**1. Introduction**

The production of shell waste by the seafood industry is, among other environmental problems, one of noteworthy concern, contributing to environmental and health hazards [1]. Indeed, a great amount of crab and shrimp shells are produced as waste by worldwide seafood companies [2]. Unfortunately, about 45% of waste resulting from processed seafood is disposed as landfill, consequently leading to environmental pollution in terms of odor and aesthetic damage to the environment [3]. To dispose of this waste, burning is proposed; however, this solution is costly due to the low burning capacity of shells [1].

However, it is worth mentioning that fishery by-products have economical value for chitin and chitosan production [3]; thus, the conversion of shell waste to commercial products could be considered an effective approach for shell waste remediation [1]. Accordingly, Premasudha et al. [4] reported that the ocean ecosystem is one of the major sources of biopolymers, particularly chitosan, increasing the interest toward this bio-waste material, which is characterized by very interesting applications due to its chemical structure and properties [4]. Indeed, chitosan, a by-product from the alkaline deacetylation process of chitin [5], is an amino polysaccharide known for its distinctive properties, as well as its biodegradability and biocompatibility [4].

Chitosan has great potential for environmental applications [6], such as the remediation of organic and inorganic contaminants, including toxic metals and dyes in soil, sediment, and water [7–10], and for the development of devices [11,12]. Among pollutants [13,14], emerging contaminants, e.g., pesticides and their metabolites, pharmaceuticals, personal and house care products, life-style compounds, food additives, industrial products and waste, and nanomaterials, are a great and important problem for the environment. The cumulative use of these substances led to their relatively recent appearance in detectable levels in soils, as well as surface and groundwater resources, with unpredictable consequences for ecosystems [15]. The removal of these pollutants from the environment must be taken into account, and the development of a more sustainable and greener technology for this purpose should be developed [16]. Addressing this concern, several studies [17,18] were reported in the literature, with the use of adsorption methods suggested as the most powerful tools. [18] Furthermore, in order to reduce the environmental impact and the associated cost, agricultural and food waste was carefully investigated as a tool for the removal of pollutants [19,20]. Starting from these considerations, with the aim of valorizing food waste, particularly chitosan from crab shell, attention in this work was focused on the removal of ketoprofen (Kp), adopted as a model emerging pollutant. The use of chitosan as a solid film (CH) is proposed, exhibiting enormous advantages in the treatment of water for Kp removal. Kp, a non-steroidal anti-inflammatory drug (NSAID), is frequently found in surface water, constituting a potential risk for aquatic ecosystems [21–23].

Indeed, for its removal, Jankunaite et al. [24] proposed the use of advanced oxidation processes (AOPs). In this regard, however, it is worth mentioning that AOPs suffer from side effects due to the potential toxicity of the induced by-products, which are often more toxic than the parent molecules [24].

Nagy et al. [25] reported the use of cyclodextrin-based polymers, working in synergy with filters, to exploit the possibility of working under dynamic conditions [25]. Madikizela et al. [26] showed the efficiency of molecularly imprinted polymers, designed for the selective extraction of ketoprofen from wastewater [26].

In addition to these studies, other proposed uses of CH to treat water for removal of the emerging contaminant Kp were outlined in our previous paper devoted to the removal of diclofenac [27]. In the present work, a deep investigation into the process is presented. The use of chitosan film from food waste should not only lower the associated adsorption processes, if compared with the previous adsorbents, but also improve the environmental impact of seafood waste, valorizing it with a simple and easy method to obtain materials for treating water with Emerging Contaminants (EC). Moreover, during this work, for the first time, in addition to the possibility of decontaminating water containing Kp, we propose the recovery of CH after adsorption, emphasizing the sustainable character of the described approach. Indeed, 10 consecutive cycles of adsorption/desorption were performed without affecting Kp removal and recovery, which were completed in a few minutes.
