AWWA MTC61237

Capillary nanofiltration (NF) enables surface water to be treated in a single step to produce high-quality permeate. Trail studies show that a stable operation is achievable using capillary NF without pretreatment (in other words direct NF). The capillary NF membrane module combines the favorable cleaning properties of capillary ultrafiltration membranes with the favorable separation properties of NF membranes. The direct use of the NF process is referred to as "direct capillary NF" (DNF). Since June 2000 the drinking water company Vitens is carrying out several feasibility studies on capillary NF for surface water treatment. The first three years of research on capillary NF were focussed on a stable production process using a pilot installation with a single 3 inch or 4 inch membrane module. During this research period several cleaning regimes were investigated. The most effective chemical cleaning procedure (within the range indicated on the membrane data sheet) showed to be subsequently soaking with H₂O₂, HCl and NaOH. In August 2003 a fully-automated pilot installation with two 8 inch capillary NF modules was installed. The aim was to achieve a long term process stability with respect to seasonal fluctuations in feed water quality. The results are very promising, i.e. flux: 25 - 30 l/m2.h, recovery: 75%, TMP: 2,5 - 4,5 bar and Membrane Transfer Coefficient (MTC): 12 - 8 l/m2.h.bar at 20 degrees Celsius. For the second semester of 2004 the objective of the investigation with DNF was also the post-treatment and the necessity of double barriers. So the DNF-permeate was treated by granular activated carbon (with short contact time of about 8 minutes) and UV-disinfection. After these treatments not only European Drinking Water Standards are fulfilled, but also the more stringent Vitens drinking water standards are achieved. Includes 4 references, tables, figures.