Denim industry wastewater treatment by a heterogeneous solar-Fenton process catalyzed by Fe supported on recycled polyethylene terephthalate (PET) by ultrasonic modification.

The textile industry is an important economic sector; however, its wastewater generates a great impact on the environment. A heterogeneous solar Fenton (HSF) process was evaluated for denim wastewater treatment. The catalyst was obtained through ultrasonic modification of recycled polyethylene terephthalate (PET) with Fe nanoparticles (PET/NPs- Fe3O4). The SFH process was optimized using surface response methodology with a face-centered central composite design considering the effects of the hydraulic retention time (10, 25, and 40 min), hydrogen peroxide dosage (500, 1000, and 1500 mg/L), and mass of the packed catalyst (4, 6 and 8 g) on the color, COD, and turbidity removal efficiencies. The operating conditions for maximum COD removal were H2O2 541.7 mg/L, HRT 33.9 min, and PET/NPs- Fe3O4 dose 7.9 g with solar radiation. The removal of 91.2% COD, 86.2% color, 90.4% turbidity, and 81.9% TOC was obtained at 14.2 kJ/L QUva. PET modification yielded 1.6 mg Fe/g PET, and the modification method does not allow Fe leaching. The effluent obtained from the SFH process complies with the maximum permissible limits in Mexican legislation in terms of COD, TOC, turbidity, and color and allows the reuse of PET.

Evaluation of Photoelectrocatalysis with Electrode Based on Ti/RuO2-TiO2 Modified with Tin and Tantalum Oxides for the Degradation of Indigo Blue Dye.

Indigo Blue (IB) is a dye widely used by the textile sector for dyeing cellulose cotton fibers and jeans, being considered a recalcitrant substance, and therefore resistant to traditional treatments. Several methodologies are reported in the literature for the removal or degradation of dyes from the aqueous medium, among which photoelectrocatalysis stands out, which presents promising results in the degradation of dyes when a dimensionally stable anode (DSA) is used as a photoanode. In the present work, we sought to investigate the efficiency of a Ti/RuO2-TiO2 DSA modified with tin and tantalum for the degradation of Indigo Blue dye by photoelectrocatalysis. For this, electrodes were prepared by the thermal decomposition method and then a physical-chemical and electrochemical analysis of the material was carried out. The composition Ti/RuO2-TiO2-SnO2Ta2O5 (30:40:10:20) was compared to Ti/RuO2-TiO2 (30:70) in the photocatalysis, electrocatalysis, and photoelectrocatalysis tests. The photocatalysis was able to degrade only 63% of the IB at a concentration of 100 mg L-1 in 3 h, whereas the electrocatalysis and photoelectrocatalysis were able to degrade 100% of the IB at the same initial concentration in 65 and 60 min, respectively.

Evaluation and Predictive Modeling of Removal Condition for Bioadsorption of Indigo Blue Dye by Spirulina platensis.

Among the different chemical and physical treatments used to remove the color of the textile effluents, bioremediation offers many benefits to the environment. In this study, we determined the potential of Spirulina platensis (S. platensis) for decolorizing indigo blue dye under different incubation conditions. The microalgae were incubated at different pH (from 4 to 10) to calibrate for the optimal discoloration condition; a pH of 4 was found to be optimal. The biomass concentration in all experiments was 1 g/L, which was able to decolorize the indigo blue dye by day 3. These results showed that S. platensis is capable of removing indigo blue dye at low biomass. However, this was dependent on the treatment conditions, where temperature played the most crucial role. Two theoretical adsorption models, namely (1) a first-order model equation and (2) a second-order rate equation, were compared with observed adsorption vs. time curves for different initial concentrations (from 25 to 100 mg/L). The comparison between models showed similar accuracy and agreement with the experimental values. The observed adsorption isotherms for three temperatures (30, 40, and 50 °C) were plotted, showing fairly linear behavior in the measured range. The adsorption equilibrium isotherms were estimated, providing an initial description of the dye removal capacity of S. platensis.

Hybrid MF and membrane bioreactor process applied towards water and indigo reuse from denim textile wastewater.

This work investigates the application of a microfiltration (MF)-membrane bioreactor (MBR) hybrid process for textile dyeing process wastewater reclamation. The indigo blue dye was efficiently retained by the MF membrane (100%), which allows its recovery from the concentrate stream. MF promotes 100% of colour removal, and reduces the chemical oxygen demand (COD) and conductivity by about 65% and 25%, respectively, and improves the wastewater biodegradability. MF flux decline was mostly attributed to concentration polarization and the chemical cleaning was efficient enough to recover initial hydraulic resistance. The MBR provides to be a stable process maintaining its COD and ammonia removal efficiency (73% and 100%, respectively) mostly constant throughout and producing a permeate that meets the reuse criteria for some industry activities, such as washing-off and equipment washdown. The use of an MF or ultrafiltration (UF) membrane in the MBR does not impact the MBR performance in terms of COD removal. Although the membrane of MBR-UF shows permeability lower than MBR-MF membrane, the UF membrane contributes to a more stable operation in terms of permeability.

Adsorption-regeneration by heterogeneous Fenton process using modified carbon and clay materials for removal of indigo blue.

Indigo blue dye is mainly used in dyeing of denim clothes and its presence in water bodies could have adverse effects on the aquatic system; for this reason, the objective of this study was to promote the removal of indigo blue dye from aqueous solutions by iron and copper electrochemically modified clay and activated carbon and the saturated materials were regenerated by a Fenton-like process. Montmorillonite clay was modified at pH 2 and 7; activated carbon at pH 2 and pH of the system. The elemental X-ray dispersive spectroscopy analysis showed that the optimum pH for modification of montmorillonite with iron and copper was 7 and for activated carbon was 2. The dye used in this work was characterized by infrared. Unmodified and modified clay samples showed the highest removal efficiencies of the dye (90-100%) in the pH interval from 2 to 10 whereas the removal efficiencies decrease as pH increases for samples modified at pH 2. Unmodified clay and copper-modified activated carbon at pH 2 were the most efficient activated materials for the removal of the dye. The adsorption kinetics data of all materials were best adjusted to the pseudo-second-order model, indicating a chemisorption mechanism and the adsorption isotherms data showed that the materials have a heterogeneous surface. The iron-modified clay could be regenerated by a photo-Fenton-like process through four adsorption-regeneration cycles, with 90% removal efficiency.