Efficient treatment of veterinary pharmaceutical industrial wastewater by catalytic ozonation process: degradation of enrofloxacin via molecular ozone reactions

The study focused on the efficacious performance of bimetallic Fe-Zn loaded 3A zeolite in catalytic ozonation for the degradation of highly toxic veterinary antibiotic enrofloxacin in wastewater of the pharmaceutical industry. Batch experiments were conducted in a glass reactor containing a submerged pump holding catalyst pellets at suction. The submerged pump provided the agitation and recirculation across the solution for effective contact with the catalyst. The effect of ozone flow (0.8-1.55 mg/min) and catalyst dose (5-15 g/L) on the enrofloxacin degradation and removal of other conventional pollutants COD, BOD5, turbidity was studied. In batch experiments, 10 g of Fe-Zn 3A zeolite efficiently removed 92% of enrofloxacin, 77% of COD, 69% BOD5, and 61% turbidity in 1 L sample of pharmaceutical wastewater in 30 min at 1.1 mg/min of O3 flow. The catalytic performance of Fe-Zn 3A zeolite notably exceeded the removal efficiencies of 52%, 51%, 52%, and 59% for enrofloxacin, COD, BOD5, and turbidity, respectively, achieved with single ozonation process. Furthermore, an increase in the biodegradability of treated pharmaceutical industrial wastewater was observed and made biodegradable easily for subsequent treatment.

Application of poly aluminum chloride and alum as catalyst in catalytic ozonation process after coagulation for the treatment of textile wastewater

Textile wastewater is ranked highly contaminated among all industrial waste. During textile processing, the consumption of dyes and complex chemicals at various stages makes textile industrial wastewater highly challenging. Therefore, conventional processes based on single-unit treatment may not be sufficient to comply with the environmental quality discharge standards and more stringent guidelines for zero discharge of hazardous chemicals (ZDHC). In this study, a novel approach was followed by recycling Poly aluminum chloride (PACl) and Alum as a catalyst for the first time in the catalytic ozonation treatment process leading to a nascent method after using them as a coagulant in Coagulation/Flocculation. In the current investigation, six different combinations were studied to remove turbidity, TSS, COD, BOD₅, color, and biodegradability (BOD₅/COD ratios) of wastewater. Moreover, Central Composite Design was implied using RSM in Minitab software. During the combination of treatment processes, it was found that the pre-coagulation/flocculation with coagulant PACl followed by post-catalytic ozonation with recycled PACl, a more effective treatment than others. The optimum R.E of turbidity, TSS, COD, and color were 84%, 86%, 89%, and 98%, respectively. Moreover, a decrease in toxicity and increase in biodegradability (BOD₅/COD ratio from 0.29 to 0.54) was observed as well. The electrical energy demand and operational costs of treatment processes were estimated and compared with other treatment processes.

Application of Fe-RGO for the removal of dyes by catalytic ozonation process

Due to continuous industrialization, the discharge of hazardous dyes has enormously disrupted the ecosystem causing environmental problems. Due to the stable recalcitrant nature of dyes, advanced catalytic ozonation processes with the latest catalyst are under investigation. Fe-RGO is an effective oxidation catalyst, and the metal loaded platform provides enhanced catalytic performance. This study aims to investigate the effectiveness of Fe-RGO/O₃ process for the removal of dyes. In the current research, the application of iron-coated reduced graphene oxide (Fe-RGO) was studied as a catalyst in the heterogeneous catalytic ozonation process to remove dyes. Methylene blue (MB) was selected as a model pollutant. RGO was prepared using the improved Hummers method and was coated with iron (Fe) implying the impregnation method. The FTIR, SEM-EDX, XRD, and BET analyses of RG and Fe-RGO were performed to characterize the catalyst. The effect of various parameters such as pH (3-10), catalyst dose (0.01-0.04 g), and radical scavengers (NaHCO₃, NaCl) on removal efficiency was elucidated. The result revealed an excellent catalytic efficiency of Fe-RGO in the ozonation process. At optimum conditions, 96% removal efficiency was achieved in catalytic ozonation at pH 7 with a catalyst dose of 0.02 g and ozone dose 0.5 mg/min, after 10 min. Interestingly, a slight decrease in removal efficiency was observed in the catalytic ozonation process in hydroxyl radical scavengers (NaCl and NaHCO₃), which makes the proposed catalyst more applicable in real conditions. Therefore, it is concluded that Fe-RGO can be used as an excellent catalyst for the removal of dyes in real conditions where radical scavengers may be present in a significant amount.

Enhancing biohydrogen production from lignocellulosic biomass of Paulownia waste by charge facilitation in Zn doped SnO2 nanocatalysts

The goal of this research was to study the role of excess charges in regulating biohydrogen production from Paulownia. The excess charges were generated through charge compensation in SnO₂ nanocatalysts by Zn doping. The maximum hydrogen yield of 335 mL was observed at 8%Zn doping with a concentration of 150 mg/L, 47% higher as compared to standard sample. It was observed that the hydrogen production rate increased with Zn doping and the highest value (77 mL/h) was observed for 8%Zn at 24 h. The decrease in the total amount of byproducts (2.52 g/L from 4.28 g/L) at 8% Zn indicates an increase in bacterial metabolism. The lowest value of oxidation-reduction potential (-525 mV) at 24 h for 8%Zn confirms that Zn doping provides excessive electrons to the fermentative medium which helps the bacteria to transfer electrons faster during the redox reaction, hence, enhancing the enzymatic process and eventually hydrogen production.

Efficient Cr(vi) photoreduction under natural solar irradiation using a novel step-scheme ZnS/SnIn4S8 nanoheterostructured photocatalysts

Removal of heavy metal pollutants from water is a challenge to water security and the environment. Therefore, in this work, multinary chalcogenide based nanoheterostructures such as ZnS/SnIn₄S₈ nanoheterostructure with different loading amounts were prepared. The prepared nanoheterostructures were utilized as photocatalysts for chromium (Cr(vi)) photoreduction. The prepared nanoheterostructures were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV-Vis spectroscopy, dynamic light scattering (DLS), and X-ray photoelectron spectroscopy (XPS) and BET measurements. The absorption spectra of the prepared nanoheterostructures revealed that they are widely absorbed in the visible range with bandgap values 2.4–3.5 eV. The photocatalytic activities of prepared nanoheterostructures were studied toward the photoreduction of heavy metal, chromium (Cr(vi)), under irradiation of natural solar light. The ZnS/SnIn₄S₈ (with ZnS molar ratio 20%) nanoheterostructures results showed a high photocatalytic activity (92.3%) after 120 min which could be attributed to its enhanced charge carrier separation with respect to the bare ZnS and SnIn₄S₈ NPs. Also, the optoelectronic, valence-band XPS and electrochemical properties of the investigated photocatalysts were studied and the results revealed that the photocatalysts behave the step-scheme mechanism. The recyclability tests revealed a beneficial role of the surface charge in efficient regeneration of the photocatalysts for repeated use.

The Cr(vi) photoreduction tests demonstrated an improved photocatalytic activity of SIS and 2Z-SIS to be 61.0% and 92.3% respectively after 120 min. The results indicated the photocatalyst's capability under sun light, allowing for its industrial use.

Subcritical and supercritical water oxidation for dye decomposition

The total annual output of synthetic dyes exceeds 7 × 10⁵ tons. About 1,000 tons of non-biodegradable synthetic dyes are released every year into the natural streams and water sources from textile wastes. The release of these colored wastewater exerts negative impact on aquatic ecology and human beings because of the poisonous and carcinogenic repercussions of dyes involved in coloration production. Therefore, with a growing interest in the environment, efficient technologies need to be developed to eliminate dyes from local and industrial wastewater. Supercritical water oxidation as a promising wastewater treatment technology has many advantages, such as a rapid reaction and pollution-free products. However, due to corrosion, salt precipitation and operational problems, supercritical water oxidation process did not gain expected industrial development. These technical difficulties can be overcome by application of non-corrosive subcritical water as a reaction medium. This work summarizes the negative impacts of dyes and role of subcritical and supercritical water and their efficiencies in dye oxidation processes.

Enhanced High-Temperature (600 °C) NO2 Response of ZnFe2O4 Nanoparticle-Based Exhaust Gas Sensors

Fabrication of gas sensors to monitor toxic exhaust gases at high working temperatures is a challenging task due to the low sensitivity and narrow long-term stability of the devices under harsh conditions. Herein, the fabrication of a chemiresistor-type gas sensor is reported for the detection of NO₂ gas at 600 °C. The sensing element consists of ZnFe₂O₄ nanoparticles prepared via a high-energy ball milling and annealed at different temperatures (600–1000 °C). The effects of annealing temperature on the crystal structure, morphology, and gas sensing properties of ZnFe₂O₄ nanoparticles are studied. A mixed spinel structure of ZnFe₂O₄ nanoparticles with a lattice parameter of 8.445 Å is revealed by X-ray diffraction analysis. The crystallite size and X-ray density of ZnFe₂O₄ nanoparticles increase with the annealing temperature, whereas the lattice parameter and volume are considerably reduced indicating lattice distortion and defects such as oxygen vacancies. ZnFe₂O₄ nanoparticles annealed at 1000 °C exhibit the highest sensitivity (0.13% ppm^–1), sharp response (τ_res = 195 s), recovery (τ_rec = 17 s), and linear response to 100–400 ppm NO₂ gas. The annealing temperature and oxygen vacancies play a major role in determining the sensitivity of devices. The plausible sensing mechanism is discussed. ZnFe₂O₄ nanoparticles show great potential for high-temperature exhaust gas sensing applications.

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview

Dyes are used in various industries as coloring agents. The discharge of dyes, specifically synthetic dyes, in wastewater represents a serious environmental problem and causes public health concerns. The implementation of regulations for wastewater discharge has forced research towards either the development of new processes or the improvement of available techniques to attain efficient degradation of dyes. Catalytic oxidation is one of the advanced oxidation processes (AOPs), based on the active radicals produced during the reaction in the presence of a catalyst. This paper reviews the problems of dyes and hydroxyl radical-based oxidation processes, including Fenton's process, non-iron metal catalysts, and the application of thin metal catalyst-coated tubular reactors in detail. In addition, the sulfate radical-based catalytic oxidation technique has also been described. This study also includes the effects of various operating parameters such as pH, temperature, the concentration of the oxidant, the initial concentration of dyes, and reaction time on the catalytic decomposition of dyes. Moreover, this paper analyzes the recent studies on catalytic oxidation processes. From the present study, it can be concluded that catalytic oxidation processes are very active and environmentally friendly methods for dye removal.

One-Step Growth of Iron-Nickel Bimetallic Nanoparticles on FeNi Alloy Foils: Highly Efficient Advanced Electrodes for the Oxygen Evolution Reaction

Electrochemical water splitting is an important process to produce hydrogen and oxygen for energy storage and conversion devices. However, it is often restricted by the oxygen evolution reaction (OER) due to its sluggish kinetics. To overcome the problem, precious metal oxide-based electrocatalysts, such as RuO₂ and IrO₂, are widely used. The lack of availability and the high cost of precious metals compel researchers to find other resources for the development of cost-effective, environmentally friendly, earth-abundant, nonprecious electrocatalysts for OER. Such catalysts should have high OER performance and good stability in comparison to those of available commercial precious metal-based electrocatalysts. Herein, we report an inexpensive fabrication of bimetallic iron-nickel nanoparticles on FeNi-foil (FeNi_4.34@FeNi-foil) as an integrated OER electrode using a one-step calcination process. FeNi_4.34@FeNi-foil obtained at 900 °C shows superior OER activity in alkaline solution with an overpotential as low as 283 mV to achieve a current density of 10 mA cm^-2 and a small Tafel slope of 53 mV dec^-1. The high performance and durability of the as-prepared nonprecious metal electrode even exceeds those of the available commercial RuO₂ and IrO₂ catalysts, showing great potential in replacing the expensive noble metal-based electrocatalysts for OER.

Highly efficient decomposition of Remazol Brilliant Blue R using tubular reactor coated with thin layer of PdO

In this work, we propose a novel approach to dye decomposition under subcritical water conditions using a continuous-flow tubular reactor coated with thin layer of PdO as a catalyst. Remazole Brilliant Blue R was used as an example of synthetic dyes. Hydrogen peroxide was used as an environmental-friendly oxidant as it leaves no residues after treatment. The effect of temperature, pressure and dye concentration on total organic carbon (TOC) removal were studied. 99.9% of TOC removal was achieved at 300 °C and 10 MPa pressure within a short residence time of 3.2 s. This method provided an efficient and rapid process that has a potential for treating a wide range of textile wastewaters.

Simple and rapid hydrogenation of p-nitrophenol with aqueous formic acid in catalytic flow reactors

The inner surface of a metallic tube (i.d. 0.5 mm) was coated with a palladium (Pd)-based thin metallic layer by flow electroless plating. Simultaneous plating of Pd and silver (Ag) from their electroless-plating solution produced a mixed distributed bimetallic layer. Preferential acid leaching of Ag from the Pd–Ag layer produced a porous Pd surface. Hydrogenation of p-nitrophenol was examined in the presence of formic acid simply by passing the reaction solution through the catalytic tubular reactors. p-Aminophenol was the sole product of hydrogenation. No side reaction occurred. Reaction conversion with respect to p-nitrophenol was dependent on the catalyst layer type, the temperature, pH, amount of formic acid, and the residence time. A porous and oxidized Pd (PdO) surface gave the best reaction conversion among the catalytic reactors examined. p-Nitrophenol was converted quantitatively to p-aminophenol within 15 s of residence time in the porous PdO reactor at 40 °C. Evolution of carbon dioxide (CO₂) was observed during the reaction, although hydrogen (H₂) was not found in the gas phase. Dehydrogenation of formic acid did not occur to any practical degree in the absence of p-nitrophenol. Consequently, the nitro group was reduced via hydrogen transfer from formic acid to p-nitrophenol and not by hydrogen generated by dehydrogenation of formic acid.