Efficient degradation and mineralization of aniline in aqueous solution by new dielectric barrier discharge non-thermal plasma

Aniline is a priority pollutant that is unfavorable to the environment and human health due to its carcinogenic and mutagenic nature. The performance of the dielectric barrier discharge reactor was examined based on the aniline degradation efficiency. Different parameters were studied and optimized to treat various wastewater conditions. Role of active species for aniline degradation was investigated by the addition of inhibitors and promoters. The optimum conditions were 20 mg/L initial concentration, 1.8 kV applied voltage, 4 L/min gas flow rate and a pH of 8.82. It was observed that 87% of aniline was degraded in 60 min of dielectric barrier discharge treatment at optimum conditions. UV-Vis spectra showed gradual increase in the treatment efficiency of aniline with the propagation of treatment time. Mineralization of AN was confirmed by TOC measurement and a decrease in pH during the process. To elicit the aniline degradation route, HPLC and LC-MS techniques were used to detect the intermediates and byproducts. It was identified that aniline degraded into different organic byproducts and was dissociated into carbon dioxide and water. Comparison of the current system with existing advanced oxidation processes showed that DBD has a remarkable potential for the elimination of organic pollutants.

Removal of Aniline and Benzothiazole Wastewaters Using an Efficient MnO2/GAC Catalyst in a Photocatalytic Fluidised Bed Reactor

This work presents an efficient method for treating industrial wastewater containing aniline and benzothiazole, which are refractory to conventional treatments. A combination of heterogeneous photocatalysis operating in a fluidised bed reactor is studied in order to increase mass transfer and reduce reaction times. This process uses a manganese dioxide catalyst supported on granular activated carbon with environmentally friendly characteristics. The manganese dioxide composite is prepared by hydrothermal synthesis on carbon Hydrodarco^® 3000 with different active phase ratios. The support, the metal oxide, and the composite are characterised by performing Brunauer, Emmett, and Teller analysis, transmission electron microscopy, X-ray diffraction analysis, X-ray fluorescence analysis, UV-Vis spectroscopy by diffuse reflectance, and Fourier transform infrared spectroscopy in order to evaluate the influence of the metal oxide on the activated carbon. A composite of MnO₂/GAC (3.78% in phase α-MnO₂) is obtained, with a 9.4% increase in the specific surface of the initial GAC and a 12.79 nm crystal size. The effect of pH and catalyst load is studied. At a pH of 9.0 and a dose of 0.9 g L^-1, a high degradation of aniline and benzothiazole is obtained, with an 81.63% TOC mineralisation in 64.8 min.

Degradation of nitrogen-containing hazardous compounds using advanced oxidation processes: A review on aliphatic and aromatic amines, dyes, and pesticides

Nitrogen-containing amino and azo compounds are widely used in textile, agricultural and chemical industries. Most of these compounds have been demonstrated to be resistant to conventional degradation processes. Advanced oxidation processes can be effective to mineralize nitrogen-containing compounds and improve the efficacy of overall treatment schemes. Due to a global concern for the occurrence of toxic and hazardous amino-compounds and their harmful degradation products in water, it is important to develop technologies that focus on all the aspects of their degradation. Our focus is to present a state-of-the-art review on the degradation of several amine- and azo-based compounds using advanced oxidation processes. The categories reviewed are aromatic amines, aliphatic amines, N-containing dyes and N-containing pesticides. Data has been compiled for degradation efficiencies of each process, reaction mechanisms focusing on specific attack of oxidants on N atoms, the effect of process parameters like pH, initial concentration, time of treatment, etc. and identification of intermediates. Several AOPs have been compared to provide a systematic overview of available literature that will drive essential aspects of future research on amine-based compounds. Ozone is observed to be highly reactive to most amines, dyes and pesticides, followed by Fenton processes. Degradation of amines is highly sensitive to pH and mechanisms differ at different pH values. Cavitation is a promising alternative pre-treatment method for cost reduction. Hybrid methods under optimized conditions are demonstrated to give synergistic effects and must be tailored for specific effluents in question. In conclusion, even though nitrogen-containing compounds are recalcitrant in nature, the use of advanced oxidation processes at carefully established optimum conditions can yield highly efficient degradation of the compounds.

Industrial wastewater treatment using a bubble photo-Fenton reactor with continuous gas supply

The present study assesses the treatability of a real industrial wastewater (WW) with a high organic load (chemical oxygen demand (COD) above 5800 mgO₂ L^-1) by photo-Fenton's oxidation with the goal of improving the organic matter degradation reached previously, in another work, where the Fenton process was applied in a bubbling reactor. Thus, the process was carried out in a bubble photo reactor (BPR) wherein continuous air supply ensures an efficient mixing of the liquid phase. The effect of the main operatory parameters that influence the WW treatment (i.e., H₂O₂ and Fe²⁺ concentrations, initial pH, and UV-Vis radiation intensity) were evaluated, being found that in the best conditions tested (pH₀ = 4.6, [Fe²⁺] = 0.1 g L^-1, [H₂O₂] = 18 g L^-1, Q_air = 1.0 L min^-1-measured at room temperature and atmospheric pressure-and irradiance of 500 W m^-2), removals of 95% and 97% for total organic carbon (TOC) and COD, respectively, were achieved. Still, a high reduction of the concentration of the main constituents of this WW was reached, being total for aniline and 86% for sulfanilic acid. The continuous air supply reactor configuration was compared with magnetic stirring; similar mineralization was achieved. However, the air bubbling promotes a good heat transfer within the reactor, minimizing temperature gradients, which is quite advantageous due to the strong exothermicity of the oxidation process during the treatment of such highly loaded real effluents.

Heterogeneous Catalytic Ozonation of Aniline-Contaminated Waters: A Three-Phase Modelling Approach Using TiO2/GAC

This work aims to study the sustainable catalytic ozonation of aniline promoted by granular active carbon (GAC) doped with TiO2. Aniline was selected as a model compound for the accelerator manufacturing industries used in the manufacture of rubber due to its environmental impact, low biodegradability, and harmful genotoxic effects on human health. Based on the evolution of total organic carbon (TOC), aniline concentration measured using high performance liquid chromatography (HPLC), pH and ozone concentration in liquid and gas phase, and catalyst loading, a three-phase reaction system has been modelled. The proposed three-phase model related the ozone transfer parameters and the pseudo-first order kinetic constants through three coefficients that involve the adsorption process, oxidation in the liquid, and the solid catalyst. The interpretation of the kinetic constants of the process allowed the predominance of the mechanism of Langmuir–Hinshelwood or modified Eley–Rideal to be elucidated. Seven intermediate aromatic reaction products, representative of the direct action of ozone and the radical pathway, were identified and quantified, as well as precursors of the appearance of turbidity, with which two possible routes of degradation of aniline being proposed.

Photochemical Oxidation Process of Copper from Electroplating Wastewater: Process Performance and Kinetic Study

An investigation of the process of ozone combined with ultraviolet radiation has been carried out in order to establish the kinetics for photochemical oxidation of copper (Cu) from electroplating wastewater. The effects of operating parameters, including initial Cu concentration, ozone dosage, UV irradiation intensity, and pH value on the photochemical oxidation of Cu have been studied comprehensively. The Cu concentration during the reaction was identified using atomic absorption spectroscopy (AAS) method. The solid product was analyzed using X-ray diffraction (XRD) and scanning electron microscope–energy-dispersive X-ray (SEM–EDX) methods. It was found that the UV-Ozone process has high performance on Cu removal compared to UV and Ozone processes due to the high production rate of HO• radicals. It was also found that the solid product from the UV-Ozone process was CuO monoclinic crystal phase. The initial Cu concentration, ozone dosage, and pH value were significantly affected the Cu removal efficiency. On the other hand, the UV irradiation intensity was not significant; however, it has responsibility in promoting the ozone photolysis. The kinetics model for the photochemical oxidation of Cu was established following the first-order kinetic model. Furthermore, the reaction mechanism was also developed.

Degradation of nitrobenzene by synchronistic oxidation and reduction in an internal circulation microelectrolysis reactor

The degradation of nitrobenzene by synchronistic oxidation and reduction was investigated using an internal circulation microelectrolysis (ICE) reactor with an active volume of 0.018 m³. Compared with a conventional fixed bed reactor with and without aeration, the ICE reactor exhibited a markedly higher nitrobenzene degradation efficiency. The effects of various operational parameters such as reaction time, aeration rate, initial nitrobenzene concentration, initial pH, and a volume ratio of iron and carbon (Fe/C) were also investigated. The optimal operating conditions (reaction time = 60 min, aeration rate = 5 × 10^-4 m³/s, initial concentration of nitrobenzene = 300 mg/L, pH = 3.0, Fe/C = 1:1) gave removal efficiencies of nitrobenzene and chemical oxygen demand of 98.2% and 58%, respectively. The biodegradability index of the treated nitrobenzene solution was 0.45, which is 22 times that of the original solution. The reaction intermediates were identified through high-performance liquid chromatography, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, and ion chromatography. The primary intermediates were determined to be aniline, phenol, and carboxylic acids, indicating that nitrobenzene was synchronously oxidized and reduced in the ICE reactor. Based on the identified intermediates, a possible pathway for nitrobenzene degradation in the ICE reactor is proposed.