腐殖酸对NH+4-N在饱和含水层中迁移的影响

通过等温吸附实验,研究了有和无腐殖酸2种情况下,NH 4＋-N在石英砂上的等温吸附过程,并运用Langmuir方程和Freundlich方程进行了拟合,计算了不同条件下NH 4＋-N在石英砂上的最大吸附量;通过室内土柱模拟实验,测定了不同时间内土柱出水中的NH 4＋-N、NO 3--N和NO 2--N的含量,分析了腐殖酸在饱和含水层中对水中NH 4＋-N迁移转化的影响,并运用伪二级动力学方程和二阶段吸附速率方程对动力学过程进行了拟合.结果表明,Langmuir方程和Freundlich方程均能很好地描述NH 4＋-N的等温吸附过程;腐殖酸的存在增加了石英砂对NH 4＋-N的吸附量,无腐殖酸时NH 4＋-N最大吸附量为0.205mg.g-1,有腐殖酸时NH 4＋-N最大吸附量为0.354 mg.g-1.室内土柱实验结果表明,在实验前期,腐殖酸通过增加吸附空间而增大了NH 4＋-N吸附量;当吸附饱和后,腐殖酸可能为硝化细菌等微生物提供碳源和能量,参与NH 4＋-N转化为NO 3--N和NO 2--N的化学反应,使有腐殖酸条件下的NH 4＋-N出水浓度始终低于无腐殖酸条件.伪二级动力学方程和二阶段吸附速率方程均能很好地描述NH 4＋-N的吸附过程（无腐殖酸条件下R2=0.992 3,R2=0.994 4;有腐殖酸条件下R2=0.997 7,R2=0.998 1）,推测石英砂对NH 4＋-N的吸附属于化学吸附过程;通过比较二阶段吸附速率常数k3（有、无腐殖酸时分别为0.247和0.143）和k4（有、无腐殖酸时分别为0.006 27和0.001 7）,发现NH 4＋-N的吸附主要表现为第一阶段吸附,不定向地吸附在石英砂表面的活性点位上,且腐殖酸的存在使NH 4＋-N的平衡吸附量qe增大.

Effect of Humic Acids on Migration and Transformation of NH+4-N in Saturated Aquifer

Isothermal adsorption experiment was used to study the adsorbing process of NH⁺₄-N in quartz sands under the conditions with and without humic acid; the Langmuir and Freundlich equations were used to fit the absorption result and the maximum adsorption capacity of NH⁺₄-N by quarts sands was calculated. Through the soil column experiments, the concentration of NH⁺₄-N, NO^-₃-N and NO^-₂-N in effluent water in the tested soil column was investigated, and the effect of humic acid on migration and transformation of NH⁺₄-N in saturated aquifer was analyzed, and Pseudo-second-order Kinetics Equation and Two-step Adsorption Kinetics Rate Equation were applied to fit the kinetic processes. The results showed that both Langmuir and Freundlich models can well describe the isothermal adsorption process of NH⁺₄-N on the surface of quartz sands, which means that NH⁺₄-N adsorbed by the quartz sand was mainly in the form of monolayer adsorption. The humic acid could increase the adsorption capacity of NH⁺₄-N on quartz sand, and the saturated adsorption capacity was 0.354 mg·g^-1 under the condition with humic acid and 0.205 mg·g^-1 with the absence of humic acid. The experiment indicated that humic acid increased the adsorption capacity of NH⁺₄-N on the surface of quartz sand by increasing adsorption space in the initial stage. After saturation, humic acid influenced the migration and transformation of NH⁺₄-N to NO^-₃-N and NO^-₂-N probably through providing carbon source and energy for microorganisms such as nitrifying bacteria and then resulting in lower NH⁺₄-N concentration in effluent water. Both Pseudo-second-order Kinetics Equation and Two-step Adsorption Kinetics Rate Equations can well describe the process of NH⁺₄-N adsorption kinetics on quartz sand(R²=0.9977 and R²=0.9981 with humic acid; R²=0.9923 and R²=0.9944 without humic acid), indicating that this process was chemical adsorption. By comparing the adsorption rate coefficient of Two-step Adsorption Kinetics Rate Equation k₃(0.247 and 0.143, respectively) and k₄(0.00627 and 0.0017) between the treatments with and without humic acid, it can be referred that NH⁺₄-N was non-orientated adsorption on active points of the quartz sand at the initial stage, and the humic acid could increase the equilibrium adsorption quantity(q _e) of NH⁺₄-N on quartz sands.