Elsevier

Water Research

Volume 191, 1 March 2021, 116815
Water Research

Tube-in-tube membrane photoreactor as a new technology to boost sulfate radical advanced oxidation processes

https://doi.org/10.1016/j.watres.2021.116815Get rights and content

Highlights

  • Tube-in-tube membrane photocatalytic photoreactor boost the efficiency of SR-AOPs.

  • The technology facilitate the transport of peroxydisulfate to the catalyst surface.

  • The SR-AOP combines photolysis and chemical electron transfer activation methods.

  • High oxidant concentrations near catalyst surface enhances TiO2- S2O82− interaction.

  • Transformation products identified show to have non-biodegradable characteristics.

Abstract

This work proposes a tube-in-tube membrane photoreactor, operated in a continuous-mode, to boost the efficiency of peroxydisulfate (PDS), through the photolytic (UV-C radiation) and photocatalytic (TiO2-P25) processes. This new technology can efficiently facilitate the transportation of PDS to the catalyst surface and water to be treated. The ultrafiltration tubular ceramic membrane was used as support for the TiO2-P25 and oxidant-catalyst/water contactor. Tests were performed using a synthetic solution and a municipal secondary effluent, both spiked with a pharmaceutical mix solution (paracetamol (PCT), furosemide (FRS), nimesulide (NMD), and diazepam (DZP); 200 μg L−1 of each). At steady-state regime, the UVC/S2O82−/TiO2 system, with radial PDS addition, showed the highest removal of pharmaceuticals in both matrices. Furthermore, twenty-two transformation products (TPs) were identified by applying LC-QTOF MS technique. Hence, the transformation pathways including hydroxylation in aromatic moiety by an electrophilic attack, electron transfer reactions, cleavage of C−O, C−N bond, H−abstraction and ring opening were proposed. TPs chemical structures were evaluated by in silico (Q)SAR approach using TOXTREE and EPI Suite™ software.

Introduction

Conventional municipal wastewater treatment plants (MWWTPs) are not able to fully degrade contaminants of emerging concern (CECs) resulting in the significant and continuous release of such compounds to the anthroposphere which constitutes a stress factor for water resources (Loos et al., 2013). Reducing CECs risks is globally urgent and new mitigation technologies are needed towards a water protection approach (One Health Initiative, 2020; US Water Alliance, 2020).

In recent years, sulfate radical-based Advanced Oxidation Processes (SR-AOPs) are gaining attention as a potential technology for removal of CECs from municipal wastewaters (Cvetnić et al., 2019; Ike et al., 2018; Wacławek et al., 2017). Sulfate radicals can be generated from peroxydisulfate (PDS), which has high stability, high solubility (730 g L−1, at 25 °C), high molar extinction coefficient (21.1 M−1 cm−1), high quantum efficiency (1.8 mol Einstein−1) at 254 nm, and comparable price (0.18 USD mol−1) when compared to other oxidants such as hydrogen peroxide (He et al., 2014; Ike et al., 2018; Wacławek et al., 2017). The activation of PDS involves the homolytic cleavage of the O−O bond that leads to the generation of SO4•−, which has a high redox potential (2.5–3.1 V vs. NHE) (Neta et al., 1988). The main activators of the PDS are: energy in different forms (e.g. heat, sonochemical, photochemical), transition metals, carbonaceous materials, alkaline conditions, electrochemical, and through its combination with other oxidants (e.g., ozone, hydrogen peroxide, and calcium peroxide) (Duan et al., 2020).

There are several limitations in SR-AOPs systems: i) the recovery of catalysts or metal ions, which requires more steps for separation; ii) catalytic performance is highly dependent on solution pH and iii) in real wastewater, the existence of a large number of organic compounds can bind to the catalyst, which also reduces the generation of radicals (Duan et al., 2020). A possible approach to overcome such barrier is the combination of two or more different activation methods (hybrid systems), such as photochemical and photocatalytic, able to produce different reactive species (synergistic effects), such as sulfate, hydroxyl and superoxide radicals, boosting the process performance of SR-AOPs. The combination of photochemical and photocatalytic processes involves: i) direct oxidation by S2O82−; ii) photolysis of S2O82− into SO4•− in the presence of UVC light; iii) photo-oxidation of H2O/S2O82− into OH/S2O8•− by holes (hVB+) of semiconductor valence band (VB) under UV light; iv) photo-reduction of S2O82−/O2 into SO4•−/O2•− by electrons (eCD) of semiconductor conduction band (CB) under UV light (Yang et al., 2019a). The addition of persulfate to the photocatalytic system i) minimizes e/h+ recombination since eCD are captured by S2O82− more easily than by H2O2 and O2, due to the higher electron affinity of S2O82− (2.1 against 1.77 and 0.44 eV, respectively) (Guerra-Rodríguez et al., 2018; Huling and Pivetz, 2006) and, ii) increases the ratio of “radicals product/electron-hole pairs consumption” for S2O82− pathway compared to that for O2 pathway (Monteagudo et al., 2019; Schneider et al., 2014). Another possible strategy is to develop new oxidant dosing methods able to reduce the dosage of PDS required and minimize the quenching reactions between radicals, decreasing the sulfate post-contamination. Vilar and co-workers proposed a low footprint tube-in-tube membrane reactor (Castellanos et al., 2020) to drive in a smart way the oxidant into the catalyst surface and water to be treated, through ”virtually” unlimited number of oxidant dosing points across the membrane and further dispersed to the annular reaction zone where the oxidant is activated by UVC light, reducing its consumption, improving the contact with the pollutants, and avoiding catalyst deactivation.

Therefore, this paper investigates, for the first time, the use of a tube-in-tube membrane reactor to boost the efficiency of UV/S2O82− and UV/S2O82−/TiO2 for the treatment of pharmaceutical compounds in municipal secondary effluent. Additional objectives are: (i) to identify the main pharmaceuticals transformation products (TPs) with proposed pathways and, (ii) to assess the potential toxicity and biodegradability of the TPs generated during the treatment.

Section snippets

Chemicals and materials

Analytical grade (purity > 98.99%) nimesulide-NMD, furosemide-FRS, paracetamol-PCT and diazepam-DZP were used in this work as target pollutants (see Table S.1). These pharmaceuticals are frequently detected in hospital and urban wastewaters (Becker et al., 2019; Papageorgiou et al., 2016). Sodium persulfate (Merck, 98%) was used as oxidant. Aeroxide TiO2-P25 powder (>99.5% w/w purity, crystalline phases: 20% wt. rutile and 80% wt. anatase) was supplied by Evonik and used as catalyst. Ethanol

S2O82– radial addition tests and steady-state conditions

Steady-state conditions for S2O82– concentration (in the absence of UVC light and pharmaceuticals - Fig. S1a and b) and for concentrations of pharmaceuticals at the reactor outlet using the UVC/S2O82– (membrane without catalyst) (Fig. S2a) or UVC/S2O82–/TiO2 (membrane coated with catalyst) (Fig. S2b) systems in the water flow side at the reactor outlet are obtained after t/τ ≥ 100 (τ is the space-time inside the illuminated ARZ). In the next sections, the conversion of pharmaceuticals will be

Conclusions

A low footprint tube-in-tube membrane photoreactor, operated in a continuous-mode, was able to boost sulfate radical advanced oxidation processes and pharmaceuticals removal due to two main points: i) combination of photolysis and chemical electron transfer activation methods for ROS production and, ii) ability to drive in an efficient way the oxidant into the catalyst surface and water to be treated, through ”virtually” unlimited number of oxidant dosing points across the membrane, providing a

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This study was financially supported by: i) Base Funding - UIDB/50020/2020 of the Associate Laboratory LSRE-LCM - funded by national funds through FCT/MCTES (PIDDAC); ii) Project NOR-WATER funded by INTERREG VA Spain-Portugal cooperation program, Cross-Border North Portugal/Galiza Spain Cooperation Program (POCTEP), iii) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001 and, iv) Brazilian authors thank CNPq (Process: 403051/2016-9). Elisabeth Cuervo

References (58)

  • X. He et al.

    Destruction of cyanobacterial toxin cylindrospermopsin by hydroxyl radicals and sulfate radicals using UV-254nm activation of hydrogen peroxide, persulfate and peroxymonosulfate

    J. Photochem. Photobiol. A Chem.

    (2013)
  • X. He et al.

    Degradation kinetics and mechanism of β-lactam antibiotics by the activation of H2O2 and Na2S2O8 under UV-254nm irradiation

    J. Hazard. Mater.

    (2014)
  • M. Ibáñez et al.

    UHPLC-QTOF MS screening of pharmaceuticals and their metabolites in treated wastewater samples from Athens

    J. Hazard. Mater.

    (2017)
  • I.A. Ike et al.

    Critical review of the science and sustainability of persulphate advanced oxidation processes

    Chem. Eng. J.

    (2018)
  • L. Ismail et al.

    Elimination of sulfaclozine from water with SO4 radicals: evaluation of different persulfate activation methods

    Appl. Catal. B Environ.

    (2017)
  • C. Laurencé et al.

    Preparative access to transformation products (TPs) of furosemide: a versatile application of anodic oxidation

    Tetrahedron

    (2011)
  • C. Laurencé et al.

    Anticipating the fate and impact of organic environmental contaminants: a new approach applied to the pharmaceutical furosemide

    Chemosphere

    (2014)
  • C. Liang et al.

    A rapid spectrophotometric determination of persulfate anion in ISCO

    Chemosphere

    (2008)
  • R. Loos et al.

    EU-wide monitoring survey on emerging polar organic contaminants in wastewater treatment plant effluents

    Water Res.

    (2013)
  • Q. Mei et al.

    Sulfate and hydroxyl radicals-initiated degradation reaction on phenolic contaminants in the aqueous phase: mechanisms, kinetics and toxicity assessment

    Chem. Eng. J.

    (2019)
  • R. Molinari et al.

    Heterogeneous photocatalytic degradation of pharmaceuticals in water by using polycrystalline TiO2 and a nanofiltration membrane reactor

    Catal. Today

    (2006)
  • J.M. Monteagudo et al.

    Effect of sodium persulfate as electron acceptor on antipyrine degradation by solar TiO2 or TiO2/rGO photocatalysis

    Chem. Eng. J.

    (2019)
  • F.C. Moreira et al.

    Tertiary treatment of a municipal wastewater toward pharmaceuticals removal by chemical and electrochemical advanced oxidation processes

    Water Res.

    (2016)
  • G. Moussavi et al.

    Oxidation of acetaminophen in the contaminated water using UVC/S2O82− process in a cylindrical photoreactor: efficiency and kinetics of degradation and mineralization

    Sep. Purif. Technol.

    (2017)
  • W.-D. Oh et al.

    Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: current development, challenges and prospects

    Appl. Catal. B Environ.

    (2016)
  • M. Papageorgiou et al.

    Seasonal occurrence, removal, mass loading and environmental risk assessment of 55 pharmaceuticals and personal care products in a municipal wastewater treatment plant in Central Greece

    Sci. Total Environ.

    (2016)
  • N.S. Shah et al.

    Efficient removal of endosulfan from aqueous solution by UV-C/peroxides: a comparative study

    J. Hazard. Mater.

    (2013)
  • J. Sharma et al.

    Oxidative removal of bisphenol A by UV-C/peroxymonosulfate (PMS): kinetics, influence of co-existing chemicals and degradation pathway

    Chem. Eng. J.

    (2015)
  • V.J.P. Vilar et al.

    Tube-in-tube membrane microreactor for photochemical UVC/H2O2 processes: a proof of concept

    Chem. Eng. J.

    (2020)
  • Cited by (29)

    View all citing articles on Scopus
    View full text