Comparative characterisation of different commercial UF membranes for drinking water production

In this study, nine commercially available ultrafiltration membranes used in drinking water production were characterised. The aim of the study was to compare the molecular weight cut-off (MWCO) and the membrane permeability of a selection of currently available ultrafiltration membranes. Permeability and MWCO are important criteria for the selection of ultrafiltration membranes with regard to efficiency and rejection of dissolved and particulate substances. This study provides an overview of the differences in cut-off and permeability between commercial UF membranes with similar specifications. To this end, tests were conducted using eight hollow fibre membranes with effective membrane surface areas of between 0.04 and 0.26 m(2) and one type of flat sheet membrane with an effective filtration area of 0.0044 m(2). Cross-flow filtration experiments using a mixture of dextrane as a feed solution were performed to determine MWCO. The molecular weight of the dextrane used in the feed solution ranged from 8-2,000 kD. The concentration distribution of the dextrane in the feed and the permeate was determined by gel permeation chromatography (GPC) in the range of 10-1,000 kD. These tests showed that, from the nine UF membranes tested, four of them displayed a MWCO of below 1,000 kD with pure water permeabilities of 180-400 l/(m(2) . h . bar). A further four displayed no MWCO in the range examined (10-1,000 kD) with pure water permeabilities of 130-880 l/(m(2) . h . bar) and therefore their cut-offs must be in the range above 1,000 kD. One membrane, which showed no rejection for any dextrane fraction with a pure water permeability of 2,700 l/(m(2) . h . bar), could be classed as a microfiltration membrane.