Investigating electrode arrangement and anode role on dye removal efficiency of electro-peroxone as an environmental friendly technology

Comparing removal of synthetic anthraquinone dye wastewater in an electrical discharge and UV-LED/WO3 reactors: using statistical Taguchi optimization approach

Advanced oxidation processes (AOPs) are an available solution for the rapid growth of the water pollution problem. In the present study, the process of UV-LED/WO3 and plasma was comparatively studied to remove reactive blue 19. The photocatalyst process efficiency was analyzed by statistical Taguchi model. The effect of experimental variables of contact time, pH, catalyst dosage, and pollutant dosage was investigated and found that the model is able to explain the process due to the high value of R > 95%, and the optimum condition was at 10 mg/L of dye concentration, 1g/L of catalyst, and 180 min of detention time in which over 75% of degradation was achieved. Based on the model, the more reaction time would increase the reactor performance, while further excessive increase of catalyst dosage over 1 g/L would deteriorate the performance. Obviously, the least amount of pollutant is the most favorable for the treatment reactor. Using plasma process for dye degradation was the next step of the research. Accordingly, the removal rate achieved over 90% of 10 mg/L of initial industrial dye in durational time of 4 min, input voltage 13.5 kV, and pH = 2. The results showed the higher oxidizing capacity of plasma than the conventional photocatalyst process.

Treatment of synthetic textile wastewater containing Acid Red 182 by electro-Peroxone process using RSM

The Azo dyes are primarily utilized in textile industries. Treatment of textile wastewater because of the presence of recalcitrant dyes using conventional processes is greatly challenging and ineffective. So far, no experimental work has been conducted on the decolorization of Acid Red 182 (AR182) in aqueous media. Hence, in this novel experimental work, the treatment of AR182 from the Azo dyes family was explored using the electro-Peroxone (EP) process. For the optimization of operating factors, including AR182 concentration, pH, applied current, and O3 flowrate in the decolorization of AR182, Central Composite Design (CCD) was utilized. The statistical optimization presented a highly satisfactory determination coefficient value and a satisfactory second-order model. The expected optimum conditions by the experimental design were as the following: AR182 concentration at 483.12 mg.L-1, applied current at 0.627,113 A, pH at 8.18284 and O3 flowrate at 1.13548 L min-1. The current density is directly proportional to dye removal. However, increasing the amount of applied current beyond a critical value has a contradictory impact on dye removal performance. The dye removal performance in both acidic and highly alkaline environments was negligible. Hence, ascertaining the optimum pH value and conduction of the experiment at that point is critical. At optimum points, the decolorization performance in predicted and experimental conditions for AR182 were 99 and 98.5%, respectively. The outcomes of this work clearly substantiated that the EP can be successfully utilized for the decolorization of AR182 in textile wastewater.

Perspective on Fe0-PS synergetic effect and reaction mechanism in the thallium(I) contaminated water treatment

Due to extreme toxicity of the element of thallium (Tl), increasing aqueous Tl pollution incidents have aroused growing concerns. As the prevalent and stable form, i.e., monovalent Tl, the highly efficient removal methodologies of Tl(I) from (waste)water remains limited and challenging. In this study, an advanced oxidation method, the feasibility of using zero valent iron (Fe⁰) coupled with persulfate (PS) to treat Tl(I)-containing synthetic wastewater was investigated. Its influence parameters, including reaction time, initial Tl concentration, dosages of PS and Fe⁰, initial and coagulation pH, temperature, coexisting ions and organic matter (NO₃^-, SO₄^2-, Cl^- and HA) were examined. The results revealed that the system can be applied to a wide range of pH and temperature and the reaction equilibrium can be reached in about 30 min. Favorable Tl(I) removal rate (>98%) was observed in the synthetic wastewater with medium and relatively high Tl(I) concentration (≤0.250 mM). The analyses of characterization results including electron spin resonance spectrometer and X-ray photoelectron spectroscopy indicated that ·OH played a vital role in the removal of Tl(I), which was oxidized and removed by co-precipitation. Fe⁰ can be served as a stable source of Fe²⁺ to efficiently catalyze PS. The remaining Fe⁰ can be easily separated because of its magnetism, assuring the promising reusability of the reactant. The study aims to provide references for treatment of real Tl polluted wastewater.

Electro-peroxone with solid polymer electrolytes: A novel system for degradation of plasticizers in natural effluents

Electro-peroxone (EP) reaction has been considered as a promising process for real effluent treatments. However, the use of the technology in natural water conditions is limited by low electrical conductivity and high operating costs. Herein, a novel electrochemical system was designed to overcome this constrain by coupling EP with a solid polymer electrolyte (EP-SPE). Performances of EP-SPE system were thoroughly evaluated by comparing the decomposition and energy efficiencies of various plasticizers in different systems. The EP-SPE system achieved 50% of pollutants mineralization in only 10 min with the electrolysis energy consumption of 1.0kWh·m^-3, While the conventional EP system (not) adding salt compounds (CEP-(N) AS) need 30 (60) min to reach 50% of pollutants mineralization with 3.8(26.6)kWh·m^-3. Kinetics and mechanisms of EP-SPE were investigated in detail, while electronic paramagnetic resonance (EPR) detection and kinetic model revealed the occurrence, transient concentration and degradation contribution of reactive oxidizing species (ROS). Furthermore, tests of variety of SPEs and natural waters demonstrated universal applicability of EP-SPE. Additionally, EP-SPE did not show any performance deterioration after 15 runs. Therefore, this work provides a feasible technology for plasticizer purification in natural water.

Valorization of food waste as adsorbents for toxic dye removal from contaminated waters: A review

Industrial contaminants such as dyes and intermediates are released into water bodies, making the water unfit for human use. At the same time large amounts of food wastes accumulate near the work places, residential complexes etc. polluting the air due to putrefaction. The need of the hour lies in finding innovative solutions for dye removal from wastewater streams. In this context, the article emphasizes adoption or conversion of food waste materials, an ecological nuisance, as adsorbents for the removal of dyes from wastewaters. Adsorption, being a well-established technique, the review critically examines the specific potential of food waste constituents as dye adsorbents. The efficacy of food waste-based adsorbents is examined, besides addressing the possible adsorption mechanisms and the factors affecting phenomenon such as pH, temperature, contact time, adsorbent dosage, particle size, and ionic strength. Integration of information and communication technology approaches with adsorption isotherms and kinetic models are emphasized to bring out their role in improving overall modeling performance. Additionally, the reusability of adsorbents has been highlighted for effective substrate utilization. The review makes an attempt to stress the valorization of food waste materials to remove dyes from contaminated waters thereby ensuring long-term sustainability.

Investigating the effect of hydrogen peroxide as an electron acceptor in increasing the capability of slurry photocatalytic process in dye removal

The hydrogen peroxide role in photocatalytic degradation of an anionic azo dye, Acid Orange 7 (AO7), was investigated in a slurry reactor. Commercial ZnO nanoparticles with an average size between 10 to 30 nm were used as catalysts. Optimum conditions for different parameters, including dye concentration (10-100 mg/L), catalyst concentration (0.1-0.5 g/L), and pH (5-10), were determined first in the absence of H₂O₂. Changes in the COD were measured for the optimum condition. The impact of adding hydrogen peroxide at different concentrations to the system operating at optimum conditions was investigated. It was observed that 0.416 mM hydrogen peroxide increased the system's efficiency and decreased reaction time by 40 min. The reaction followed first-order kinetic. Hydrogen peroxide alone did not contribute to oxidizing the contaminant, and its positive impact was attributed to decreasing electron-hole recombination in the photocatalytic process. Not only can the hydrogen peroxide-assisted photocatalytic process decrease retention time in treatment units, but it can also result in more contaminant degradation. Therefore, it can reduce the treatment cost.

Enhancement of the electro-activated persulfate process in dye removal using graphene oxide nanoparticle

This study aimed to improve the speed of the electrochemical process by graphene oxide nanoparticle as a current accelerator in Acid Blue 25 removal from aqueous solutions. To do so, the effect of different parameters including pH, dye concentration, sodium persulfate concentration, the ratio of sodium persulfate to iron (II) sulfate concentration, current density, and the distance between electrodes was investigated on dye removal. Under optimal conditions of pH = 5, dye concentration = 200 mg/L, sodium persulfate concentration = 500 mg/L, iron (II) sulfate concentration = 100 mg/L, current density = 16.67 mA/cm², and electrode distance = 2 cm, 95% of dye was removed after 60 min in the electro-activated persulfate process; while the modified electro-activated persulfate process achieved 95% dye removal after only 40 min under the same conditions. This system was able to remove 90% of dye after 60 min at a higher concentration (300 mg/L). Also, the modified electro-activated persulfate process obtained the removal of 80% of COD, and 54% of TOC after 180 min in the mentioned conditions, for the dye concentration of 300 mg/L.

Effects of coagulation-sedimentation-filtration pretreatment on micropollutant abatement by the electro-peroxone process

The electro-peroxone (EP) process has been considered an attractive alternative to conventional ozonation for micropollutant abatement in water treatment. However, how to integrate the EP process into the water treatment trains in water utilities has yet to be investigated. This study compared micropollutant abatement during the EP treatment of potable source water with and without pretreatment of biological oxidation, flocculation, sedimentation, and filtration. Results show that this pretreatment train removed 39% of dissolved organic carbon (DOC) and 28% of the UV₂₅₄ absorbance of the raw water, leading to higher ozone (O₃) stability in the treated water. By electrochemically generating hydrogen peroxide to accelerate O₃ decomposition to hydroxyl radicals (•OH), the EP process considerably shortened the time required for ozone depletion and micropollutant abatement during the treatment of both the raw and pretreated water to ∼1 min, compared to ∼3 and 7.5 min during conventional ozonation of the raw and treated water, respectively. For the same specific ozone dose of 1 mg O₃ mg^-1 DOC (corresponding to 4.3 and 2.8 mg O₃ L^-1 for the raw and treated water, respectively), the abatement efficiencies of micropollutants with moderate and low ozone reactivity were increased by ∼10-15%, while the energy consumption for micropollutant abatement was decreased by ∼24-56% during the EP treatment of the treated water than the raw water. These results indicate that partial removal of DOC and ammonia from the raw water by the pretreatment train has a beneficial effect on enhancing micropollutant abatement and reducing energy consumption of the EP process. Therefore, it is more cost-effective to integrate the EP process after the pretreatment train in water utilities for micropollutant abatement.

Recent Achievements in Dyes Removal Focused on Advanced Oxidation Processes Integrated with Biological Methods

In the last 3 years alone, over 10,000 publications have appeared on the topic of dye removal, including over 300 reviews. Thus, the topic is very relevant, although there are few articles on the practical applications on an industrial scale of the results obtained in research laboratories. Therefore, in this review, we focus on advanced oxidation methods integrated with biological methods, widely recognized as highly efficient treatments for recalcitrant wastewater, that have the best chance of industrial application. It is extremely important to know all the phenomena and mechanisms that occur during the process of removing dyestuffs and the products of their degradation from wastewater to prevent their penetration into drinking water sources. Therefore, particular attention is paid to understanding the mechanisms of both chemical and biological degradation of dyes, and the kinetics of these processes, which are important from a design point of view, as well as the performance and implementation of these operations on a larger scale.