Evaluation of compressive strength and phosphate fixation characteristics of wastewater filter media using coal bottom ash and oyster shells.

The excessive concentration of phosphate in coastal areas results in environmental problems such as red tide and eutrophication. Filter media (FM) is used in wastewater treatment facilities to decrease phosphate concentration. This study aims to investigate the optimal mixing ratio for high compressive strength and phosphate fixation ability using coal bottom ash (CBA) and oyster shells (OS) -derived FM. Compressive strength experiments were conducted using mixed CBA and OS with different mixing ratios, 1:3 (GBO13), 1:1 (GBO11), and 3:1 (GBO31). The highest compressive strength of 0.93 MPa was observed in GBO11. GBO11 had similar elemental proportions with Portland cement, promoting a pozzolanic reaction and forming calcium-silicate-hydrate. The phosphate fixation capability of GBO11 was evaluated through an up-flow column filtration experiment. GBO11 fixed phosphate through precipitation and adsorption, and the maximum amount of phosphate fixation was estimated to be 1.403 mg-P/g. This study demonstrates that the combination of CBA and OS can be promising FM with high compressive strength and phosphate fixation properties.