses was applied to three PDSs. Water quality and iron, copper and lead scale formation was monitored for the one year study duration. The first article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on surface characteristics of iron corrosion products in a changing water quality environment. Surface compositions of iron surface scales for iron and galvanized steel coupons incubated in different blended waters in the presence of ZOP inhibitor were investigated using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) / Energy Dispersive X-ray Spectroscopy (EDS). Based on surface characterization, predictive equilibrium models were developed to describe the controlling solid phase and mechanism of ZOP inhibition and the role of zinc for iron release. The second article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total iron release in a changing water quality environment. Development of empirical models as a function of water quality and ZOP inhibitor dose for total iron release and mass balances analysis for total zinc and total phosphorus data provided insight into the mechanism of ZOP corrosion inhibition regarding iron release in drinking water distribution systems. The third article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total copper release in a changing water quality environment. Empirical model development was undertaken for prediction of total copper release as a function of water quality and inhibitor dose. Thermodynamic models for dissolved copper based on surface characterization of scale that were generated on copper coupons exposed to ZOP inhibitor were also developed. Surface composition was determined by X-ray Photoelectron Spectroscopy (XPS). The fourth article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total lead release in a changing water quality environment. Surface characterization of lead scale on coupons exposed to ZOP inhibitor by X-ray Photoelectron Spectroscopy (XPS) was utilized to identify scale composition. Development of thermodynamic model for lead release based on surface analysis results provided insight into the mechanism of ZOP inhibition and the role of zinc.