Raw and Calcined Eggshells as P-Reactive Materials in a Circular Economy Approach

Phosphorus (P) is a crucial factor influencing both plant growth and the enrichment of the aquatic environment. Agriculture is the primary sector of the economy where the demand for phosphorus is the highest. Due to the depletion of P, more and more attention is being paid to the possibility of recovering and reusing P through the idea of a circular economy (CE). The main objective of this study was to compare raw eggshells (R-ESs) and calcined eggshells (C-ESs) for P removal from wastewater and assess the possible use of agro-waste materials according to CE requirements in non-flow conditions. A synthetic indicator, the zeroed unitarization method, was calculated to evaluate the critical aspects of materials according to the CE. The sorption of R-ESs and C-ESs equaled 0.90 and 1.66 mgP-PO4/g for an initial concentration of 17.3 mgP-PO4/L. The C-ESs were characterized by an almost two times higher reduction rate than R-ESs. The calculated indicator for the CE requirements equaled 0.89 and 0.72 for R-ESs and C-ESs, respectively. This means that R-ESs are more sustainable than C-ESs. Although C-ESs potentially have a more significant environmental impact, it is worth considering that this method of P elimination is beneficial from an ecological perspective.