Date of Award

August 2018

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Yin Wang

Committee Members

Yin Wang, Shangping Xu, Qian Liao

Keywords

Drinking water, Inhibitors, Lead corrosion, Lead service lines, Phosphate, water chemistry

Abstract

Lead-containing materials that include lead pipes, fittings, solder, and fixtures are widely present in drinking water distribution systems in North America and Europe. Their internal corrosion provides the most significant source of lead in drinking water. Several mechanisms contribute to the corrosion of lead-containing materials, including material heterogeneity, galvanic interaction, and reaction with progressively water constituents and to protect consumers from lead exposure, the Lead and Copper Rule (LCR) set the lead action level to 15 μg/L for a 1-L first-draw sample of tap water. Today more than half of the water treatment utilities in the U.S. are using phosphates as a corrosion inhibitor for lead release in plumbing systems. Despite good efficiency, phosphate found in the effluent of water treatment plants may have negative impacts on the environment. Also, to comply with disinfection byproduct regulations, many utilities have chosen to use chloramines rather than chlorine for residual maintenance. However, the switch to chloramines may expose these systems to another health risk, increased concentrations of lead.

This project investigated the capability of a suite of low-cost, environmentally friendly, and phosphate-free inorganic inhibitors in mitigating lead release from aged metallic lead materials under conditions relevant to Chicago and Milwaukee drinking water distribution in 2 phase, literature review and batch experiments on corrosion inhibitors including (1) metal sulfates: SnSO4 (2 mg/L as Sn) and ZnSO4 (2 or 4 mg/L as Zn), (2) sodium oxyanions: Na2SiO3, Na2Si3O7 (20 mg/L as SiO2), and Na2B4O7 (5 mg/L as BO3 )and also pH adjustment.

The results showed that pH adjustment on 9.2 would decrease the lead release significantly. However, it could trigger some other reactions in the system which increase the concentration of Iron, copper, magnesium, manganese, etc and the taste, color and odor of drinking water could be affected. Therefore, further investigation regarding pH adjustment may be needed.

Sodium silicate showed the capability of decreasing lead leaching in the system over time. Probably the reasons could be pH increase in the system and the creation of a protective layer on the surface of pipe. Also, Tin sulfate showed the capability of decreasing the lead leaching in the system.

Based on the experimental results, pH adjustment, silicate addition, and use of SnSO4 were promising in minimizing lead release. Further recommendation includes

(1) identifying the optimum inhibitor formulations in a wide range of environmental matrices that are relevant to drinking water distribution,

(2) evaluating the long-term performance of the optimum inhibitor formulations

(3) conducting pilot-scale pipe loop studies to better represent the scenarios in real distribution systems.

Also, it will be beneficial to determine the combinative use of phosphate and phosphate-free inhibitors that may effectively mitigate lead release in tap water and reduce the loads of phosphate in wastewater utilities in the meantime. Cost-benefit analysis and life cycle assessment may also be needed to promote the technology adoption in the field.

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