Date of Award
Spring 2015
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil Engineering
First Advisor
Mayer, Brooke K.
Second Advisor
McNamara, Patrick
Third Advisor
Zitomer, Daniel H.
Abstract
Geologic and anthropogenic heavy metals contaminate drinking water for hundreds of millions of people worldwide. Electrocoagulation -- the in situ generation of coagulant by electrolytic oxidation of metal electrodes -- is a century-old process gaining new traction for metal removal from water and wastewater. However, the low conductivity of drinking water and low target contaminant concentrations required for human consumption present challenges for electrocoagulation of drinking water. This study is unique in that it addresses seven different metal contaminants at the trace concentrations of concern to human consumption and investigates the wide range of possible source water matrices. The goal of this study was to determine the feasibility of electrocoagulation to remove trace heavy metals from drinking water. This goal was addressed by first demonstrating removal of contaminant metals to below regulatory concentrations. Seven metals were tested for removal to meet U.S. Environmental Protection Agency requirements for drinking water: chromium, nickel, copper, zinc, arsenic, cadmium and lead. Next, the effects of electrode material (aluminum versus iron) and post-treatment separation of flocs (micro-filtration versus settling alone) were tested in a mixed-contaminant scenario. In addition, the importance of source water pH and ionic composition was tested for the same five metals. A bench-scale, batch reactor was used with a galvanostatic DC power supply providing 0.5 A current. Metal concentrations were determined by inductively-coupled plasma mass spectrometry (ICP-MS). Removal of five metals was demonstrated to below regulatory concentrations for drinking water: chromium, copper, arsenic, cadmium and lead. Iron electrodes vastly out-performed aluminum electrodes in removing chromium and arsenic. Aluminum electrodes were slightly more effective at removing nickel, cadmium and lead, but only at pH 6.5. Microfiltration enhanced contaminant removal and reduced the variance of effluent concentration. Microfiltration also dramatically reduced the residual concentration of aluminum and iron after treatment. Electrocoagulation removed nickel and cadmium more efficiently at pH 8.5 than 6.5, though chromium, arsenic and lead showed no significant effect from initial pH in the range tested. All metals exhibited poorer removal efficiencies as the ionic strength of the background electrolyte increased, particularly in the very high-solids, synthetic groundwaters.