Photocatalytic Degradation of Textile Dye and Wastewater

In this study, the photocatalytic degradation of commercial azo dye (Remazol Red 133) in the presence of titanium dioxide (TiO₂) suspensions as photocatalyst was investigated. The effect of various operational parameters, such as pH of dye solution and catalyst concentration on the photocatalytic degradation process, was examined. The mineralization of dye was also evaluated by measuring the chemical oxygen demand of the dye solutions. The extent of photocatalytic degradation was found to increase with increasing TiO₂ concentration. For the Remazol Red dye solutions, a 120-min treatment resulted in 97.9% decolorization and 87.6% degradation at catalyst loading of 3 g/L. Experiments using real textile wastewater were also carried out. Textile wastewater degradation was enhanced at acidic conditions. The decolorization and degradation efficiencies for textile wastewater were 97.8% and 84.9% at pH 3.0, catalyst loading of 3 g/L, and treatment time of 120 min.     

Photocatalytic Degradation of Herbicide Quinmerac in Various Types of Natural Water

The efficiency of the photocatalytic degradation of the herbicide quinmerac in aqueous TiO₂ suspensions was examined as a function of the type of light source, TiO₂ loading, pH, temperature, electron acceptors, and hydroxyl radical (^?OH) scavenger. The optimum loading of catalyst was found to be 0.25?mg?mL^?1 under UV light at pH?7.2, with the apparent activation energy of the reaction being 13.7?kJ?mol^?1. In the first stage of the reaction, the photocatalytic degradation of quinmerac (50???M) followed approximately a pseudo-first order kinetics. The most efficient electron acceptor appeared to be H₂O₂ along with molecular oxygen. By studying the effect of ethanol as an ^?OH scavenger, it was shown that the heterogeneous catalysis takes place mainly via ^?OH. The results also showed that the disappearance of quinmerac led to the formation of a number of organic intermediates and ionic byproducts, whereas its complete mineralization occurred in about 120?min. The reaction intermediates (7-chloro-3-methylquinoline-5,8-dione, three isomeric phenols hydroxy-7-chloro-3-methylquinoline-8-carboxylic acids, and 7-chloro-3-(hydroxymethyl)quinoline-8-carboxylic acid) were identified and the kinetics of their appearance/disappearance was followed by LC?CESI?CMS/MS. Tentative photodegradation pathways were proposed and discussed. The study also encompassed the effect of quality of natural water on the rate of removal of quinmerac.     

Photocatalytic Degradation of Azo Dye Reactive Orange 16 by TiO2

Water, Air, & Soil Pollution - Several recent reports document increasing concentrations of chloride in surface waters of northeastern and midwestern North America. These patterns, together...     

Adsorptive Removal of Pentachlorophenol by Anthracophyllum discolor in a Fixed-Bed Column Reactor

This study investigates pentachlorophenol (PCP) adsorption by the white-rot fungus Anthracophyllum discolor in a fixed-bed column reactor. PCP adsorption at different concentrations (20, 30, and 50?mg?L^?1) and pH values (5.0, 5.5, and 6.0) was determined and modeled using the Thomas model. Fourier transform infrared spectroscopy (FTIR) was used to identify functional groups of biomass that may participate in the interaction of PCP. The biosorption capacity of A. discolor was pH-dependent, and the PCP adsorbed increased with the decrease in the pH solution. Acid pH values of the influent gave an increase in saturation time in all PCP concentrations. By contrast, the increase in PCP concentration caused that the binding sites were filled quickly, resulting in a decrease in saturation time. The Thomas model was found suitable for describing the entire dynamic of the column with respect to the PCP concentration and pH of the solution. FTIR results showed that amines, carboxylates, alkanes, and C?CO groups might participate in the PCP adsorption on the biomass surface. It was concluded that A. discolor biomass was a good adsorbent for PCP removal from influent with mainly acidic pH.     

Decolorization and Degradation of Reactive Dye in Aqueous Solution by Ozonation in a Semi-batch Bubble Column Reactor

The decolorization and degradation of anionic sulphonated azo dye (Reactive orange 16 (RO16)), which is suspected to be carcinogenic, were investigated using ozone. The decolorization process of the reactive dye was carried out by bubbling ozone at the bottom of a bubble column reactor containing the dye solution. The effect of pH, reaction time, dye concentration, ozone concentration, and decolorization time was studied. Also, degradation products and possible degradation mechanism were investigated. The results showed that ozonation was a highly effective way to remove color from wastewater. The color of a synthetic waste solution containing water-soluble reactive dye was reduced to 69.69 % under the basic condition (pH 12), with complete RO16 degradation occurring in 8 min. Ozone consumption continued for a further 16 min after which time most of the degradation reactions were complete. Kinetic studies showed that direct ozonation of the aqueous dyes represented a pseudo-first-order reaction with respect to the dye. The apparent rate constant increased with both the applied ozone dose and higher pH values and declined logarithmically with the initial dye concentration. Intermediates such as 6-acetylamino-3-aminonaphthalene-2-sulfonic acid, 2-(4-nitrosophenyl) sulfonylethyl hydrogen sulfate, and 6-acetamido-4-hydroxy-3-nitroso naphthalene-2-sulfonic acid were detected by gas chromatograph coupled with mass spectrometry in the absence of pH buffer, while nitrate and sulfate ions and formic, acetic, and oxalic acids were detected by ion chromatography.     

Copper Oxide Nanoparticle-Coated Quartz Sand as a Catalyst for Degradation of an Organic Dye in Water

Copper oxide nanoparticles were immobilized on quartz sand and their catalytic activity for the degradation of an organic dye was investigated. The use of nanoparticles as catalysts for non photo-induced oxidation of water contaminants is relatively new. The CuO catalyst has shown promising results when suspended in free form in batch systems. Because heterogeneous catalysis is often the preferred mode of operation for application of catalytic technology, we studied the effect of immobilization of the nanoparticles on quartz sand in a flow-through system and its implication for the catalytic process. The coated sand was packed in a column and its catalytic activity for the degradation of an organic dye was investigated in a series of flow-through experiments with hydrogen peroxide as the oxidant. Control experiments with uncoated sand were also performed for comparison. The coated sand demonstrated high catalytic ability, achieving complete oxidation of the dye. During the reaction, CO₂ was produced, leading to a decrease in the water saturation in the column and reduced contact surface between the nano-CuO catalysts and the dye solution. The degradation was improved by enabling a longer residence time of the dye in the column, yielding up to 85% degradation of the dye. These results suggest that CuO nanoparticle-coated sand is an efficient catalyst for complete degradation of the organic dye.     

Comparative Study on Photocatalytic Degradation of Mono Azo Dye Acid Orange 7 and Methyl Orange under Solar Light Irradiation

The objective of this study was to investigate and compare the kinetic photocatalytic degradation of mono azo dyes Acid Orange 7 (AO7) and Methyl Orange (MO) under solar light irradiation with titanium dioxide (TiO₂) as a photocatalyst. Several operational parameters affecting the photocatalytic degradation of dye were evaluated such as different azo dyes, initial dye concentration, TiO₂ dosage, with and without aeration and sunlight irradiation. The data obtained was well fitted with the Langmuir?CHinshelwood kinetic model. It was observed that the pseudo-first-order rate constants for AO7 were higher than MO in all cases, indicating that the photocatalytic degradation of AO7 was easier and more rapid than MO. The analysis of chemical oxygen demand and UV?CVis spectra shows the AO7 and MO not only being decolorized due to the breakdown of azo bond but also being mineralized if the azo dye solutions were continually exposed to solar light irradiation after the decolorization process.     

Investigation of Arsenic Removal from Water by Iron-Mixed Mesoporous Pellet in a Continuous Fixed-Bed Column

Natural clay combing with iron oxide and iron particle was developed to be iron-mixed mesoporous pellet that was packed in a fixed-bed column for removing arsenic from water. The performance of the column in terms of breakthrough curve analysis was investigated with the variations of influent flow rate, adsorbent bed height, initial solution pH, and initial adsorbate concentration. The results indicated that increasing in the flow rate decreased the removal capacities of the adsorbent. A relatively low bed height provided a better and beneficial performance. Higher adsorption capacity was observed with an increase of initial adsorbate concentration. At higher initial solution pH, the repulsive process occurred between adsorbate species and the surface charge of the adsorbent, resulting in a poor performance of the column. The Thomas model fitted very well to the experimental data for all cases. Estimated from the model, the highest adsorption capacity for arsenite and arsenate was found to be about 509 and 430 μg/g, respectively. The Adam-Bohart model provided only a relatively satisfactory fit to the initial part of the experimental data. From a practical view, the new developed pellet could be used as the effective and efficient adsorbent to treat elevated arsenic contaminated groundwater.     

Natural Diffusers for the Treatment of Residual Water in an Aerobic System

The adsorption capacity of vermiculite, a natural clay, for removing dibenzothiphene (DBTP) from water solutions was investigated. DBTP is an organic compound with sulfur, commonly found in fossil fuels and coal. This compound can also be found in the environment due accidental spills of oil and derivatives. Due to its structure and physical–chemical properties it is considered a persistent compound. Vermiculite (VT) was used as an adsorbent in its natural form, impregnated with copper ions (Cu-VT), and hydrophobically modified (HDTMA-VT) by replacement sodium cations by hexadecyltrimethyl ammonium ion. The results showed that DBTP was adsorbed in considerable amounts by HDTMA-VT; however, the Cu-VT adsorbed DBTP in some proportions of HDTMA-VT. Because of the presence of sulfur atoms in the structure of the molecule, π complexation can be observed. The adsorption isotherms were treated by the Freundlich equation. The values of K _f are similar to Cu-VT and HDTMA-VT, showing that the adsorption may be either through hydrophobic interactions or interactions through the formation of π complex. Meanwhile, the results with the VT (natural form) showed a much smaller value of K _f. It is believed, compared with the literature, and because of the chemical composition of the vermiculite, that the adsorption mechanism is also conducted by π complexation, considering the absence of organic carbon content.     

Removal of Remazol Brilliant Blue Dye from Dye-Contaminated Water by Adsorption Using Red Mud: Equilibrium, Kinetic, and Thermodynamic Studies

Utilization of industrial solid wastes for the treatment of wastewater from another industry could help environmental pollution abatement, in solving both solid waste disposal as well as liquid waste problems. Red mud (RM) is a waste product in the production of alumina and it poses serious pollution hazard. The present paper focuses on the possibility of utilization of RM as an adsorbent for removal of Remazol Brilliant Blue dye (RBB), a reactive dye from dye-contaminated water. Adsorption of RBB, from dye-contaminated water was studied by adsorption on powdered sulfuric acid-treated RM. The effect of initial dye concentration, contact time, initial pH, and adsorbent dosage were studied. Langmuir isotherm model has been found to represent the equilibrium data for RBB?CRM adsorption system better than Freundlich model. The adsorption capacity of RM was found to be 27.8?mg dye/g of adsorbent at 40?°C. Thermodynamic analysis showed that adsorption of RBB on acid-treated RM is an endothermic reaction with ?H ⁰ of 28.38?kJ/mol. The adsorption kinetics is represented by second-order kinetic model and the kinetic constant was estimated to be 0.0105?±?0.005?g/mg?min. Validity of intra-particle diffusion kinetic model suggested that among the mass transfer processes during the dye adsorption process, pore diffusion is the controlling step and not the film diffusion. The process can serve dual purposes of utilization of an industrial solid waste and the treatment of liquid waste.     

Design,Evaluation and Application of a Continuously Stirred Tank Reactor System for Use in Nitric Acid Air Pollutant Studies

Nitric acid (HNO₃) vapor is a significant component of air pollution. Dry deposition of HNO₃ is thought to be a major contributor to terrestrial loading of anthropogenically-derived nitrogen (N), but many questions remain regarding the physico-chemical process of deposition and the biological responses to accumulation of dry-deposited HNO₃ on surfaces. To examine these processes experimentally, a continuously stirred tank reactor (CSTR) fumigation system has been constructed. This system enables simultaneous fumigation at several concentrations in working volumes 1.3 m dia by 1.3 m ht, allowing for simultaneous fumigation of many experimental units. Evaluation of the system indicates that it is appropriate for long-term exposures of several months duration and capable of mimicking patterns of diurnal atmospheric HNO₃ concentrations representative of areas with different levels of pollution.     

Improvement of Photocatalytic Degradation of Naphthol Green B Under Solar Light Using Aluminum Doping of Zinc Oxide Nanoparticles

The photocatalytic degradation of dyes under sunlight irradiation has received much attention not only because the attempt is aimed at decomposition of pollutants but also at finding methods of making use of solar energy. Following this line, zinc oxide nano-particles were prepared using solvent thermal method in order to decompose Naphthol Green B in presence of sunlight. Complete mineralization and decolorization of Naphthol Green B were achieved in 14?h. In order to reduce the band gap of zinc oxide and increase its photocatalytic activity in sunlight, it was doped with different concentrations of aluminum (1?%, 3?%, 5?%, and 10?%). The obtained band gap energy of the Al-doped ZnO nanoparticles was investigated as a function of Al content. Reduction of band gap energy for the heavily doped ZnO nanoparticles (10?% Al) was observed from 3.29 to 3.23?eV leading to fast transfer for electron from the excited state of dye to conduction band of ZnO. Therefore, by using the 10?% Al-doped ZnO nanoparticles, the complete mineralization and decolorization of Naphthol Green B were achieved in 6?h under sunlight. These results suggested that the heavily doped ZnO nanoparticles with aluminum has a positive effect towards photocatalytic reactions with dye under solar energy.     

Photo-Assisted Degradation,Toxicological Assessment,and Modeling Using Artificial Neural Networks of Reactive Gray BF-2R Dye

This work investigates the degradation of Reactive Gray BF-2R dye (a blend of reactive yellow 145, reactive orange 122 and reactive black 5 dyes) using UV/H₂O₂, Fenton, and photo-Fenton-advanced oxidative processes, with artificial sunlight and UV-C radiations. The photo-Fenton process employing UV-C radiation was the most efficient under the conditions studied. The ideal conditions for the degradation of the dye, determined using a factorial design 2³ and a study of the concentration of hydrogen peroxide ([H₂O₂]), were [H₂O₂] equal to 40 mg L^?1, iron concentration [Fe] of 1 mg L^?1, and pH between 3 and 4. The Chan and Chu non-linear kinetic model predicted the kinetic data with a degradation of over 98% for color and 68% for aromatics after 60 min. The behavior of the chemical oxygen demand fitted the first-order kinetic model well, with a degradation of 64% after 60 min. The Multilayer Perceptron 7-11-2 artificial neural network model enabled to model the degradation process of the aromatics and accurately predict the experimental data. Toxicity tests indicated that the post-treatment samples were non-toxic for Escherichia coli bacteria, and Portulaca grandiflora and Basil sabory seeds. However, they inhibited the growth of Lactuca sativa seeds and Salmonella enteritidis bacteria. The photo-Fenton process with UV-C radiation degraded the dye studied efficiently and the degradation percentages were, on average, 7% and 5% higher for color than those observed when employing the Fenton and UV/H₂O₂ processes, respectively. With the aromatic, however, they were 84% and 62% higher, thus justifying the use of this process.     

Visible-Light-Driven Photocatalytic N-Doped TiO<Subscript>2</Subscript> for Degradation of Bisphenol A (BPA) and Reactive Black 5 (RB5) Dye

Bisphenol A (BPA) and reactive black 5 (RB5) dye are among the most persistent and non-biodegradable contaminants in water which require an urgent need for the development of effective removal method. The ubiquitous existence of both contaminants could interfere with the human health and aquatic environmental balance. Photocatalytic process as one of advanced oxidation processes (AOPs) has shown high performance for degradation of organic compounds to the harmless materials under sensible condition. Therefore, this study aims to develop a visible-light-driven photocatalyst that can efficiently degrade BPA and RB5 present in household water. N-doped TiO₂ were successfully synthesized via simple and direct sol–gel method. The prepared TiO₂ nanoparticles were characterized by field emission scanning microscope (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Brunauere Emmette Teller (BET) analysis. The incorporation of nitrogen in TiO₂ lattice exhibited excellent optical responses to visible region as revealed by UV–Vis–NIR spectroscopy absorption capability at 400–600 nm. The photocatalytic activity of the N-doped TiO₂ nanoparticles was measured by photocatalytic degradation of BPA and RB5 in an aqueous solution under visible-light irradiations. Degradation of BPA and RB5 was 91.3% and 89.1%, respectively after 360 min illumination. The degradation of BPA and RB5 by N-doped TiO₂ was increased up to 89.8% and 88.4%, respectively under visible-light irradiation as compared to commercial TiO₂ P25. This finding clearly shows that N-doped TiO₂ exhibits excellent photocatalytic degradation of BPA and RB5 under visible irradiation, hence have a promising potential in removing various recalcitrant contaminants for water treatment to fulfill the public need to consume clean water.

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土壤中有机农药的自然降解行为

有机农药是一类典型的环境污染物,自然降解是其在土壤中消除的主要过程。本文阐述了土壤中有机农药生物降解、光解、水解和化学氧化等自然降解机制,综述了土壤中有机农药自然降解的研究方法及研究现状,指出了目前自然降解研究中存在的一些问题并展望了今后的研究方向。     

天然矿物改良剂在微咸水灌溉土壤中应用效果的研究

利用10种不同天然矿物作为土壤改良剂，对矿化度4～5g／L的微咸水灌溉农田土壤进行改良效果试验。结果表明：改良剂1能够降低土壤容重12.23％，提高土壤孔隙度12.28％。参试的改良剂均能够降低0～5cm土壤全盐量，最大降幅为72.5％，并能降低0～40cm土壤中CO3^2-和HCO3^-离子，最大降幅达100％，改良剂4能够增加土壤中的Ca^2＋、Mg^2＋离子、降低土壤中的K^＋＋Na^＋离子。天然矿物土壤改良剂能够有效地改善土壤物理和化学环境。