Determination of mass transport characteristics for natural organic matter (NOM) in ultrafiltration (UF) and nanofiltration (NF) membranes

This study is mainly concerned with establishing a reliable method of the quantitative analysis of natural organic matter (NOM) transport characteristics through ultrafiltration (UF) and nanofiltration (NF) membranes with molecular weight cutoffs of 8000 (GM) and 250 (ESNA), respectively. Filtrations were conducted with a cross-flow filtration unit and hydrodynamic operating conditions were controlled by a J₀/k ratio (the ratio of initial permeate flux [J₀] to a back diffusional mass transfer coefficient [k]). A four-parameter (the apparent mass transfer coefficient [k_a], the solute concentration near the membrane surface [Cm], the solute permeability [P_m], and the reflection coefficient (σ) model based on concentration polarization and irreversible thermodynamics was used to manipulate experimental results quantitatively. With the values of the determined parameters, the transport characteristics of NOM due to different solution chemistries such as pH and ionic strength through UF/NF membrane pores were investigated. This model was also used to demonstrate the effects of NOM structure (hydrophobic/transphilic/hydrophilic) on transport through the membranes, with XAD-8/4 resins fractionation and isolation procedures. Four parameters estimated through the model were revealed to be relevant to elucidate the behaviors of NOM in membranes and corresponding transport-related results were in good agreement with the theoretical descriptions related to the interactions between NOM molecules and membrane surface/pores.