Abstract
Despite that diclofenac has been embodied to the European watch list of priority substances of concern, studies on diclofenac biodegradation are limited and the diversity of diclofenac-degrading microbiota remains unknown. In this work, an immobilized cell biofilter was constructed and operated to evaluate its effectiveness to depurate high strength diclofenac wastewater and to identify the diclofenac-degrading community accommodated in activated sludge by employing high-throughput sequencing techniques. After a two-month adaptation period, biofilter removal efficiencies reached values as high as 97.63 ± 0.62%, whereas utilization of diclofenac in the immobilized cell biofilter led to a drastic pH decrease. Based on Illumina sequencing, the major bacterial taxa identified in the immobilized cell biofilter were members of the species Granulicella pectinivorans and Rhodanobacter terrae, followed by members of the species Castellaniella denitrificans, Parvibaculum lavamentivorans, Bordetella petrii, Bryocella elongata and Rhodopseudomonas palustris. The ability of such taxa to utilize a wide range of carbon sources and to effectively adapt under acidic conditions seemed to be the main parameters, which favored their prevalence in the immobilized cell biofilter. In addition, Wickerhamiella was the predominant fungal taxon in the immobilized cell biofilter, which appears to be actively involved in diclofenac degradation in activated sludge systems.
Highlights
The detection of non-steroidal anti-inflammatory drugs (NSAIDs) in aquatic environments is a result of various sources of pollution, exhibiting a negative impact on health and the environment
WWTPs are designed mainly to remove conventional pollutants contained in municipal and industrial wastewater and fail to effectively remove NSAIDs [1,2], a fact that has led to the detection of numerous pharmaceuticals in the effluents of WWTPs as well as in surface water and groundwater systems [3,4]
Toxic effects of diclofenac on bacteria, algae, microcrustaceans and fish have been reported at concentrations similar to those measured in aquatic habitats [13]
Summary
The detection of non-steroidal anti-inflammatory drugs (NSAIDs) in aquatic environments is a result of various sources of pollution, exhibiting a negative impact on health and the environment. Diclofenac, as other pharmaceuticals, is not effectively removed by conventional WWTPs, a consequence of its large quantities consumed and its low biodegradation potential [4,16,17]. Behera et al [22] reported diclofenac average removal efficiency of 68% in six WWTPs. Even in the use of non-conventional wastewater treatment configurations, like membrane bioreactors (MBR), residual diclofenac concentrations greater than 50% have been determined [23]. Despite the importance of degrading NSAIDs, scientific findings on diclofenac biodegradation are limited Such reports include the isolation of a Brevibacterium sp. An immobilized cell biofilter was installed and operated for an extended time period under diclofenac selection pressure to favor the enrichment of the diclofenac-degrading microbiota that are present in the activated sludge. This set up allowed us to investigate the effectiveness of this biofilter for the depuration of high strength diclofenac wastewater and to identify the diclofenac-degrading microbial community accommodated in the activated sludge through the implementation of high-throughput sequencing techniques
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