The mechanism of nitrogen migration aceoss sediment-water core manipulated by oxygen-loaded zeolite
Dissolved oxygen is essential for the migration of nitrogen in the sediment.In this study,we prepared oxygen-loaded zeolite using three kinds of fly ash,then explored the removal efficiency and mechanisms toward nitrogen in sediment-water systems by capping the surface sediment with the oxygen-loaded zeolite(with thicknesses of 0.5,1.0,and 2.0cm).The results showed that the oxygen-loaded zeolite was able to reduce the nitrogen content in the sediment-water system and control the release of nitrogen from the sediment through the adsorption and oxygen release,and the effect is positively correlated with the thickness of the capping materials.The dissolved oxygen concentrations at the sediment-water interface in the 0.5,1.0,and 2.0cm thickness treatment groups reached 1.79,3.69,and 6.26mg/L after 25 days of incubation,respectively.Meanwhile,the removal rate of total nitrogen in the overlying water was 22.77%in the 0.5cm thickness group,30.37%in the 1cm thickness group,and 39.10%in the 2cm thickness group.Compared with the control group,the ammonia release flux across the sediment-water interface was reduced by 31.4%,47.0%,and 50.47%,respectively.In addition,the oxygen-loaded zeolite increased the abundance of microorganisms involved in nitrification and denitrification.The abundance of nitrification functional genes(amoA),denitrification functional genes(narG,napA,nirS,and nirK),and aerobic denitrification genes(napA)in the surface sediments was substantially promoted,demonstrating that a coupled aerobic-anoxic denitrification process may occur in the surface sediments.The results from this study may provide a new perspective for the utilization of fly ash and management of the international nutrients loading.
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