Abstract

Chemical oxidation and adsorption are feasible options to treat toxic effluents; however, the lack of empirical design data impairs their implementation at industrial scale. This paper reports experimental results on a detoxification system based on enhanced oxidation using ozone in the presence of activated carbon. The study focuses on four representative model toxic phenolic compounds, i.e. 3-chlorophenol, 4-chlorophenol, 2-methoxyphenol, and pyrocatachol. The experimental system consisted of a 1.5 dm3 stirred reactor and an ozonizer with a mean production capacity of 0.1 mmol O3 s-1 from pure oxygen. Adsorption and absorption processes were studied in the absence and presence of chemical reactions at pH 2, within the temperature range 15-35°C and solid/liquid ratio 0.05-0.005 w/w. Results showed that all these contaminants are readily oxidized by ozone, with a pseudo-second order rate constant in the range 0.02-0.08 mmol-1 dm3 s-1 at pH2 and temperature 15-35°C. Fast phenolic oxidation reactions at the gas-liquid interphase increased the ozone absorption rate by a factor of 3-10, as compared with physical absorption only. The presence of activated carbon during ozonation significantly improved ozone selectivity. Adsorption isotherms and ozone self-decomposition data are also reported. Chemical oxidation and adsorption are feasible options to treat toxic effluents; however, the lack of empirical design data impairs their implementation at industrial scale. This paper reports experimental results on a detoxification system based on enhanced oxidation using ozone in the presence of activated carbon. The study focuses on four representative model toxic phenolic compounds, i.e. 3-chlorophenol, 4-chlorophenol, 2-methoxyphenol, and pyrocatachol. The experimental system consisted of a 1.5 dm3 stirred reactor and an ozonizer with a mean production capacity of 0.1 mmol O3 s-1 from pure oxygen. Adsorption and absorption processes were studied in the absence and presence of chemical reactions at pH 2, within the temperature range 15-35°C and solid/liquid ratio 0.05-0.005 w/w. Results showed that all these contaminants are readily oxidized by ozone, with a pseudo-second order rate constant in the range 0.02-0.08 mmol-1 dm3 s-1 at pH2 and temperature 15-35°C. Fast phenolic oxidation reactions at the gas-liquid interphase increased the ozone absorption rate by a factor of 3-10, as compared with physical absorption only. The presence of activated carbon during ozonation significantly improved ozone selectivity. Adsorption isotherms and ozone self-decomposition data are also reported.