Fouling studies with three different molecular weight cut-off (MWCO) (100 kDa, 30 kDa and 10 kDa) membranes in regenerated cellulose were carried out in the presence of Acros humic acids (HA) at pH 3.0, 6.7 and 9.5. It was shown that the tighter membranes were less fouled compared with the higher MWCO membranes. 100 kDa membrane showed the highest degree of fouling. The role of pH showed that the highest degree of fouling happened at a neutral pH (pH 6.7) and the lowest degree of fouling happened at a basic pH (pH 9.5). Effectiveness of a novel pre-treatment method was applied to the 100 kDa membrane. We added in the HA solution clay particles, homemade synthetized from natural bentonite and denoted Mont-CTAB. We observed a gain in productivity of 25%. 2D-fractal dimension parameter decreased under 1.5, showing a deorganization of the cake due to clay particles in/on the cake and a specific resistance of 4.4 x 10(11) m/kg was obtained in presence of clays versus 3.6x 10(14) m/kg with HA alone. Finally the development of clay assisted ultrafiltration process changes the cake morphology limiting fouling impact and it is hope that for long term experiments, formation of a gel-layer should be limited. (C) 2012 Elsevier B.V. All rights reserved.