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Calcined Eggshell as a P Reactive Media Filter—Batch Tests and Column Sorption Experiment

Bus, Agnieszka, Karczmarczyk, Agnieszka, Baryła, Anna
Water, air, and soil pollution 2019 v.230 no.1 pp. 20
algorithms, egg shell, models, sand filters, septic systems, sorption, sorption isotherms, temperature
The goal of the study was to assess the sorption properties of calcined eggshells (CEs) as a P reactive media filter. The CEs were calcined in a temperature of 900 °C. A double stage test was performed: batch studies (kinetic and equilibrium) and small-scale column experiment. The estimation of optimal mass ratio of CEs for perspective usage was the additional benefit of column experiment. The short kinetic tests showed that 5 min of contact time with solution of initial concentration of 6.020 mgP-PO₄ L⁻¹ is enough to reduce the P-PO₄ in 100%. The equilibrium studies were conducted with P-PO₄ solution of 6.020 to 977.7 mg L⁻¹ with contact time of 30 min. The obtained data was compensated by non-linear regression using the Marquardt algorithm in the Statgraphics Centurion XVI. The eggshell calcined characterized by high sorption capacity (Sₘₐₓ = 72.87 mg g⁻¹) obtained from the Langmuir isotherm model with a good fit (96.77%). To choose the appropriate ratio of a sand filter to eggshells amendment, four small columns were constructed and fed with P-PO₄ solution (Cᵢₙ ≈ 5 mg L⁻¹). The percentage mass (m/m) of CEs in the columns was 0.0 (the reference one); 1.0; 2.5; and 5.0. The unit sorption obtained during 95 days of column experiment was 10.668, 4.277, and 2.286 mg P-PO₄ g⁻¹ for 1.0, 2.5, and 5.0%, respectively. For practical implementation, the most recommended addition seems to be 1% of CEs. It corresponds, e.g., to the mass of 49 kg CEs for septic tank system.