(563b) Membrane Based Process for Polyphenols Recovery from Winery Effluents

Winery effluents are rich in added-value compounds, among which the polyphenols stand out by their antioxidant properties. In wine-producing regions, these effluents are abundant and a cheap and attractive source for the recovery of these natural antioxidants [1]. The recovery of these compounds reduces the environmental impact of wineries, representing a significant enhancement in maintaining the environmental balance, with gains in economic and environmental issues. In this regard, the development of efficient and environmentally friendly processes for the recovery and concentration of polyphenols from agro-industrial effluents is required.

In this sense, due to their inherent characteristics (low energy requirement, no additives, mild operating conditions, separation efficiency and easy scaling up), membrane processes like ultrafiltration and nanofiltration have been employed to recover and concentrate polyphenols from agro-food extracts and effluents.

In a previous work [2], a sustainable process of aqueous extraction associated to microfiltration (MF) for the recovery of natural antioxidants from wine lees, generated in the second racking of red wine making, was developed. More than 20% of the total content of polyphenols present in the raw effluent were recovered in the MF permeates. These are complex mixtures mainly composed of polyphenols, anthocyanins, organic acids, polysaccharides and minerals.

Literature data [3] report that membrane processes applied to concentrate complex mixtures containing polyphenols lead to drastic permeation fluxes decline and severe problems of membrane fouling. The present work addresses the ultrafiltration(UF) and the nanofiltration (NF) of the MF permeates obtained in a previous work [2] and evaluates the effect of operating conditions of transmembrane pressure and feed flow rate on the productivity (permeation fluxes) and on the selectivity (solute rejections). The quantification of this effect and the assessment of concentration polarization is carried out through the film theory model.

Materials and Methods

Permeation experiments were realized in laboratory flat-cell units with a membrane surface area of 14.5 x 10^-4 m², using the NF270 and ETNA01PP membranes, with molecular weight cut-off (MWCO) of 300 and 1000 Da, respectively. Experiments were conducted in total recirculation mode, where the permeate and the retentate streams were recirculated to the feed tank to study the variation in the permeate fluxes and the solute rejection coefficients. The stabilization time for each experimental run was 30 min, after which permeate samples were taken for chemical analysis. These permeation runs were performed at feed flow rates of 100, 150 and 200 L h^-1, transmembrane pressures of 3, 5, 7 and 15 bar and using as feed solution the MF permeates with the composition characteristics displayed in Table 1.

Table 1. Physico-chemical characteristics of the feed solution.

Results and Discussion

Nanofiltration permeation fluxes with the NF270 membrane increase linearly with transmembrane pressure and are independent of the feed circulation flow rate.

The ETNA01PP membrane displayed typical patterns of UF permeation fluxes, where at low transmembrane pressures (up to ~5 bar) the permeation fluxes increase linearly and at higher transmembrane pressures the limiting flux is reached. In fact, working at feed flow rates of 100 and 150 L h^-1, the ETNA01PP membrane do not yielded substantial difference in permeation fluxes, while at 200 L h^-1higher permeation fluxes were achieved. Besides, for the investigated membranes, the solution permeability decreases with increasing the membrane MWCO. This drop in permeability is boosted by increasing pressure and lowering feed circulation flow rate, that is, such conditions favor the occurrence of concentration polarization phenomenon, a precursor of the membrane fouling.

The tighter membrane (NF270) displayed higher rejection coefficients, i.e., 90% for polyphenols and close to 100% for anthocyanins, providing a permeate with very low antioxidant activity. On the other hand, the ETNA01PP showed moderate polyphenols and anthocyanins rejections (40-50%), showing that the polyphenols preferably permeate this UF membrane. Besides, for both the membranes, the rejection coefficients for polyphenols increase with increasing transmembrane pressure and are virtually independent of feed circulation flow rate. This behavior is attributed to the fact that at higher transmembrane pressures concentration polarization phenomenon is more severe, leading to the formation of a more selective layer on the membrane surface, and therefore increasing the rejection coefficients. The occurrence of concentration polarization was quantified by the film theory model, showing that the concentration of solutes on the boundary layer adjacent to the membrane (C_am) increased with adverse hydrodynamics (low values of feed circulation rates and high values of transmembrane pressure).

Thus, according to the aforementioned data, the integration of different membrane separation processes is an alternative for the recovery and concentration of antioxidants (phenolic compounds and anthocyanins) from the second racking effluents. In such a process, a permeate with antioxidant compounds can be obtained by means of microfiltration associated with water dilutions (aqueous extraction), and can subsequently be concentrated by nanofiltration, resulting in a product with high antioxidant properties.

Acknowledgements

The authors are grateful to the Brazilian funding agencies (FAPERGS, SEBRAE/RS, CAPES and CNPq) and to the Portuguese funding agency (FCT) for their financial support, as well as to the Vinícola Almaúnica (Brazil) by the financial support and for providing the effluents.

References

[1] Balboa, E. M., Soto, M. L., Nogueira, D. R., González-López, N., Conde, E., Moure, A., Vinardell, M. P., Mitjans, M., Domínguez, H., Potential of antioxidant extracts produced by aqueous processing of renewable resources for the formulation of cosmetics, Industrial Crops and Products, Vol. 58, No. 0, pp 104-110, 2014.

[2] Giacobbo, A., do Prado, J. M., Meneguzzi, A., Bernardes, A. M., de Pinho, M. N., Microfiltration for the recovery of polyphenols from winery effluents, Separation and Purification Technology, Vol. 143, No. 0, pp 12-18, 2015.

[3] Minhalma, M., Dias, C., De Pinho, M., Membrane fouling in ultrafiltration of cork processing wastewaters, Advances in Environmental Research, Vol. 3, No. 4, pp 539-549, 2000.