Mineralization of hetero bi-functional reactive dye in aqueous solution by Fenton and photo-Fenton reactions.

This study focused on the advanced oxidation of the hetero bi-functional reactive dye Sumifix Supra Yellow 3RF (CI Reactive Yellow 145) using dark Fenton and photo-Fenton conditions in a lab-scale experiment. A 2(3) factorial design was used to evaluate the effects of the three key factors: temperature, Fe(II) and H2O2 concentrations, for a dye concentration of 250 mg L(-1) with chemical oxygen demand (COD) of 172 mg L(-1) O2 at pH=3. The response function was the COD reduction. This methodology lets us find the effects and interactions of the studied variables and their roles in the efficiency of the treatment process. In the optimization, the correlation coefficients for the model (R2) were 0.948 and 0.965 for Fenton and photo-Fenton treatments, respectively. Under optimized reaction conditions: pH=3, temperature=298 K, [H2O2]=11.765 mM and [Fe(II)]=1.075 mM; 60 min of treatment resulted in a 79% and 92.2% decrease in COD, for the dye taken as the model organic compound, after Fenton and photo-Fenton treatments, respectively.

Degradation pathways of the commercial reactive azo dye Procion Red H-E7B under solar-assisted photo-Fenton reaction.

Reactive azo dye Procion Red H-E7B solutions have been submitted to solar-assisted photo-Fenton degradation. The solution color quickly disappears, indicating a fast degradation of the azo group. Nevertheless, complete DOC removal was not accomplished, in accordance with the presence of resistant triazine rings at the end of the reaction. The intermediates generated along the reaction time have been identified and quantified. LC-(ESI)-TOF-MS analysis allowed the detection of 18 aromatic compounds of different size and complexity. Some of them shared the same accurate mass, and consequently, the same empirical formula, but appeared at different chromatographic retention times, evidencing their different molecular structures. Heteroatom oxidation products like NH4+, NO3-, Cl-, and SO4(2-) have also been quantified and explanations of their release are proposed. Short chain carboxylic acids are also detected at long reaction times, as a previous step to complete dye mineralization. A link between the disappearance of the largest intermediate products and the increase of the solutions biodegradability has been established. Finally, taking into account all the findings of the present study and previous related works, the evolution from the original dye to the final products (triazine and CO2) is proposed in a general reaction scheme.

The testing of several biological and chemical coupled treatments for Cibacron Red FN-R azo dye removal.

Several biological and chemical coupled treatments for Cibacron Red FN-R reactive azo dye degradation have been evaluated. Initially, a two-stage anaerobic-aerobic biotreatment has been assessed for different dye concentrations (250, 1250 and 3135 mg l(-1)). 92-97% decolourisation was attained during the anaerobic digestion operating in batch mode. However, no dissolved organic carbon (DOC) removal neither biogas production was observed during the process, indicating that no methanogenesis occurred. Additionally, according to Biotox and Zahn-Wellens assays, the anaerobically generated colourless solutions (presumably containing the resulting aromatic amines from azo bond cleavage) were found to be more toxic than the initial dye as well as aerobically non-biodegradable, thus impeding the anaerobic-aerobic biological treatment. In a second part, the use of an advanced oxidation process (AOP) like photo-Fenton or ozonation as a chemical post-treatments of the anaerobic process has been considered for the complete dye by-products mineralisation. The best results were obtained by means of ozonation at pH 10.5, achieving a global 83% mineralisation and giving place to a final harmless effluent. On the contrary, the tested photo-Fenton conditions were not efficient enough to complete oxidation.

Environmental assessment of different photo-Fenton approaches for commercial reactive dye removal.

An environmental study using life cycle assessment (LCA) has been applied to three bench-scale wastewater treatments for Cibacron Red FN-R hetero-bireactive dye removal: artificial light photo-Fenton process, solar driven photo-Fenton process and artificial light photo-Fenton process coupled to a biological treatment. The study is focused on electricity and chemicals consumption, transports and atmosphere and water emissions generated by the different processes involved. Results show that the artificial light photo-Fenton process is the worst treatment in terms of environmental impact. On the other hand, both solar driven and coupled to biological photo-Fenton processes reduce significantly the environmental damage, although none can be identified as the best in all impact categories. The major environmental impact is attributed to the H2O2 consumption and to the electrical energy consumption to run the UVA lamp. An economic analysis of the different photo-Fenton processes has also been performed and the results are discussed together with those obtained from the environmental assessment.

Environmental assessment of different advanced oxidation processes applied to a bleaching Kraft mill effluent.

Different advanced oxidation processes (AOPs) have been applied to remove the organic carbon content of a paper mill effluent originating from the Kraft pulp bleaching process. The considered AOPs were: TiO(2)-mediated heterogeneous photocatalysis, TiO(2)-mediated heterogeneous photocatalysis assisted with H(2)O(2), TiO(2)-mediated heterogeneous photocatalysis coupled with Fenton, photo-Fenton, ozonation and ozonation with UV-A light irradiation. The application of the selected AOPs all resulted in a considerable decrease in dissolved organic carbon (DOC) content with variable treatment efficiencies depending upon the nature/type of the applied AOP. A Life Cycle Assessment (LCA) study was used as a tool to compare the different AOPs in terms of their environmental impact. Heterogeneous photocatalysis coupled with the Fenton's reagent proved to have the lowest environmental impact accompanied with a moderate-to-high DOC removal rate. On the other hand, heterogeneous photocatalysis appeared to be the worst AOP both in terms of DOC abatement rate and environmental impact. For the studied AOPs, LCA has indicated that the environmental impact was attributable to the high electrical energy (power) consumption necessary to run a UV-A lamp or to produce ozone.

Degradation of Procion Red H-E7B reactive dye by coupling a photo-Fenton system with a sequencing batch reactor.

A bench-scale study combining photo-Fenton reaction with an aerobic sequencing batch reactor (SBR) to degrade a commercial homo-bireactive dye (Procion Red H-E7B, 250mgl(-1)) was investigated. The photo-Fenton process was applied as a pre-treatment, avoiding complete mineralisation, just to obtain a bio-compatible water able to be treated by means of the SBR in a second step. In this sense, different Fenton reagent concentrations were assessed by following dye solution biodegradability enhancement (BOD(5)/COD), as well as the toxicity (EC(50)), DOC, colour (Abs(543.5)) and H(2)O(2) evolution with photo-Fenton irradiation time. Obtained pre-treated solutions were biologically oxidized in a SBR containing non-acclimated activated sludge. Different hydraulic retention time (HRT) in the bioreactor were tested to attain the maximum organic load removal efficiency. Best results were obtained with 60min of 10mgl(-1) Fe(II) and 125mgl(-1) H(2)O(2) photo-Fenton pre-treatment and 1 day HRT in SBR.

Experimental design of Fenton and photo-Fenton reactions for the treatment of cellulose bleaching effluents.

Multivariate experimental design was applied to the treatment of a cellulose conventional bleaching effluent in order to evaluate the use of the Fenton reagent under solar light irradiation. The effluent was characterised by the general parameters total organic carbon (TOC), chemical oxygen demand and color, and it was analysed for chlorinated low molecular weight compounds using GC-MS. The main parameters that govern the complex reactive system: Fe(II) and H(2)O(2) initial concentration, and temperature were simultaneously studied. Factorial experimental design allowed to assign the weight of each variable in the TOC removal after 15 min of reaction. Temperature had an important effect in the organic matter degradation, especially when the ratio of Fenton reagents was not properly chosen. Fenton reagent under solar irradiation proved to be highly effective for these types of wastewaters. A 90% TOC reduction was achieved in only 15 min of treatment. In addition, the GC-MS analysis showed the elimination of the chlorinated organic compounds initially detected in the studied bleaching effluents.

Fenton and photo-Fenton oxidation of textile effluents.

The simultaneous use of Fenton reagent and irradiation for the treatment of textile wastewaters generated during a hydrogen peroxide bleaching process is investigated. The experimental conditions tested during this study provide the simultaneous occurrence of Fenton, Fenton-like and photo-Fenton reactions. The batch experimental results are assessed in terms of total organic carbon reduction. Identification of some of the chemical constituents of the effluent was performed by means of GC-MS. Other pollution related features of the initial effluent-like COD and color were also measured. The main parameters that govern the complex reactive system, i.e., light intensity, temperature, pH, Fe(II) and H2O2 initial concentrations have been studied. Concentrations of Fe(II) between 0 and 400 ppm, and H2O2 between 0 and 10,000 ppm were used. Temperatures above 25 degrees C and up to 70 degrees C show a beneficial effect on organic load reduction. A set of experiments was conducted under different light sources with the aim to ensure the efficiency of using solar light irradiation. The combination of Fenton, Fenton-like and photon-Fenton reactions has been proved to be highly effective for the treatment of such a type of wastewaters, and several advantages for the technique application arise from the study.