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Gomes A.C.,Research Unit of Textile and Paper Materials | Gomes A.C.,University of Beira Interior | Nunes J.C.,Research Unit of Textile and Paper Materials | Simoes R.M.S.,Research Unit of Textile and Paper Materials | Simoes R.M.S.,University of Beira Interior
Journal of Hazardous Materials | Year: 2010

To study the fast kinetic decolourisation of textile dyes by ozone a continuous quench-flow system was used. This system has not been used before for these purposes. Reaction times in the range of 7-3000ms were explored. The reaction was quenched with potassium iodide, which proved to be very effective, and the indigo method was used to follow the ozone concentration. Dyes from the most representative chemical classes currently used in the textile industry, i.e. azo and anthraquinone, were selected. Using the initial slope method, the effect of dye and ozone concentrations was researched and the kinetic equations thus established. Using tert-butyl alcohol, as radical scavenger, and pH close to 2.5, the second-order rate constant of the reactant dyes at 280K varies in the range of 1.20×104-7.09×105M-1s-1; the Acid Orange 7 exhibiting thus its lowest value, the Acid Blue 45 its highest value and the Acid Green 25 and 27 and Direct Yellow 4 intermediate values (≈1.6×105M-1s-1). Without radical scavenger and the pH close to 4, the reaction rate increases one order of magnitude, but, on the reverse, the efficiency of ozone to decolourisation decreases. © 2010 Elsevier B.V. Source

Gomes A.C.,Research Unit of Textile and Paper Materials | Gomes A.C.,University of Beira Interior | Fernandes L.R.,Research Unit of Textile and Paper Materials | Fernandes L.R.,University of Beira Interior | And 2 more authors.
Chemical Engineering Journal | Year: 2012

Different dyes can exhibit markedly different reaction rates with ozone. These observations can raise the concern that in a mixture of dyes one of them can be over-oxidized while the other remains under-oxidized, . i.e. exhibiting colour. In addition, the effect of pH on decolourisation also deserves additional investigation. The influence of pH on the oxidation rate of the monoazo dye Acid Orange 7 (AO7), one of the most difficult dyes to degrade, was studied in a homogeneous medium. The results have revealed an increase of nearly two orders of magnitude in the AO7 decolourisation rate when pH increased from 3 to 8.2. This effect was only slightly diminished when the radical scavenger was added. Competitive studies were performed between AO7 and the anthraquinone dye Acid Green 27 (AG27), which exhibits a much faster reaction rate. When the two dyes are mixed together, the AO7 decolourisation rate increases markedly, approaching the AG27 values, even under conditions that favour the undissociated species (pH. =. 2.7). This is a very positive practical result as the charged ozone can be consumed almost indistinctly by the two dyes. © 2012 Elsevier B.V.. Source

Santos D.C.,University of Beira Interior | Santos D.C.,Research Unit of Textile and Paper Materials | Silva L.,University of Beira Interior | Silva L.,Research Unit of Textile and Paper Materials | And 5 more authors.
Bioresource Technology | Year: 2013

Cork boiling wastewater pollutants were fractionated by sequential use of four ultrafiltration membranes and five fractions were obtained: four retentates (>100, 50-100, 20-50 and 10-20kDa) and one permeate (<10kDa); which were used to study the correlation of molecular size with biodegradability and toxicity before and after ozonation. The results show that molecular size is correlated with organic load and restrains biodegradability. The fraction with >100kDa corresponds to 56% of the organic load and the one with <10kDa only 8%. The biodegradability of fractions increased 182% with fractions molecular size reduction from >100 to <10kDa and the chemical oxygen demand (COD) was from 3436 to 386mgL-1. For biodegradability enhancement the best outcome of ozonation was obtained with compounds having molecular size >20kDa and range from 5% up to 175% for applied ozone doses to COD ratios between 0.15 and 0.38. © 2013 Elsevier Ltd. Source

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