Oxidative degradation of levofloxacin in aqueous solution by S2O82−/Fe2+, S2O82−/H2O2 and S2O82−/OH− processes: A comparative study

doi:10.1016/j.jece.2015.04.019

Journal of Environmental Chemical Engineering

Volume 3, Issue 2, June 2015, Pages 1207-1214

https://doi.org/10.1016/j.jece.2015.04.019 Get rights and content

Abstract

The performance of levofloxacin (LFX) degradation in aqueous solutions in ferrous ion-activated persulfate (S₂O₈²⁻/Fe²⁺), peroxide-activated persulfate (S₂O₈²⁻/H₂O₂), and base-activated persulfate (S₂O₈²⁻/OH⁻) systems was evaluated and compared. The LFX degradation by all studied activated persulfate systems was divided into two oxidation periods: a fast degradation of target compound within the first minute and subsequent gradual oxidation within the remaining reaction time. Notably, without consideration of the first minute, the rest of the LFX degradation in the S₂O₈²⁻/Fe²⁺ and S₂O₈²⁻/H₂O₂ system followed the pseudo-first-order kinetic model. Among the studied activation techniques, the Fe²⁺-activated persulfate system demonstrated the highest efficacy in LFX degradation, mineralization and persulfate utilization, followed by the peroxide-activated persulfate oxidation. Generally, all studied sulfate radical-based advanced oxidation technologies proved to be promising tool for the treatment of LFX contaminated water/wastewater and, especially, groundwater.

Introduction

Antibiotics are one of the most important pharmaceuticals used worldwide in human and veterinary medical practices [1]. The primary pathways for antibiotics release in to the environment are wastewater treatment plants (WWTPs) effluents, animal waste and municipal landfill leachate [2]. Once administered, antibiotics are metabolized to varying degrees, and then excreted as metabolites or unchanged parent compounds, which subsequently can undergo further modifications due to biological and chemical processes in both WWTPs and receiving water bodies [3]. Nevertheless, antibiotics are known to be resistant to conventional biological oxidation and usually escape intact from WWTPs, causing long-term concerns in the environment such as bioaccumulation and contributing to the spread of antibiotic resistance in microorganisms. Particularly, the continuous introduction of antibiotics into the environment can affect natural waters quality and potentially impact drinking water supplies, ecosystem and human health [1], [3]. Thus, developing effective treatment technology for degradation of antibiotics in aqueous matrices is of a great scientific, environmental and public concern.

The application of advanced oxidation technologies (AOTs) could be a viable solution for the prevention of antibiotics escape into the environment as well as for the in situ treatment of already existing groundwater contamination. The radicals involved in AOTs are mainly the hydroxyl radical (HO radical dot , E° = 2.73 V [4]) and sulfate radical (SO₄⁻, E° = 2.5–3.1 V [5], [6]). The former can be generated by combination of strong oxidants (hydrogen peroxide, ozone) with activators (transition metals, semiconductors), UV/vis and ultrasound irradiation [7]. The HO reacts with organic compounds mainly by abstracting hydrogen-atom from C single bond H, NH, or OH bonds, adding to double and triple bonds, or adding to aromatic rings [4], [8]. The advantages of HO radical dot -AOTs as aqueous matrices treatment techniques include high reaction rates and non-selective oxidation due to HO, which allow the simultaneous degradation of multiple organic contaminants including pharmaceuticals [2], [9], [10], [11], [12], [13], [14], [15], [16]. The most common technique used for SO₄ radical dot ⁻ generation is persulfate activation by heat, transition metal, UV or ultrasound irradiation, base, or peroxide [17], [18] in accordance with Eq. (1):S₂O₈²⁻ + activator → SO₄⁻ + (SO₄⁻ + SO₄²⁻)

The activated persulfate oxidation has several advantages over HO radical dot -AOTs. Accordingly, different from hydroxyl radicals, sulfate radicals are more stable, more selective for oxidizing unsaturated bond and aromatic constituents, and preferably undergo electron transfer reactions with organics [17], [18]. The SO₄⁻-AOTs have been recently used for the degradation of organic pollutants in aqueous matrices [19], [20], [21], [22], [23], [24]. However, only few studies concerning antibiotics abatement using activated persulfate systems can be found in the literature [25], [26]. Generally, high aqueous stability, relatively low cost and benign end products make persulfate oxidation a promising choice for in situ groundwater treatment among the other AOTs.

Owning to the advantages of cost effectiveness, high activity and the environmentally friendly nature, ferrous iron (Fe²⁺) has been commonly selected as the activator of persulfate in practical applications [17]:S₂O₈²⁻ + Fe²⁺ → Fe³⁺ + SO₄ radical dot ⁻ + SO₄²⁻

Moreover, several studies have shown that Fe²⁺-activated persulfate system proved effective to degrade various persistent organic pollutants in aqueous matrices [27], [28], [29], [30]. Conversely, the data on the use of other persulfate activation techniques promising for in situ applications such as peroxide and base have not been fully evaluated.

In the present study, a broad-spectrum antibiotic of the fluoroquinolone (FQ) drug class levofloxacin (LFX) was selected as the target compound due to its and other FQs frequent detection in aquatic environment [31]. LFX is principally used to treat severe or life-threatening bacterial infections, since it has substantial activity against a broad array of Gram-positive and -negative bacteria [32]. Similarly to other FQs, it is known to be extremely resistant to conventional biological oxidation and usually escapes intact from wastewater treatment plants [31], [33]. The main goal of this work was to investigate and compare the performance of LFX degradation and mineralization in S₂O₈²⁻/Fe²⁺, S₂O₈²⁻/H₂O₂ and S₂O₈²⁻/OH⁻ systems. To the best of our knowledge, the comparison of different persulfate activation techniques efficacies for FQs as well as other antibiotics degradation in aqueous matrices has not been investigated yet. Generally, the data obtained within this study provides valuable knowledge for further implementation in water/wastewater treatment and in situ groundwater purification by means of activated persulfate oxidation.

Section snippets

Chemicals and materials

Hydrogen peroxide (Perdrogen™, ≥30%), ferrous sulfate heptahydrate (FeSO₄·7H₂O, ≥99%), levofloxacin (Fig. 1; C₁₈H₂OFN₃O₄, ≥98%, molecular weight 361.37 g mol⁻¹, pK_a 5.33 and 8.07 [34], log K_ow − 0.39 [35]), sodium persulfate (Na₂S₂O₈, ≥99%), and sodium sulfite (Na₂SO₃, ≥98%) were purchased from Sigma–Aldrich. All other chemicals of analytical grade were used without further purification. Stock solutions were prepared in ultrapure water (Millipore Simplicity^® UV System). Sodium hydroxide (NaOH) and

Results and discussion

In all studied persulfate systems, a fast decomposition of the target compound during 1 min (the first measured time point after the beginning of the reaction) with subsequent gradual degradation within the remaining reaction time was observed. Accordingly it was suggested to divide the entire persulfate oxidation reaction into two main phases: the first period of rapid LFX degradation and the second period of steady target compound oxidation. Additionally, the obtained data processing revealed

Conclusions

The ferrous ion-activated, peroxide-activated and base-activated persulfate systems proved to be promising techniques for the degradation of LFX in aqueous solution. The main conclusions of this work are summarized in the following points:

•
The performance of the studied processes in target compound oxidation was as follows: the S₂O₈²⁻/Fe²⁺ system > the S₂O₈²⁻/H₂O₂ system > the S₂O₈²⁻/OH⁻ system.
•
The highest mineralization and more complete persulfate utilization were observed in the Fe²⁺-activated

Acknowledgments

The financial support provided by institutional research funding IUT (1–7) of the Estonian Ministry of Education and Research is gratefully acknowledged. The authors thank Ms. Ave Kaskla for her assistance with the experiments.

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Oxidative degradation of levofloxacin in aqueous solution by S2O82−/Fe2+, S2O82−/H2O2 and S2O82−/OH− processes: A comparative study

Abstract

Introduction

Section snippets

Chemicals and materials

Results and discussion

Conclusions

Acknowledgments

Chemosphere

Chemosphere

J. Environ. Manage.

J. Environ. Chem. Eng.

J. Photochem. Photobiol. A Chem.

Environ. Int.

Sci. Total Environ.

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J. Environ. Sci. (China)

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Chem. Eng. J.

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Sep. Purif. Technol.

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Sci. Total Environ.

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Oxidative degradation of levofloxacin in aqueous solution by S₂O₈²⁻/Fe²⁺, S₂O₈²⁻/H₂O₂ and S₂O₈²⁻/OH⁻ processes: A comparative study