Phosphorus removal from urban wastewater through adsorption using biogenic calcium carbonate

Phosphorus (P) removal from urban wastewater is increasingly relevant in the wastewater treatment sector. The present work aims to contribute to the study of the adsorption process as a P removal technology. Biogenic calcium carbonate from industrial eggshell waste prepared by milling and calcination was used as an adsorbent. Batch adsorption experiments were conducted using real wastewater with 40 mg P/L (orthophosphate), original pH 7.33, under stirring conditions (100 rpm). The adsorbent was characterized using SEM-EDS, XRD, and FTIR-ATR before and after adsorption. From an initial screening of calcination times (15, 30, 60, and 120 min) and considering a balance between P removal and energy saving, the adsorbent selected was eggshell calcined at 700 °C for 60 min. The Langmuir isotherms describe the experimental data with a maximum adsorption capacity of 4.57 mg P/g at 25 °C. The adsorption process reached equilibrium within 120 min for different dosages (5, 10, and 20 g/L at 25 °C). Batch experiments showed that SO₄^2-, at a concentration of 2689 mg/L reduced the P adsorption selectivity for dosages ≤10 g/L at 25 °C. Characterization of the loaded adsorbent shows that P adsorption from real wastewater is mostly electrostatic attraction, with the contribution of ligand exchange and microprecipitation. The adsorption capacity and behavior of the selected adsorbent seem promising for P removal from urban wastewater compared with other low-cost adsorbents.