水力停留时间对潜流湿地净化效果影响及脱氮途径解析

利用连续进水的垂直潜流人工湿地和水平潜流人工湿地，比较分析了4种水力停留时间对常规污染物去除效果的影响，在最佳水力停留时间下探究了两种湿地内部各基质层硝化、反硝化和氨氧化功能基因丰度以及硝化与反硝化作用强度；通过对两种湿地脱氮影响因素的冗余分析和方差分解分析，得出影响湿地氮去除的主要因素.结果表明，当水力停留时间为24 h时，两种湿地系统对常规污染物（COD、TP、TN和NH₄⁺-N）去除效果最佳，去除率均大于70%，此时湿地内部对NH₄⁺-N和TN的去除率以及硝化和反硝化强度皆表现出沿水流方向逐级递减的趋势；3种功能基因中，反硝化功能基因（nirS）丰度远高于硝化功能基因（nxrA）和氨氧化功能基因（AOB-amoA）.在本研究中，两种潜流人工湿地氮去除能力均受环境因素和微生物因素共同影响，其中，微生物因素对脱氮贡献率最高（55%和48%）.除此之外，TN和NH₄⁺-N的去除率均与DO、基质比表面积、COD浓度和硝化功能基因及反硝化功能基因丰度呈正比，与pH值成反比.因此，为提高两种系统氮去除效果，均可通过提高基质层溶解氧和碳源含量以及适当地降低pH值来实现，水平潜流人工湿地还可通过更换比表面积较大的基质层来显著提高系统脱氮效果.本研究为人工湿地的设计以及最佳水力停留时间的选择提供了理论基础，脱氮途径的定量化解析对深入理解人工湿地氮去除机制以及提高氮素去除率具有重要的指导意义.

Effect of Hydraulic Residence Time on Removal Efficiency of Pollutants in Subsurface Flow Constructed Wetlands and Analysis of Denitrification Mechanism

This study used vertical and horizontal subsurface constructed wetlands with continuous inflow, to compare and analyze the effects of four hydraulic residence times on the removal efficiency of conventional pollutants. Using the optimal hydraulic retention time, the two types of wetlands were examined in terms of the stromal layer nitrification, denitrification, and ammonia oxidation abundance of functional genes, as well as the intensity of nitrification and denitrification. In addition, redundancy analysis and variance decomposition analysis were used to determine the main factors affecting nitrogen removal in the two kinds of wetlands, so that targeted improvement measures can be suggested. The best removal efficiency of conventional pollutants (COD, TP, TN, and NH₄⁺-N) was achieved with a hydraulic retention time of 24 h, resulting in a removal rate of more than 70%. With a 24 h retention time, the removal rate of NH₄⁺-N and TN and the intensity of nitrification and denitrification exhibited a gradually decreasing trend along the flow direction. Among the three functional genes, the abundance of denitrification functional genes (nirS) was much higher than that of nitrification functional genes (nxrA) and ammonia oxidation functional genes (AOB-amoA). In this study, the nitrogen removal ability of the two subsurface flow constructed wetlands was jointly affected by environmental factors and microbial factors, among which microbial factors contributed the most to nitrogen removal (55% and 48%). In addition, the removal rates of TN and NH₄⁺-N were proportional to DO, specific surface area of substrate, COD concentration, as well as nitrification and denitrification functional genes, but inversely proportional to pH. Therefore, in order to improve the nitrogen removal efficiency of both systems, the amount of dissolved oxygen and carbon sources in the substrate layer should be increased, while the pH value should be appropriately reduced. Moreover, the horizontal subsurface constructed wetland significantly improves the nitrogen removal efficiency of the system, as the substrate layer has a larger specific surface area. This study provides a theoretical basis for the design of constructed wetlands and the selection of an optimal hydraulic residence time. Quantitative analysis of nitrogen removal pathways is of great significance for understanding the nitrogen removal mechanism and improving the nitrogen removal rate in constructed wetlands.