Comparison of the performance of UF membranes in olive mill wastewaters treatment.

Olives are known to contain an appreciate amount of phenols with good antioxidant properties which are lost in large part in olive mill wastewaters (OMWs) during olive oil production. Membrane technology offers several advantages (low energy consumption, no additive requirements, no phase change) over traditional techniques to recover phenolic compounds from OMWs. The aim of this work was to evaluate the performance of different UF membranes in the treatment of OMWs finalized to the recovery of polyphenols. For this purpose, OMWs were processed, in selected operating conditions, with four flat-sheet UF membranes characterized by different molecular weight cut-off (MWCO) (4, 5 and 10 kDa) and polymeric material (regenerated cellulose and polyethersulphone). Permeate fluxes, fouling index and retention coefficients towards phenolic compounds, total antioxidant activity (TAA) and total organic carbon (TOC) were evaluated. Regenerated cellulose membranes exhibited lower rejections towards phenolic compounds, higher permeate fluxes and lower fouling index if compared with PES membranes.

Recovery and concentration of polyphenols from olive mill wastewaters by integrated membrane system.

The purpose of this work was to analyse the potentialities of an integrated membrane system for the recovery, purification and concentration of polyphenols from olive mill wastewater (OMW). The proposed system included some well-known membrane operations such as microfiltration (MF) and nanofiltration (NF), as well as others not yet investigated for this specific application, such as osmotic distillation (OD) and vacuum membrane distillation (VMD). The OMW was directly submitted to a MF operation without preliminary centrifugation. This step allowed to achieve a 91% and 26% reduction of suspended solids and total organic carbon (TOC), respectively. Moreover, 78% of the initial content of polyphenols was recovered in the permeate stream. The MF permeate was then submitted to a NF treatment. Almost all polyphenols were recovered in the produced permeate solution, while TOC was reduced from 15 g/L to 5.6 g/L. A concentrated solution enriched in polyphenols was obtained by treating the NF permeate by OD. In particular, a solution containing about 0.5 g/L of free low molecular weight polyphenols, with hydroxytyrosol representing 56% of the total, was produced by using a calcium chloride dihydrate solution as brine. The obtained solution is of interest for preparing formulations to be used in food, cosmetic and pharmaceutical industry. Besides the OD process, VMD was applied as another way for concentrating the NF permeate and the performance of both processes was compared in terms of evaporation fluxes.

Chromium (III) removal by supported liquid membranes: a comparison among D2HEPA, DNNSA, and a novel extractant as carriers.

A facilitated transport study in supported liquid membranes (SLM) using the extraction reagents di-2-ethylexilfosphoric acid (D2HEPA), dinonylnaftalene sulfuric acid (DNNSA), and a novel complexing agent, trimethyl cis,cis-1,3,5-tripropyl-1,3,5 cyclohexenetricarboxilic acid (TTCHTCA) as carriers has been carried out. Organic solvents with different dielectric constants as diluents have been used to obtain the highest extraction and transport values. The results obtained have shown that, by using different organic phases (carrier and/or diluent), SLMs with different ion flux and transport ability can be obtained. The carrier concentration in the membrane and the chromium (III) [Cr(III)] ions concentration in aqueous phase have been varied to see the effect on transport of Cr(III) ions across the membrane. For the carriers D2HEPA and TTCHTCA, the transport of Cr(IlI), both in batch and in recirculation operation mode, has been studied. Very good results in terms of flux and transport have been obtained using TTCHTCA.

Effects of organic solvents on ultrafiltration polyamide membranes for the preparation of oil-in-water emulsions.

Hydrophilic ultrafiltration membranes made of polyamide with molecular weight cutoff 10 and 50 kDa have been studied for the preparation of oil-in-water emulsions by a cross-flow membrane emulsification technique. Isooctane and phosphate buffer were used as disperse and continuous phase, respectively. The permeation of apolar isooctane through the polar hydrophilic membrane was achieved by pretreatment of membranes with a gradient of miscible solvents of decreasing polarity to remove water from the pores and replace it with isooctane. Four different procedures were investigated, based on the solvent mixture percentage and contact time with membranes. After pretreatment, the performance of the membranes in terms of pure isooctane permeate flux and emulsion preparation was evaluated. The influence of organic solvents on polyamide (PA) membranes has been studied by SEM analysis, which showed a clear change in the structure and morphology of the thin selective layers. The effects proved stronger for PA 10 kDa than for 50 kDa. In fact, similar pretreatment procedures caused larger pore size and pore size distribution for PA 10 kDa than for 50 kDa. The properties of emulsions in terms of droplet size distribution reflected the membrane pore sizes obtained after pretreatment. The correlation between pore size and droplet size, for the physicochemical and fluid dynamic conditions used, has been evaluated.

Novel composite poly(4-vinylpyridine)/polypropylene membranes with recognition properties for (S)-naproxen.

In the last few years, molecular imprinting technology has entered in different fields of chemistry, biochemistry, biotechnology and medicine. The technique allows us to introduce the molecular memory of the substrate to be recognized in a polymeric material during its preparation. In the present paper, molecularly imprinted enantioselective polymer membranes were prepared by photo-copolymerization of commercial polypropylene membranes with the functional monomer 4-vinylpyridine. The (S)-naproxen was used as a template molecule. Enantioselectivity studies in a dead-end filtration system showed the recognition properties of the imprinted membranes, which exhibited a selective transport of the (S)-enantiomer.

Membrane distillation of human plasma ultrafiltrate and its theoretical applications to haemodialysis techniques.

Membrane Distillation (MD) is a technique that allows the extraction of water from aqueous solutions. The basic principle is that vapour, but not liquid water, can pass through hydrophobic micro-porous membranes, along a temperature gradient, with consequent separation of water from solutes. In this study we evaluated the possibility to utilise MD to extract water from Plasma Ultrafiltrate (PU) of patients with Chronic Renal Failure (CRF). The experiments were carried out in vitro by a hydro-phobic polypropylene hollow-fibre distillation module; PU was obtained by a CRF patient utilising a high permeability polisulphone membrane. The results show that water can be extracted by MD from PU of CRF subjects at a constant rate and that none of the substances analysed in PU was able to pass through the polypropilene membrane. In the future MD could integrate extra-corporeal blood purification techniques allowing the re-utilisation of plasmatic water thus ameliorating the treatment of uraemia.

The effect of surface roughness of microporous membranes on the kinetics of oxygen consumption and ammonia elimination by adherent hepatocytes.

In membrane hybrid liver support devices (HLSDs) using isolated hepatocytes where oxygen is transported only by diffusion to the cells, about 15-40% of the cell mass is likely to be in direct contact with the semipermeable membranes used as immunoselective barriers: quantitative effects of membrane surface properties on the kinetics of hepatocyte metabolic reactions may also affect HLSD performance. In this paper, we report our investigation of the effects of surface morphology of two microporous commercial membranes on the kinetics of oxygen consumption and ammonia elimination by primary hepatocytes in adhesion culture. Isolated rat hepatocytes were cultured on polypropylene microporous membranes with different surface roughness and pore size in a continuous-flow bioreactor whose fluid dynamics was optimized for the kinetic characterization of liver cell metabolic reactions. Collagen-coated membranes were used as the reference substratum. Hepatocyte adhesion was not significantly affected by membrane surface morphology. The rates of the investigated reactions increased with ammonia concentration according to saturation kinetics: the values of kinetic parameters Vmax and K(M) increased as cells were cultured on the membrane with the greatest membrane surface roughness and pore size. For the reaction of oxygen consumption, Vmax increased from 0.066 to 0.1 pmol h(-1) per cell as surface roughness increased from 70 to 370 nm. For the kinetics of ammonia elimination. K(M) increased from 0.23 to 0.32 mM and Vmax increased from 1.49 to 1.79 pmol h(-1) per cell with membrane surface roughness increasing from 70 to 370 nm. Cells cultured on collagen-coated membranes consistently yielded the highest reaction rates. The Vmax values of 0.18 and 2.84 pmol h(-1) per cell for oxygen consumption and ammonia elimination, respectively, suggest that cell functions are also affected by the chemical nature of the substratum.