Molecular weight distribution and hydrophilicity of wastewater effluent organic matter and effect on NF membrane fouling

The membrane with molecular weight cutoff (MWCO) ranged from 2kDa to 100kDa and XAD-8 resin were employed to identify the characteristic of MW distribution of wastewater effluent organic matter(EfOM) in terms of TOC and UV254, as well as the amounts of the hydrophilic/hydrophobic organic fractions in different MW range, and then the fouling experiments were carried out using the above fractionated water to investigate the effect on NF membrane flux decline and rejection. 45.61% of the organic MW lower than 2kDa, among which the hydrophilic matter sheared 28.07% and hydrophobic 17.54%. In particular, the hydrophilic fraction was found to be the most abundant fraction in the effluents. MW exhibited a significant effect on NF membrane specific flux decline. When the MW was less than 30kDa, the lower the MW, the larger the specific flux decline, and in the condition of MW higher than 30kDa, the higher MW according to the more rapid flux decline. With the same MW distribution range, specific flux decline of hydrophilic organic was much lower and the rejection was also smaller than the raw Water rejection. It indicated that the hydrophobic organic fraction can enhance the rejection, but the main factor to cause flux decline.