Date of Award
Spring 2019
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil and Environmental Engineering
First Advisor
Mayer, Brooke K.
Second Advisor
Starke, Jeffery
Third Advisor
Young, Kyana
Abstract
Small drinking water systems serve approximately 20% of the US population, but they can struggle to comply with the Total Coliform Rule and the Disinfectant and Disinfection Byproduct Rule. Issues with insufficient funds to effectively treat the water and difficulties with the transportation of required chemicals can affect compliance. Electrochemical processes may offer an alternative approach for small water systems as they have demonstrated some advantages over traditional treatments, such as reduced handling and storage of chemicals and cost effectiveness. Sequential electrochemical processes have yet to be tested for the treatment of E. coli in drinking waters. In this study, electrocoagulation (EC) and electrooxidation (EO) were investigated using two model surface waters and two model groundwaters to determine the efficacy of sequential EC-EO for mitigating E. coli. At a current density of 1.67 mA/cm2 for 1 minute, bench-scale EO alone achieved 4-logs mitigation of E. coli in the model shallow aquifer. Increasing the EO current density to 6.67 mA/cm2 for 1 minute provided similar levels of E. coli mitigation in the model deep aquifer (characterized by lower initial chloride concentrations compared to the shallow aquifer). Using a current density of 10 mA/cm2 for 5 minutes EC achieved 1-log or greater E. coli mitigation in all model waters. No additional mitigation beyond EC alone was achieved using sequential EC-EO. Reductions in the initial pH of the surface waters to target higher natural organic matter (NOM) removal did not enhance E. coli treatment with EC-EO compared to EC alone. In fact, an average of 64% of NOM was removed no matter the change in pH, which likely limited E. coli mitigation. Additional reasons for the lack of improvement in E. coli treatment may have included the presence of iron following EC or insufficient EO current density. Decreasing the initial water pH did improve E. coli mitigation using EO when pretreated by EC compared to the baseline water matrix pH. Total EC residual iron concentration also increased, and it correlated slightly with E. coli mitigation. This correlation and oxidation of ferrous iron may indicate that Fenton-like reactions occurred during EO after EC pretreatment.