Effects of Enhanced Nitrogen and Phosphorus Pollutants Removal from Stormwater Runoff by Magnesium-modified Red Mud
The traditional bio-retention system has the problem of a single composition of the filler layer and unstable nitrogen and phosphorus removal efficiency.To evaluate the feasibility of red mud as a bio-retention system filler layer modifier,this study used Bayer red mud as a raw material to prepare magnesium-loaded modified red mud.Through modification experiments,isothermal adsorption experiments and material characterization,this study explored the effect of magnesium-loaded modified red mud on the removal efficiency and adsorption mechanism of nitrogen and phosphorus in rainwater runoff.The results show that the optimal concentration for preparing modified red mud using MgCl2 solution was 0.5 mol/L.Compared with red mud(RM),modified red mud(RM0.5)increased the average removal rates of NH4+-N and PO43--P by 17.15%and 5.74%,with average removal rates of 41.83%and 97.24%,respectively.RM and RM0.5 can be described as Langmuir monolayer adsorption for ammonium nitrogen adsorption,whereas they exhibit the opposite behavior for phosphate adsorption,which is more in line with the Freundlich isothermal adsorption model.The theoretical saturation adsorption amount of RM0.5 for nitrogen was 1.383 mg/g,which was 1.83 times that of RM.The surface of the modified red mud was rougher than that of the original red mud,and a magnesium oxide coating was formed on the surface.RM0.5 has a slightly better removal effect on PO43--P than RM,while for NH4+-N,RM0.5 is sig-nificantly better than RM.Therefore,when dealing with high-concentration nitrogen-containing rainwater runoff,RM0.5 is more likely to be selected as a filler modifier.
red mudmodified red mudbioretention systemsammonium nitrogenphosphorusisothermal adsorption
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