# Nanomaterials for the Abatement of Pharmaceuticals and Personal Care Products from Wastewater
## 3 Removal of PPCPs by Conservative Methods Envisaging the Use of Nanomaterials  
Non-reactive (conservative) methods imply the removal of the pollutant. The best results with micro-pollutants like PPCPs are usually obtained with either membrane technology (i.e., by reverse osmosis (RO) or nanofiltration (NF)) or adsorption [6]. RO is a method based of a semipermeable membrane able to remove certain ions and particles from a liquid stream. NF is a similar treatment, based on a membrane, but giving a coarser filtration without removing minerals, which are otherwise removed during the RO process. Figure 2: Molecular structure of (**a**) Tylosin, an antibiotic used in husbandry; (**b**) Erythromycin, an antibiotic used for human beings. RO and NF are particularly useful methods for the removal of micro-pollutants from drinking water, though there is still some lack of knowledge about their actual performance, which is influenced by several factors [6; 24; 25], such as the selectivity of organic and inorganic compound removal, salt permeability, pressure and temperature, recovery and feed water concentration. RO membranes are very energy intensive, but the occurrence of pore sizes in the 1.0-5.0 nm range may lead to more than 90% separation of organic molecules from the liquid phase. NF membranes have larger pores (5.0-10 nm range) with respect to RO membranes and show a good performance only for big molecules, like pesticides, whereas they do not remove small molecules, such as ions. Generally, the rejection efficiency (and thus the separation performance) of a membrane is influenced both by mechanisms of size exclusion (molecular sieving) and type of sorption interactions at the liquid-solid interface (van der Waals forces, dipole-dipole forces, etc.). The sieving effect, with the related mass-transfer phenomena occurring during diffusion and separation, controls the performance of RO membranes, whereas the type of sorption interaction controls that of NF membranes. A study concerning the removal of EDCs showed that RO membrane efficiency increases with the molar mass of the target species if the latter are neutral molecules [26], whereas the efficiency of NF membranes increases with the charge and the molar mass of ionic compounds [27]. During membrane operation, some deposition phenomena at the membrane surface may occur that, in some cases, may lead to an improved separation efficiency of the membrane, whereas in other cases may lead to undesired fouling phenomena that have to be taken into account [26; 28; 29]. Polyamide NF/RO cationic membranes have been used for the rejection of 11 compounds including both EDCs and other pharmaceutical active compounds (PhACs) [30]. Two types of membranes were considered, namely a polyamide membrane and a cellulose acetate membrane. The former exhibited a better performance in terms of rejection of the selected compounds, but retention was only in the 57-91% range. It was found that the two most common ways adopted to evaluate the membrane rejection properties (i.e., molecular weight cut-off and salt rejection) were not appropriate to provide quantitative information for EDC/PhAC rejection by NF/RO membranes. As a whole, molecular weight exclusion controlled the rejection in polyamide membrane, whereas polarity mostly controlled rejection in cellulose acetate membrane. As a conclusion [30], each present (and future) material adopted in NF/RO membranes will exhibit different trends for the rejection of micro-pollutants depending on the physico-chemical properties of the target compounds. Activated carbons (ACs) and other adsorbents, including naturally occurring materials (wood, keratin) are considered as NMs reference for the separation of organic pollutants. It is generally acknowledged that sorption kinetics are controlled by mass-transfer phenomena at the liquid/solid interface, with retention being controlled by the sorbent/sorbate properties [31].