Application of microfiltration and ultrafiltration processes to cork processing wastewaters and assessment of the membrane fouling

The filtration of wastewaters generated in the cork industrial process is investigated by using three membranes in tangential filtration laboratory equipment. The three membranes used were two microfiltration membranes with pores sizes of 0.65 and 0.1 μm (DUR-0.65 and DUR-0.1 membranes), and a ultrafiltration membrane with a molecular weight cut-off of 300 kDa (BIO-300K membrane). The water hydraulic permeability was determined for each membrane (values of 860, 248 and 769 L h⁻¹ m⁻² bar⁻¹ were found), and the influence on the permeate flux of the main operating variables, such as transmembrane pressure, feed flow rate, temperature and nature of the membranes, was established. The effectiveness of the different membranes and operating conditions was evaluated by determining the removal obtained for several parameters which measure the global pollutant content of the effluent: COD, absorbance at 254 nm, tannic content, color and ellagic acid, which is selected as a major model pollutant among the different organic compounds present in this wastewater. The values of the corresponding retention coefficients depended on the operating conditions, but in all cases were in the sequence: ellagic acid and color > absorbance at 254 nm > tannic content > COD. Globally, the higher removals were obtained for the BIO-300K membrane at 20 °C, with Q_F = 5.3 L h⁻¹ and TMP = 1.8 bar. Finally, the fouling of the membranes was assessed, and the corresponding mechanism for each membrane was established by fitting the experimental data to various filtration fouling models reported in the literature.