Degradation of organic contaminants in effluents-synthetic and from the textile industry-by Fenton, photocatalysis, and H2O2 photolysis

A Review of Gallic Acid-Mediated Fenton Processes for Degrading Emerging Pollutants and Dyes

Diverse reducing mediators have often been used to increase the degradation of emerging pollutants (EPs) and dyes through the Fenton reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + HO^● + HO^-). Adding reductants can minimize the accumulation of Fe³⁺ in a solution, leading to accelerated Fe²⁺ regeneration and the enhanced generation of reactive oxygen species, such as the HO^● radical. The present study consisted in reviewing the effects of gallic acid (GA), a plant-extracted reductant, on the Fenton-based oxidation of several EPs and dyes. It was verified that the pro-oxidant effect of GA was not only reported for soluble iron salts as a catalyst (homogeneous Fenton), but also iron-containing solid materials (heterogeneous Fenton). The most common molar proportion verified in the studies was catalyst:oxidant:GA equal to 1:10-20:1. This shows that the required amount of both catalyst and GA is quite low in comparison with the oxidant, which is generally H₂O₂. Interestingly, GA has proven to be an effective mediator at pH values well above the ideal range of 2.5-3.0 for Fenton processes. This allows treatments to be carried out at the natural pH of the wastewater. The use of plant extracts or wood barks containing GA and other reductants is suggested to make GA-mediated Fenton processes easier to apply for treating real wastewater.

Current Trends in the Utilization of Photolysis and Photocatalysis Treatment Processes for the Remediation of Dye Wastewater: A Short Review

Development in the textile industry leads to an increased demand for the use of various dyes. Moreover, there is the use of some dyes in the food industry as well as medical diagnostics. Thereby, increased demand for dyes in various fields has resulted in dye-containing wastewater. Only a small portion of the generated wastewater is adequately treated. The rest is usually dumped or otherwise directly discharged into the sewage system, which ultimately enters rivers, lakes, and streams. The handling and disposal of such concentrated wastewater, especially the dye-containing wastewater, is considered to be a major environmental issue from the moment of its generation to its ultimate disposal. Conventional water treatment methods such as flotation, filtration, adsorption, etc., are non-destructive physical separation processes. They only transfer the pollutants to other phases, thereby generating concentrated deposits. The advanced oxidation process (AOP) is one of the most effective emerging methods for the treatment of wastewater containing chemical pollutants. The method involves the formation and interaction of highly reactive hydroxyl radicals under suitable activation conditions. These radicals are non-selective and efficient for the destruction and eventual mineralization of recalcitrant organic pollutants. This review aims at the pros and cons of using photocatalysis as an efficient AOP to degrade dye-containing wastewater.

Enhanced photocatalytic activity of novel Canthium coromandelicum leaves based copper oxide nanoparticles for the degradation of textile dyes

The present study focused to synthesize the copper oxide nanoparticles (CuONPs) using novel Canthium coromandelicum leaves in a cost-effective, easy, and sustainable approach. The obtained Canthium coromandelicum-copper oxide nanoparticles (CC-CuONPs) were characterized using UV-Visible spectroscopy, FT-IR analysis, FESEM, HR-TEM imaging, and XRD study. The XRD pattern verified the development of crystalline CC-CuONPs with an average size of 33 nm. The biosynthesized CC-CuONPs were roughly spherical, according to HR-TEM and FESEM analyses. FT-IR research verified the existence of functional groups involved in CC-CuONPs production. Cu and O₂ have high-energy signals of 78.32% and 12.78%, respectively, according to data from EDX. The photocatalytic evaluation showed that synthesized CC-CuONPs have the efficiency of degrading methylene blue (MB) and methyl orange (MO) by 91.32%, 89.35% respectively. The findings showed that biosynthesized CC-CuONPs might effectively remove contaminants in an environmentally acceptable manner.

Cartap removal from simulated water matrices by fluidized-bed Fenton process: optimization of process parameters

Cartap is a thiocarbamate pesticide widely-used to protect rice crops, one of the most mass-produced cereals worldwide. Effluents containing cartap pose serious environment and health risks due to the acute toxicity of this emerging contaminant. This work evaluates the capabilities of the Fenton process to efficiently remove cartap from water matrices. Process parameters such as hydrogen peroxide dosage, ferrous ion concentration and operating pH were optimized using Box-Behnken design. Results showed complete cartap removal with Fenton oxidation in a fluidized-bed reactor while eliminating sludge generation during treatment. Fluidized-bed Fenton process had improved reduction in chemical oxygen demand and total organic carbon due to the contribution of heterogeneous Fenton catalysis to the overall degradation of cartap species compared to conventional Fenton in a batch reactor. Furthermore, competitive reactions and scavenging effects in complex natural water matrices were simulated with the use of inorganic ions such as nitrate, chloride, and phosphate. Results demonstrated the detrimental effect of phosphate ions on Fenton oxidation due to the precipitation of soluble catalysts as iron phosphates, which stops the catalytic Fenton cycle and thus the production of oxidants for contaminant degradation.

Effects of Technical Textiles and Synthetic Nanofibers on Environmental Pollution

Textile manufacturing has been one of the highest polluting industrial sectors. It represents about one-fifth of worldwide industrial water pollution. It uses a huge number of chemicals, numerous of which are carcinogenic. The textile industry releases many harmful chemicals, such as heavy metals and formaldehyde, into water streams and soil, as well as toxic gases such as suspended particulate matter and sulphur dioxide to air. These hazardous wastes, may cause diseases and severe problems to human health such as respiratory and heart diseases. Pollution caused by the worldwide textile manufacturing units results in unimaginable harm, such as textile polymers, auxiliaries and dyes, to the environment. This review presents a systematic and comprehensive survey of all recently produced high-performance textiles; and will therefore assist a deeper understanding of technical textiles providing a bridge between manufacturer and end-user. Moreover, the achievements in advanced applications of textile material will be extensively studied. Many classes of technical textiles were proved in a variety of applications of different fields. The introductory material- and process-correlated identifications regarding raw materials and their transformation into yarns, fibers and fabrics followed by dyeing, printing, finishing of technical textiles and their further processing will be explored. Thus, the environmental impacts of technical textiles on soil, air and water are discussed.

Visible light-driven photocatalytic degradation of methylene blue dye over bismuth-doped cerium oxide mesoporous nanoparticles

A series of Bi³⁺-doped ceria nanoparticles (0 to 20 wt% of Bi³⁺) were synthesized by sol-gel assisted hydrothermal method at a lower temperature of 150 °C. The synthesized nanoparticles were found to be effective photocatalysts for the degradation of methylene blue dye under visible light irradiation. The synthesized photocatalysts were well characterized by crystallographic, microscopic and spectroscopic methods. XRD patterns showed that the developed photocatalysts have cubic fluorite structure, and the absence of any impurity peaks in the XRD patterns of doped samples emphasizes the effective doping in host lattice. All samples exhibited mesoporous nature as evident from the adsorption and desorption pore size measurement. The shift of band gap energy from UV to visible region (2.90-2.77 eV) of the undoped and doped ceria results in the photo degradation of methylene blue dye in the visible light.

Optimization and toxicity assessment of a combined electrocoagulation, H2O2/Fe2+/UV and activated carbon adsorption for textile wastewater treatment

In this study, the potential application of sequential Electrocoagulation + Fenton (F) or Photo-Fenton (PF) + Active carbon adsorption (EC + F/PF + AC) processes were analyzed as alternatives for the treatment of an industrial textile wastewater resulting from an industrial facility located in Medellín (Colombia). In order to maximize the organic matter degradation, each step of the treatment was optimized using the Response Surface Methodology. At first, the optimal performance of EC was achieved with Fe electrodes operating at pH = 7, j_EC = 10 mA/cm² and 60 rpm, during 10 min of electrolysis. At these conditions, EC let to remove 94% of the dye's color, 56% of the COD and 54% of the TOC. Next, sequentially applied Fenton or photo-Fenton process (i.e., EC + F/PF), operating at the optimized conditions (pH = 4.3, [Fe²⁺] = 1.1 mM, [H₂O₂] = 9.7 mM, stirring velocity = 100 rpm and reaction time = 60 min.), improved the quality of the treated effluent. The EC + F let to achieve total color reduction, as well as COD and TOC removals of 72 and 75%, respectively. The EC + PF reached 100% of color, 76% of COD and 78% of TOC reductions. The EC + F/PF processes were more efficient than EC in elimination of low molecular weight (<5 kDa) compounds from wastewater. Moreover, the BOD₅/COD ratio increased from 0.21 to 0.42 and from 0.21 to 0.46 using EC + F and EC + PF processes, respectively. However, EC + F/PF were not fully effective for the removal of acute toxicity to Artemia salina: 20% and 60% of reduction in toxicity using EC + F and EC + PF, respectively, comparing to very toxic (100%) raw textile wastewater. Thus, activated carbon adsorption was applied as an additional step to complete the treatment. After AC adsorption, the acute toxicity decreased to 10% and 0% using EC + F and EC + PF, respectively. The total operational costs, including chemical reagents, electrodes, energy consumption and sludge disposal, were of 1.65 USD/m³ and 2.3 USD/m³ for EC + F and EC + PF, respectively.