Effects of humic substance characteristics on UF performance

The role of humic substances in general and hydrophobicity of humic substances in particular on membrane permeate flux is unclear. The main goal of the present study is to evaluate the effect of fractionated humic substances on ultrafiltration (UF) performance. A commercial humic solution was subjected to a hydrophobic resin for fractionation of the hydrophobic and hydrophilic fraction. These fractions were further fractionated into different molecular wight groups, using gel filtration chromatography. The hydrophobic fraction accounts for 85% organic carbon recovered and has a significantly high THM (trihalomethane) formation potential, or 190 μg/mg C. The hydrophilic fraction exhibits the worst flux decline despite little solute rejection. The results of molecular weight fractionation of both hydrophobic and hydrophilic fractions further indicate that those molecules with the largest molecular weight (6.5–22.6 kDa) exhibit the worst flux decline. The UF system evaluated is unable to remove a significant portion of THM precursors, resulting in potentially high THMs in the permeate. The use of powdered activated carbon (PAC) for the pretreatment of hydrophobic/hydrophilic humic substances or in an integrated PAC-UF system exhibits an enhanced membrane fouling.