Removal of oxalic acid, oxamic acid and aniline by a combined photolysis and ozonation process.

Aniline (ANL), an aromatic amine, oxalic acid (OXA) and oxamic acid (OMA), short-chain carboxylic acids, were chosen as model organic pollutants for testing the combined effect of neat photolysis and ozonation in the treatment of aqueous effluents. In order to better understand the results, single ozonation and neat photolysis were also carried out. OXA has a high refractory character relatively to single ozonation and neat photolysis only accounted for 26% conversion of OXA after 2 h of reaction. On the other hand, OXA complete degradation was observed in less than an hour when ozone and light were used simultaneously. Despite OMA, a compound never studied before by a combined ozonation and photolysis treatment, being highly refractory to oxidation, more than 50% was removed by photo-ozonation after 3 h of reaction. In the case of ANL, both single ozonation and photo-ozonation resulted in 100% removal in a short reaction period due to the high reactivity of ozone to attack this type of molecules; however, only the combined method leads to efficient mineralization (89%) after 3 h of reaction. A significant synergetic effect was observed in the degradation of the selected contaminants by the simultaneous use of ozone and light, since the mineralization rate of combined method is higher than the sum of the mineralization rates of the individual treatments. The promising results observed in the degradation of the selected contaminants are paving the way to the application of photo-ozonation in the treatment of wastewater containing this type of pollutants.

Sonolysis of an oxalic acid solution under xenon lamp irradiation.

The photosonolysis of oxalic acid was carried out in an Ar atmosphere. The detectable products of sonolysis were CO(2), CO, H(2), and H(2)O(2). The yield of CO(2) was higher than that for the sum of sonolysis and photolysis reactions. Namely, a synergistic effect was observed during simultaneous irradiations of 200 kHz ultrasound and Xe lamp. The degradation of oxalic acid was promoted by active species such as H(2)O(2) produced from water by sonolysis. An oxalic acid-H(2)O(2) complex is likely to be present in the solution, but could not be detected. The effects of not only the photo-irradiation but also the thermal or incident energy during Xe lamp illumination were also considered.

A new approach to the decontamination of asbestos-polluted waters by treatment with oxalic acid under power ultrasound.

A suspension of chrysotile asbestos fibres in aqueous 0.5M oxalic acid was subjected to power ultrasound with the aim to disrupt and detoxify the mineral by the leaching action of oxalic acid on its structural cations acting simultaneously with a vigorous acoustic cavitation. Sonication was performed in a "cavitating tube", a vertical hollow vibrating cylinder made of titanium, operating at 19.2 kHz and 150 W. Treatment lasted from 2.5 to 21 h. Scanning electron microscopy (SEM) showed that the joint action of the chelating agent and ultrasound (though not of either when applied independently) mostly converted asbestos fibres into micrometric aggregates and nano-sized debris, whose morphology totally differed from asbestos fibres. When treated suspensions were filtered through CA membranes (pore size 0.20 microm), more than half of the asbestos went through the filter because it had either been brought in solution or dispersed in the form of extremely small particles. Most of the structural metal ions were brought into solution (ICP-AES). After the treatment the BET surface area of the recovered solid was tenfold greater than the original. The crystalline fraction of residual solids, though resembling the original sample in XRD, was shown by micro-Raman spectra to be made of antigorite, a polymorph form of serpentine. Furthermore, as the length of these antigorite fibrils lay outside the fibre range rated as a health hazard under worldwide regulations, our procedure can be employed for the decontamination of chrysotile-polluted waters and sediments.

WO3 thin films for photoelectrochemical purification of water.

Tungsten trioxide thin films on transparent substrates (glass and F:SnO(2) or ITO-coated glass) were prepared by layer-by-layer brush painting and spin-coating using organic precursors. Well-crystallized WO(3) with monoclinic structure was formed on all substrates after annealing at 500 degrees C or above. The dense semiconducting films are specular and transparent outside the band-gap. Their photoactivity in junctions with aqueous electrolytes extends up to 470 nm, with incident photon to current conversion efficiencies around 0.9 at 313 nm and up to 0.1 at 436 nm. Films of 10 cm x 10 cm were used for the study of solute degradation reactions in a thin-film reactor under backside illumination. Dilute aqueous solutions of model substances for contaminants like oxalic acid were decomposed under continuous flow using broadband UVA illumination and electrical bias. Operation under solar illumination was also feasible. The advantage over operation without bias (conventional photocatalysis) prevailed for all decomposition reactions studied.

Pilot scale mineralization of organic acids by electro-Fenton process plus sunlight exposure.

The viability of the electro-Fenton degradation of aqueous solutions of benzoic acid, 2,4-dichlorophenoxyacetic acid and oxalic acid has been studied at 20 A using a pilot flow reactor containing an anode and an oxygen diffusion cathode, both of 100 cm(2) section. Pollutants were preferentially oxidized by hydroxyl radicals formed in solution from reaction of Fe(2+) with electrogenerated H(2)O(2), allowing mineralization of benzoic acid and 2,4-D. For oxalic acid no electrochemical mineralization was observed. After electrolysis, samples of the different effluents were exposed to sunlight (Helielectro-Fenton process) and almost complete mineralization was reached after ca. 30-50 min without additional cost. Effects of parameters such as electrolysis time, pH and solar irradiation time on the process efficiencies were studied.

Hydrogen peroxide evolution during V-UV photolysis of water.

Hydrogen peroxide evolution during the vacuum-ultraviolet (V-UV, 172 nm) photolysis of water is considerably affected by the presence of oxalic acid (employed as a model water pollutant) and striking differences are observed in the absence and in the presence of dioxygen.

New possibilities for routine use of oxalic acid solutions in in-pile dosimetry.

New data are given on the use of oxalic acid, in light and heavy water solutions, for in-pile chemical dosimetry. The method of calculating the absorbed doses in low-Z materials is described. Results of chemical measurements in the core of the heavy-water-moderated reactor at Vinca (Yugoslavia) are compared with the results of calorimetric measurements conducted under identical conditions.