Nitrogen removal by modified zeolites coated with Zn-layered double hydroxides (Zn-LDHs) prepared at different molar ratios
Ye Yuan, Xiangling Zhang, Yu Lei, Yinghe Jiang, Zhouying Xu, Shiyang Zhang, Jingtian Gao, Shuangjie Zhao
Index: 10.1016/j.jtice.2018.03.010
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Abstract
The study aimed to determine the best Zn-LDHs-modified zeolites that had the highest removal efficiencies of nitrogen in simulated unplanted vertical-flow constructed wetlands. ZnFe-LDHs and ZnAl-LDHs were prepared at different Zn2+/Fe3+, Al3+ molar ratios (1, 2 and 3) via co-precipitation method. The results of Scanning Electron Microscope (SEM) and X-ray Fluorescence Spectrometer (XRFS) indicated that the Zn-LDHs were successfully loaded on the original zeolites. The control group with microbe inhibited was compared to experimental group to determine the intensity of microbial effect in nitrogen removal process. The ZnFe-LDHs-modified (3:1) zeolites had the best TN removal efficiency of 62.88%, and TN removal rate belonged to microbial effect was 16.42%. Meanwhile, microbial analysis also confirmed that ZnFe-LDHs (3:1) had significantly promoted the microbial growth. Besides, Zn-LDHs-modified zeolites had a higher Langmuir adsorption capacity and stronger surface bond energies compared to original zeolites. The kinetic data of Zn-LDHs-modified zeolites was better described by pseudo-second-order model. It could be inferred that ZnFe-LDHs-modified (3:1) zeolites had the best TN removal efficiency and an excellent adsorption capacity for NH4+-N, and the cost of synthesis was only RMB ¥ 0.0741/kg with a rough estimation. Therefore ZnFe-LDHs-modified (3:1) zeolites were a better choice of substrates for constructed wetlands.