Date of Award
Master of Engineering Science
Civil and Environmental Engineering
Dr. Clare Robinson
Dr. Jose E. Herrera
A geochemical model has been developed to predict lead dissolution and solid phase transformations in water distribution systems for varying water chemistry conditions and corrosion scale compositions. The equilibrium model is developed in PhreeqC.v.2.16.03 with reactions and thermodynamic constants validated by comparing simulation results with laboratory batch dissolution experiments. The experiments were conducted on pipe corrosion scale samples from the water distribution system of London, ON and on pure phase lead compounds at different water chemistry conditions. While prior geochemical models have focused primarily on predicting soluble lead concentrations; our model is also able to successfully predict equilibrium solid phase compositions. With the inclusion of thermodynamic lead (IV) oxide parameters the model is also able to provide insight into the phase transformations between lead (II) to lead (IV) phases. The results indicate that at low chlorine concentrations soluble lead levels are governed by the solubility of lead (II) carbonates. Simulations and laboratory experiments of a complex corrosion scale containing lead and aluminum silicate phases demonstrate that the presence of aluminum silicate phases has negligible effect on soluble lead concentrations for typical water chemistry conditions. Sensitivity analyses conducted to examine the effectiveness of zinc orthophosphate for the inhibition of lead corrosion shows that the application of 3-5 mg PO4/L reduces soluble lead concentrations for low alkalinities. Moreover the model predicts that the formation of lead (IV) oxide is inhibited by orthophosphate. This model developed is a valuable tool that may be applied for municipalities to better predict the effectiveness of a corrosion control strategy.
Hassan, Tanvir, "A GEOCHEMICAL MODEL FOR PREDICTING CORROSION- SCALE DISSOLUTION AND PHASE TRANSFORMATIONS IN DRINKING WATER DISTRIBUTION SYSTEMS" (2011). Digitized Theses. 3235.