Degradation of Textile Dyeing Wastewater by a Modified Solar Photo‐Fenton Process Using Steel Scrap/H2O2

This experimental research deals with using steel scrap as a heterogeneous catalyst. This catalyzes the oxidation reaction of real textile dye wastewater based on a modified solar photo‐Fenton oxidation process. Morphologic analysis and mapping of the elementary composition of the steel scrap have been carried out by scanning electron microscopy. The effects of concentration of H₂O₂, the pH of the solution and the catalyst loading on the degradation of textile dye wastewater are elucidated. Kinetic studies have been performed for the decolorization of wastewater under optimum conditions. It could be concluded that the steel scrap is a potential substitute for ferrous salts as a catalyst for the solar photo‐Fenton reaction.     

Treatment of Refractory Organics Contained in Actual Agro‐Industrial Wastewaters by UV/H2O2

In this work, the treatment of actual agro‐industrial wastewaters (IWW) by a UV/H₂O₂ process has been investigated. The aqueous wastes were received from industrial olive oil mills and then treated by laboratory scale physicochemical methods, i. e., coagulation using ferrous and aluminum sulfate, decantation, filtration and adsorption on activated carbon. These wastes are brown colored effluents and have a residual chemical oxygen demand (COD) in the range of 1800 to 3500 mgO₂ L^–1, which cannot be further eliminated with physicochemical processes. The UV/H₂O₂ treatments were carried out under monochromatic irradiation at 254 nm using a thermostated reactor equipped with a mercury vapor lamp located in an axial position. The effects of initial H₂O₂ concentration, initial COD, pH and temperature have been studied in order to determine the optimum conditions for maximum color and COD removals. The experimental results reveal the suitability of the UV/H₂O₂ process for both removal of high levels of COD and effectively decolorizing the solution. In particular, 95% of color removal and 90% of COD removal were obtained under conditions of pH = 5 and 32°C using 2.75 g H₂O₂ g^–1 COD L^–1 during 6 h of UV‐irradiation. The treatment is unaffected by pH over the range 2 to 9. In addition, the COD removal is improved by increasing the temperature, whereas the color removal has not been affected by this parameter. The results show that the hydroxyl radicals generated from the catalytic decomposition of H₂O₂ by UV‐irradiation of the solution could be successfully used to mineralize the organics contained in IWW. The mineralization of the organics seems to occur in three main sequential steps: the first is the rapid decomposition of tannins leading to aromatic compounds, which are confirmed by the decolorization of the IWW; the second step corresponds to the oxidation of aromatics leading to aliphatic intermediates, which occurs by the cleavage of an aromatic ring, and is established by the removal of aromatics, and the final step is the slow oxidation of the aliphatic intermediates, which is measured by the COD removal.     

Carbamazepine Removal from Groundwater: Effectiveness of the TiO2/UV,Nanoparticulate Zero‐Valent Iron,and Fenton (NZVI/H2O2) Processes

Pharmaceutical compounds, widely produced and used all around the world, are partly responsible for the widespread water pollution in the environment. Carbamazepine (CBZ) is an antiepileptic drug that persists in the environment for many years. In the present study, we used the TiO₂/UV, nanoparticulate zero‐valent iron (NZVI), and NZVI/H₂O₂ treatment processes to compare efficiency of CBZ removal from water. Influence of NZVI loading, H₂O₂ concentration, TiO₂ loading, UV lamp power, and the matrix (distilled water and groundwater) on CBZ removal efficiency was evaluated using full factorial design. Results indicated that the NZVI/H₂O₂ process oxidized CBZ within 5 min. On the other hand, the NZVI process alone did not reduce CBZ concentration after 120 min of process time. The NZVI/H₂O₂ process was equally effective in CBZ removal from both distilled water and groundwater whereas the TiO₂/UV process was less effective due to the presence of ions in groundwater. CBZ removal efficiency of the TiO₂/UV process declined 30% when the matrix was changed from distilled water to groundwater. Negative divalent ions, i.e., and , were the main cause of reduction of CBZ removal efficiency from groundwater. It is likely that these two ions adsorb onto, and consequently prevent the superoxide anion and hydroxyl radical OH^? from being generated on, the surface of the TiO₂.     

Degradation of Aqueous Atrazine and Metazachlor Solutions by UV and UV/H2O2 — Influence of pH and Herbicide Concentration Abbau von Atrazin und Metazachlor in wäßriger Lösung durch UV und UV/H2O2 — Einfluß von pH und Herbizid-Konzentration

The degradation of two pesticides: atrazine and metazachlor was investigated in aqueous solution under UV-irradiation with and without H₂O₂. Rate constants of the photochemical degradation were determined applying a first order kinetics and quantum yields of the processes were calculated. This approach leads to an apparent decrease of the quantum yield with increasing initial pesticide concentration. At low H₂O₂ initial concentrations, the pesticide degradation was shown to be much more efficient than the degradation under UV-irradiation only. However, at high H₂O₂ concentrations (>2 mmol L^?1), the efficiency of the UV/H₂O₂ system dropped down and the quantum yields of degradation were lower than for the direct photolysis. In the absence of H₂O₂, no influence of the pH value on the photodegradation of the pesticides could be noticed in a range between pH 3 and pH 11. At low H₂O₂ initial concentrations, the photochemical degradation of the pesticides was much faster at pH 3 and pH 7 compared with the degradation at pH 11. The results emphasize the potential of optimized reaction conditions in advanced oxidation.     

Photochemical Degradation of Hydrophilic Xenobiotics in the UV/H2O2-process. Influence of Humic Matter on the Degradation Rate of 2-Amino-1-naphthalenesulfonate and Ethylenediaminetetraacetate

Photochemical oxidation methods are able to eliminate hydrophilic xenobiotics with a high efficiency. In waters with high DOC values caused by humic substances (HS) which are able to absorb UV light, problems can result. The degradation rates of the micropollutants using irradiation wavelengths in the range between λ = 200 nm to λ = 260 nm are significantly influenced by HS. This is mainly caused by the high absorption of the HS at shorter wavelength. In the presence of HS, the photolytic degradation of EDTA and FeEDTA was slowed down by an inner filter effect. A similar tendency could be seen for the photolytic degradation of 2-amino-1-naphthalenesulfonate where additional effects to the inner filter effect were also operating. In the UV/H₂O₂-process, the decrease of the degradation rate could be assigned to the ability of the HS to scavenge HO radicals.     

Photochemical Degradation of Hydrophilic Xenobiotics in the UV/H2O2-process. Influence of Bicarbonate on the Degradation Rate of EDTA, 2-Amino-1-naphthalenesulfonate,Diphenyl-4-sulfonate,and 4,4′-Diaminostilbene-2,2′-disulfonate

Hydrophilic xenobiotics can be eliminated in the UV/H₂O₂-process. The oxidation in this process is enhanced by the photolytically generated HO radicals. Bicarbonate is able to scavenge HO radicals. So it was expected that the degradation rates of the investigated xenobiotics were affected by the influence of bicarbonate. In contrast to the widely described decrease of the degradation rate, a much more complex situation was found in this investigation. The degradation rates of 2-amino-1-naphthalenesulfonate and diphenyl-4-sulfonate were decreased and reached for high concentrations of bicarbonate the values of the photolytical degradation rate. The degradation of 4,4′-diaminostilbene-2,2′-disulfonate was accelerated significantly in the presence of bicarbonate. The degradation rate of EDTA was increased at small concentrations of bicarbonate and decreased at higher concentrations.