## 5 Conclusions  
This review provides a summary of studies related to the preparation and utilization of ES composites over the last decade. This includes the ES pretreatment, preparation of composites, and characterization of the adsorption properties of ES composites at equilibrium and kinetic conditions. This overview is unique since many review articles that discuss ES particles focus largely on two types of general applications of value-added products: (i) industrial applications as structural composites in polymer, metal matrix, additives, and catalysts in biodiesel production and (ii) medical applications for utility in dentistry and orthopedics, food, and drug supplements. Various results for the adsorption of pollutants (dyes, insecticides, metal ions, anions, and oxyanions) that employ ESP biocomposites over the last decade was presented. The equilibrium isotherms and thermodynamic and kinetic parameters reported for the effective removal of various pollutants reveal the utility and feasibility of various ES adsorbents. In general, ES composite adsorbents generally display enhanced adsorption properties over ES materials in their pristine form or ES particles that are modified by chemical or thermal treatment (by calcination or pyrolysis). Pretreatment of ES was generally done by washing, oven-drying, grinding, and sieving, while final preparations involved mixing certain quantities of additives (inorganic to organic) to afford formation of ES composites via physical blending to yield products with variable composition with tailored properties. Figure 15: Application of eggshell in treatment of water containing metal-ion species. Copied with permission [197]. CES was reported to be more efficient in the removal of pollutants due to increased surface area and pore sizes; the characterization revealed that calcite is present in ESP biocomposite as the dominant polymorph of calcium carbonate that is often employed in many industrial applications. A major influence on the role played by ESP relates to the release of charged particles on the surface of the biosorbents via ion-exchange. The adsorption mechanism of organic and inorganic pollutant removal with eggshell powder and its composites can be physisorption or chemisorption. This includes chemical and electrostatic interactions, precipitation, and hydrogen bonding, metal complexation, ion exchange, electric double layer effects, and weak valence forces leading to sharing or exchange of electrons. Usage of ESP biocomposites allow the modification of the physicochemical properties of the multicomponent systems to achieve composites that can be developed further for applications with tailored physicochemical properties. The importance of developing such composites is attributed to their end-use applications (Table 10). We anticipate that this review will inspire further research on ES utilization for the development of composite materials to address a number of global challenges: (i) sustainability challenges for the diversion of ES waste, (ii) the valorization and utilization of ES waste, and (iii) the end-use applications with an emphasis on adsorbent technology for adsorption-based processes (slow fertilizer release, environmental remediation, chemical separations, catalytic processes, etc.). Adsorption science and technology holds the promise of addressing controlled removal of pollutants that serve to address water security to address environmental remediation and concerns related to the health of ecosystems and human health. In turn, ESP biocomposite adsorbents are envisaged to have broad appeal across many sectors of industry and technological processes, such as remediation of chemical pollutants in industrial wastewater and advanced drinking water treatment processes. This review highlights the importance of utilization and valorization of ES waste from a sustainability perspective, which will promote a circular economy design strategy via recycling of an abundant source of biogenic calcite.