Process enhancement at near neutral pH of a homogeneous photo-Fenton reaction using ferricarboxylate complexes: Application to oxytetracycline degradation

Abstract

This work demonstrates the application at near neutral pH of a photo-Fenton reaction mediated by ferri-carboxylates on the treatment of aqueous solutions containing the antibiotic Oxytetracycline (OTC) under solar irradiation. The formation of a Fe:OTC complex after Fe 2+ oxidation to Fe 3+ , in the presence of H2O2, showed the inconvenience of using the conventional Fe 2+ /H2O2/UV-Vis process at near neutral pH levels, as the complex is retained in the filter. To overcome this, a Fe 3+ /Oxalate/UV-Vis or Fe 3+ /Citrate/H2O2/ UV-Vis process was proposed. The higher tendency of Fe 3+ to form complexes with carboxylates avoids the formation of Fe:OTC complexes and allows for proper OTC detection along reaction times. The photo-Fenton process itself is improved by the extension of the iron solubility to higher and more practical pH values, by the increase of the quantum yield of Fe 2+ production and by presenting stronger radiation absorption at wavelengths up to 580 nm. In this way, process efficiency 2 was evaluated for different variables such as Fe 3+ concentration, pH, temperature and irradiance, using a compound parabolic collector (CPC) photoreactor at lab-scale under simulated solar radiation. Reaction rates were compared in the presence of different inorganic anions and humic acids, and in two different real wastewater matrixes. Results obtained in a CPC pilot-scale plant under natural solar light, using an iron/oxalate molar ratio of 1:3 ([Fe 3+ ]=2 mg L -1 , the maximum allowable discharge limit imposed by Portuguese regulations), at an initial pH of 5.0, showed that the antibiotic is quickly removed from solution, with consequent loss of activity on Escherichia coli (DSM 1103). The original DOC was decreased by 51%, with a remaining high percentage of low-molecular-weight carboxylate anions, and the final pH is within the legal discharge limits.

Enhancement effects of chelating agents on the degradation of tetrachloroethene in Fe(III) catalyzed percarbonate system

“…Soluble Fe(III) combined with metal chelating agents can minimize non-specific losses of soluble Fe catalyst. For example, ferric iron chelated with CIT, OA, or EDTA retains a catalytic ability to increase rates of hydroxyl radical generation at natural pH regimes (pH = 5-7) by avoiding the precipitation of iron [17]. …”

Application of high intensity UVC-LED for the removal of acetamiprid with the photo-Fenton process

“…11.142 1385-8947/Ó 2014 Elsevier B.V. All rights reserved. the iron redox cycle to generate hydroxyl radicals and has been successfully used as a polishing treatment of wastewater after physico-chemical and biodegradation steps [8,9]. It is often applied using solar radiation as the photon source because the photoFenton process is photoactive in the UV and near visible spectrum up to 560 nm [7].…”

Synthesis of an inorganic‐framework molecularly imprinted Fe‐doped TiO2 composite and its selective photo‐Fenton‐like degradation of acid orange II

“…Various AOP techniques, such as ozone oxidation, photocatalytic oxidation, Fenton, photo‐Fenton‐like and solar photo‐Fenton‐like have been widely utilized to eliminate organic pollutants through radical mediated oxidation processes . The photo‐Fenton‐like process (homogeneous) is emerging as a promising alternative because of its economic feasibility and high efficiency, and has intrigued scientists worldwide . In the photo‐Fenton‐like system, degradation of the contaminants is conducted by the combination of the classical Fenton process with the photoassisted regeneration of the hydroxyl radicals and the iron ions …”

“…21,22 The photo-Fenton-like process (homogeneous) is emerging as a promising alternative because of its economic feasibility and high efficiency, and has intrigued scientists worldwide. 20,23 In the photo-Fenton-like system, degradation of the contaminants is conducted by the combination of the classical Fenton process with the photoassisted regeneration of the hydroxyl radicals and the iron ions. 24,25 Despite the effectiveness of the homogeneous photo-Fentonlike treatment, its industrial application is restricted because of some defects, which include strict pH range limits, H 2 O 2 consumption, iron sludge in post-treatment, and difficulties in recycling.…”