Effect of molecular weight distribution and hydrophobicity of wastewater effluent organic matter(EfOM) on nanofiltration membrane fouling

Ultrafiltration membranes with molecular weight cutoff(MWCO) ranging from 2k to 100k and XAD-8 resin were employed to identify the characteristics of the molecular weight(MW) distribution of wastewater effluent organic matter(EfOM).TOC and UV254,as well as the amounts of the hydrophilic/ hydrophobic organic fractions in different MW ranges were measured.Nanofiltration membrane fouling experiments were carried out to investigate the effect of MW distribution and hydrophilic/hydrophobic characteristics of EfOM on membrane flux decline,using the fractionated water samples above.According to the experimental results,45.61% of the total organics are low MW.The percentage of the hydrophilic organics with low MW(less than 2k) was up to 28.07%,while that of the hydrophobic organics was 17.54%.The MW distribution has a significant effect on the membrane fouling.When the MW was less than 30k,the lower the MW,the larger the specific flux decline;while for MW higher than 30k,the higher the MW,the larger the specific flux decline.The degree of flux decline from filtering low MW organics was larger than that for the high MW organics.With the same MW distribution range,specific flux decline of the hydrophilic organics was much slower than that of the hydrophobic organics which indicated that the hydrophobic organic fraction contributes most to the flux decline.