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- Concentration polarization quantification and minimization in cork process wastewater ultrafiltration by an ozone pretreatmentPublication . Minhalma, Miguel; De Pinho, Maria Norberta; Dominguez, Joaquin R.Concentration polarization and membrane fouling have been identified as the main problems during the ultrafiltration treatment of cork processing wastewaters. These problems drastically reduce the permeate fluxes and, therefore, their potential applications. In this work, a soft ozonation pretreatment was applied to minimize these undesirable effects. A new systematic study was carried out for membranes with different molecular weight cut-offs and at different operating conditions to monitor and quantify the concentration polarization caused by the wastewater's remaining ozonated compounds. Film theory was used to correlate the mass transfer coefficient, k, and the intrinsic rejection coefficient, f ', with the resistance introduced by concentration polarization. The ultrafiltration treatment was carried out under varying hydrodynamic operating conditions (circulating flow rates of 100-200 L/h) and transmembrane pressures (1-3 bar) for a set of four cellulose acetate membranes covering a wide range of molecular weight cut-offs (5000-100,000 Da) and hydraulic permeabilities (25-110 kg/h/m(2)/bar). The ozone pretreatment (at wastewater pH) reduced the phenolic content selectively (direct oxidation) by more than 50%, reducing membrane fouling and concentration polarization and increasing permeate fluxes (by 22-45%) and mass transfer coefficients (up to six times).
- Synthesis and bactericide activity of nanofiltration composite membranes - Cellulose acetate/silver nanoparticles and cellulose acetate/silver ion exchanged zeolitesPublication . Beisl, Stefan; Monteiro, Silvia; Santos, Ricardo; Figueiredo, Ana Sofia; SANCHEZ-LOREDO, MARIA GUADALUPE; Lemos, Maria Amélia; Lemos, Francisco; Minhalma, Miguel; De Pinho, Maria NorbertaThe present work addresses the synthesis of nanofiltration composite membranes with bactericide properties. The cellulose acetate based membranes with polyvinylpyrrolidone coated silver nano particles, silver ion-exchanged beta-zeolite and beta-zeolite are casted by the phase inversion technique and subjected to an annealing post-treatment. They are characterized in terms of the nanofiltration permeation performance and antibacterial properties. The incorporation of silver nanoparticles produces a threefold increase in the membrane hydraulic permeability when compared to the silver-free membranes and the incorporation of silver ion loaded zeolite resulted in a 56.3% increase in hydraulic permeability. In contrast to the influence of silver presence, either in nanometric or in the ionic form, the presence of zeolite does not significantly influence the hydraulic permeability. The rejection coefficients to salts range from 83% to 93% for the silver ion-exchanged zeolite membrane and from 84% to 97% for the polyvinylpyrrolidone coated silver nanoparticles membrane. They are higher for sulfate salts than for chloride salts. The antibacterial properties of the membranes were evaluated against Escherichia coli. The results have shown that the silver ion-exchanged beta-zeolite membrane was effective in inactivating Escherichia coli after just 210 min of contact time. No bacterial activity was detected following 24 h of contact time with the membrane containing polyvinylpyrrolidone coated silver nanoparticles. A reduction of more than 6-log, in the number of Escherichia coli, was achieved for both membranes. The different patterns of bactericide activity are associated to the silver speciation in metallic or ionic form. The high flux nanofiltration composite membranes with bactericidal properties represent a strong asset in water treatment biofouling control.