二级出水中溶解性有机物亲疏水性对超滤膜污染的影响

Effect of hydrophilicity/hydrophobicity of DOM in the WWTP secondary effluent on the ultrafiltration membrane fouling

利用相对分子质量分布、三维荧光光谱仪及红外光谱仪等方法研究了城市污水二级出水中溶解性有机物亲疏水性对超滤膜污染的影响。结果表明:城市污水二级出水中疏水性酸占42.8%,过渡亲水性酸占19.1%,亲水性有机物占38.1%;水中疏水性酸、过渡亲水性酸和亲水性有机物分别使膜通量减小32.8%、29.9%和18.6%,膜阻力增大106.6%、92.2%和58.6%;过渡亲水性酸为蛋白质类,相对分子质量主要在4000~30000 Da;亲水性有机物为脂肪类,主要集中在6 000 Da以下;疏水性酸物质为腐殖酸类,主要集中在4 000 Da以下,其中疏水性酸物质更容易引起超滤膜污染。

To investigate the impact of the behaviors of hydrophilicity/hydrophobicity of DOM in the urban secondary effluent on the ultrafiltration membrane fouling,the present paper has chosen the effluent of the SWTP（the sewage treatment plant） by the combined XAD-4 and XAD- 8 resin.The results of our investigation and analysis have shown that there are three fractionations of the DOM in the urban secondary sewage effluent：the hydrophobic acids,which account for 42.8%,the transitional hydrophilic acids,which account for 19.1%,and the hydrophilic organic matters,which occupies 38.1%.The fractionations left-over from the effluent tend to result in the decrease of the flux of4000- Da PES membrane by 32.8%,29.9%and 18.6%but in the increase of the membrane resistance by 106.6%,92.2%and58.6%,respectively.Detailed analyses over the molecular weight distribution,the 3DEEM（3D excitation-emission matrix）fluorescence and FI- IR（Fourier transform infrared spectroscopy）,may let us identify the transitional hydrophilic acids from the protein-like substances,with the MW being in a range of4000- 30000 Da,whereas the hydrophilic organic matters have been found to be lipid-like substances with its MW being less than 6 000 Da.On the other hand,the hydrophobic acids turn to be humic acid-like substances with MW being less than 4 000 Da,which tends to lead easily to the UF membrane fouling.The membrane fouling mechanisms of the aforementioned three fractionations can be remarkably different.Whereas the hydrophobic acids are easily blocked and consequently narrowed with their membrane pores due to their relatively low MW,their main components of the humic-like substances with positive charge holes tend to be tightly bound with the membrane stuff.Since the transitional hydrophilic acids tend to result in a cake layer on the membrane surface with their relatively large MW,the said cake layer should be regarded as being loose in structure,with their major components of protein-like substances loosely charged and the hydrophilic organic matters co-influenced on the membrane fouling by the membrane pore blocking and the cake layer formulated,due to the complicated nature of their components of lipidlike substances that may occur on the membrane surface by the hydrogen bridging.Thus,in comparison with the different charge properties of DOM hydrophilicity/hydrophobicity,MW can be found to be the dominant factor leading to the membrane fouling.