Membrane fouling in ultrafiltration of cork processing wastewaters (Reprinted from Advances in Environmental Research, vol 3, pg 539-549, 2000)

This work addresses the evaluation of membrane fouling in the ultrafiltrati on of cork processing wastewaters, which are rich in phenolic/tannic colloi dal matter. The performance of a commercial membrane, TS60 (Ropur), and fou r cellulose acetate membranes covering a wide range of molecular weight cut -offs (MWCOs of 4-98 kDa) was investigated under varied operating condition s (hydrodynamics and transmembrane pressure). The film theory was used to c orrelate the mass transfer coefficient, k, with the resistance introduced b y concentration polarization and the rejection coefficient, f', with the fo uled membrane resistance. The results show that for the membrane with the l ower MWCO, TS60, very high rejections (similar to 100%) of organic matter a nd very low fluxes were obtained while the cellulose acetate membranes yiel ded rejections from 50% to 90% and much higher fluxes. Among the CA membran es, the decrease in rejection of organic matter was not accompanied by a si gnificant gain in the permeate fluxes due to greater fouling of the higher MWCO membranes. The ATR-FTIR spectra of used and non-used CA membranes were compared. The shift of the nu(OH) band to higher wavenumbers observed in t he spectra of used membranes may be ascribed to the presence of fouling mat erial in the pores of the membranes. For the TS60 membrane, mass transfer w as found to be controlled by concentration polarization and for the CA memb ranes both concentration polarization and membrane surface adsorption acted as resistances to mass transfer.