Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA.
Water Res. 2013 May 1;47(7):2231-40. doi: 10.1016/j.watres.2013.01.053. Epub 2013 Feb 19.
The mobility of humic-substance dominated natural organic matter (NOM) concentrated from a freshwater wetland by reverse osmosis was examined in sand columns at pH 5-8, in 0.001 M and 0.01 M NaClO4. Greater mobility was observed at higher pH and lower ionic strength, although breakthrough curves (BTCs) for bulk NOM exhibited extensive tailing under all conditions examined. Based on observations from previous batch experiments indicating preferential adsorption of intermediate to high molecular weight (MW) NOM, we postulate that 'adsorptive fractionation' of the NOM pool leads to the observed tailing behavior, and develop a novel approach to assess the effects of polydispersity on transport of NOM and associated contaminants. BTCs for different NOM fractions were constructed by separating column effluent MW distributions determined by high-pressure size exclusion chromatography into five discrete intervals or 'bins' and calculating the mass of NOM within each bin at four sampling times. Observed retardation factors (Ro), reflecting median arrival time relative to that of a nonreactive tracer, ranged from 1.4 to 7.9 for the various bins and generally increased with MW. NOM retarded transport of the contaminant metal Cd (2.5 ppm, in 0.01 M NaClO4) slightly at pH 5 and more substantially at pH 8. Although Cd had little or no effect on bulk NOM transport, retention of the more aromatic, IMW-HMW NOM appeared to be slightly enhanced by Cd. Study results demonstrate that heterogeneity in retardation as a function of MW is likely a major factor contributing to bulk NOM BTC tailing and may have important implications for contaminant transport.
采用反渗透法从淡水湿地中浓缩的腐殖质为主的天然有机物（NOM）在 pH 5-8、0.001 M 和 0.01 M NaClO4 的砂柱中的迁移性进行了研究。在较高 pH 值和较低离子强度下，观察到更大的迁移性，尽管在所有检查条件下，总体 NOM 的穿透曲线（BTC）都存在广泛的拖尾。根据先前的批处理实验观察到的优先吸附中高分子量（MW）NOM 的结果，我们假设 NOM 池的“吸附分馏”导致了观察到的拖尾行为，并开发了一种新的方法来评估多分散性对 NOM 和相关污染物传输的影响。通过将高压尺寸排除色谱法确定的柱流出物 MW 分布分为五个离散间隔或“箱”，并在四个采样时间计算每个箱内的 NOM 质量，构建了不同 NOM 分数的 BTC。观察到的阻滞因子（Ro）反映了相对于非反应示踪剂的中值到达时间，对于各个箱的范围从 1.4 到 7.9，并且通常随 MW 增加而增加。NOM 略微延迟了在 pH 5 时的污染物金属 Cd（2.5ppm，在 0.01 M NaClO4 中）的传输，而在 pH 8 时则更为显著。尽管 Cd 对总体 NOM 传输几乎没有或没有影响，但保留更具芳香性、IMW-HMW NOM 的能力似乎略有增强。研究结果表明，MW 作为阻滞函数的异质性很可能是导致总体 NOM BTC 拖尾的主要因素，并且可能对污染物的传输具有重要意义。
