Mechanism and Kinetics of Low Concentration Total Phosphorus and Reactive Phosphate Recovery from Aquaculture Wastewater via Calcined Eggshells

Elevated concentration of total phosphorus (TP) or reactive phosphate (PO 4 3− ) in aquaculture wastewater (AW) can cause eutrophication in the wastewater discharge ponds. This study delves into the effectiveness of calcined eggshells (CESs) in recovering low concentrations of TP and PO 4 3− from AW. Eggshell waste collected from domestic sources was pyrolyzed at 800 °C for 30 min. Characterization indicated that the functional groups of CES portray a significant role in the adsorption process. The nonlinear form of the Freundlich model fitted well for TP and PO 4 3− adsorption processes from AW. CES could recover up to 96.6 and 97.3% of low concentration TP and PO 4 3− , respectively, from AW. The adsorption indicated chemisorption activity by CES. The thermodynamic studies suggested that the adsorption of TP and PO 4 3− were feasible, spontaneous, and exothermic in nature. This recovery process does not create secondary waste, and the recovered spent adsorbents can be utilized as garden fertilizer or as pest repellant in the aquaculture farm.