MEMBRANE PERFORMANCE WITH A PULP-MILL EFFLUENT - RELATIVE CONTRIBUTIONS OF FOULING MECHANISMS

Severe flux decline was observed during ultrafiltration of a pulp mill effluent. Membrane fouling was the result of varying combinations of adsorption, pore plugging and concentration polarization or gel layer formation. A wide range of membrane materials and pore sizes were eval uated, showing the relationship between the membrane material, pore si ze and the relative contribution of the different fouling mechanisms. Individual resistances were evaluated for adsorption, R(a), pore plugg ing, R(pp), and concentration polarization, R(cp), using a series resi stance model. These were based on the pure water flux for(1) the new m embrane, J(i), (2) after static adsorption with the mill effluent, J(a ), (3) the product rate when ultrafiltering the effluent, J(v), and (4 ) the pure water permeability with the fouled membrane, J(f). These re sistances were shown to be misleading in terms of the observed flux lo ss for cases with significant adsorptive fouling. Adsorptive fouling w as underestimated and concentration polarization overestimated. An alt ernative method, which we shall call flux loss ratios, is proposed, wh ich is based on the flux decline due to a particular mechanisms as a f raction of the overall flux decline. These new measures more accuratel y reflect the flux decline attributable to each fouling mechanism.