Journal of Environmental Conservation Engineering

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Presence of chlorinated organic pesticides in water is a serious health concern, whereas oxidation under high pressure and temperature is a promising treatment method for water and wastewater contaminated with organics. This paper aims to shed light on degradation and mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) in water with subcritical and supercritical conditions, using laboratory batch experiments. The experiments with 0.45 mM aqueous solution of 2,4-D were carried out under five different pressures (4.1-28.5 MPa) and five different temperatures (250-400^oC). We found that 2,4-D did not degrade at 250^oC and 4.1 MPa. The pesticide gradually degraded with an elapsed reaction time at 300^oC and 8.8 MPa, but aromatic intermediates such as 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol and others were produced. The pesticide almost disappeared at higher temperature and pressure in subcritical (360^oC, 19.5 MPa) and supercritical (380-400 ^oC, 24.0-28.5 MPa) regions during the same reaction time. Chloride ion concentrations gradually increased with decreasing 2,4-D concentrations in a series of experiments. Furthermore, total organic chlorine (TOX) and total organic carbon (TOC) decreased remarkably at the supercritical condition (400 ^oC, 285 MPa). Dechlorination was thought to be a major step in 2,4-D oxidation by this method. The results exhibit that supercritical water oxidation of chlorinated aromatic pesticides like 2,4-D is a very promising purification method.

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A simplified electrophoresis reactor using a porous electrode was developed to rapidly separate ions from aqueous solutions. In this study, a stainless plate, a titanium plate, titanium powder packing, porous carbon material, and porous carbon material coated with platinum were selected as electrodes. An ammonium sulfate liquid was used as a testing solution. The concentrations of ions (NH₄⁺ and SO₄2-^{) in the electrophoresis cell were measured under various experimental conditions. The use of the porous carbon electrodes decreased the ion concentrations in the cell. The decreasing rates of ion concentrations changed, depending on the applied voltage and electric current. Additionally, the use of the porous carbon material coated with platinum was found to reduce the electrode resistance. In the experiment using the titanium powder-packing electrode, ion concentrations in the cell decreased gradually, however, changes of ion concentrations were not recognized in the experiments carried out using the plate electrodes. These results show that the use of porous carbon electrodes coated with platinum can enhance the performance of the electrophoresis reactor.

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