O3, O3/UV and O3/UV/ZnO for abatement of parabens in aqueous solutions: Effect of operational parameters and mineralization/biodegradability improvement

https://doi.org/10.1016/j.psep.2019.03.032Get rights and content

Highlights

  • PBs degradation was reached ∼100% by O3/UV/ZnO in 20 min.

  • TOC removal efficiency up to 42% was obtained for PBs decomposition by O3/UV/ZnO.

  • BOD5/COD ratio was raised from 0.25 to 0.76 after treatment with O3/UV/ZnO.

  • Hydroxylation of Methylparaben was the major reaction of PBs degradation.

Abstract

Methyl-, Ethyl-, Propyl-, Butyl-, & Benzyl-paraben degradation is investigated by combination of ZnO-based photo-catalysis and ozonation in a batch cylindrical photo-reactor to evaluate the influence of ZnO concentration, ozone dose, and pH. The results reveal that parabens removal increases by rising the ozone dosage up to 1.8 g/h and ZnO loading climb up to 1 g/L. Optimum pH value for parabens removal is 9, in 1 g/L of ZnO and 1.1 g/h of ozone dose in 20 min reaction time, which leads to complete removal of methyl-paraben by the combined photocatalytic ozonation (O3/UV/ZnO).

Introduction

A group of substances which are used as preservatives are Parabens (Błędzka et al., 2014). They are known as the esters of 4-hydroxybenzoic acid, which include an alkyl (from ethyl to butyl) or benzyl group. They can be used in different industries such as those which are producing foodstuff, cosmetics, pharmaceuticals, and personal care goods (Frontistis et al., 2017; Gryglik et al., 2009). Methyl-, ethyl-, propyl-, butyl-, benzyl-, and heptylparabens are the most useful types (Mauricius et al., 2016). They are stable is acidic solutions and their hydrolyze rate in alkaline solutions decrease by increasing their alkyl chain length (Błędzka et al., 2014). Despite the fact that they are popular, they have some dramatic harmful effects due to their (i) widely discharges to aquatic environments, (ii) toxicity for microorganisms (Gmurek et al., 2015a), and (iii) moderate estrogenicity (Papadopoulos et al., 2016; Terasaka et al., 2006). Even though, it is considered that they are safe additives to food as well as pharmaceutical and personal care products, recently they have received an emerging concern because of their toxic properties (Evgenidou et al., 2015). Nowadays, parabens are contemplated as endocrine-disrupting compounds (Moreta et al., 2015) and are recognized as environmental pollutants (Orak et al., 2017). Therefore, their extraction from the aquatic environments samplings has been reported repeatedly (Błędzka et al., 2009; Radovan et al., 2008).

All over the world, many countries have established legislations to limit the parabens usage and release to the environment. Regarding this, the maximum allowable concentration (MAC) of individual parabens in cosmetics is set at 0.4% in China and 1.0% in Japan (Shen et al., 2007). The European community as well as the food and drug administration of United State, restricts the cosmetic products with methyl, ethyl, propyl, butyl, and benzyl paraben (MP, EP, PP, BuP, and BzP) to a MAC of 0.4% (w/w) for single parabens and 0.8% (w/w) for paraben mixtures (Błędzka et al., 2014).

It is worth to note that Metyl and propylparaben which are widely used in cosmetic products, are the most detected parabens in the environment (Peng et al., 2008). The parabens can be found in different water bodies (rivers, lakes, etc.), in the drinking water, soil and sediments, and even in the ambient air or dust (Gao et al., 2014). Similarly, their presence in the effluents of wastewater treatment units is evidence for their poor treatability in conventional treatment systems (Karthikraj et al., 2017). Generally, their concentration in the environment changes by seasonal changes (Loraine and Pettigrove, 2006). Even though they are commonly in use and widely spread in the environment, the results of studies show there may be a link between parabens and human breast cancer (Byford et al., 2002). Thus their safety is not accepted without reservation (Boberg et al., 2010). This is while due to their inertness, low costs of production, no perceptible odor, and other interesting features their replacement with other substances is very difficult (Błędzka et al., 2014). These facts have led to search for solutions to reduce the undesirable effects.

Several methods such as heterogeneous photo-catalysis (Lin et al., 2011), ozonation (Tay et al., 2010), UV photolysis (Gmurek et al., 2015b), Fenton, photo-Fenton (Orak et al., 2017) and adsorption (Chin et al., 2010; Feng et al., 2014; Zúñiga-Benítez et al., 2016) have been reported in previously studies for their removal from water. The results of studies reveal that lower amounts of ozone are used in parabens removal by photocatalytic ozonation processes (Gomes et al., 2017b). Despite the fact that the removal efficiency of catalytic ozonation is strongly related to the type of catalyst, it needs lower doses of ozone compared with single ozonation (Gomes et al., 2017a). The efficiency of Fenton oxidation process may be effected by pH, H2O2 dose, ferrous sulfate dose, initial pollutant concentration, and time (Ebrahiem et al., 2017). Recent studies have reported removal efficiency of around 100% for some kinds of parabens using integrated magnetic ion exchange resins and nanofiltration (López-Ortiz et al., 2018).

Advance oxidation process (AOPs) is a technology that can be used for oxidation of polluted waters contaminants. To do so, it uses potent chemical oxidants (Glaze et al., 1987). In addition of declining the waters contaminant level, it can kill microbes, remove odor, and improve taste of water. AOPs leads to these results by bringing the biological activity of pollutants down (Sharma et al., 2018). Since advanced oxidation processes leads to better reduction of toxicity and mineralization of organic pollutants, it has gained a higher attention for degradation of nonbiodegradable organic compounds compared to conventional wastewater treatment processes (Martínez-Costa et al., 2018; Shahidi et al., 2015). Many studies have repoerted that application of AOPs leads to more efficient removal of parabens from aqueous solutions (Błędzka et al., 2014). Non-photochemical process and photochemical process are two main types of advance oxidation process. In the non-photochemical type, hydroxyl radicals are generated in the absence of light while in the photochemical process they are generated under the UV light radiation. According to the contaminant type, suitable AOPs process can be selected (Sharma et al., 2018).

Despite their different physical–chemical nature, all organic pollutants show high reactivity to oxidizing reagents. It has been proved that AOPs are efficient due to their free hydroxyl radicals (radical dotOH) (Varanasi et al., 2018) and high oxidation potential that enables rapid oxidation of the polluting organic molecules to CO2 (Orak et al., 2017). It was considered that AOPs dos not generate any toxicity but the results of recent studies show that oxidation of parent compounds may lead to generation of toxicity (Sharma et al., 2018). In this regard complete oxidation of the pollutants is important.

The latest oxidant that is used for remediation of organic components is persulfate (Zhou et al., 2018). Dhaka and etal. used oxidants like persulfate, hydrogen peroxide, and peroxymonosulfate for degradation of ethyl paraben by UV-C-mediated advance oxidation. According to their results, considering the energy intensity and total cost, the efficiency of system when persufate is used is more than other oxidants (Dhaka et al., 2018).

Catalytic Ozonation Process (COP) is kown as an ozone-based AOP treatment technologies. In COP catalytic materials are added to the sole ozonation process (SOP) to decomposit O3 and hereby reactive radicals are generated. COP is an AOP with application of a catalyst for increasing the soluble ozone decomposition, which leads to generation of highly reactive species like hydroxyl radicals (Jung et al., 2007). Using COP, toxic compounds and refractory organic matters are degrading more efficiently and are obtaining greater mineralization rate with radicals compared to SOP (Rahmani et al., 2012). Based on the used catalyst substance, the COPs are divided into homogeneous and heterogeneous processes. The catalyst retrieval from the reaction media is completely easier in heterogeneous catalytic ozonation over the homogenous one. Also simplicity of operation, no residual catalyst in effluent, lower cost and less radical scavenging are other advantages for heterogeneous processe. In this regard, capability of ZnO catalyst within the UV irradiation is evaluated in this work.

As a novel AOP, the simultaneous combination of ozone and a photo-catalyst in presence of UV radiation, so-called photocatalytic ozonation, has attracted high interests (Agustina et al., 2005). In addition of ozone aqueous classical decomposition and its photo-dissociation, in photocatalytic ozonation systems that assisted by photoactive semiconductor, hydroxyl radicals are generated by formation of ozonide radical from ozone molecules on surface of the catalyst. Rapid reaction of the ozonide radical with the H+ gives HOradical dot3 and subsequently hydroxyl radicals are produced (Yıldırım et al., 2011). Fig. 1, shows the main pathways involved in photocatalytic ozonation systems.

Therefore, with a semiconductor catalyst in photocatalytic ozonation for parabens removal from the aqueous solutions surface reactions can do a main role along with UV irradiation, wherein positive holes (h+) are created when electrons (e) of semiconductor valence band migrate to the conduction band as indicated in Eqs. (1), (2), (3), (4). In the presence of ZnO and UV radiation, adsorbed ozone acts as a very strong electrophilic agent that generates ozonide radicals while further reactions produce eventually hydroxyl radicals in the adsorption layer (Addamo et al., 2005; Rajeswari and Kanmani, 2009).ZnO+hve+h+O3ads+ecbO3·O3·+H+HO3·HO3·HO·+O2Electrons in the conduction band (ecb) of ZnO photo-catalysis are the exited ones from valence band and the adsorbed ozone on ZnO takes up the electrons and converts to ozonide, which is an anion radical, this reaction is remarked in Eq. (2). Given the described mechanism only one hydroxyl radical is generated per each trapped electron.

In the photo-catalyst applications, ZnO always is considered as a main candidate because of its unique characteristics, such as direct and wide band gap in near-UV spectral region, strong oxidation ability, good photocatalytic property and a large free-exciting binding energy that causes excitonic emission on the room temperature (Janotti and Van de Walle, 2009).

To our knowledge, no research has been conducted on the photocatalytic ozonation treatment of parabens using a combination of ZnO, ozone techniques and UV as a light source. The combined effect of O3/UV/ZnO on the degradation of Methyl-, Ethyl-, Propyl-, Butyl-, & Benzyl-paraben aqueous solutions are the main aim of this work and effects of operating parameters such as pollutant initial concentration, reaction time, ZnO loading, ozone dosage and pH are also investigated. The ozonation synergistic effect on ZnO photo-catalysis is evaluated and compared with individual techniques.

Section snippets

Chemicals

MP, EP, PP, BuP & BzP (purity ≥ 99) were purchased from Sigma-Aldrich (USA). Then standard solutions were prepared with deionization and kept away from light in a storage temperature of 4 °C. The solutions were weekly refreshed in the same manner. Except the HPLC-grade acetonitrile, all other chemical agents such as (KI), (Na2S2O5), (Na2SO3), sulfuric acid, nitric acid, Sodium Hydroxide, (KCr2O7), (Ag2SO4), (HgSO4), NaH2PO4 and tert-butyl alcohol were analytical grade reagents. Nano-ZnO, with a

Characteristics of the catalyst

XRD graph (Fig. 3) shows a well purity for the used nano-ZnO. The graph indicates ZnO crystalline types given the Miller indices. In this step of the research, the scanning electron microscopy image (Fig. 4) shows granular morphology of the ZnO nanoparticles.

Effect of initial pH

Decomposition mechanism of the parabens is mainly affected by the solution pH, hence, it is important to evaluate this parameter on photocatalytic ozonation of each of the selected parabens. Therefore, the effect of initial pH of the

Conclusions

This study explored the novel advanced oxidation routes for methyl-, Ethyl-, propyl-, buthyl, & benzylparabens in aqueous phase using O3, O3/UV and photocatalytic ozonation (O3/UV/ZnO). The results revealed that O3 could degrade MP, EP, PP, BuP & BzP but the photocatalytic ozonation system enhances degradation rate. Degradations of PBs followed pseudo-first-order kinetics. The increased O3 dosage improved the degradation rate (kobs), while the kobs decreased in higher concentrations of MP, EP,

Acknowledgments

The authors would like to gratefully appreciate Iran University of Medical Sciences for financial support (Grant No:30057).

References (65)

  • S. Dhaka et al.

    Degradation of ethyl paraben in aqueous medium using advanced oxidation processes: efficiency evaluation of UV-C supported oxidants

    J. Clean. Prod.

    (2018)
  • E.E. Ebrahiem et al.

    Removal of organic pollutants from industrial wastewater by applying photo-Fenton oxidation technology

    Arab. J. Chem.

    (2017)
  • F. Erol et al.

    Catalytic ozonation with non-polar bonded alumina phases for treatment of aqueous dye solutions in a semi-batch reactor

    Chem. Eng. J.

    (2008)
  • E.N. Evgenidou et al.

    Occurrence and removal of transformation products of PPCPs and illicit drugs in wastewaters: a review

    Sci. Total Environ.

    (2015)
  • P. Faria et al.

    Catalytic ozonation of sulfonated aromatic compounds in the presence of activated carbon

    Appl. Catal. B: Environ.

    (2008)
  • X. Feng et al.

    Photodegradation of parabens by Fe (III)-citrate complexes at circumneutral pH: matrix effect and reaction mechanism

    Sci. Total Environ.

    (2014)
  • Z. Frontistis et al.

    Solar photocatalytic decomposition of ethyl paraben in zinc oxide suspensions

    Catal. Today

    (2017)
  • Y. Gao et al.

    Computational consideration on advanced oxidation degradation of phenolic preservative, methylparaben, in water: mechanisms, kinetics, and toxicity assessments

    J. Hazard. Mater.

    (2014)
  • M. Gmurek et al.

    Application of photoactive electrospun nanofiber materials with immobilized meso-tetraphenylporphyrin for parabens photodegradation

    Catal. Today

    (2015)
  • M. Gmurek et al.

    Photodegradation of single and mixture of parabens–kinetic, by-products identification and cost-efficiency analysis

    Chem. Eng. J.

    (2015)
  • J.F. Gomes et al.

    Noble metal–TiO2 supported catalysts for the catalytic ozonation of parabens mixtures

    Process Saf. Environ. Prot.

    (2017)
  • J.F. Gomes et al.

    Photocatalytic ozonation using doped TiO2 catalysts for the removal of parabens in water

    Sci. Total Environ.

    (2017)
  • J.F. Gomes et al.

    Detoxification of parabens using UV-A enhanced by noble metals—TiO2 supported catalysts

    J. Environ. Chem. Eng.

    (2017)
  • F.E.R. Gomes et al.

    Photolysis of parabens using medium-pressure mercury lamps: toxicity effects in MCF7, Balb/c 3T3 cells and Ceriodaphnia dubia

    Chemosphere

    (2018)
  • A.G. Gonçalves et al.

    Ceria dispersed on carbon materials for the catalytic ozonation of sulfamethoxazole

    J. Environ. Chem. Eng.

    (2013)
  • R. Karthikraj et al.

    Occurrence and fate of parabens and their metabolites in five sewage treatment plants in India

    Sci. Total. Environ.

    (2017)
  • B. Kasprzyk-Hordern et al.

    Catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment

    Appl. Catal. B: Environ.

    (2003)
  • S. Kotzamanidi et al.

    Solar photocatalytic degradation of propyl paraben in Al-doped TiO2 suspensions

    Catal. Today

    (2018)
  • L. Lei et al.

    Catalytic oxidation of highly concentrated real industrial wastewater by integrated ozone and activated carbon

    Appl. Catal. A: Gen.

    (2007)
  • Y. Lin et al.

    Study of benzylparaben photocatalytic degradation by TiO2

    Appl. Catal. B: Environ.

    (2011)
  • C.M. López-Ortiz et al.

    The use of combined treatments for reducing parabens in surface waters: ion-exchange resin and nanofiltration

    Sci. Total Environ.

    (2018)
  • J.I. Martínez-Costa et al.

    Individual and simultaneous degradation of the antibiotics sulfamethoxazole and trimethoprim in aqueous solutions by Fenton, Fenton-like and photo-Fenton processes using solar and UV radiations

    J. Photochem. Photobiol. A: Chem.

    (2018)
  • Cited by (45)

    View all citing articles on Scopus
    View full text