Direct nanofiltration of surface water using capillary membranes: comparison with flat sheet membranes

This article explores the possibilities of a new capillary nanofiltration membrane (manufactured by Stork/X-Flow, The Netherlands), designed to reduce membrane fouling and thus allowing to omit or reduce the extensive pretreatment usually required for the implementation of nanofiltration in drinking water production. In the laboratory, the membrane performance (flux decline and flux recovery) during nanofiltration of surface water from the river Dijle, Flanders, Belgium was compared with that of a series of nine commercial flat sheet membranes. All membranes showed flux decline to some extent. For the capillary membrane, the water flux could, however, easily be increased and maintained at a stable level by a combination of forward flushing and airflushing, which is not possible with the flat sheet membranes. Furthermore, the water permeability for the capillary membrane was three to 15 times higher than for the commercial flat sheet membranes, which leads to lower operating pressure and a correspondingly lower energy consumption. For the capillary membrane rejections of organic and inorganic compounds were satisfactory to reach for COD and conductivity standards in one step starting from the Dijle water. Rejections for most flat sheet membranes were comparable to the rejections obtained with the capillary membrane, but the rejection of ions was usually higher, except for the N30F and NF PES 10 membranes (Nadir, Germany). Low ion rejections are advantageous for drinking water production because demineralization is avoided. (C) 2002 Elsevier Science B.V. All rights reserved.