Adsorption of ciprofloxacin from water: A comprehensive review

https://doi.org/10.1016/j.jiec.2020.09.023Get rights and content

Highlights

  • Ciprofloxacin (CIP) uptake from aqueous media was reviewed.

  • Magnetic N-doped carbon had the highest adsorption capacity (1564 mg/g) for CIP.

  • Uptake in adsorption columns was always best-fit to the Thomas and Yoon-Nelson models.

  • Future studies could explore novel hybrid processes and adsorbent modification.

Abstract

In this paper, the adsorption of Ciprofloxacin (CIP) from water in studies over the last decade was reviewed. The purpose of this review is to analyse the vast body of literature on the subject, identify key empirical findings on specific investigation domains, establish knowledge gaps and grey areas that could serve as a foundation for other investigations by researchers and predict future perspectives in the research area. The highest reported adsorption capacity for CIP was 1564 mg/g for magnetic N-doped porous carbon. The major mechanisms of CIP uptake are electrostatic interactions, π-π interactions, H-bonds, hydrophobic interactions and pore diffusion. CIP uptake was best-fit to either the Langmuir and Freundlich isotherm and the pseudo-second-order kinetic model. For most adsorbent types, reusability of up to 4 cycles could be achieved with good retention of uptake capacity. The review further showed that CIP uptake in adsorption columns was majorly best fitted to the Thomas and Yoon-Nelson models. In competitive adsorption scenarios, the presence of other pharmaceuticals usually decreases the uptake of CIP. Looking to the future, studies on novel hybrid processes, adsorbent modification, composite adsorbent development, neural network modelling, molecular simulations and used adsorbent disposal techniques are likely to increase for CIP adsorption.

Introduction

There is a need to ensure significant human health and environmental sustainability sequel to the persistent human population growth and its associated anthropogenic effects [1], [2]. This has necessitated the enactment of waste disposal laws and regulations [3], [4]. The bulk of such legislations are directed at the biologically persistent and highly toxic carcinogenic chemicals, as well as industrial intermediates [5]. Some of these highly harmful chemicals come from highly essential pharmaceuticals and personal care products (PCPPs) [4], hence their heavy usage [6], [7]. Contrary to the majority of other chemicals contaminants, PCPPs is expected to remain for a long time in the environment (with serious negative consequences), unless eliminated by an effective treatment process [8], [9], [10].

CIP is a broad-spectrum antibiotic and notably, antibiotics are the most widely used PCPPs [11], [12], [13], [14]. Klein et al. [15] analysed antibiotic usage trends and drivers in 76 countries between 2000 and 2015. Their report depicted about 65% (defined daily doses of 34.8 trillion) increase in antibiotics consumption within the said period. The study also predicted that the global consumption of antibiotics could rise by 200% compared with 2015 data (if no policy changes are made) [15]. Since the consumed antibiotics are mainly removed by excretion, huge quantities of these antibiotics and their by-products (unaltered or metabolised) eventually reach the sewage system [11]. Except these antibiotics are effectively degraded or eliminated from wastewaters, they pose a threat to the flora and fauna of the ecosystem [16]. The occurrence of antibiotics residue has been reported in the ground, surface and potable waters [17], [18], [19].

Ciprofloxacin (CIP) is among the leading fluoroquinolones (FQs) of choice and also the most widely used chemotherapeutic antibiotics worldwide [4], [20]. It was first marketed in 1987 and offers a broad spectrum antibacterial activity [21]. CIP works by preventing the cellular replication of the bacteria and ultimately compromise their proliferation [22]. CIP in surface water has been found at levels ranging from 2.45 × 104 mg/L [23] and 6.3 × 104 mg/L [24] and from 7.0 × 104 to 0.1245 mg/L [21], [25] in hospital effluent. The global concentration of CIP in surface water was reported to be within the range of 0.0018 nmol/L [26] and a high value of 19 617 nmol/L [27]. CIP like other antibiotics could accumulate in the body of organisms, thus posing a serious health threat [28], [29], [30]. Therefore, with due recourse to their high-level concentration in the several wastewaters, stability, resistance to degradation, and potential ecotoxicity, the effective removal of CIP is plausible [31], [32].

Various technologies such as bioremediation [33], [34], advanced oxidation processes [35], ozonation [36] etc. have been proposed for the remediation of the CIP polluted wastewater. Nevertheless, these approaches have associative limitations such as inefficient elimination, complicated procedures and high energy demands [37]. Adsorption using various adsorbents holds greater application potentials due to its low cost, high performance, and flexibility [38], [39], [40], [41]. Various adsorbents such as carbon-based materials, polymers and resins [42], [43], metal-organic frameworks [44], [45], clays and minerals [46], [47] have been explored for antibiotic adsorption.

Considering the unique advantages offered by adsorption technique, its application in the uptake of CIP from aqueous media is an important concept that needs a well-structured review. Meanwhile, judging from the author's extensive search, there is no systematic review directly devoted to the adsorption of CIP from aquatic media despite the decades of work in the research area. Our preference for CIP as the target adsorbate was due to their broad use and prevalence in wastewaters, particularly in developing countries. Studies reported within the last decade was of focus in the review. Nevertheless, older studies with substantial relevance to the subject under review were also captured.

Therefore, this review focuses on elucidating the various adsorbents’ performance for CIP uptake from aqueous media. Insight into the adsorption isotherms, kinetics, and thermodynamic modelling, as well the elaborate discussion of CIP adsorption mechanism was also provided. Furthermore, the adsorbents’ desorption/reusability studies, column adsorption, competitive adsorptive systems and molecular modelling and simulation, in the CIP adsorption were discussed. The aforementioned review focuses were achieved by analysing and summarising the vast body of literature on the subject, identify key empirical findings on specific investigation domains, establish knowledge gaps and grey areas that could serve as a foundation for other investigations by researchers and predict future perspectives in the research area. The pool of literature for the review are all indexed papers on the subject published in the last decade.

Section snippets

Ecotoxicology of CIP

This section provides a brief discussion on the ecotoxicology of CIP which is useful for enlightening the readers on the adverse effect of CIP contamination in an aqueous environment. The piece also doubles as a justification for effective CIP uptake from aqueous environment. Ciprofloxacin (CIP) is mainly used in human medicine, especially in the treatment of urinary tract infections in men [48], [49]. The general chemical structure of CIP is shown in Fig. 1.

CIP is one of the pharmaceutically

Overview of mitigation strategies for CIP

The various mitigation approaches used for CIP are deliberated in this section. This was done to reveal the significance of adsorption and its advantage over other mitigation approaches for CIP, thereby supporting the choice of emphasis of this review. The treatment methods adopted by different authors for the management of CIP polluted waters may be divided into physical (nanofiltration [61], [62], ultrafiltration [63], [64], [65], reverse osmosis [66] and adsorption [67]), chemical (advanced

Adsorbent performance for CIP uptake from aqueous media

In this section, the adsorbent performance for the uptake of CIP from aqueous media is discussed. The performance is reported in terms of the maximum adsorption capacity (qmax). Removal efficiency is not used because it is highly dependent on the initial concentration of CIP and the dosage of the adsorbent. This will not give a true representation of the adsorbent performance. The adsorption capacity on the other hands represents the inherent capacity of the specific adsorbent for CIP. The

CIP adsorption mechanism

In this section, the mechanism of CIP uptake from aqueous media is discussed. The mechanism of adsorption is highly dependent on the solution chemistry [130], [245]. Key information on the solution pH, adsorbent point of zero charge (pHzc) and the pKa of the adsorbate help researchers gain insight on of the solution chemistry and how it determines which mechanisms come into play. The pKa of CIP is a known value of 5.9 (pKa1) and 8.9 (pKa2) [246]. In combining these, alongside results from

Equilibrium and kinetics modelling

The efficiencies and capacities of adsorbents for the removal of pollutants from effluents can be described empirically using several models [262]. These models depict the chemical kinetics during the adsorption of targeted pollutant(s) at constant temperature and equilibrium conditions. From Table 3, it can be observed that the pattern of interactions between CIP and various adsorbents during adsorption were majorly predicted by either Langmuir and Freundlich isotherms. This follows the fact

Thermodynamics modelling

The discussion of the thermodynamics of CIP adsorption will be based on the nature of the adsorbents, for instance, activated carbon (AC) from biosorbents, magnetic carbon composites, metal-organic frameworks (MOFs) and soil minerals. This is because the nature of the adsorbent plays an important role in adsorption thermodynamics. The change in Gibbs free energy (ΔG) is given by Eq. (7)ΔG=-RTInKWhere R is the universal gas constant, T is the temperature in Kelvin, and K is equilibrium constant.

Desorption and reusability studies

Reusability studies is an essential parameter of concern in ascertaining the possibility of adsorbents for industrial adaptation. If the expended adsorbent is discharged into the environment without regeneration, they may cause another environmental concern. Regeneration of adsorbents is carried out by desorbing the adsorbent through an eluent [314]. Desorption can also be an important investigation when the goal of the initial adsorption study was drug release [265], [295], [315].

It was

Column adsorption studies

Investigations on the performance of adsorption in a column set-up are quite popular given a potential industrial application of the findings of a research study [317]. Industrial processes are majorly continuous to avoid down-time. Column adsorption is easier to effect in such industrial applications. Darweesh and Ahmed [318] studied the adsorption of CIP onto granular AC in a fixed-bed column. The study observed that both the Thomas and Yoon-Nelson models were a good fit to the experimental

Competitive adsorption and ionic strength effects

The competitive adsorption of CIP is an important investigation because it gives more information on the adsorption process. It is known that the presence of other ionic species affects CIP uptake [279]. It informs of the adsorbent selectivity for the adsorbate in light of other competing species in solution [326], [327]. This is very important for investigations where the adsorbent performance needs to be determined ahead of potential use in pharmaceutical of hospital effluent containing CIP.

Molecular modelling and simulation of CIP adsorption

In this section, the molecular modelling of CIP uptake is discussed. Several studies in literature have used in silico platforms to model the adsorption of CIP unto a variety of adsorbents. Cheng et al. [334] developed quantitative models to predict the adsorption of CIP to swine manure. This study was geared towards understanding the mobility of the adsorbate into the environment from livestock farming. CIP usually get into the environment from their manure when these antibiotics are used in

Knowledge gaps and future perspectives

Based on this review, the authors herein discuss prospects for the research area and potential areas of interest that could be explored in future work.

  • i

    Looking at the scope of work done, different types of adsorbent materials have been investigated for the adsorption of CIP. Research studies now focus on adsorbent modification and the development of composite adsorbents to achieve high sorption capacities. Recent studies have achieved sorption capacities for CIP greater than the adsorbent weight

Conclusion

Although a wide array of adsorbents has been employed for CIP uptake over the past decade, magnetic N-doped porous carbon, silica-based ƛ-carrageenan adsorbent and MgO/chitosan/graphene oxide nanosheets had shown better performance (threshold of qmax >1000 mg/g). The highest reported adsorption capacity for CIP was 1564 mg/g by Tang et al. [142] for magnetic N-doped carbon. The major mechanisms of CIP uptake are electrostatic interactions, π-π interactions, H-bonds, hydrophobic interactions and

Declaration of interests

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.

Conflict of interest

The authors declare that there are no conflicts of interest.

Compliance with ethical standards

This article does not contain any studies involving human or animal subjects.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgement

There was no official funding or research grant for this work. All authors whose work are cited in the review are hereby acknowledged for their efforts.

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