I. Arslan

Advanced chemical oxidation of reactive dyes in simulated dyehouse effluents by ferrioxalate-Fenton/UV-A and TiO2/UV-A processes

Abstract Effective degradation of various mono- and bifunctional aminochlorotriazine reactive dyes in simulated dyehouse wastewater was achieved by the application of ferrioxalate-photo-Fenton [Fe(C 2 O 4 ) 3 3− /H 2 O 2 /UV-A; 300 nm>λ>400 nm] and titanium dioxide-mediated heterogeneous photocatalytic (TiO 2 /UV-A) treatment processes. These so-called advanced oxidation processes were studied in a novel batch photoreactor that was irradiated by a solar simulating installation. Decolorization by the ferrioxalate-photo-Fenton oxidation process was found to proceed three times faster than the photocatalytic process, while the latter was more efficient in reducing the optical density at 280 nm wavelength (UV 280nm ). Complete decolourization and partial mineralization with 17–23% total organic carbon (TOC) and 73–86% UV 280nm removals were achieved by the ferrioxalate-Fenton/UV-A and TiO 2 /UV-A processes, respectively, within a 1-h treatment time. Emphasis was placed on the effect of dyehouse effluent strength on decolourization kinetics, along with possible advantages of the ferrioxalate-Fenton/UV-A process over the conventional photo-Fenton (Fe 2+ /H 2 O 2 /UV-C) process. The results of these experiments showed that the more dilute the dyehouse effluent the faster the decolourization rate. On the basis of spectrophotometric measurements, dye decomposition could be successfully fitted to the empirical Langmuir–Hinshelwood kinetic model.

DEGRADATION OF COMMERCIAL REACTIVE DYESTUFFS BY HETEROGENOUS AND HOMOGENOUS ADVANCED OXIDATION PROCESSES: A COMPARATIVE STUDY

Advanced oxidation of the commercially available reactive dyestuffs Remazol Black B and Remazol Turquoise Blue G 133 in aqueous solution with TiO2-mediated photocatalytic and photoinduced and dark Fenton/Fenton-like reactions has been studied. Initial decolourization rates, effectiveness in removal of UV254 nm, COD as well as TOC were compared and evaluated. It was found that all advanced oxidation systems were capable of completely decolourizing the azo dye Remazol Black in feasible treatment times and at concentrations typically found in dyehouse effluents, whereas COD and TOC removal efficiencies ranged between 77–98% and 51–86%, respectively. Photo-Fentons oxidation gave the best decolourization reaction, which proceeded 20 times faster than TiO2-mediated photocatalytic oxidation. Moreover, photocatalytical treatment of Remazol Black followed the empirical Langmuir–Hinshelwood kinetics in the concentration range 25–100 mg/l. However, none of the advanced oxidation systems was effective in the degradation of the copper phthalocyanine dye Remazol Turquoise Blue for which colour and COD removal was mainly attributable to adsorption on the photocatalyst surface or the coagulating effect of iron applied in the homogenous advanced oxidation reactions.

Effect of common reactive dye auxiliaries on the ozonation of dyehouse effluents containing vinylsulphone and aminochlorotriazine dyes

Abstract Ozonation of the commercially important reactive dyes Procion yellow HE4R (Reactive Yellow 84) and Remazol Black SB (Reactive Black 5) in actual dye rinse waters and simulated exhausted dye bath liquors has been studied. The effect of common dye auxiliaries (NaCl and Na2CO3) as well as the initial dye concentration on advanced oxidation kinetics was investigated. Decolourization was complete within a few minutes of ozonation in all cases whereas UV254 (absorbance at 254 nm wavelength), COD and TOC removals required higher ozone doses. It was found that NaCl did not affect the ozonation process at the present reaction conditions, whereas the addition of Na2CO3 resulted in a significant inhibition in the abatement of all selected process parameters except decolourization. Increasing the initial dye concentration had an even more negative effect on decolourization, oxidation and mineralization kinetics. A simple kinetic model describing the effect of inhibitor concentrations on COD and/or colour removal rate constants has been proposed.

Advanced oxidation of raw and biotreated textile industry wastewater with O3, H2O2 /UV-C and their sequential application

The advanced chemical oxidation of raw and biologically pretreated textile wastewater by (1) ozonation, (2) H2O2 /UV − C oxidation and (3) sequential application of ozonation followed by H2O2 /UV − C oxidation was investigated at the natural pH values (8 and 11) of the textile effluents for 1 h. Analysis of the reduction in the pollution load was followed by total environmental parameters such as TOC, COD, UV–VIS absorption kinetics and the biodegradability factor, fB. The successive treatment combination, where a preliminary ozonation step was carried out prior to H2O2 /UV − C oxidation without changing the total treatment time, enhanced the COD and TOC removal efficiency of the H2O2 /UV − C oxidation by a factor of 13 and 4, respectively, for the raw wastewater. In the case of biotreated textile effluent, a preliminary ozonation step increased COD removal of the H2O2 /UV − C treatment system from 15% to 62%, and TOC removal from 0% to 34%. However, the sequential process did not appear to be more effective than applying a single ozonation step in terms of TOC abatement rates. Enhancement of the biodegradability factor (fB) was more pronounced for the biologically pretreated wastewater with an almost two-fold increase for the optimized Advanced Oxidation Technologies (AOTs). For H2O2 /UV − C oxidation of raw textile wastewater, apparent zero order COD removal rate constants (kapp), and the second order OH· formation rates (ri) have been calculated. © 2001 Society of Chemical Industry

Oxidative treatment of simulated dyehouse effluent by uv and near-UV light assisted Fenton's reagent

UV/Fenton, near-UV-visible/Fenton, dark Fenton, and H2O2/UV reactions have been used to treat simulated dyehouse effluents representing wastewater from the textile dyeing and rinsing process. Experiments were carried out in a lab - scale photochemical reactor using concentrations of 0.5–25 mM H2O2, 0.04-0.5 mM Fe2+-ion and different dilutions of textile wastewater. To assess the extent of mineralization, decolourization kinetics and the effect of different fight sources on treatment efficiency, DOC, optical density at 254 nm and 600 nm wavelength and residual H2O2 concentrations were measured during the course of the advanced oxidation reactions. Comparative evaluation of the obtained results revealed that the decolourization rate increased with applied H2O2 and Fe2+-ion dose as well as the strength of the synthetic textile wastewater. The best results were obtained by the near - UV/visible/Fenton process with a decolourization rate constant of 1.57 min−1, a UV254nm reduction of 97% and a DOC removal of 41% at relatively low doses of the H2O2 oxidant and Fe2+-ion catalyst within 60 min treatment time.

Advanced Oxidation of Synthetic Dyehouse Effluent by O3, H2O2/O3 and H2O2/UV Processes

Ozonation, hydrogen peroxide combination with ozone, and UV light processes were investigated for the treatment of synthetic dyehouse effluent containing six reactive dyestuffs and their assisting chemicals. The decrease in DOC, UV - absorbance at 254 nm, decolourization kinetics, and acute toxicity towards the bioluminescent marine bacteria Vibrio fischeri were used to examine the treatment performance of these oxidation processes. Data indicated that in all examined processes rapid and complete decolourization could be achieved, but optimum oxidation conditions such as H2O2 dose and reaction pH had to be established for effective treatment. Toxicity of the samples decreased abruptly to non - detectable levels during the first minutes of all advanced oxidation processes. However, none of the oxidation combinations was able to bring about effective mineralization of the wastewater within 60 min reaction period. For comparative purposes, the electrical energy requirements per order of pollutant removal wer...

Application of photocatalytic oxidation treatment to pretreated and raw effluents from the Kraft bleaching process and textile industry

Abstract Treatability of mixed raw, coagulated and biologically pretreated textile and pulp wastewater and effluents from different process stages by enhanced heterogenous photocatalytic oxidation process was investigated. Treatment performances have been evaluated in terms of COD, TOC, BOD5, and colour removal. Results clearly indicate that photocatalytic oxidation process enhanced with 15 mM H2O2 was more efficient in removal of pollutants for pretreated wastewater samples. By the application of photocatalytic treatment, 52 and 87% COD removals were obtained for biotreated Kraft bleaching and textile effluents, respectively. Addition of only 1 mM ferric ion speeded up the oxidation time of the textile effluent significantly, but it had no impact on total COD reduction. While complete colour removal of the textile wastewater was achieved within the first hour of photocatalytic treatment, complete decolourisation could not be obtained for pulp effluents, except for the coagulated wastewater throughout the reaction period. Biologically pretreated textile wastewater was found to have potential for reuse after photocatalytic treatment.

Treatability of simulated reactive dye‐bath wastewater by photochemical and non‐photochemical advanced oxidation processes

Abstract A number of photochemical and non‐photochemical advanced oxidation processes were employed for the treatment of simulated dyehouse effluents containing six commercial reactive dyestuffs and various assisting chemicals at concentrations typically found in the textile dyeing and rinsing process stages. Effects of oxidant (H2O2) and catalyst (Fe2+‐ion) dose on decolourization kinetics, reduction in UV254nm and DOC were evaluated for each oxidation process. Treatment efficiencies were also assessed in terms of EE/O and EE/M values to compare electrical energy requirements of the investigated AOPs. UV‐light assisted treatment processes were found more effective in DOC and UV254nm removal, whereas the non‐photochemical O3/OH‐ and O3/H2O2 oxidation systems were significantly faster in decolourization of the dyehouse effluent than the H2O2/UV treatment process. Results clearly revealed that once optimal reaction conditions were established, the inhibiting effect of the complex wastewater matrix could be overcome and dyehouse effluent ingredients degraded successfully by all examined AOPs at feasible treatment times and electrical energy consumption.

Photochemical and Photocatalytic Detoxification of Reactive Dyebath Wastewater by the Fenton’s Reagent and Novel TiO2 Powders

The study described herein aimed to investigate the homogeneous (Fenton/UV-C) and heterogeneous (TiO2/UV-A) advanced oxidation of commonly used reactive dyestuffs in simulated dyebath effluents. For the Photo Fenton (Fe2+/H2O2/UV-C) reaction the effect of the initial H2O2 dose on the oxidative reaction rates was examined. Further, the photocatalytic treatment efficiency of two novel anatase TiO2, powders (Millennium PC 500 and Sachtleben Mikroanatas) and platinized Degussa P25 TiO2, type were compared with that of the more conventional P25 at different reaction pH’s. In the case of the Photo Fenton reactions, the treatment performance was strongly affected by the initial H2O2, concentration, whereas for the TiO2/UV-A process only the PC 500 TiO2, powder exhibited a significantly pH dependent reaction efficiency. The decolourization rates followed the decreasing order of Fenton/UV-C > Pt-P25/UV-A > Mikroanatas/UV-A > P25/UV-A > PC 500/UV-A, whereas the decreasing order for TOC removal efficiency was Fenton/UV-C > Mikroanatas/UV-A > Pt-P25/UV-A > P25/UV-A > PC 500/UV-A for the selected reaction conditions. Removal of optical density at 254 nm wavelength ranged between 75 % (Mikroanatas/UV-A) and 96 % (P25/UV-A).