Abstract
This paper reported the first example on the use of chitosan films, without further modification, to remove and recover, through bio-sorption processes, the emerging pollutant Diclofenac from water. The latter was adopted as a model, among non-steroidal anti-inflammatory drugs, by obtaining a maximum adsorption capacity, qmax, on chitosan of about 10 mg/g, under the applied experimental conditions of work. The literature gap about the use of chitosan films, which was already used for dyes and heavy metals removal, to adsorb emerging pollutants from water was covered, claiming the wide range application of chitosan films to remove a different class of pollutants. Several parameters affecting the Diclofenac adsorption process, such as the pH and ionic strength of solutions containing Diclofenac, the amount of the bio-sorbent and pollutant, and the temperature values, were investigated. The kinetics and the adsorption isotherms, along with the thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were also evaluated. The process occurred very efficiently, and Chitosan/Diclofenac amounts dependent, remove about the 90% of the pollutant, in 2 h, from the tested solutions, through electrostatic interaction involving the carboxylic moiety of Diclofenac and Chitosan amino groups. This finding was confirmed by the pH and salt effects on the bio-sorption process, including swelling measurements of Chitosan films and by FTIR-ATR analysis. In detail, the maximum adsorption was observed at pH 5, when pollutant and Chitosan were negatively and positively charged, respectively. By reducing or increasing the pH around this value, a reduced affinity was observed. Accordingly, the presence of salts retarded the Diclofenac removal screening its charges, which hinders the interaction with Chitosan. The sorption was spontaneous (ΔG° < 0) and endothermic (ΔH° > 0) following the pseudo-second order kinetic model. The process was Diclofenac and Chitosan amount dependent. In addition, the Freundlich and Temkin isotherms well described the process, which showed the heterogeneous character of the process. Experiments of the complete desorption were also performed by using NaCl solutions 0.25 M (like sea water salt concentration) proposing the reuse of the pollutant and the recycling of the bio-sorbent lowering the associated costs. The versatility of the adsorbent was reported by exploring the possibility to induce the Diclofenac light-induced degradation after the adsorption and by-products adsorption onto chitosan films. To emphasize the chitosan capacity of treating water, the removal of another pollutant such as Ketoprofen and the mixture of Diclofenac and Ketoprofen were investigated. In this way, a green and eco-friendly production-pollution prevention technology for removing emerging pollutants from water was presented, which reduced the overall environmental impact. This illustrated experiments both in static and dynamic conditions for potential industrial applications.
Highlights
With a growing world population, in recent years, the human consumption of pharmaceuticals has increased, which is leading to an increased concentration of pharmaceutical compounds in wastewater [1]
The DCF removal from water was investigated by monitoring its UV-Vis absorption spectrum in aqueous solutions, which are purposely contaminated with the pollutant
Considering the actual problem related to the water decontamination from pollutants, this paper reports high efficiency in the DCF removal, and, of Non-Steroidal Anti-Inflammatory Drug (NSAID) emerging pollutants (EPs), from water, by using chitosan film
Summary
With a growing world population, in recent years, the human consumption of pharmaceuticals has increased, which is leading to an increased concentration of pharmaceutical compounds in wastewater [1]. Most of them are persistent in conventional wastewater treatment plants and, they are released in the treated water for human need, as tap water. This represents risk for human health [1,2]. Medicines are considered a worrying class of emerging pollutants (EPs) since they induce a physiological response affecting both non-target individuals and species [3] Regarding this concern, there are no legal discharge limits for these pollutants, some regulations have been published, and the Directive 2000/60/EC was the first mark in the European water policy, which established a strategy to describe how to prioritize high-risk substances.
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