Physicochemical characterization of traditionally fried Moroccan fish bones: A preliminary assessment based on iodine number determination

With its geographical location between the Atlantic and the Mediterranean a stretch of approximately 3500 km, Morocco has significant fishery resources. It is one of the leading fish producers on the African continent and plays a leading role in the marine fisheries sector in Africa. As a result, it has one of the highest rates of seafood consumption among Mediterranean countries, consisting mainly of small pelagic species such as sardines, horse mackerel, hake, and anchovies. This consumption is particularly high in coastal regions, where ports and fish markets facilitate access to fresh seafood. Popular restaurants offer inexpensive dishes within the budget of day laborers and merchants in non-sedentary sectors. Fried fish prepared in vegetable oil remains one of the most commonly consumed dishes, generating significant amounts of post-consumption waste in the form of fish skeletons containing residual organic matter, lipids, and biodegradable compounds. When improperly discarded, these residues may undergo decomposition, contributing to odor generation, the release of organic degradation products, and microbial proliferation, which can negatively affect environmental quality. The aim of this study was to develop a sustainable valorization pathway for this type of waste by investigating its physicochemical characteristics and performing a preliminary assessment based on iodine number determination. Waste from Sardina pilchardus and Trachurus trachurus , collected from a traditional restaurant in the city of Fez, Morocco, was pretreated and preliminarily analyzed for moisture content, volatile matter, ash, surface acid-base functions, and the zero-charge pH (pHpzc). It was then characterized physicochemically using scanning electron microscopy coupled with EDX, X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma atomic emission spectroscopy, and thermogravimetry. Sardina pilchardus waste was used to produce a carbonized material by oxygen-limited pyrolysis at 450 °C under −0.8 bar using a patented reactor (MA 57219 B1). The resulting material was preliminarily evaluated through iodine number determination, which provides an indirect indication of accessible microporosity. The results show that the samples exhibit mass losses of approximately 60% between 100°C and 600°C, with a pHpzc of 7.2. The samples exhibit apatite-type crystalline structures with a fibrous, porous, and homogeneous appearance that improve with increasing treatment temperature. The carbonized material exhibited an iodine number of 210.5 ± 8.3 mg g −1 , providing a preliminary indication of accessible microporosity. However, further investigations involving adsorption kinetics, equilibrium isotherms, and pollutant removal studies are required to confirm its suitability for water treatment applications.