Evaluation of sediment capping with active barrier systems (ABS) using calcite/zeolite mixtures to simultaneously manage phosphorus and ammonium release

The efficiency and mechanism of sediment capping with an active barrier system (ABS) using calcite/zeolite mixtures to simultaneously prevent phosphorus (P) and ammonium (NH4+) release from eutrophic lake sediments under anaerobic conditions was investigated through a series of batch and sediment incubation experiments. For this, natural calcite and various zeolites (natural, NaCl-pretreated and CaCl2-pretreated zeolites) were applied. Batch tests showed that the calcite was efficient for the removal of phosphate in aqueous solution and the zeolite was an efficient adsorbent for the removal of NH4+ from aqueous solution. Sediment incubation experiments showed that the P and NH4+ fluxes from the anaerobic sediments were significantly reduced by the ABS using the mixture of calcite and natural zeolite. Higher calcite dosage was found to be favorable for the prevention of P release from the sediments using the ABS. For controlling the P release from the sediments, the mixture of calcite and CaCl2-pretreated zeolite as a capping material was more efficient than that of calcite and natural zeolite, whereas the mixture of calcite and NaCl-pretreated zeolite was less efficient than that of calcite and natural zeolite. Batch and sediment incubation experiments proved that the zeolite as a component of the ABS using the mixture of calcite and CaCl2-pretreated zeolite has a dual function: (i) preventing NH4+ release from the sediments; and (ii) supplying Ca2+ through a Ca2+/NH4+ exchange to improve the ability of the capping material to immobilize P release from the sediments.

Research Highlights
► Sediment capping with calcite/zeolite mixture reduced P and NH4+ release.
► Higher calcite dosage was favorable for mixture to reduce P release from sediment.
► Calcite/CaCl2-treated zeolite mixture was best in reducing P release from sediment.
► Ca2+ supplied from CaCl2-treated zeolite improved mixture to reduce P release.