Effects of hydrodynamic conditions (diffusion vs. convection) and solution chemistry on effective molecular weight cut-off of negatively charged nanofiltration membranes

• Published in: Desalination Vol. 352; pp. 136 - 141
• Main Authors: Kang, Eunyoung, Lee, Yunho, Chon, Kangmin, Cho, Jaeweon
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2014; Elsevier
• Subjects: Applied sciences; Chemical engineering; Cut-off; Diffusion; Diffusion to convection ratio; Exact sciences and technology; Fluid dynamics; Fluid flow; Heat and mass transfer. Packings, plates; Hydrodynamics; Hydrodynamics of contact apparatus; Membrane separation (reverse osmosis, dialysis...); Membranes; Molecular weight cut-off; Nanofiltration; Natural organic matter; Pollution; Polyethylene glycol; Rejection; Molecular weight cut-off; Nanofiltration; Polyethylene glycol; Natural organic matter; Diffusion to convection ratio; Organic matter; Prediction; Hydrodynamics; Convection; Mass transfer; Operating conditions; Transport process; Rejection; Membrane separation; Pollution; Mass transfer coefficient; Manufacturer; Diffusion
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/j.desal.2014.08.016

The apparent and effective molecular weight cut-off (MWCO) values of negatively charged nanofiltration (NF) membranes were determined using the fractional rejection of solutes of interest, including neutral polyethylene glycols and natural organic matter (NOM) containing ionizable functional groups. Varying the hydrodynamic operating conditions, denoted by the J/k ratio (where J represents the permeate water flux/convectional transport and k represents the mass transfer coefficient/back diffusional transport), produced changes in both the nominal and effective MWCO. Consequently, a higher J/k ratio resulted in reduced solute rejection and a higher MWCO. It was confirmed that the nominal MWCO provided by the membrane manufacturers might not be capable of predicting performance with respect to the different characteristics of various solutes (i.e., contaminants) since the predicted nominal MWCO values were nearly twice as high as those measured in this investigation. The effective MWCO values of the NF membranes with respect to NOM were slightly higher than the corresponding nominal MWCO when the NOM was relatively hydrophilic. •Nominal MWCO may not be suitable to predict rejection rates of various solutes.•Higher J/k ratio yields reduced solute rejection and a higher MWCO.•Nominal MWCO values at varying J/k ratios are lower than the effective MWCO values.•Ionizable functional groups are crucial in the determination of an effective MWCO.•The apparent MWCO should be determined under actual filtration conditions.