The main problem during the operation of nanofiltration or reverse osmosis membrane plants is fouling of feed spacers in membrane elements due to biofouling and particulate fouling. In order to control biofouling and particulate fouling in membrane elements, both daily air/water cleaning (AWC) and daily copper sulphate dosing (CSD) were investigated and compared to a reference without daily cleaning. A pilot study was carried out for I 10 days with three parallel spiral wound membrane elements; AWC, CSD and the reference which were fed by tap water enriched with a biodegradable compound (100 mu g acetate-C/L). The CSD element, which combined daily copper sulphate dosing and sporadically air/water cleaning, performed best with an increase in pressure drop of 18% and a biomass concentration of 8000 pg ATP/cm(2) within 110 days. This was followed by the AWC element with a pressure increase of 37% and biomass concentration of 20,000 pg ATP/cm(2) within 110 days. The reference element showed a pressure increase of 120% within 21 days. The presented approach is considered very successful in controlling particulate fouling and biofouling, especially when air/water cleaning is combined with copper sulphate dosing. (c) 2006 Elsevier B.V. All rights reserved.