AOPs

The photocatalytic degradation of Toluidine Blue dye (TB) in aqueous solution was investigated under UV light in the presence of magnesium oxide (MgO) as a photocatalyst at different operating parameters. The operating
conditions were photocatalyst dose, initial dye concentration and the pH of the solution. Increasing of photocatalyst dose from 10 to 70 mg enhanced the degradation rate of TB dye. However, the increasing of TB dye concentration from 2 to 8 mg/L negatively affected the degradation rate. It was found that the percent of dye
removal reached the maximum value at high acidic medium. In dark condition, 15 % of dye was adsorbed by MgO. Furthermore, the kinetics involved in the degradation of TB dye was examined and the degradation was found to follow pseudo first order kinetic model.

This paper examined the possibility of applying ozone (O 3) and O 3 combined with ultraviolet (UV) to degrade the content of seawater containing Direct Yellow 50 dye. The Experimental parameters such as initial dye concentration and time of reaction were assessed in a batch reactor to achieve the optimum operating circumstances. The Results of this study showed that more than 88% color removal was obtained after 35 min of O 3 treatment (for 100 ppm dye concentration) and also partially removal of COD. These results also indicated that the application of O 3 is more effective than UV assisted Ozonation to reduce the reaction time. Also, Gas Chromatography Mass Spectrum analysis of treated synthetic dye solution was performed at the end of the pre-treatment time to the final degradation products of Direct Yellow 50 dye and showed no toxic compounds. 1. Introduction The existence of organic impurities such as dyes, surfactants, pesticides, etc. in the hydrosphere is of particular concern for the fresh water and marine environments because of their non-biodegradability and possible carcinogenic nature of most of these complexes [1-12]. The textile industry is considered one of the basic industries in Egypt with respect to the number of labor, the exports cost, and the local production cost. This industry has been revealed as an important supplier for the environmental pollution, and the streams, mainly the wet processes where risky chemicals are used. The Egyptian textile industry consist of 31 public sector companies and about 3000 private sector and joint venture facilities, [13,14]. Direct dye is still the most extensively used in dying printing process of the textile industry. Most of the printing process-textile plants belong to the small factory group (home-made textile products). Great volumes of synthetic dyes are used by numerous industries including textile dyeing (60%), plastic matter (10%) and paper (10%), [15-19]. Ozone reacts with wastewater compounds in two different techniques namely direct molecular and indirect radical type chain reactions [20-22]. Simplified reaction mechanisms of ozone at alkaline pH are given in below; 3O 3 + H 2 O → 2 ·OH + 4 O 2 (1) Photolysis of ozone in water in the existence of UV radiation in the range of 200-280 nm can lead to hydrogen peroxide creation. Hydroxyl radicals can be produced by this as given equations below: O 3 + hv + H 2 O → H 2 O 2 + O 2 (2) H 2 O 2 + hv → 2 ·OH (3)

This study conducted a comparison of the CaO2-based Fenton (CaO2/Fe(II)) and Fenton-like (CaO2/Fe(III)) systems on their benzene degradation performance. The H2O2, Fe(II), Fe(III), and HO variations were investigated during the benzene degradation. Although benzene has been totally removed in the two systems, the variation patterns of the investigated parameters were different, leading to different benzene degradation patterns. In terms of the Fe(II)/Fe(III) conversion, the CaO2/Fe(II) and CaO2/Fe(III) systems were actually inseparable and had the inherent mechanism relationships. For the CaO2/Fe(III) system, the initial Fe(III) must be converted to Fe(II), and then the consequent Fenton reaction could be later developed with the regenerated Fe(II). Moreover, some benzene degradation intermediates could have the ability to facilitate the transformation of the Fe(III) to Fe(II) without the classic H2O2-associated propagation reactions. By varying the Fe(II) dosing method, an effective degradation strategy has been developed to take advantage of the two CaO2-based oxidation systems. The proposed strategy was further successfully tested in TCE degradation, therefore extending the potential for the application of this technique.

This paper examines the possibility of applying ozone (O 3) and O 3 combined with ultraviolet (UV) to degrade the content of synthetic wastewater Mordant Violet 40 dye (MV-40). The experimental parameters included pH, initial dye concentration and time of reaction; all were assessed in a batch reactor to achieve the optimum operating circumstances. The results obtained showed that the pH and initial MV-40 dye concentration controlled the decolorization process. The maximum decolorization of MV-40 dye solution was obtained at pH 9. More than 98% of color removal was obtained within 20 minutes for both UV assisted O 3 and individual O 3 treatment of 100 ppm dye concentration. Kinetic analyses showed that the decolorization of MV-40 dye followed the second-order kinetics. The degree of decolorization of MV-40 dye solution was indirectly proportional to the initial dye concentration. Gas Chromatography Mass Spectrum analysis of treated synthetic dye solution was performed at the end of the pre-treatment time to the final degradation products of MV-40 dye. The obtained results explained that the advanced oxidation processes enhanced the biodegradability and lowered the zooplankton toxicity of the treated MV-40 dye solution.

The colour manufacturing industry represents a relatively small part of the overall chemical industry. Dyes and pigments are highly visible material. A major source of colour release into the environment is associated with the incomplete exhaustion of dyes onto textile fibre from an aqueous dyeing process and the need to reduce the amount of residual dye in textile effluent has become a major concern in recent years. The aim of this work is to evaluate the efficiency of ozone and UV on the removal of five different dyes from fresh and sea water, followed by determination of the final compounds after ozone and ozone-UV treatment using GC-Ms analysis. Finally, assess the effect of the treated water which contains the final decomposed compounds on the selected marine organisms for water reuse.

"Background: Titanium dioxide (TiO2)-mediated photocatalysis has been found to be an efficient method of water treatment and is capable of degrading a wide range of organic pollutants and microbial agents with high efficiency. The microorganism Pseudomonas aeruginosa is resistant to chemicals and UV irradiation. Bacteria which are resistant to UV-induced oxidative damage of the cell membrane are susceptible to photocatalytic technology. The main objective of this research was to examine the photocatalytic removal of P. aeruginosa upon UV irradiation in the presence of TiO2 nanoparticles.
Methods: Polluted water samples were prepared by the addition of P. aeruginosa colonies into water, followed by contact with UV, TiO2, or a combination of the two in separate stages. The effect of various parameters, including contact time, pH, and TiO2 concentration, on reaction efficiency was examined.
Results: The highest efficiency of bacterial disinfection was achieved with UV irradiation in the presence of TiO2 nanoparticles, with complete (100%) removal of P. aeruginosa observed upon irradiation for 60 min in the presence of 0.4 g/L TiO2 under conditions of neutral pH.
Conclusions: The results of this study suggest that from a technical and economic perspective, the UV/TiO2 process may be effectively applied for the disinfection of polluted water. This process could be considered a promising method of cleaning and purification, and applicable for water disinfection."

Background: Agriculture is one of the most important sources of national income for Egypt. But it is one of the most important human activities contaminated watercourses. Egypt suffers from a severe shortage, that reflected on the water quality and the amount of pollution in the watercourses. Several studies have shown the contamination of many watercourses in Egypt with different nitrogen forms. The advanced oxidation processes (AOPs) one of the most competent methods in the disposal of pollutants. The effect of AOPs using UV, UV/H 2 O 2 , Fenton and photo-Fenton treatment on disposal NH 3 were investigated at laboratory scale. Experiments were conducted to optimize the operating variables like pH, H 2 O 2 conc. and H 2 O 2 /Fe 2+ molar ratio. Results: The removal rate of NH 3 obeys the following sequence: photolysis < UV/H 2 O 2 < Fenton < Photo-Fenton. The Photo-Fenton treatment had removed 92.11% of NH 3 content of the sample, at that conditions (900 mg L-1 H 2 O 2 , H 2 O 2 /Fe 2+ molecular ratio=20, and pH=3). Conclusions: Most AOPs was capable of NH 3 disposal with varying degrees of success. The most effective processors were the photo-Fenton, but it needs to reduce the pH value. Which, requiring many additional and costly economic treatments. Therefore, it is necessary to conduct other experiments to increase the effectiveness of that process at pH 7.

H2O2 production is the decisive factor of Electro-Fenton performance on contaminants degradation. Herein, a novel but simple strategy was proposed for drastically enhanced H2O2 production from anodic O2 electroreduction. H2O2 concentration at steady-state is 99.5% higher under pulsed current of “2sON + 2sOFF” than under constant current when using reticulated vitreous carbon foam (RVC foam) cathode. This was caused by the facilitated H2O2 diffusion from the porous cathode to bulk as H2O2 electroreduction pathway was weakened. Additionally, the enhancement effect is more significant for RVC foam with low PPI. This strategy is also applicable to graphite felt (GF) cathode, in which a 56.0% higher H2O2 concentration was observed at steady-state under pulsed current of “2sON + 2sOFF”. Investigation on pulse frequency shows there exists an optimal frequency that achieves both effective H2O2 electrogeneration and decreased H2O2 electroreduction.

This study investigates the effect of palladium (Pd) form on the electrochemical degradation of chlorobenzene in groundwater by palladium-catalyzed electro-Fenton (EF) reaction. In batch and flow-through column reactors, EF was initiated via in-situ electrochemical formation of hydrogen peroxide (H2O2) supported by Pd on alumina powder or by palladized polyacrylic acid (PAA) in a polyvinylidene fluoride (PVDF) membrane (Pd-PVDF/PAA). In a mixed batch reactor containing 10 mg L−1 Fe2+, 2 g L−1 of catalyst in powder form (1% Pd, 20 mg L−1 of Pd) and an initial pH of 3, chlorobenzene was degraded under 120 mA current following a first-order decay rate showing 96% removal within 60 min. Under the same conditions, a rotating Pd-PVDF/PAA disk produced 88% of chlorobenzene degradation. In the column experiment with automatic pH adjustment, 71% of chlorobenzene was removed within 120 min with 10 mg L−1 Fe2+, and 2 g L−1 catalyst in pellet form (0.5% Pd, 10 mg L−1 of Pd) under 60 mA. The EF reaction can be achieved under flow, without external pH adjustment and H2O2 addition, and can be applied for in-situ groundwater treatment. Furthermore, the rotating PVDF-PAA membrane with immobilized Pd-catalyst showed an effective and low maintenance option for employing Pd catalyst for water treatment.

The Fenton system (Fe2+/H2O2) generates ·OH with a high oxidation potential. However, as reactants themselves, H2O2 and Fe2+ can act as ·OH initiators as well as ·OH scavengers, leading to the need for a high dosage of reactants and increased costs. As a mixing-sensitive reaction, the ·OH-related reaction kinetics (·OH with Fe2+, H2O2, and RhB) was determined from the reaction rates (which were a constant in this work) and stoichiometry, in which the latter could be regulated by an addition strategy of Fenton reagents. This suggests that ·OH competitive reactions could be controlled by applying a macrolevel addition strategy. Herein, the effects of different addition approaches of Fe2+ and H2O2 on ·OH competitive reactions were quantitatively and systematically studied by analyzing the removal of the model pollutant RhB. We found that without stirring, and compared with a one-time addition, once H2O2 or Fe2+ was added in a step-wise pattern (e.g., one drop by one drop, 2 times, or 4 times), a high concentration of H2O2 or Fe2+ existed in a localized place for a longer period, resulting in a lower proportion of ·OH reacting with RhB, which we ascribed to an enhanced reaction between Fe2+, H2O2, and ·OH. However, when H2O2 and Fe2+ were added from two close points without stirring, a larger proportion of ·OH was scavenged by H2O2 and Fe2+; while under stirring, even a one-time addition of H2O2 or Fe2+ could cause severe scavenging of ·OH. The results also revealed a linear relationship between the RhB removal percentage and wavelength blue-shifts. This study showed that microlevel ·OH competitive reactions could be controlled by applying a macrolevel addition strategy of Fenton reagents without the addition of external chemicals. The results suggest this methodology can also offer an approach to lower ·OH invalid consumption by regulating the addition strategy in bigger reactors.

Nowadays, underground water is the main source of drinking water that contamination to organic pollutants such as MTBE is an important issue. One of the suitable methods for these types of pollutants is the advanced oxidation methods. Advanced oxidation processes (AOPs) are involved in the production of highly reactive hydroxyl radicals that oxidize organic matter such as MTBE and even lead to its full mineralization. The use of light in the presence of catalysts is one of the methods of advanced oxidation processes. Photocatalytic methods widely used for a wide range of toxic and none degradable pollutants. Recent advances in the fabrication and characterization of Nano scale materials have extensively developed research into methods for the preparation of highly effective Nano-sized catalysts for the removal of chemical contaminants. This review article discusses the work on the photo catalysis of MTBE in water using different types of photo catalysts.

The ultraviolet light activation of persulfate (PS) was evaluated for the degradation of cobalt cyanocomplexes, which are considered as some of the most recalcitrant compounds present in mining wastewater. The influence of the solution pH (11 and 13), initial concentration of PS (0.1, 0.3, 0.5, 0.7 and 0.9 g/L), dissolved oxygen and initial concentration of contaminant were evaluated. Photolysis results showed that  is photosensitive to UVC radiation, while the activation of PS by alkaline pH does not contribute to the degradation of the cyanocomplex. There was no presence of  at both solution pH values using UVC/PS. But at pH 13, the degradation of cobalt cyanocomplexes and the pseudo-first-order rate constant increased. This was attributed to the effective conversion of  to  and to the increase in the oxidative photolysis of PS at high pH. Additional tests demonstrated better performance of UVC/PS in the absence of oxygen which may be caused by the quenching effect of  to the higher energy excited state of the cyanocomplex that must be reached to initiate degradation reactions. Increasing the initial concentration of  will increase the amount of Co removed but it represents the higher specific energy consumption.

The reason for the prominent error in the hydroxyl radical detection method by UV-vis spectrophotometry with fast blue BB salt (FBBs) as the chromogenic agent was detected, and a modified method was proposed. The simultaneous extraction of FBBs in the diazosulfone extraction process was proven to have a distinct influence on the test results. In the modified method, FeSO4 was adopted to limit the extraction of FBBs by a toluene/butanol extraction agent, which sharply decreased the influence of FBBs on diazosulfone detection. The FBBs amount and extraction time played an important role in its extraction. The appropriate FBBs/MSIA ratio was 50, and the reasonable extraction time was 300 s for the modified method. ·OH concentration in the directional decomposition of the Fenton system was detected. The test error was about 7%. This method is quite significant to test ·OH quantificationally to better understand Fenton reaction mechanisms and promote the generation of ·OH.