Removal of Acid Orange 7 (AO7) by UV/H2O2 oxidation in the presence of dye auxiliaries
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies-I: Extraction & Remediation (T1-4P)
Keywords: Advanced oxidation processes; UV/H2O2; Acid Orange 7; kinetics
Colour removal from textile wastewater has been a matter of considerable interest during the last two decades, not only because of the potential toxicity of certain dyes but often due to their visibility in receiving waters and to their low biodegradability. Due to the limited success of some physical and chemical techniques for the treatment of dye effluents it is necessary to develop destructive systems leading to complete mineralization or, at least, to less harmful or easy-to-treat compounds. Advanced oxidation processes (AOP) employing hydrogen peroxide with UV-light have been found to be very effective in the degradation of dye pollutants (3) and are therefore one of the Best Available Techniques (BAT) for the treatment of waste waters from the textile industry (1).
A large percentage of the total emission load from textile industry activities is attributable to salts and carboxylic acids employed in the finishing mills (1). Although the effect of some dye auxiliary chemicals (2,4) has already been investigated on the removal of reactive dyes by different types of AOPs, their effect on the destruction of acid dyes needs to be evaluated. The aim of this experimental study is the analysis of the effect of dye auxiliary chemicals highly used in dyeing processes on the treatment of aqueous solutions of the dye Acid Orange 7 (AO7) by UV/H2O2 oxidation: sodium chloride, sodium sulphate, sodium carbonate and acetic acid.
In all the experiments the initial dye concentration was 150mg/L. The initial pH of the simulated dyehouse effluent was adjusted to 3. Previous experiments and literature reports established this pH value as optimum in the UV/H2O2 oxidation of acid dyes. The effect of the auxiliary chemicals (NaCl, Na2SO4, Na2CO3, CH3COOH) was investigated at three different concentrations (1, 5 and 10g/L) of each individual chemical in binary mixtures of AO7 and the auxiliary chemical, and finally in a complex mixture containing all the components.
Addition of sodium chloride, sodium sulphate and acetic acid decreased the removal efficiency of AO7, though no significant effect of Na2CO3 was observed. The effects were quantified through the variation of the pseudo-first order kinetic constant of the reaction of removal of AO7. The degradation rate diminished as the concentration of chloride increased, in the range o Cl- concentration 1<Cl-<5 g/L. Higher amounts of chloride had a minor effect on the kinetics of AO7 degradation. The chloride ions seems to act as hydroxyl radicals scavengers.
These results show the importance of considering the presence of auxiliary chemicals in the evaluation of UV/H2O2 oxidation process of real wastewaters of textile industries.
Acknowledgement
This research was financially supported by the Ministry of Education and Science (Spain) under projects PPQ2003-00934
References:
(1) B.R.E.F. Document. Integrated Pollution Prevention and Control (IPPC). Reference Document on Best Available Techniques for the Textile Industry. (November 2002).
(2) Kiwi, J. ; Lopez, A ; Nadtochenko, V.. Mechanism and Kinetics of the OH Radical Intervention during Fenton Oxidation in the Presence of a Significant Amount of Radical Scavenger (Cl-). (2000) Env. Sci. Technol.. 34, 2162-2168.
(3) Advanced oxidation processes for water and wastewater treatment. (2004) Ed: S.Parsons. I.W.A. Pub.
(4) Arslan, I.; Kornmuller, A.; Jekel, M.R.. Ozonation of Spent Reactive Dye-Baths: Effect of HCO3-/CO32- Alkalinity. (2002). J. Env. Eng.. 128
Presented Monday 17, 13:30 to 15:00, in session Sustainable & Clean technologies - I: Extraction-Remediation (T1-4P).
