The main operational problem of nanofiltration or reverse osmosis membrane plants is fouling of feed spacers in membrane elements due to biofouling and particulate fouling. In order to remove biomass and particulate matter from membrane elements, both hydraulic and chemical action are investigated respectively by daily air/water cleaning (AWC) and daily copper sulphate dosing (CSD). In a pilot set-up three parallel spiral wound membrane elements were fed by tap water enriched with a 100 mu g/l sodium acetate solution. The first reference membrane element (REF) fouled severely within 21 days indicated by an increase of the normalized pressured drop to 200%. In the second membrane element (AWC) the normalized pressure drop increased 51% during a period of 110 days, while the third membrane (CSD with occasional AWC) increased 18% during this period. It was concluded that both air/water cleaning and daily copper sulphate dosing proved to be very effective methods in reducing membrane fouling due to feed spacer fouling.