## 1 Introduction  
Nanotechnology is considered to be a \"key technology\" in the future and its contribution to water and wastewater treatment innovations has already been significantly high. The word nanotechnology includes a wide range of technologies performed on a nanometer scale for many applications [1]. Nanomaterials have been widely used for various environmental applications, such as the treatment of complex wastewaters, showing significant removal efficiency for both organic and inorganic contaminants [2; 3]. Mediterranean countries are major producers of olive oil, and as a consequence, olive mill wastewater (OMW). The composition of OMW may vary much and depends on the type of processed olives, their ripeness, and the extraction process adopted (traditional press method or centrifugation method) [4]. The treatment of OMW is a challenging task due to the high pollutant load (in terms of chemical oxygen demand (COD)), high concentration of recalcitrant compounds (namely lignins and tannins), long-chain fatty acids, phenolic compounds, and biotoxicity [5]. Therefore, for its treatment and disposal, OMW requires a feasible solution from a technical and economical point of view [6]. Recently, a vast number of studies have been reported on the development of chemical and biological technologies for the degradation of organic and inorganic pollutants in aqueous matrices [7]. Efficient and novel methods such as advanced oxidation processes (AOPs) have been considered as one of the best technologies for treating a wide range of recalcitrant materials such as organic pollutants from water and wastewater [8]. Application of solar TiO\({}_{2}\) photocatalysis and solar photo-Fenton for OMW processing was reported initially, with 85% COD and up to 100% of phenol index removal in OMW [9]. Sustainable technologies for agro-food industry wastewater treatment to valorization is another potential aspect, which would reduce global climate change [10; 11]. The phenolic compounds extraction from OMW and their benefits are reported by several studies [12; 13]. Physical-chemical processes such as coagulation-flocculation and oxidation have also been employed in OMW treatment since both are simple and cheap, as well as easy to operate. Additional chemicals are used in these processes to destabilize the suspended and colloidal matter of OMW to form an insoluble solid that can be removed easily from the waste. Oil, suspended solids, COD, and biological oxygen demand (BOD) are decreased in this way. Destabilization of these colloids can be achieved either by reducing or increasing pH (neutralization) or by the addition of coagulants [14]. Chitosan is the only natural animal-based organic coagulant successfully tested. Chitosan itself is a nontoxic biopolymer and has a wide variety of applications in the fields of biotechnology, biomedical, environmental, microbiology, and pharmaceutical studies [15]. Phenols species, which may also be indicated as total phenols or phenolics, are widely employed in many manufacturing processes [16; 17]. Phenol is highly toxic and carcinogenic compound and more resistant to degradation by many biological treatments or chemical adsorption processes. However, it may cause serious damage to human and animal ecosystems because of its inertness, toxicity, endocrine-disrupting abilities, and carcinogenic behavior. Phenols can be removed by physical processes such as flocculation, precipitation, adsorption onto granular activated carbon (GAC), or reverse osmosis (RO) [18]. Commonly used approaches are often ineffective because they simply haul the organic pollutants from water to another medium without degrading or mineralizing them. Among AOPs, the Fenton-like process is considered as a widely investigated method for wastewater treatment [19; 20]; recently, the photo-Fenton process was applied to OMW treatment and achieved 80% microcontaminant degradation [21].