Ultrafiltration/nanofiltration for the tertiary treatment of leather industry effluents

Biologically treated effluents from the leather industry pose severe problems for the environment due in part to both the inorganic charge and the high nitrogen content associated with the organic charge. Pressure-driven membrane processes, namely ultrafiltration/nanofiltration (UF/NF) technology, were investigated for their selective retention of the organics and permeation of the inorganic fraction. Permeation experiments were carried out with two model solutions representative of a treated tannery effluent. UF and NF of these model solutions were assessed in terms of both their inorganic/organic fractionation capability and their permeation productivity. The UF membranes with MWCOs ranging from 10,000 to 1000 Da yield retentate streams enriched in organic compounds and permeate streams enriched in salts. Despite their high capacity for pure water permeation, they displayed low permeation fluxes, as the result of concentration polarization and fouling phenomena. NF 200 and NF 270 membranes associated fractionation capability with high permeation rates. Furthermore, these membranes demonstrated the highest permeate fluxes -30 kg/h/m(2) and 16 kg/h/m(2) for different model solutions, at the transmembrane pressure of 8 bar. Although these membranes had lower hydraulic permeabilities relative to the other membranes tested, they exhibited the best characteristics in terms of minimization of colloidal fouling.