Detoxification of Ciprofloxacin in an Anaerobic Bioprocess Supplemented with Magnetic Carbon Nanotubes: Contribution of Adsorption and Biodegradation Mechanisms.

Ana R Silva,Luciana Pereira,M Fernando R Pereira,Andreia F Salvador,Ana J Cavaleiro,O Salomé G P Soares,M Madalena Alves,Cátia S.N Braga

doi:10.3390/ijms22062932

Ana R Silva, Luciana Pereira + Show 6 more

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https://doi.org/10.3390/ijms22062932

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Abstract

In anaerobic bioreactors, the electrons produced during the oxidation of organic matter can potentially be used for the biological reduction of pharmaceuticals in wastewaters. Common electron transfer limitations benefit from the acceleration of reactions through utilization of redox mediators (RM). This work explores the potential of carbon nanomaterials (CNM) as RM on the anaerobic removal of ciprofloxacin (CIP). Pristine and tailored carbon nanotubes (CNT) were first tested for chemical reduction of CIP, and pristine CNT was found as the best material, so it was further utilized in biological anaerobic assays with anaerobic granular sludge (GS). In addition, magnetic CNT were prepared and also tested in biological assays, as they are easier to be recovered and reused. In biological tests with CNM, approximately 99% CIP removal was achieved, and the reaction rates increased ≈1.5-fold relatively to the control without CNM. In these experiments, CIP adsorption onto GS and CNM was above 90%. Despite, after applying three successive cycles of CIP addition, the catalytic properties of magnetic CNT were maintained while adsorption decreased to 29 ± 3.2%, as the result of CNM overload by CIP. The results suggest the combined occurrence of different mechanisms for CIP removal: adsorption on GS and/or CNM, and biological reduction or oxidation, which can be accelerated by the presence of CNM. After biological treatment with CNM, toxicity towards Vibrio fischeri was evaluated, resulting in ≈ 46% detoxification of CIP solution, showing the advantages of combining biological treatment with CNM for CIP removal.

Highlights

Pharmaceuticals are considered emergent micropollutants by the European Commission due to their potential environmental, ecotoxicological, and sociological risk [1]
The most prescribed pharmaceuticals coincide with the ones detected in the wastewater treatment plants (WWTP) [7,8], as, e.g., ciprofloxacin (CIP), a broad-spectrum fluoroquinolone antibiotic, that is extensively used for the treatment of bacterial infections in humans and animals
Previous carbon nanomaterials (CNM) characterization by TEM [37], revealed that pristine carbon nanotubes (CNT) structure consisted in aggregates of tubes highly entangled, curved, and twisted with each other, and that the ball-milling reduced significantly this entanglement because the mechanical treatment breaks up the tubes, shortening the CNT, and increasing the surface area (Figure S1; Table 1)

Summary

Introduction

Pharmaceuticals are considered emergent micropollutants by the European Commission due to their potential environmental, ecotoxicological, and sociological risk [1]. A wide range of pharmaceuticals, such as antibiotics, anti-inflammatory drugs, anxiolytics and hormones, are not totally metabolized by humans and animals, being excreted to the environment. As well as domestic wastewater, are potential sources of contamination [2]. In wastewater treatment plants (WWTP), these compounds are not completely removed nor mineralized, and end up in natural water bodies or in soils, as well as in drinking waters, and biomagnify in food chains [2,3,4,5]. The most prescribed pharmaceuticals coincide with the ones detected in the WWTP [7,8], as, e.g., ciprofloxacin (CIP), a broad-spectrum fluoroquinolone antibiotic, that is extensively used for the treatment of bacterial infections in humans and animals

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