Oxidation of EDTA with H2O2 catalysed by metallophthalocyanines

Heterogeneous Fenton-like degradation of EDTA in an aqueous solution with enhanced COD removal under neutral pH

By providing the key carbon and nitrogen elements needed for eutrophication, the potential toxicity of ethylenediaminetetraacetic acid (EDTA) prompts the exploration of effective treatment methods to minimize the amount of EDTA released into the environment. In this study, Fe₃O₄ magnetic nanoparticles (MNPs) were prepared and used as catalysts to study the mineralization of EDTA in Fenton-like reactions under neutral pH. Fe₃O₄ MNPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET). The effects of pH, ferric ion leaching, and H₂O₂ concentration on chemical oxygen demand (COD) removal of EDTA were investigated. The morphological characterization of the nanoparticles suggests a quasi-spherical structure with small particle size and a surface area of 49.9 m²/g. The results show that Fe₃O₄ MNPs had good catalytic activity for the mineralization of EDTA under pH 5.0-9.0. The optimum conditions for the COD removal of 45% at pH 7.0 were: 40 mM H₂O₂, 10 mM Fe₃O₄, and 1 g/L EDTANa₂·2H₂O at 303 K. Fe₃O₄ MNPs maintained high catalytic activity after five cycles of continuous degradation of EDTA. According to reactive oxidizing species measurements obtained by electron spin resonance (ESR), it was confirmed that HO· free radicals, presented in the H₂O₂/Fe₃O₄ MNPs heterogeneous Fenton-like reaction, were the primary active group in the removal of EDTA. These features can be considered beneficial to the application of Fe₃O₄ MNPs towards industrial wastewater treatment.

Enhanced Degradation of Phenol by a Fenton-Like System (Fe/EDTA/H2O2) at Circumneutral pH

This work deals with the degradation of phenol based on the classical Fenton process, which is enhanced by the presence of chelating agents. Several iron-chelating agents such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriamine pentaacetic acid (DTPA), and ethylenediamine-N,N’-diacetic acid (EDDA) were explored, although particular attention was given to EDTA. The effect of the molar ligand to iron ratio, EDTA:Fe, initial pH, and temperature on the oxidation process was studied. The results demonstrate that the proposed alternative approach allows the capacity for degrading phenol to be extended from the usual acidic pH (around 3.0) to circumneutral pH range (6.5–7.5). The overall feasibility of the process depends on the concentration of the chelating agent and the initial pH of the solution. The maximum phenol conversion, over 95%, is achieved using a 0.3 to 1 molar ratio of EDTA:Fe, stoichiometric ratio of H2O2 at an initial pH of 7.0, and a temperature of 30 °C after 2 hours of reaction, whereas only 10% of phenol conversion is obtained without EDTA. However, in excess of ligand (EDTA:Fe > 1), the generation of radicals seems to be strongly suppressed. Improvement of the phenol removal efficiency at neutral pH also occurs for the other chelating agents tested.

Unsubstituted metallophthalocyanine catalysts for the removal of endocrine disrupting compounds using H2O2 as oxidant

Advanced oxidation processes have become increasingly important to treat non-biodegradable compounds entering environmental waters. In recent decades, water-soluble metallophthalocyanines have been shown to catalyse H₂O₂-containing oxidation reactions through the production of unique reactive species, nucleophilic metal-peroxo complexes. Few reports in the literature have examined water insoluble metallophthalocyanines (MPc). The oxidative catalytic activity of water insoluble manganese- and iron-phthalocyanine (MnPc, FePc) at pH 7 has been shown through the decolourisation of methylene blue and removal of bisphenol A. These studies expand on this previous study, exploring the catalytic activity of a range of metallophthalocyanines catalysts under both acidic and neutral conditions. FePc, while only active under neutral conditions, was the best performing catalyst. This activity was significantly improved upon by the addition of acetonitrile as a co-solvent, as well as increasing the ratio of H₂O₂ to catalyst. MnPc was catalytically active at both pH 3 and 7. FePc and MnPc catalysts showed the ability to remove bisphenol A in the presence of dam water. Reaction rates were reduced for bisphenol A removal with FePc as a catalyst but were unchanged in the presence of MnPc. The removal of 17β-estradiol, estrone, and coumestrol was successfully demonstrated, with greater than 96% removal of all tested EDC's achieved. This is the first reported study showing the removal of the phytoestrogen, coumestrol. Even though considerably lower concentrations of costly catalysts and oxidation reagents were used in our work, the removal extent of EDC's by the MPc-catalysed oxidation reactions achieved here compares favourably with literature.

Efficiency of hydroxyl radical formation and phenol decomposition using UV light emitting diodes and H2O2

A novel process combining hydrogen peroxide (H2O2) and radiation emitted by ultraviolet light emitting diodes (UV LEDs) has been investigated. The UV LEDs were used as UV-C light sources emitting radiation in the range 257-277 nm for decomposition of the model substance phenol in water. In addition, the effect of H2O2 to phenol molar ratio and initial phenol concentration was examined. Two parameters, the decomposition efficiency of phenol and characterization of hydroxyl radical (HO*) production from H2O2 when illuminated with UV radiation, were selected to provide detailed information regarding the performance of the UV LEDs in the treatment process. A new concept was introduced to characterize and describe the production of HO* radicals produced when photons were absorbed by H2O2 molecules. The phenol decomposition efficiency at the initial concentration of 100 mg/L was the most pronounced at the lowest emitted wavelength. A significant correlation was found between the phenol decomposition efficiency and the photons absorbed by H2O2 (i.e. formation of radicals).

Natural organic matter removal by coagulation during drinking water treatment: a review

Natural organic matter (NOM) is found in all surface, ground and soil waters. An increase in the amount of NOM has been observed over the past 10-20 years in raw water supplies in several areas, which has a significant effect on drinking water treatment. The presence of NOM causes many problems in drinking water and drinking water treatment processes, including (i) negative effect on water quality by causing colour, taste and odor problems, (ii) increased coagulant and disinfectant doses (which in turn results in increased sludge volumes and production of harmful disinfection by-products), (iii) promoted biological growth in distribution system, and (iv) increased levels of complexed heavy metals and adsorbed organic pollutants. NOM can be removed from drinking water by several treatment options, of which the most common and economically feasible processes are considered to be coagulation and flocculation followed by sedimentation/flotation and sand filtration. Most of the NOM can be removed by coagulation, although, the hydrophobic fraction and high molar mass compounds of NOM are removed more efficiently than hydrophilic fraction and the low molar mass compounds. Thus, enhanced and/or optimized coagulation, as well as new process alternatives for the better removal of NOM by coagulation process has been suggested. In the present work, an overview of the recent research dealing with coagulation and flocculation in the removal of NOM from drinking water is presented.