Valorization of artichoke wastewaters by integrated membrane process.

In this work an integrated membrane system was developed on laboratory scale to fractionate artichoke wastewaters. In particular, a preliminary ultrafiltration (UF) step, based on the use of hollow fibre membranes, was investigated to remove suspended solids from an artichoke extract. The clarified solution was then submitted to a nanofiltration (NF) step. Two different 2.5 × 21 in. spiral-wound membranes (Desal DL and NP030) with different properties were investigated. Both membranes showed a high rejection towards the phenolic compounds analysed (chlorogenic acid, cynarin and apigenin-7-O-glucoside) and, consequently, towards the total antioxidant activity (TAA). On the other hand, the Desal DL membrane was characterized by a high rejection towards sugar compounds (glucose, fructose and sucrose) (100%) when compared with the NP030 membrane (4.02%). The performance of selected membranes in terms of permeate flux, fouling index and water permeability recovery was also evaluated. On the base of experimental results, an integrated membrane process for the fractionation of artichoke wastewaters was proposed. This conceptual process design permitted to obtain different valuable products: a retentate fraction (from the NP030 membrane) enriched in phenolic compounds suitable for nutraceutical, cosmeceutical or food application; a retentate fraction (from the Desal DL membrane), enriched in sugar compounds, of interest for food applications; a clear permeate (from the Desal DL membrane) which can be reused as process water or for membrane cleaning.

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.