Enhanced electro-catalytic degradation of chloroorganic compounds in the presence of ultrasound.

The application of finely divided (black) Pd and Pd-Fe powder in the sono-electro-catalytic reduction of chlorophenoxy herbicides (2,4-D) and chlorophenols (2,4-DCP) in aqueous solutions allows for effective destruction of toxic chlorinated aromatic compounds. At 20 degrees C complete conversion of these compounds is observed within 10 min. On bimetallic Pd/Fe catalyst, intermediates due to the oxidation reaction are detected in addition to the products of dechlorination. The bimetallic catalyst appears to be energetically and economically superior to the Pd. In both cases, the reaction times were considerably shortened in comparison with traditional electro-catalytic processes.

Detector for particulate polycyclic aromatic hydrocarbons in water.

It is estimated that most polycyclic aromatic hydrocarbons (PAHs) in environmental water are not dissolved but rather in particulate form. Nevertheless, the currently available optical detectors are not suited for proper sampling of solid PAHs. A new setup for direct sampling and quantification of suspended particulate PAHs in water is suggested. It is based on a polymeric film that has the capability of dissolving PAH particulates, coupled to a traditional laser-induced fluorescence probe. Kinetics and performance of two sampling modes have been studied: bulk sampling, by immersing the probe into the water, and surface sampling, by laying the film on the water surface. The latter method has proved to be more sensitive; however, it is diffusion-limited. Linear calibration plots have provided quantification over a wide concentration range with detection limits in the ppb range (these could be improved by using a modified probe). The effects due to other particulates in water have been studied and only little interferences have been observed. The possibility of analysis of PAH mixtures has been addressed and it has been concluded that multivariate analysis is needed.

A new sono-electrochemical method for enhanced detoxification of hydrophilic chloroorganic pollutants in water.

A new method for detoxification of hydrophilic chloroorganic pollutants in effluent water was developed, using a combination of ultrasound waves, electrochemistry and Fenton's reagent. The advantages of the method are exemplified using two target compounds: the common herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and its derivative 2,4-dichlorophenol (2,4-DCP). The high degradation power of this process is due to the large production of oxidizing hydroxyl radicals and high mass transfer due to sonication. Application of this sono-electrochemical Fenton process (SEF) treatment (at 20 kHz) with quite a small current density, accomplished almost 50% oxidation of 2,4-D solution (300 ppm, 1.2 mM) in just 60 s. Similar treatments ran for 600 s resulted in practically full degradation of the herbicide; sizable oxidation of 2,4-DCP also occurs. The main intermediate compounds produced in the SEF process were identified. Their kinetic profile was measured and a chemical reaction scheme was suggested. The efficiency of the SEF process is tentatively much higher than the reference degradation methods and the time required for full degradation is considerably shorter. The SEF process maintains high performance up to concentrations which are higher than reference methods. The optimum concentration of Fe2+ ions required for this process was found to be of about 2 mM, which is lower than that in reference techniques. These findings indicate that SEF process may be an effective method for detoxification of environmental water.