Conducting polypyrrole films as a potential tool for electrochemical treatment of azo dyes in textile wastewaters

Spectral deconvolution associated to the Gaussian fit as a tool for the optimization of photovoltaic electrocoagulation applied in the treatment of textile dyes

The objective of this study was to investigate the color removal in a binary mixture of azo dyes from the photovoltaic electrocoagulation (EC) technique, using spectral deconvolution and the Gaussian fit for qualitative and quantitative determination of the physical color parameter. Initially, a conventional energy source was used to feed the EC reactor and the experimental design was conducted according to the Rotational Central Compound Design (RCCD). The spectral deconvolution method associated to the Gaussian fit aided in the description of the composition of the sample matrix, In the first step, through the Analysis of Variance, the RCCD and the three-dimensional surface response graphs, the optimized operating conditions were identified, which corresponded to 1320 A m^-2 with an reaction time of 16.6 min, and an expected removal of 98.40% for Scarlet Red (SR) dye and 1160 A m^-2 with a run time of 15.7 min and 97.9% removal for Turquoise Blue (TB) dye. Using the photovoltaic module as the power source of the EC reactor, a maximum removal of 97 ± 0.43% for TB dye and 98% ± 0.81 for SR was obtained. The results encourage the applicability of photovoltaic module-fed EC technology as a promising alternative for the treatment of effluents containing textile dyes, as well as the use of the spectral deconvolution method associated with the Gaussian fit, for the reliability and precision of the results.

Removing Disperse red 60 and Reactive blue 19 dyes removal by using Alcea rosea root mucilage as a natural coagulant

In terms of health, dyes have carcinogenic, mutagenic and toxic properties and can have adverse effects on health and the environment. Therefore, sewage containing to dyes must be purified before being discharged into the environment. The current study aimed to investigate the effectiveness of Alcea rosea root extract in Disperse red 60 and Reactive blue 19 dyes removal from synthetic sewage. In this study, the effect of different indices including pH (5–11), Alcea rosea concentration (50–300 mg/L) and initial dye concentration (10–80 mg/L) was investigated. During the tests, the coagulant was stirred with rapid mixing at a speed of 250 rpm for 2 min. In the following, the speed (30–60 rpm) and the time (10–25 min) were used for slow mixing and after mixing the effect of settling time (10–60 min) and temperature (20–70) on removal efficiency of Disperse and Reactive dyes was investigated. The results showed that the maximum of removal efficiency of Disperse and Reactive dyes in optimum conditions including (pH = 11, coagulant concentration = 200 and 250 mg/L, dye concentration 40 and 20 mg/L, speed 60 rpm, during 15 min with settling time 60 min and temperature 60 °C obtained 86% and 68%, respectively. According to the result, the Alcea rosea coagulant has the best ability in removing dyes from aqueous solutions and sewage, especially Disperse dyes. Disperse dye is much eliminated in the coagulation process due to its lower solubility, higher suspending materials and less required solved chemical oxygen demand to the total chemical oxygen demand (SCOD/TCOD).

Oxidant-templating fabrication of pure polypyrrole hydrogel beads as a highly efficient dye adsorbent

Polypyrrole (PPY) is a type of dye adsorbent with good adsorbing capability. Fabrication of PPY with a porous architecture, though technically challenging, can further enhance its dye adsorbing capability due to the tremendous increase of surface area. In this manuscript, an oxidant-templating strategy was developed to fabricate pure PPY hydrogel (PHG) beads comprising nanofibrous networks, which were utilized as highly efficient dye absorbents. For instance, PPY hydrogel beads showed a maximum adsorption capacity of 236.9 mg g-1 for methyl orange (MO), which was significantly higher than that of PPY powder. The minimal effective concentration of MO for the adsorption was as low as 0.4 ppm. Besides that, the PPY hydrogel beads displayed good regeneration performance for adsorbing organic dyes. Thus, the PPY hydrogel beads with low solid contents and large surface area could be considered as a promising organic dye absorbent for wastewater treatment in various industrial fields.

Fabrication of NiFe2O4 magnetic nanoparticles loaded on activated carbon as novel nanoadsorbent for Direct Red 31 and Direct Blue 78 adsorption

In this research, magnetic nickel ferrite NiFe₂O₄/hazelnut-shell-based activated carbon (NiFe₂O₄/AC) was used to eliminate anionic dyes (Direct Red 31(DR31) and Direct Blue 78 (DB78)) from aqueous solution. The morphological, structural, particle size and surface charge properties of as-prepared nanoadsorbent were characterized. TEM (Transmission electron microscopy) images revealed that the size of NiFe₂O₄ particles in the structure of AC was in the range of 8-12 nm, which is compatible with the results obtained by the analysis of DLS (Dynamic light scattering). The results of the BET (Brunauer-Emmett-Teller) analysis indicated that the surface area, the pore volume and average pore diameters of the NiFe₂O₄ were 288 m²/g, 0.3338 cm³/g and 5.05nm, respectively. The as-prepared nanocomposite showed excellent adsorption capacity for DR31 and DB78 dyes with the highest adsorption capacity obtained at pH=2.0 and rapid dye adsorption equilibrium attained after 20 and 25 min for DR31 and DB78, respectively. The equilibrium study showed the maximum adsorption capacity (q_max) of 299.67 mg/g and 209.13 mg/g for DR31 and DB78, respectively. In addition, thermodynamic study revealed the endothermic and spontaneous nature of adsorption process. The adsorption of DR31 and DB78 onto the NiFe₂O₄/AC is a physisorption process, during which electrostatic adsorption was the main driving force.

Pretreatment technologies for industrial effluents: Critical review on bioenergy production and environmental concerns

The implementation of different pretreatment techniques and technologies prior to effluent discharge is a direct result of the inefficiency of several existing wastewater treatment methods. A majority of the industrial sectors have known to cause severe negative effects on the environment. The five major polluting industries are the paper and pulp mills, coal manufacturing facilities, petrochemical, textile and the pharmaceutical sectors. Pretreatment methods have been widely used in order to lower the toxicity levels of effluents and comply with environmental standards. In this review, the possible environmental benefits and concerns of adopting different pretreatment technologies for renewable energy production and product/resource recovery has been reviewed and discussed.

Enhanced decolorization of methyl orange in aqueous solution using iron-carbon micro-electrolysis activation of sodium persulfate

Reactivity of sodium persulfate (PS) in the decolorization of methyl orange (MO) in aqueous solution using an iron-carbon micro-electrolysis (ICE) method was investigated. The effects of sodium persulfate doses, pH, Fe-to-C mass ratios, initial MO concentration as well as the reaction temperature were comprehensively studied in batch experiments. The ICE-PS coupled process was more suitable for wide ranges of pH, initial MO concentration and reaction temperature, accompanied by the reduction of Fe compared ICE. The MO removal efficiency improved substantially by ICE-PS technique, 76.03% for ICE and 91.27% for ICE-PS at experimental conditions of pH 3.0, Fe-to-C mass ratio 3:1, PS addition 10 mM and initial MO concentration 0.61 mM. Furthermore, the biodegradability index (BI) dramatically increased from 0.26 to 0.65. The binary hydroxyl and sulfate radicals that non-selectively degrade MO to the derivatives with small molecules are ascribed to ICE-PS method as detected by the UV-vis spectra. The PS activation resource was Fe²⁺ through the hydroxyl radical quenching reaction by the additive tert-butanol (TBA). This study provides an in-depth theoretical understanding of the development and wide commercial application of the ICE technology to refractory industrial dye wastewater treatment.

Electrochemical Oxidation of EDTA in Nuclear Wastewater Using Platinum Supported on Activated Carbon Fibers

A novel Pt/ACF (Pt supported on activated carbon fibers) electrode was successfully prepared with impregnation and electrodeposition method. Characterization of the electrodes indicated that the Pt/ACF electrode had a larger effective area and more active sites. Electrochemical degradation of ethylenediaminetetra-acetic acid (EDTA) in aqueous solution with Pt/ACF electrodes was investigated. The results showed that the 3% Pt/ACF electrode had a better effect on EDTA removal. The operational parameters influencing the electrochemical degradation of EDTA with 3% Pt/ACF electrode were optimized and the optimal removal of EDTA and chemical oxygen demand (COD) were 94% and 60% after 100 min on condition of the electrolyte concentration, initial concentration of EDTA, current density and initial value of pH were 0.1 mol/L, 300 mg/L, 40 mA/cm² and 5.0, respectively. The degradation intermediates of EDTA in electrochemical oxidation with 3% Pt/ACF electrode were identified by gas chromatography-mass spectrum (GC-MS).

A method for dye extraction using an aqueous two-phase system: Effect of co-occurrence of contaminants in textile industry wastewater

This paper reports a green and efficient procedure for extraction of the dyes Malachite Green (MG), Methylene Blue (MB), and Reactive Red 195 (RR) using an aqueous two-phase system (ATPS). An ATPS consists mainly of water, together with polymer and salt, and does not employ any organic solvent. The extraction efficiency was evaluated by means of the partition coefficients (K) and residual percentages (%R) of the dyes, under different experimental conditions, varying the tie-line length (TLL) of the system, the pH, the type of ATPS-forming electrolyte, and the type of ATPS-forming polymer. For MG, the best removal (K = 4.10 × 10(4), %R = 0.0069%) was obtained with the ATPS: PEO 1500 + Na2C4H4O6 (TLL = 50.21% (w/w), pH = 6.00). For MB, the maximum extraction (K = 559.9, %R = 0.258%) was achieved with the ATPS: PEO 400 + Na2SO4 (TLL = 50.31% (w/w), pH = 1.00). Finally for RR, the method that presented the best results (K = 3.75 × 10(4), %R = 0.237%) was the ATPS: PEO 400 + Na2SO4 (TLL = 50.31% (w/w), pH = 6.00). The method was applied to the recovery of these dyes from a textile effluent sample, resulting in values of K of 1.17 × 10(4), 724.1, and 3.98 × 10(4) for MG, MB, and RR, respectively, while the corresponding %R values were 0.0038, 0.154, and 0.023%, respectively. In addition, the ATPS methodology provided a high degree of color removal (96.5-97.95%) from the textile effluent.

The Structural, Photocatalytic Property Characterization and Enhanced Photocatalytic Activities of Novel Photocatalysts Bi₂GaSbO₇ and Bi₂InSbO₇ during Visible Light Irradiation

In order to develop original and efficient visible light response photocatalysts for degrading organic pollutants in wastewater, new photocatalysts Bi₂GaSbO₇ and Bi₂InSbO₇ were firstly synthesized by a solid-state reaction method and their chemical, physical and structural properties were characterized. Bi₂GaSbO₇ and Bi₂InSbO₇ were crystallized with a pyrochlore-type structure and the lattice parameter of Bi₂GaSbO₇ or Bi₂InSbO₇ was 10.356497 Å or 10.666031 Å. The band gap of Bi₂GaSbO₇ or Bi₂InSbO₇ was estimated to be 2.59 eV or 2.54 eV. Compared with nitrogen doped TiO₂, Bi₂GaSbO₇ and Bi₂InSbO₇, both showed excellent photocatalytic activities for degrading methylene blue during visible light irradiation due to their narrower band gaps and higher crystallization perfection. Bi₂GaSbO₇ showed higher catalytic activity compared with Bi₂InSbO₇. The photocatalytic degradation of methylene blue followed by the first-order reaction kinetics and the first-order rate constant was 0.01470 min⁻¹, 0.00967 min⁻¹ or 0.00259 min⁻¹ with Bi₂GaSbO₇, Bi₂InSbO₇ or nitrogen doped TiO₂ as a catalyst. The evolution of CO₂ and the removal of total organic carbon were successfully measured and these results indicated continuous mineralization of methylene blue during the photocatalytic process. The possible degradation scheme and pathway of methylene blue was also analyzed. Bi₂GaSbO₇ and Bi₂InSbO₇ photocatalysts both had great potential to purify textile industry wastewater.

Enhanced coagulation-photocatalytic treatment of Acid red 73 dye and real textile wastewater using UVA/synthesized MgO nanoparticles

Sequencing coagulation - photocatalytic degradation using UVA/MgO nanoparticles process was investigated for Acid red 73dye removal and then treatment of a real textile wastewater. Effective operational parameters including pH and coagulant and photocatalyst dosage were studied in synthetic wastewater and then the process was applied for real wastewater. Both coagulation and photocatalytic processes were pH dependent. At coagulant dosage of 200 mg/L and initial pH of 6, the dye concentration decreased from 200 to 31 mg/L. Complete removal of AR73 was observed with MgO nanoparticles of 0.8 g/L, initial pH of 5 and reaction time of 60 min. Langmuir-Hinshelwood model was well fitted with removal results (R(2): 0.939-0.988 for different initial dye concentration). In the case of real textile wastewater, the sequence coagulation-UVA/MgO nanoparticles photocatalytic degradation yielded considerable total COD and TOC removal 98.3% and 86.9%respectively, after 300 min.

Mn2+ oxidation, playing counteractive role in electro-oxidation of ammonia, hinders the generation of free chlorine

The influence of coexisting metal ions on NH₃ removal and the concentration changes of intermediate products was explored. The removal rate of NH₃ reached 93.57% by removing Mn²⁺ which seriously affected NH₃ removal.

Facile synthesis of methyl propylaminopropanoate functionalized magnetic nanoparticles for removal of acid red 114 from aqueous solution

The removal of AR-114 from aqueous solution by novel nano-adsorbent Fe₃O₄@SiO₂–MPAP through hydrogen bonding interactions.

Role of surfactant derived intermediates in the efficacy and mechanism for radiation chemical degradation of a hydrophobic azo dye, 1-phenylazo-2-naphthol

A combined methodology involving gamma and pulse radiolysis, product analysis and toxicity studies has been adopted to comprehend the degradation process of a model hydrophobic azo dye, 1-phenylazo-2-naphthol, emphasizing the role of the surfactant, which is an integral part of textile waste. Two new and important findings are underlined in this article. The first is the direct attestation of the hydrazyl radical-parent adduct, formed in the reaction of the dye with e(-)aq followed by protonation and subsequent addition to the unreacted dye molecule. This has been confirmed from concentration dependent studies. Secondly, we have clearly shown that in the reaction of hydroxyl radical with the dye in Triton X-100 media, the initially produced TX radicals cause reductive degradation of the dye. Identification and detailed analysis of HPLC and GCMS data reveals that similar products are formed in both the reactions of e(-)aq and OH radicals. Moreover, the cytotoxicity of 10(-4)moldm(-3) dye was found to be reduced significantly after irradiation. Thus, the present study not only depicts new pathways for the degradation of hydrophobic azo dye, but also demonstrates the role of a surfactant in the entire process.