Destruction of Pentachlorophenol Using Glow Discharge Plasma Process

Pentachlorophenol (PCP), found in wood preservatives and pesticides, is an acutely toxic recalcitrant organochlorine carcinogenic compound. A point-to-plane glow discharge plasma (GDP) process was used to study the destruction of 30−50 ppm (120−188 μM) sodium salt of pentachlorophenol (PCP) in an aqueous solution. PCP was converted to less than 10% of its initial concentration in 1−3 h, at room temperature and low pressure (50 Torr). Effects of varying the headspace gas chemistry, stirring rate, pH, and current upon rate of PCP conversion were investigated. Organic acids, including formate, acetate, butyrate, and oxalate, were formed as byproducts after 1−3 h of GDP treatment of PCP. The chloride recovery suggests 50−70% dechlorination. The PCP removal rate exhibited mixed order kinetics. A reaction model developed to verify mixed order kinetics compares well with the experimental data. The increase in order may be due to the production and subsequent destruction of several reaction products throughout the process. An increase in current and stirring rate increased the rate of PCP removal in the GDP reactor. However, the rate of PCP removal decreased when the initial pH of the solution is raised to 11.4. Rapid removal of PCP was observed when the headspace gas was argon, air, or oxygen. Bench scale data was used to compare the power efficiency of the GDP process with atmospheric pressure corona discharge. Results suggest that the cost of power for PCP conversion by glow discharge was less than that of atmospheric pressure corona discharge. Additionally, the operating cost for PCP destruction in aqueous solution using UV based advanced oxidation technologies was found to be comparable with power costs for PCP conversion using GDP.