Degradation of Contaminants in Drinking Water by Electrical Discharge Plasma
Mentor: Dr. Selma Mededovic
Department: Chemical and Biomolecular Engineering
Pharmaceuticals, like estrogen, cholesterol-lowering drugs, pain relievers, antibiotics and anti-depressants, have been detected in lakes, rivers and streams. It is recognized that these waterways get contaminated through the wastewater which is usually not treated for the pharmaceutical drugs. Consequently, many of these molecules diffuse into the water supplies and contaminate drinking water. Recent results demonstrated that U.S. drinking water contains over 2300 cancer-causing chemicals. Conventional methods for water remediation, including carbon adsorption, biological treatment, and chlorine treatment, suffer from various limitations and generally are either not active in destroying the target species or have very slow rates of destruction. To solve this problem, new technologies based on the in-situ production of oxidative and reductive species are being considered as alternatives to conventional technologies to degrade inorganic and organic pollutants. Advanced oxidation technologies utilize UV/H2O2, direct ozone, ozone/H2O2, photocatalysis, high energy irradiation and pulse radiolysis to produce hydroxyl radicals, species which are, because of their high oxidation potential, capable of degrading virtually any organic compound in the solution. In recent years, various types of high voltage electrical discharges have emerged as an alternative advanced oxidation technology for the degradation of aqueous phase contaminants. One type of high voltage discharge utilizes a pulse forming electrical network to produce an electrical discharge directly in the liquid phase between the high-voltage and the grounded electrode. In the streamer discharge, a plasma channel originates from the high-voltage electrode but never reaches the grounded electrode. However, when the distance between the electrodes is too small or the applied voltage is too high, the plasma channel bridges the electrode gap and the streamer discharge becomes a spark discharge. Because of the higher energy inside the plasma channel, spark discharges are more intense than streamer discharges and, consequently, the temperature and pressure inside the plasma channel are significantly higher. Recent studies on liquid-phase discharges suggest that temperatures and pressures in the plasma spark channel that surrounds the tip of the high voltage electrode could be as high as several thousand degrees Kelvin and 2-3 GPa, respectively. Generally, strong electric fields applied to water initiate both chemical and physical processes such as ultraviolet radiation, overpressure shock waves and, especially, formation of various reactive chemical species. The published literature on spark electrical discharges in water is very scarce, thus fundamental as well as practical application studies could assist in elucidating not only elementary processes inside the plasma, but also introduce spark discharges as a new water-treatment technology. The goal of this research is to assess the efficiency of spark electrical discharges in water for the degradation of pharmaceutical drugs. Specific focus will be placed on estrogen hormones (cause feminization of the male fish), antibiotics, anti-inflammatory drugs (ibuprofen) and chlorinated aromatic compounds. The REU participant will study the effects of input power, electrode material and different electrolytes on the concentration of radicals in the plasma and the initial concentration of the targeted molecule in the bulk solution. Moreover, s/he will compare the positive and negative polarity spark electrical discharge in water and thus obtain discharge parameters for achieving the highest degradation efficiency. This research will involve the use of various analytical and spectroscopic tools to (i) measure the concentration of the ions and molecules in the water and (ii) identify radical species in plasma.