Utilizing a granulated coal bottom ash and oyster shells for nutrient removal in eutrophic sediments

Field experiments on chemical and biological changes of thin-layer oyster shells capping sediments in dense aquaculture area

Thin-layer oyster shell capping has been proposed as a method for improving contaminated coastal environments. Field experiments were conducted to investigate the effects of oyster shell capping on nutrient concentrations, microorganisms, and macrobenthic communities. The concentration of PO4-Pin the experimental area decreased by approximately 38% more than in the control, due to phosphorus fixation of oyster shells and the presence of Proteobacteria. Ammonia-oxidizing bacteria such as the order Pirellulales (phylum Planctomycetes) were related to the low ratio of NH3-N found in dissolved inorganic nitrogen in the experimental area, indicating nitrification promotion. The reduction in annular benthic organisms observed in the experimental area indicates a decline in sediment organic matter, which could potentially mitigate eutrophication. Oyster shell capping was confirmed to be an effective material for restoring coastal sediments by improving their chemical and biological properties.

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.