Combining Ultrafiltration and Nanofiltration to Obtain a Concentrated Extract of Purified Polyphenols from Wet Olive Pomace

Abstract

Despite the environmental concerns raised every year by the generation of high volumes of wet olive pomace, it contains valuable phenolic compounds that are essential for the valorization of this by-product. In this work, an integrated process to recover phenolic compounds from wet olive pomace is proposed. It consists of ultrasound-assisted solid-liquid extraction, followed by ultrafiltration and nanofiltration. Several commercial membranes were studied at different operational conditions. The ultrafiltration stage allowed the purification of biophenols, which were obtained in the permeate stream. Regarding organic matter, satisfactory rejection values were obtained with both commercial UH030 and UP005 membranes (Microdyn Nadir), but the latter provided more efficient purification and higher values of permeate flux, above 18 L·h^-1·m^-2 at 2.5 bar and 1.5 m·s^-1. Later, this permeate stream was concentrated by means of a nanofiltration process, obtaining polyphenol rejection values that surpassed 85% with the commercial NF270 membrane (DuPont), then achieving the concentration of the previously purified polyphenols.

Keywords: integrated process; nanofiltration; phenolic compounds; rejection; ultrafiltration; wet olive pomace.

Figure 1

Schematic diagram of the recovery of phenolic compounds from wet olive pomace by the proposed integrated process consisting of solid–liquid extraction (SLE), ultrafiltration (UF) and nanofiltration (NF). ¹ COD: chemical oxygen demand.

Figure 2

Evolution of permeate flux with the volume reduction factor (VRF) for the UH030 membrane (left) and the UP005 membrane (right) when the extract was treated.

Figure 3

Rejection values obtained at the different volume reduction factors (VRFs) for the UH030 membrane (A) and the UP005 membrane (B).

Figure 4

Rejection of each phenolic compound detected in the aqueous extract of wet olive pomace, obtained with the UP005 membrane at a volume reduction factor of 2. The operational conditions were 1.5 m·s⁻¹ and 2.5 bar.

Figure 5

Permeate flux obtained with the NF270 membrane after the ultrafiltration of the extract with the UH030 membrane (A) and the UP005 membrane (B).

Figure 6

Rejection values obtained with the NF270 membrane at a volume reduction factor of 2.5 after the treatment of the permeate obtained with the UH030 membrane (A) and the UP005 membrane (B).