Photo-Fenton Degradation of Diclofenac:  Identification of Main Intermediates and Degradation Pathway

Abstract

In recent years, the presence of pharmaceuticals in the aquatic environment has been of growing interest. These new contaminants are important because many of them are not degraded under the typical biological treatments applied in the wastewater treatment plants and represent a continuous input into the environment. Thus, compounds such as diclofenac are present in surface waters in all Europe and a crucial need for more enhanced technologies that can reduce its presence in the environment has become evident. In this sense, advanced oxidation processes (AOPs) represent a good choice for the treatment of hazardous nonbiodegradable pollutants. This work deals with the solar photodegradation of diclofenac, an antiinflammatory drug, in aqueous solutions by photo-Fenton reaction. A pilot-scale facility using a compound parabolic collector (CPC) reactor was used for this study. Results obtained show rapid and complete oxidation of diclofenac after 60 min, and total mineralization (disappearance of dissolved organic carbon, DOC) after 100 min of exposure to sunlight. Although diclofenac precipitates during the process at low pH, its degradation takes place in the homogeneous phase governed by a precipitation-redissolution-degradation process. Establishment of the reaction pathway was made possible by a thorough analysis of the reaction mixture identifying the main intermediate products generated. Gas chromatography-mass spectrometry (GC/ MS) and liquid chromatography coupled with time-of-flight mass spectrometry (LC/TOF-MS) were used to identify 18 intermediates, in two tentative degradation routes. The main one was based on the initial hydroxylation of the phenylacetic acid moiety in the C-4 position and subsequent formation of a quinone imine derivative that was the starting point for further multistep degradation involving hydroxylation, decarboxylation, and oxidation reactions. An alternative route was based on the transient preservation of the biphenyl amino moiety that underwent a similar oxidative process of C-N bond cleavage. The proposed degradation route differs from those previously reported involving alternative degradation processes (ozonization, UV/H2O2, or photolysis), indicating that diclofenac degradation follows different pathways, depending on the treatment applied.

Pharmaceuticals and personal care products in effluent matrices: A survey of transformation and removal during wastewater treatment and implications for wastewater management

“…In a pilot-scale study of the removal of diclofenac by photo-Fenton's reagent using a compound parabolic collector (CPC) exposed to sunlight, complete oxidation was attained within 60 min, and complete mineralization in 100 min. 98 Comparison with other oxidative treatments, namely O 3 , UV/H 2 O 2 and photolysis, showed that degradation pathways differed between these AOPs. Similarly, Radjenovic et al 99 found similar, but not identical pathways for the degradation of atenolol by heterogeneous photocalatyis and homogeneous photo-Fenton treatment in the same CPC setup.…”

Photochemical characteristics of diclofenac and its photodegradation of inclusion complexes with β-cyclodextrins

“…2 These contaminants are important because many of them are not degraded by the typical biological treatments applied in wastewater treatment plants and represent a continuous input into the environment. 3 Within the aquatic environment, in river and surface waters, diclofenac is one of the most frequently detected pharmaceuticals. 4 Diclofenac is considerably stable under normal environmental conditions and the most probable decomposition pathway for its onsite elimination is photodecomposition.…”

Avaliação da degradação do diclofenaco sódico utilizando H2O2/fenton em reator eletroquímico

“…Observando ainda o decaimento da concentração do fármaco, verificou-se que a degradação do diclofenaco está associada diretamente à corrente aplicada ao sistema, pois as maiores correntes alcançaram as maiores reduções do diclofenaco e em um menor tempo de experimento. [6][7][8][9] Diversos trabalhos publicados mostram que a degradação de compostos via H 2 O 2 ocorre através do ataque do • OH na molécula orgânica, porém esse ataque é lento devido à baixa taxa de conversão do H 2 O 2 em • OH; devido a esse fato, ocorreu um acúmulo de peróxido residual, no qual o tempo de eletrólise não foi suficiente para a conversão para…”

“…[6][7][8][9][13][14][15][16][17][18][19][20] Na Figura 6 observa-se o comportamento da concentração do diclofenaco durante as eletrólises no reator na presença de íons Fe 2+ . A concentração do fármaco diminui rapidamente nos primeiros 20 min de experimento, comportamento que se reproduz em todas as eletrólises.…”

“…[6][7][8][9] O objetivo deste artigo foi estudar o tratamento eletroquímico de efluentes simulados da indústria farmacêutica, contento compostos biologicamente ativos, utilizando reatores de fluxo construídos com catodo de EDG e anodo de DSA ® .…”