Reductive treatment of drinking water contaminants and disinfection by-products using aqueous phase corona discharge.

Abstract

With increasing global population comes an increase in the need to safe and clean drinking water. Contaminants can arise in drinking water either naturally, or by the interaction of disinfection chemicals with naturally occurring materials, or simply due to by-products of the disinfection mechanism itself. Due to the oxidative nature of our disinfection treatments, these species are in highly oxidized states, and in some cases require chemical reduction to become less harmful.

The present work demonstrates the capabilities of aqueous phase corona plasma in reductive treatment of oxidized contaminants found in drinking water. This study focuses on the treatment of the nitrate ion, bromate ion, chlorate ion and monobromoacetic acid, all of which can be found in typical drinking water systems.

The second and third chapters within this thesis establish the optimal water matrix conditions for the treatment of bromate, chlorate and nitrate. These experiments investigate the influence of pH, temperature, presence and types of oxidative scavengers, dissolved gases and by-products that are made by this treatment process with these compounds. The main conclusion of these works is that aqueous phase corona discharge is capable of producing chemical compounds with sufficient energy to chemically reduce the nitrate, bromate and chlorate anions. Acidic conditions, under low dissolved oxygen scenarios facilitated the highest amount of reduction of the target contaminants, as well as having the presence of oxidative species scavengers. It was also observed that the anoxic environment could be obtained by introducing alcohols into the contaminated solution which generated sufficient cavitation and bubbling to strip the oxygen from solution. Through a comparison of various carbonaceous compounds as oxidative species scavengers, it was determined that the volatile alcohols provided a better performance than other soluble carbon sources, due to the decrease in dissolved oxygen.

The fourth chapter considers different methods of introducing argon, oxygen and nitrogen into the test solution for the effect they would have on the treatment of solutions containing the bromate anion or monobromoacetic acid. The optimal pH for the treatment of monobromoacetic acid was also established, where again the acidic conditions prevailed. Tests were conducted to consider the effect of having the solution pre-saturated with the test gas, continually sparged, or with the gas passing through a hollow discharge electrode. The tests in which gas was blown through the discharge electrode greatly surpassed all other treatment regimes, where nitrogen provided the best removal for both contaminants under acidic conditions for bromate and under acidic and basic conditions for monobromoacetic acid.

The fifth chapter provides conclusions for the overall thesis and recommendations for future work.