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Ultrafiltration of Nonionic Surfactants and Dissolved Organic Matter

机译：非离子表面活性剂的超滤和溶解的有机物

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A brownwater sample with a high content of humic substances (HS) was fractionated by multistage ultrafiltration (mst-UF) into five fractions with nominal molecular weights ranging from >30 to <1 kDa. Fractions were characterized with respect to molecular size distribution and structure. Size exclusion chromatography with online DOC detection revealed that mst-UF yielded fractions with decreasing M{sub}p (molecular weight at peak maximum) and polydispersities from nominally large to small mst-UFfractions. 13{sup left}C MAS NMR analysis showed thatthe content of carbohydrate structures decreased from the original sample toward smaller molecular weight (MW) fractions, which in turn contained more carboxylic groups and branched aliphatic structures. Specific UV absorbances (SUVA{sub}254) were highest in the >30 kDa fraction and decreased with decreasing MW. To evaluate whether separation mechanisms other than size exclusion were of importance during the fractionation, the behavior of low molecular weight model compounds (MC) with a range of polarities was studied. Recoveries decreased with increasing hydrophobicity of the MC. For selected nonylphenol ethoxylates and 4-nonylphenol the recovery correlated well with the hydrophile-lipophile balance value. The presence of dissolved organic matter (DOM) caused an additional loss of hydrophobic MC, possibly because of sorption of the compounds onto DOM fouling layers. The hydrophilic MC caffeine was recovered almost completely (85-86%) regardless of the DOM content of the model solution. It was concluded that size exclusion was the dominant fractionation mechanism for caffeine, whereas hydrophobic interactions played a major role during the mst-UF fractionation of nonpolar contaminants. For a better understanding of the behavior of polyfunctional molecules such as HS, the effect of other physicochemical properties needs to be investigated in further studies.
机译：通过多级超滤（mst-UF）将具有高腐殖质含量（HS）的褐水样品分离为五个标称分子量范围> 30至<1 kDa的馏分。相对于分子大小分布和结构来表征级分。带有在线DOC检测的尺寸排阻色谱法表明，mst-UF产生的馏分的M {sub} p（峰最大分子量）降低，多分散度从名义上的大到小的mst-UF馏分。 13 C MAS NMR分析表明，碳水化合物结构的含量从原始样品开始向较小的分子量（MW）级分降低，从而包含更多的羧基和支链的脂肪族结构。在> 30 kDa的分数中，特定的UV吸收率（SUVA {sub} 254）最高，并且随着MW的降低而降低。为了评估分离过程中除大小排阻以外的分离机制是否重要，研究了具有一定极性范围的低分子量模型化合物（MC）的行为。随着MC疏水性的增加，回收率下降。对于选定的壬基酚乙氧基化物和4-壬基酚，回收率与亲水亲脂平衡值具有很好的相关性。溶解有机物（DOM）的存在会导致疏水性MC的额外损失，这可能是因为这些化合物吸附在DOM结垢层上。不管模型溶液中的DOM含量如何，亲水性MC咖啡因几乎都能完全回收（85-86％）。结论是，尺寸排阻是咖啡因的主要分级分离机制，而疏水相互作用在非极性污染物的mst-UF分级分离中起主要作用。为了更好地了解多官能分子（例如HS）的行为，需要进一步研究其他物理化学性质的影响。

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