Elsevier

Chemical Engineering Journal

Volume 346, 15 August 2018, Pages 1-10
Chemical Engineering Journal

Removal of atorvastatin in water mediated by CuFe2O4 activated peroxymonosulfate

https://doi.org/10.1016/j.cej.2018.03.113Get rights and content

Highlights

  • Effective removal of ATV from water was achieved by CuFe2O4/PMS.

  • Degradation intermediates were identified and degradation pathways were proposed.

  • Intermediate distribution was influenced by the dosage of PMS.

  • The main factor affecting the removal of ATV in actual wastewater is organic matter.

Abstract

Atorvastatin (ATV) has been widely detected in wastewater treatment plant and aquatic environment. Limited mineralization ratio of ATV in current wastewater treatment processes may result in the accumulation of its transformation intermediates in effluent and cause additional ecological risk to the environment. In this study effectiveness of peroxymonosulfate (PMS) activated by CuFe2O4 on the degradation of ATV in water were examined. Complete removal of ATV was achieved by using 40 ppm CuFe2O4 and 25 μ mol dm−3 PMS. Eight intermediates were identified and four degradation pathways were proposed. The distribution of major intermediates ATV lactone (P541), hydroxylated ATV lactone (P557) and the pyrrole ring-open intermediate (P416) were monitored with different PMS dosages. As PMS concentration increased from 25 to 150 μ mol dm−3, the main intermediates accumulated were evolved from P541 and P557 to P557 and P416, and all intermediates were completely degraded with 750 μ mol dm−3 PMS. 61.72% TOC removal was achieved at pH 7.0 with 100 ppm CuFe2O4 and 3 m mol dm−3 PMS, which indicated that ATV could be well mineralized if PMS and CuFe2O4 dosages were reasonably used. Overall, this study provided practical knowledge for ATV removal by CuFe2O4/PMS at ambient temperature.

Introduction

Statins are widely used around the world for the treatment of hyperlipidemia by inhibiting the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, which is the key enzyme to the production of cholesterol [1], [2]. The currently marketed statins include atorvastatin (ATV), simvastatin, fluvastatin, lovastatin, pitavastatin, rosuvastatin and pravastatin [3], in which ATV was the most prescribed one with annual sales of 10 billion dollars worldwide [4]. In 2008, the total retail sales of ATV was 5.88 billion dollars in the United States [5]. Increasing amount of ATV were released into wastewater treatment plant (WWTP) and aquatic environment because of its extensive usage and human excretion [6]. The average concentration of ATV in influent and effluent samples collected from 11 wastewater treatment plants located in Ontario, Canada were 166 and 77 ppt, respectively [7]. The influent concentration of ATV was reported as 1.56 ppb in a medium scale sewage treatment plant located in southeastern USA [8]. Furthermore, the concentration of ATV found in Tennessee River water was 101.3 ppt [9]. Therefore, attention needs to be paid to the potential risk of ATV and its degradation products to aquatic organisms.

Some reports have shown that ATV has certain threat to aquatic organisms. Slightly thicker yolk extension and pericardial edema were observed in zebrafish embryos exposed to 10 μ mol dm−3 ATV for 48 h [10]. The numbers of hemorrhagic zebrafish caused by vessel rupture in the head region were increased with increasing ATV concentration when the 6 h post-fertilization zebrafish embryo were exposed to different ATV concentrations (0.05, 0.15, 0.3, 0.5 and 1 μ mol dm−3) for 48 h [11]. In plants, ATV also inhibited the synthesis of sterols. When L. gibba was exposed to ATV, the concentration of sterols, which regulated the water permeability of phospholipid bilayer and affected the function of membrane-bound proteins were decreased with the increasing of ATV concentration, and the EC50 value was 64 ppb [12]. Although the acute toxicity of ATV to aquatic organisms was negligible at environmentally relevant concentrations, it may have a synergistic effect with other stains in the actual environment. In this sense, it is imperative to develop an effective treatment technique for the removal of ATV and its transformation intermediates in wastewater.

Previous studies have shown that ATV can be removed by indirect photolysis in aqueous solution with long half lifetime (4.89 × 103 s) [13]. It is difficult to completely remove ATV by biodegradation, resulting in the frequent detection of ATV in sludge [5], [14]. Advanced oxidation processes (AOPs), such as ozone oxidation, photocatalytic oxidation, Fenton oxidation, has been widely explored in wastewater treatment [15], [16], [17], [18]. Sulfate radical (SO4radical dot)-based AOPs have been recognized as effective alternative method to degrade organic pollutants in wastewater because SO4radical dot is more selective and possesses higher mineralization ability towards organic pollutants than hydroxyl radical (radical dotOH) [19], [20], [21]. SO4· can be generated by activation of peroxodisulfate (S2O82−, PS) or peroxymonosulfate (HSO5, PMS) via heat, UV, transition metals, mixed metal and alkaline [22], [23], [24], [25], [26], [27]. Mixed metal catalysts have attracted great interests in activation of PS and PMS because of their polyfunctionality, stability and better catalytic activity [28]. Copper ferrite (CuFe2O4) has been reported as an effective heterogeneous catalyst in activating persulfates. Zhang et al. have found that CuFe2O4 showed higher activity and lower Cu2+ leaching than CuO at the same dosage [29]. Guan et al. and Jaafarzadeh et al. have reported that atrazine and 2,4-dichlorophenoxyacetic acid could be degraded quickly by using CuFe2O4 to activate PMS [30], [31]. In addition, Ding et al. have found that 10 ppm TBBPA could be completely removed in 30 min by using 100 ppm CuFe2O4 and 0.2 m mol dm−3 PMS [32]. Therefore, CuFe2O4 was used to activate PMS for the degradation of ATV in this study.

The main purpose of this study is to systematically investigate the oxidative degradation process of ATV by CuFe2O4/PMS. Firstly, the key factors influencing the transformation of ATV were evaluated including solution pH, PMS concentration and CuFe2O4 dosage. Secondly, major oxidative species were identified by radical quenching experiment. Thirdly, the identification of transformation intermediates was studied using TOF-LC-MS. Fourthly, the degradation pathways of ATV were proposed, which was verified by the Gaussian theoretical calculations. Then, the distribution of transformation intermediates was analyzed. Finally, the removal efficiency of ATV in actual wastewater was examined.

Section snippets

Chemicals and reagents

Atorvastatin (ATV, 98.0%) was purchased from J&K Scientific Co. Ltd. Peroxymonosulfate (Oxone, KHSO5·0.5KHSO4·0.5K2SO4, KHSO5 ≥ 47%), copper iron oxide (CuFe2O4, 98.5%) and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) ammonium salt (ABTS, 98%) were obtained from Sigma-Aldrich (Shanghai, China). Standards of ATV lactone and 2-hydroxy ATV calcium salt were purchased from Toronto Research Chemicals (Toronto, Canada). HPLC grade methanol was obtained from Tedia Company (Fairfield, USA).

Degradation of ATV at different reaction conditions

The effect of initial pH on the degradation of ATV was illustrated in Fig. 1. The removal rate of ATV increased with the increase of pH from acid to neutral and decreased under alkaline condition (Fig. 1a). The removal rate of ATV in 30 min varied from 9.8% to 73.9% at pH range from 3.0 to 10.5 with the highest rate at pH 7 (73.9%). The phenomenon can be explained in the following aspects: CuFe2O4 nanoparticles are easily dissolved under acidic conditions to release metal ions (shown in Fig. S5a

Conclusion

Effective removal of ATV from water was achieved by CuFe2O4/PMS. The results revealed that increasing the PMS concentration and CuFe2O4 dosage enhanced the degradation efficiency. Optimized removal of ATV was achieved under neutral condition, which was determined by pKa of ATV, species of PMS, and pHpzc of CuFe2O4. Four degradation pathways were proposed by the structural analysis of intermediates and the studies of frontier electron densities. The distribution of ATV intermediates at different

Acknowledgments

The authors are very grateful for the financial support from the Commonwealth and Environmental protection project for the MEP grant (201509053) and the National Natural Science Foundation of China (No. 21577059).

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