Abstract
In this work, the degradation of 4-ethylpyridine (4EP) in water by a heterogeneous photo-Fenton process (H2O2/Fe3O4/ultraviolet irradiation (UV)) was investigated. More rapid and effective 4EP degradation was obtained with H2O2/Fe3O4/UV than Fenton-like (H2O2/Fe3O4) and UV/H2O2, which is due to the larger production of hydroxyl radicals from the chemical and photolytic decomposition of H2O2. The operational conditions were varied during 4EP degradation experiments to evaluate the effects of pH, catalyst, concentration, and temperature on the kinetics and efficiency of H2O2/Fe3O4/UV oxidation. Under optimal conditions (100 mg/L 4EP, [H2O2] = 1000 mg/L, Fe3O4 = 40 mg/L, pH = 3 and room temperature, 300 rpm), 4EP was totally declined and more than 93% of the total organic carbon (TOC) was eliminated. Liquid chromatography analysis confirmed the formation of aromatic and aliphatic intermediates (4-hydroxypyridine, 4-pyridone, malonic, oxalic, and formic acids) that resulted in being mineralized. Ion chromatography analysis demonstrated the stoichiometric release of NH4+ ions during 4EP degradation by heterogeneous photo-Fenton oxidation. The reuse of the heterogeneous catalyst was evaluated after chemical and heat treatment at different temperatures. The heat-treated catalyst at 500 °C presented similar activity than the pristine Fe3O4. Accordingly, heterogeneous photo-Fenton oxidation can be an alternative method to treat wastewaters and groundwater contaminated with pyridine derivatives and other organic micropollutants. The combination of heterogeneous photo-Fenton oxidation with classical biological methods can be proposed to reduce the overall cost of the treatment in large-scale water treatment plants.
Highlights
Pyridine derivatives are synthetic compounds that are commonly used in the production of commercial products such as food aromas, paints, dyes, rubber products, waterproof fabrics, coatings, pesticides, fungicides, and antioxidants [1,2,3]
Total organic carbon (TOC) was measured by an Analytik Jena total organic carbon (TOC) analyzer to follow up the mineralization of 4EP in aqueous solutions
The TOC removal during the treatment of 100 mg/L 4EP aqueous solution using the homogeneous photo-Fenton process (UV/H2O2/Fe2+: 1000 mg/L H2O2, 10 mg/L Fe2+) achieved 98% at pH 3.0, 72% at pH 5.0, 56% at pH 7.0, and 37% at pH 9.0 after 360 min. These results demonstrated that the initial pH affects the efficiency of the treatment for both heterogeneous and homogeneous photo-Fenton processes; the lower effect on TOC removal was observed with the heterogeneous photo-Fenton
Summary
Pyridine derivatives are synthetic compounds that are commonly used in the production of commercial products such as food aromas, paints, dyes, rubber products, waterproof fabrics, coatings, pesticides, fungicides, and antioxidants [1,2,3]. 4-ethylpyridine (4EP) is among the pyridine derivatives utilized in coking, chemical synthesis, pharmaceutical, and pesticide industries [4,5,6,7,8]. Sci. 2019, 9, 5073 and difficult to biodegrade [10,11,12,13,14]. It is largely spread across the environment due to its extensive use and can contaminate groundwater and surface waters [8,9,10,11,12,13,14]. The conventional biological remediation process treatment methods are not able to completely remove 4EP from contaminated water [15,16,17]
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