Elsevier

Science of The Total Environment

Volume 624, 15 May 2018, Pages 1095-1105
Science of The Total Environment

Effective removal of the antibiotic Nafcillin from water by combining the Photoelectro-Fenton process and Anaerobic Biological Digestion

https://doi.org/10.1016/j.scitotenv.2017.12.159Get rights and content

Highlights

  • Complete elimination of the antibiotic Nafcillin by photoelectron-Fenton process follow by anaerobic digestion process.

  • Total removal of antibiotic Nafcillin produces the elimination of the associated antimicrobial activity.

  • The decay of the concentration of the antibiotic follows pseudo-first-order kinetic.

  • Electrochemical degradation of antibiotic Nafcillin produces organic intermediates that remain in solution.

  • Organic intermediates are eliminated during the biologic process.

Abstract

The elimination of the antibiotic Nafcillin (NAF), which is usually used in hospitals and veterinary clinics around the world, was assessed through a combination of three advanced electrochemical oxidation processes followed by anaerobic digestion process. In the first stage different electrochemical advanced oxidation processes (EAOPs) were used: electro-oxidation with hydrogen peroxide (EO-H2O2), electro-Fenton (EF) and Photo electro-Fenton (PEF). After PEF, almost complete and highly efficient degradation and elimination of NAF was achieved, with the concomitant elimination of the associated antimicrobial activity. The fast degradation rate produced by PEF is explained by the oxidative action of hydroxyl radicals (•OH) together with the direct UV photolysis of complexes formed between Fe3 + and some organic intermediates.

Total removal of NAF occurs after 90 min of electrolysis by PEF, with the generation of organic intermediates that remain in solution. However, when this post PEF process solution was treated with an anaerobic biological process, the intermediates generated in the electrochemical degradation of NAF were completely eliminated after 24 h.

The kinetic degradation of NAF as well as the identification/quantification of products and intermediates formed during the degradation of antibiotic, such as inorganic ions, carboxylic acids and aromatic compounds, were determined by chromatographic and photometric methods. Finally, an oxidation pathway is proposed for the complete conversion to CO2.

Introduction

Antibiotics are chemicals that contain active ingredients, designed to treat bacterial infections in humans, but also used in veterinary medicine for therapeutic, prophylactic and growth promotion purposes (Katzung et al., 2013). However, in spite of their usefulness, a great amount and variety of antibiotics are discharged into natural sources through wastewater carrying human excreta; by improper disposal of medications thrown into the toilet; and by liquid agricultural residues, including livestock manure (Kim et al., 2013). These actions generate a great deal of concern about the emergence of bacterial resistance and its consequences for human health, and about the toxic effects on aquatic ecosystems (Serna-Galvis et al., 2015, Serna-Galvis et al., 2016a, Serna-Galvis et al., 2016b).

β-lactams are among the antibiotics frequently detected in hospital wastewater and livestock, and one of them is Nafcillin (NAF) (Kummerer, 2009). NAF belongs to the penicillin family, and has a broad spectrum and intrinsic antibacterial activity. Furthermore, NAF is used in infections caused by Gram (+) germs, such as hemolytic and non-hemolytic streptococci, S. pneumoniae, non-β-lactamase staphylococci, Clostridia spp., B. anthracis, Listeria monocytogenes and most strains of enterococci (Kemper, 2008).

Currently, β-lactam antibiotics are very difficult to remove by means of conventional biological processes. Due to their low biodegradability, they can cause adverse effects on the strains of microorganisms used in wastewater treatment plants. In addition, these antibiotics are also photoresistent and escapes conventional physical treatments such as coagulation (Giraldo-Aguirre et al., 2015, Sirés and Brillas, 2016).

For all the reasons above, the use of non-conventional technologies such as electrochemical advanced oxidation processes (EAOPs) becomes necessary, as it allows the degradation of recalcitrant organic compounds like antibiotics into CO2 or products that could be more biodegradable, facilitating the exchange with biological systems.

EAOPs are based on the in-situ generation of the hydroxyl radical, the most powerful radical oxidant (with a standard potential of 2.80 V/SHE), which can react non-selectively with most organics up to their mineralization to CO2, water and inorganic ions (García-Segura et al., 2013, García-Rodríguez et al., 2016, Benito et al., 2017).

EAOPs based on Fenton's reaction chemistry such as electro-Fenton and photoelectro-Fenton processes have been widely used in the treatment of wastewater containing persistent and emergent organic pollutants (Brillas et al., 2009, Brillas and Martínez-Huitle, 2015). In these Fenton-based processes, the Fe2 + ion is added to the water solution as a catalyst that reacts with H2O2, producing •OH from Fenton's reaction with an optimum pH 2.8, as shown by Eq. (1) (Olvera-Vargas et al., 2015, Pereira et al., 2016).Fe2++H2O2Fe3++OH+OH

H2O2 used in the Fenton reaction is electrogenerated on the cathode in-situ by injecting oxygen or air (Eq. (2)), for example, at a carbon-PTFE gas (O2 or air) diffusion cathode (Salazar et al., 2011).O2+2H++2eH2O2

Eq. (1) is catalytic and can be mainly propagated from the Fe3 + reduction to Fe2 + at the cathode.

When an undivided cell is used in EF, organics can also be attacked by heterogeneous •OH formed on the anode surface showed in Eq. (3) (Espinoza et al., 2016, Trellu et al., 2016). Organic compounds can achieve a total mineralization in an aqueous medium by the action of physisorbed M(•OH) formed during the electrolysis of water to O2, a method that is called electro-oxidation process (EO) (Salazar et al., 2016, Pérez et al., 2017, Raschitor et al., 2017). Currently, the preferred anode for EO-H2O2 is the Boron-doped diamond (BDD) thin-film electrode, which have: i) an inert surface, ii) low adsorption properties, iii) remarkable corrosion stability and iv) a high O2-overvoltage in aqueous medium, which results in the production of reactive BDD(•OH), as shown by Eq. (3). (García-Segura et al., 2015, Martínez-Huitle et al., 2015).BDD+H2OBDDOH+H++e

In PEF, the degradation rate of organic pollutants is enhanced under the simultaneous irradiation of the solution with UV light due to: (i) the greater Fe2 + regeneration and •OH production by photolysis of Fe(OH)2 + (the pre-eminent Fe3 + species in solution at pH near 3), as shown in Eq. (4); and (ii) the photodecarboxylation of complexes of Fe(III) with generated carboxylic acids, which are attacked by •OH, Eq. (5) (El-Ghenymy et al., 2015, Vidal et al., 2016, García-Segura et al., 2017).FeOH2++Fe2++OHFeOOCR2++Fe2++CO2+R

During the last time, EAOPs have been combined with biological treatments to remove contaminants that are not biologically eliminated (Moreira et al., 2015). In aerobic digestion, a group of microorganisms (mainly bacteria and protozoa) act in the presence of oxygen on both the dissolved organic matter and the dissolved, colloidal and suspended inorganic matter found in wastewater, transforming them into gases and cellular matter that can be easily separated by sedimentation (Eq. (6)) (Chiavola et al., 2014, Zhou et al., 2017). The union of organic matter, bacteria and mineral substances forms flocs and set, it knows as biological sludge (Inyang et al., 2016).Organic matter+Microorganisms+Nutrients+O2CO2+H2O+NH3+Newmicroorganisms+Energy

On the other hand, one process less studied but very attractive at the energy level is anaerobic digestion. Anaerobic digestion produces the decomposition of organic matter in the absence of molecular oxygen. In this process organic matter is biologically converted, into methane (CH4) and carbon dioxide (CO2) (Eq. (7)); CH4 could be used as fuel future (Amaral et al., 2014, Ikumi et al., 2014, Vidal et al., 2016). The anaerobic degradation requires the intervention of several groups of facultative microorganisms, which use the metabolic products generated in each stage in a sequential way. This process involves three large trophic groups and four stages of transformation: hydrolysis: bacteria hydrolyze the organic compounds in simpler monomers; acidogenesis, fermentative bacteria produce the conversion of the monomers into short chain volatile fatty acids; acetogenesis: acetogenic bacteria convert short chain volatile fatty acids into acetic acid, carbon dioxide and hydrogen and methanogenesis; methanogenic archaea produce methane gas (Montalvo and Lorna, 2003).Organic matter+Microorganisms+NutrientsCH4+CO2+Newmicroorganisms

In this work, the degradation of the antibiotic Nafcillin by means of the combination of coupled treatments was studied. As a primary treatment, three electrochemical advanced oxidation processes (electro-oxidation in the presence of hydrogen peroxide ((EO-H2O2), EF and SPEF) were applied to find the best process to degrade and mineralize NAF. After the application of each treatment, the antimicrobial activity of the electrolyzed solutions was evaluated. Finally, anaerobic digestion was applied to reach the complete mineralization of the solutions.

Section snippets

Reagents

Sodium Nafcillin (CAS number: 985-16-0, C21H22N2NaO5S, 99.9% of purity) supplied by Sigma-Aldrich® was used as received. The chemical structure as well as some characteristics of NAF are shown in Table 1. Analytical grade oxamic and malic acids were from Sigma-Aldrich®, while oxalic, maleic, formic and acetic were from Merck®. Solutions of anhydrous sodium sulfate, used as supporting electrolyte, and iron sulfate II heptahydrate are analytical grade from Merck. All solutions were prepared with

Electrochemical degradation of NAF

EO-H2O2, EF, PEF and a photolysis processes were applied to degrade NAF in order to find the most effective before treating NAF solutions with a biologic process. These experiments were performed using a concentration of 50 mg L 1 in 0.05 M Na2SO4 with 1 mg L 1 Fe2 + (for EF and PEF experiments) in 0.250 L solution at pH 2.8. The change in the concentration of NAF was followed by reversed-phase UHPLC, where concentration displayed a well-defined peak at 6.7 min of rt. Fig. 1A shows the change in the

Conclusions

It was determined that the antibiotic NAF can be degraded and partially mineralized by PEF using a BDD anode, air diffusion cathode, and exposure to UV radiation. Complete degradation and elimination of antimicrobial activity in an aqueous antibiotic solution after 90 min of electrolysis was achieved by applying a current density of 2 mA cm 2 in the presence of 1.0 mg L 1 concentration of Fe2 + in an electrolytic medium of Na2SO4 0.05 M at pH 2.8. PEF allows greater decay of the antibiotic

Acknowledgements

The authors thank the financial support of FONDECYT Grant 1170352, DICYT-USACH, CONICYT FONDEQUIP/UHPLC-MS/MS EQM 120065 and to COLCIENCIAS project “Desarrollo y evaluación de un sistema electroquímico asistido con luz solar para la eliminación de contaminantes emergentes en agua (No. 111565842980 Convocatoria 658, 2014). J. Vidal thanks CONICYT for the National PhD scholarship 21140248 and Pacific Alliance Scholarship. Finally, we are grateful to “Proyectos Basales y Vicerrectoría de

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