CETvol87
DOI: 10.3303/CET2187061
Paper Received: 3 November 2020; Revised: 26 February 2021; Accepted: 16 April 2021
Please cite this article as: Cassano A., Conidi C., Drioli E., 2021, Integrated Membrane Systems as an Innovative Approach for the Recovery
of High Value-added Compounds from Agro-food By-products, Chemical Engineering Transactions, 87, 361-366 DOI:10.3303/CET2187061
CHEMICAL ENGINEERING TRANSACTIONS
VOL. 87, 2021
A publication of
The Italian Association
of Chemical Engineering
Online at www.cetjournal.it
Guest Editors: Laura Piazza, Mauro Moresi, Francesco Donsì
Copyright © 2021, AIDIC Servizi S.r.l.
ISBN 978-88-95608-85-3; ISSN 2283-9216
Integrated Membrane Systems as an Innovative Approach for
the Recovery of High Value-Added Compounds from Agro-
Food By-Products
Alfredo Cassano,* Carmela Conidi, Enrico Drioli
Istituto per la Tecnologia delle Membrane, ITM-CNR, c/o Università della Calabria, via Pietro Bucci, 17/C - 87036 Rende
(Cosenza)
a.cassano@itm.cnr.it
The valorization of available food manufacturing waste with high potential to manufacture value-added
products, in line with the main goal of the circular economy, is actually one of the current challenges for
scientists.
Membrane-based processes are an emerging tool to improve the currently adopted valorisation protocols of
agro-food by-products, within a sustainable biorefinery strategy, with remarkable improvements of the
environmental and economical sustainability of the overall approach.
This work aims at providing a critical overview of the on ongoing research studies for the recovery of high
value-added compounds from agro-food by-products such as olive mill wastewaters, citrus by-products and
wastes from the wine industry by membrane-based operations. In particular, the development of integrated
membrane systems on lab-scale unit for the separation, fractionation and concentration of phenolic
compounds and their derivatives from these sources will be presented and discussed.
Experimental results clearly indicate that the combination of membrane unit operations in integrated systems
offers interesting perspectives in terms of recovery of primary resources, reduction of the environmental
impact, formulation of innovative food products and rationalization of conventional food manufacturing
processes.
1. Introduction
The food industry yearly produces a considerable amount of solid and liquid wastes that mainly result from
production, preparation, consumption and disposal processes. The characteristics of a specific waste depend
mainly on the product being processed (e.g., fruit, vegetable, oils, dairy, meat and fish) and the processing
methods. Generally, these wastes contain large amount of macro-pollutants and are only partially recycled for
specific uses such as spread on land, animal feeding and composting, whereas the main volumes are
managed as waste of environmental concern, with relevant negative effects on the overall sustainability of the
food processing industry (Federici et al., 2009). On the other hand, many of these residues are a precious
resource of potentially useful chemical substances after either direct recovery or chemical transformation and
can be potentially reused into other production systems, trough e.g. bio-refineries (Mirabella et al., 2014), and
for developing new products with a market value (i.e. functional foods). In this view, the exploitation of
vegetable by-products as a source of bioactive compounds represents a promising opportunity to obtain
added-value products for food or pharma industries.
Pressure-driven membrane operations such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and
reverse osmosis (RO) have become key technologies in the food processing industry over the last 35 years.
The basic properties of these processes make them ideal for the treatment of both food products and by-
products; high selectivity, possibility to operate under mild conditions of temperature, low energy consumption,
modularity, easy scale-up, no phase change and no use of chemical additives are typical advantages over
conventional separation technologies. The large variety of membrane materials available, as well as the
diversity of membrane processes developed, underlines one of the strengths of membrane separations: the
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possibility of designing and fine-tuning the membrane and the membrane process for a specific task.
Relatively new membrane processes, such as membrane distillation (MD), osmotic distillation (OD) and
membrane emulsification (ME), offer new interesting solutions for the concentration and encapsulation of
target compounds.
In this work, an overview of some applications of membrane-based operations recently investigated on
laboratory scale for the recovery of high value-added compounds from agro-food wastewaters is given. In
particular, case studies related to the implementation of membrane processes in integrated systems for the
recovery of bioactive compounds from olive mill wastewaters (OMWs), citrus and wine by-products are
reviewed and discussed.
2. Olive mill wastewaters
Intensive researches in the field of OMWs management suggest that these effluents are an useful resource for
the recovery of fine chemicals and for different biotechnological applications such as the production of
important metabolites. In particular, OMWs are characterized by presence of more than 30 different types of
biophenols and related compounds including tyrosol, hydroxytyrosol and oleuropein well recognized for their
antioxidant, cardioprotective, antiatherogenic, chemopreventive and anti-inflammatory activities (Obied et al.,
2005). Therefore, utilizing OMWs as potentially cheap source of pharmacologically active compounds ensures
sustainability in terms of material recovery, reduced new material consumption and prevention of
environmental pollution.
Driven by economic factors, environmental concern and technological advancement, membrane-based
processes have been largely investigated over the last 30 years for the valorization of OMWs. Integrated
systems based on the use of selected membrane operations in a sequential design provide significant
improvements of the performance thanks to the synergistic effect among the different unit operations. In this
approach, MF or UF membranes are mostly employed as a pre-treatment step to remove suspended particles
and colloids while allowing the polyphenols and other soluble contaminants to pass through. Tight UF
membranes and NF membranes are useful to fractionate the permeate stream in order to improve purity of
phenolic compounds. Phenolic fractions can be finally concentrated by RO or OD.
The selection of proper membranes in terms of membrane material, pore size and module design as well as
the optimization of operating and fluid-dynamic conditions are key factors to improve permeation fluxes and
selectivity towards target compounds which are both highly dependent on concentration polarization and
membrane fouling phenomena.
Flat-sheet UF membranes with different molecular weight cut-off (MWCO) (4, 5 and 10 kDa) and polymeric
material (regenerated cellulose and polyethersulfone) were evaluated for their retention coefficients towards
phenolic compounds, total antioxidant activity and total organic carbon. All selected membranes showed lower
rejection towards free low molecular weight phenolic compounds in comparison with values observed for total
polyphenols. This was in agreement with the molecular weight of the investigated phenols which is in the
range 138-284 g/mol and hence lower than the MWCO of each UF membrane. For example, regenerated
cellulose membranes with MWCO of 5 e 10 kDa exhibited lower rejections towards phenolic compounds,
higher permeate fluxes and lower fouling index when compared with polyethersulfone membranes having a
similar MWCO. Indeed polyphenols, also aggregated with polysaccharides, has a higher affinity for the
polyethersulfone membranes leading to severe fouling by pore narrowing and blocking under UF conditions
(Cassano et al., 2011).
In the process implemented by Cassano et al. (2013), raw OMWs were pretreated by hollow fiber UF
membranes (with a pore size of 0.02 μm) in order to remove suspended solids and colloids; then the UF
permeate was processed with a flat-sheet UF membrane with a MWCO of 1000 Da. This step allowed to
remove most part of organic substances from phenolic compounds in agreement with the reduced total
organic carobon (TOC)/polyphenols ratio (from 9.2 in the original UF feed to 3.8 in the UF permeate). A
concentrated phenolic solution containing more than 85 mg/L of low MW polyphenols was produced by
treating the UF permeate with a spiral-wound NF membrane having a MWCO of about 200 Da. The hybrid
process allowed to produce three different valuable fractions: a concentrated solution containing high MW
organic substances (retentate of both UF processes) which can be submitted to an anaerobic digestion for the
production of biogas; a concentrated solution (NF retentate) enriched in polyphenolic compounds suitable for
cosmetic, food and pharmaceutical industries as liquid, frozen, dried or lyophilized formulations; a water
stream (NF permeate) which can be reused for irrigation, membrane cleaning and as process water (Figure
1). By referring to the sustainability of the process, membrane filtration has been considered as one of the
most effective processes in terms of organics reduction and economic viability among different investigated
methods of OMWs treatment, thanks to the profit derived from the exploitation of phenolic content and the
fraction rich in nutrient components (Zaklis et al., 2013).
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Figure 1: Schematic of the integrated membrane process proposed for the recovery of flavonoids from orange
press liquor (UF, ultrafiltration; NF, nanofiltration; OD, osmotic distillation) (adapted from Cassano et al., 2014)
In another approach, raw OMWs were submitted to an acidification/MF pretreatment and then processed by
NF before a final concentration by OD (Bazzarelli et al., 2016). Relatively high fluxes, with respect to literature
data, were obtained in both MF and NF steps (60 and 7 L/m2h, respectively); by referring to low MW
polyphenols the NF membrane exhibited rejections higher than 90% for cathecol, tyrosol, caffeic acid and
vanillic acid and of 83% for hydroxytyrosol. The concentration of the NF retentate by OD produced an
enriched fraction of low MW polyphenols according to a concentration factor of 7. This fraction was also
formulated by membrane emulsification for the production of a W/O emulsion with an encapsulation efficiency
of 90%. According to the process mass balance, related to the treatment of 1000 L of OMWs, 1463 g of
phenolic compounds (85% of the initial phenolic content) and 800 L (80% of the initial volume) of purified
water can be recovered, respectively.
Recently, Tundis et al. (2020) analysed the phenolic composition and the antioxidant, hypoglycaemic and
hypo-lipidemic properties of OMWs fractions obtained to a combination of MF, NF and RO membranes in
order to prospect a potential use in pharmaceutical, nutraceutical, and cosmeceutical industries. As reported
in Table 1, hydroxytyrosol, oleuropein, tyrosol and 4-hydroxyphenyl acetate were the most abundant phenolic
compounds in the raw wastewaters. All compounds were highly recovered in the MF permeate. For the NF
membrane, the measured rejections were strongly correlated with the molecular weight of phenolic
compounds. In particular, the retention towards tyrosol was 4.8%, while phenolic compounds with MW higher
than 194 g/mol were completely retained.
Table 1: Analysis of phenolic compounds (mg/L) in samples of olive mill wastewaters treated by integrated
membrane process (Tundis et al, 2020)
Phenolic Compounds Feed MF-P NF-R NF-P RO-R RO-P
Caffeic acid 8.1 ± 0.5 7.6 ± 0.5 27.7 ± 1.4 1.8 ± 0.2 45.7 ± 1.2 0.5 ± 0.03
p-Coumaric acid 6.4 ± 0.4 4.3 ± 0.2 12.2 ± 0.8 2.6 ± 0.2 35.9 ± 1.6 nd
Ferulic acid 6.9 ± 0.6 6.3 ± 0.3 20.1 ± 1.1 nd 51.3 ± 1.4 nd
Luteolin 15.2 ± 0.6 13.7 ± 1.1 71.5 ± 2.7 nd 82.8 ± 3.1 nd
4-Hydroxyphenyl
acetate
72.6 ± 1.8 67.0 ± 2.6 29.6 ± 1.2 64.0 ± 3.2 57.1 ± 1.2 nd
Hydroxytyrosol 373.3 ± 4.8 320.1 ± 5.8 1017.5 ± 8.8 268.3 ± 1.2 1522.2 ± 7.3 18.8 ± 1.2
Oleuropein 106.8 ± 4.0 85.2 ± 2.7 263.2 ± 4.2 nd 510.0 ± 5.5 nd
Tyrosol 89.7 ± 2.1 68.1 ± 5.1 157.3 ± 4.3 64.8 ± 1.2 519.0 ± 6.2 5.0 ± 0.6
Vanillic acid 29.4 ± 0.3 27.8 ± 1.7 97.0 ± 2.5 6.5 ± 0.9 116.2 ± 3.1 1.4 ± 0.1
Verbascoside 26.7 ± 1.1 18.0 ± 1.3 82.8 ± 3.4 nd 130.9 ± 1.2 nd
MF, microfiltration; NF, nanofiltration; RO, reverse osmosis; P, permeate; R, retentate; nd, not detectable.
Flocculant
Pre-filtration (5μm)
Olive mill
wastewater
Solids
NF
Retentate
pH adjustment
enzymatic
treatment
Composting
Anaerobic digestion
NF
Permeate
Nutraceuticals
Food supplements
Pharmaceuticals
Cosmeticals
Process water
Irrigation
Membrane cleaning
UF
permeate
UF retentate
(suspended solids,
polisaccharides,
proteins, etc.)
UF
Permeate
UF (0.02 μm)
UF (1,000 Da)
NF (200 Da)
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As expected, all compounds were completely or almost completely rejected by the RO membrane. Therefore,
the RO retentate (RO-R) exhibited the highest bioactive compounds content. In particular, the hydroxytyrosol
content (1522.2 ± 7.3 mg/L) was about five times higher than the MF feed. In the RO permeate (RO-P) only
hydroxytyrosol (18.8 ± 1.2 mg/L), tyrosol (5.0 ± 0.6 mg/L), vanillic acid (1.4 ± 0.1 mg/L), and caffeic acid (0.5 ±
0.03 mg/L) were identified. Accordingly, the RO retentate showed the highest antioxidant activity in the ABTS
test (IC50 6.9 ± 1.9 μg/mL), while NF permeate and RO permeate were the less active. Similar results were
found in samples analysed by the DPPH test and for hypoglycaemic activity.
The set of results suggested that RO polyphenol-enriched fractions are effective in scavenging radicals and
protecting lipid-oxidations and in inhibiting key enzymes such as lipase, α-amylase, and α-glucosidase, useful
therapeutic targets for the development of functional products for obesity and diabetes type 2 prevention.
3. Citrus wastewaters
Citrus by-products are enriched in bioactive compounds, such as flavonoids and phenolic acids, recognized
for their beneficial implications in human health due to their antioxidant activity and free radical scavenging
ability. The UF process allows to recover these compounds in a permeate stream having a total soluble solids
content and an acidity level approximating similar to that of the press liquor; suspended solids, such as
proteins and fibers and high molecular weight carbohydrates such as pectins associated with cloud, are
retained by the UF membrane. Polysulphone (PS) UF membranes in hollow fiber configuration and a MWCO
of 100 kDa produced steady-state value of about 45 L/m2h when the raw press liquor was processed
according to a bath concentration configuration in selected operating conditions up to a volume reduction
factor (VRF) of 14. Operating conditions were optimized, according to the response surface methodology in
order to maximize permeate flux and improve the recovery of phenolic compounds in the clarified liquor
(Ruby-Figueroa et al., 2012). NF membranes can be used to fractionate the clarified liquor producing a
retentate stream enriched in phenolic compounds. In particular, polyethersulphone (PES) membranes with
MWCO of 1,000 Da were able to produce a pre-concentrated liquor at 32 °Brix from the clarified liquor
exhibiting rejections of 97.4 % and 98.9 % towards flavanones and anthocyanins, respectively. The final
concentration of the NF retentate by OD produced a concentrated solution at 47 °Brix. OD was performed at
an operating temperature of 28 °C by using polypropylene hollow fiber membranes with a pore size of 0.2 μm.
The NF retentate was recirculated in the shell side of the membrane module, while calcium chloride dehydrate
was recirculated in the lumen side. The concentration factor of phenolic compounds in the OD retentate
resulted in agreement with the concentration factor of total soluble solids due to the water removal. The final
product, containing about 20 g/L of anthocyanins and about 100 g/L of flavanones, showed interesting
perspectives for its use as natural colorant and/or for nutraceutical applications. The conceptual design
proposed for the recovery of phenolic compounds from citrus press liquor is depicted in Figure 2.
4. Wastes from wine industry
The winemaking industry generates a large amount of solid and liquid by-products in a short period of time,
including grape pomace, wine lees, spent filter cakes, vinasses and winery wastewater that must be treated,
disposed of or reused properly in order to avoid negative environmental impacts. These by-products constitute
a valuable source of phenolic compounds and, therefore, can be used for valorization of functional ingredients
or bioactive phytochemicals that can be devoted to the generation of pharmaceutical, food, and cosmetic
ingredients (Teixeira et al., 2014).
Traditional extraction methods, based on the use of maceration assisted by solvent extraction, are
characterized by several limitations such as loss of compounds due to hydrolysis and oxidation during
extraction, long extraction time and potential environmental pollution due to large volumes of organic solvent
used. In this context, the development of “green” extraction and separation procedures is of great importance
into industrial processes to reduce or eliminate the use and generation of hazardous substances.
Sustainable extractive technologies, such as ultrasound- and microwave-assisted extraction, followed by
membrane separation methods represent a promising tool for the recovery of high-added value compounds
from winery wastes and by-products.
Arboleda Mejia et al. (2019) investigated a combination of microwave/hydro-alcoholic extraction and
membrane operations for the recovery of phenolic compounds from red wine lees. The hydro-alcoholic extract
was previously microfiltered in order to reduce its turbidity and then fractionated with different flat-sheet
polymeric membranes with MWCO in the range of 150-1,000 Da. Among the selected membranes, the 1,000
Da membrane exhibited the highest productivity in selected operating conditions (in agreement with its higher
MWCO) but lower retention of phenolic compounds and sugars in comparison with the other membranes. On
the other hand, the 150 Da membrane presented retention coefficients higher than 70% for all detected free
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low molecular weight phenolics (Figure 3). Therefore, an integrated process based on the combination of
microwave-extraction, microfiltration (polyvinylidene fluoride membrane, pore size 0.15 μm) and nanofiltration
(polyamide membrane, MWCO 150 Da) was considered of practical interest for the production of concentrated
fractions of bioactive compounds from red wine lees.
Figure 2: Schematic of the integrated membrane process proposed for the recovery of flavonoids from orange
press liquor (UF, ultrafiltration; NF, nanofiltration; OD, osmotic distillation) (adapted from Cassano et al., 2014)
Figure 3: Rejection of polymeric membranes towards specific compounds of clarified red wine lees extract
(adapted from Arboleda Meija et al., 2019)
Recently, cellulose acetate NF membranes were prepared and investigated for the recovery of phenolic
compounds from red grape pomace extract obtained through ultrasound-assisted enzymatic extraction
(Arboleda Mejia et al., 2020). The average permeate flux of prepared membranes measured in selected
operating conditions (operating pressure and temperature of 20 bar and 25 °C, respectively) resulted higher
than that of the NF90 membrane, an aromatic polyamide commercial membrane with a MWCO of 200 Da.
These results were in agreement with the rejection values measured for different solutes and data of water
permeability. In particular, it was inferred a strong correlation between the solute retention and the permeate
flux values (Table 2). Among the prepared membranes, the CA400-22 membrane showed a rejection of about
73% to the total polyphenols and a rejection of about 60-70% to the antioxidant capacity. This membrane
showed almost a total retention towards proantocyanidins (about 93%) and allowed to recover most part of
glucose and fructose in the permeate stream (rejection values of 19.5% and 12.5%, respectively) obtaining a
permeate rich in sugars. Therefore, this membrane offered the best performance in terms of separation
between sugars and phenolic compounds.
UFNF
Fruit discarge
Juice extraction
concentrated
brine
diluted
brine
OD
Essential oil PeelOrange juice
Suspended
solids
Press liquor
Milling
Water, sugars,
minerals
Concentrated
phenolic solution
Washing
Oil removal
Industrial colorants
Nutraceuticals
Pharmaceuticals
Food additives
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100 UF, Composite fluoro-polymer, 1000 DaNF, aromatic polyamide, 150-300 Da
NF, aromatic polyamide, 150 Da
365
Table 2: Nanofiltration of grape pomace extract. Permeate flux (Jp) (at 20 bar and 25 °C) and rejection of
selected membranes towards specific solutes
Membrane type Jp
(L/m2h)
Glucose rejection
(%)
NaCl rejection
(%)
Na2SO4 rejection
(%)
NF90 26.09 ± 1.25 100 95 99
CA316-70 43.38 ± 0.9 95 77 97
CA316 44.44 ± 1.05 50 27 86
CA400-22 50.58 ± 2.55 11 10 47
5. Conclusions
Pressure-diven membrane operations, also combined in a sequential design, has been investigated for the
treatment of agro-food by-products according to a logic of circular economy. Tailor made processes for
specific by-products have been identified through a proper selection of membrane characteristics (membrane
material, pore size, geometry) as well as through the optimization of operating and fluid-dynamic conditions in
order to reduce and control membrane fouling phenomena which have a strong influence on membrane
productivity and selectivity towards target compounds. Experimental results indicate that these processes
successfully meets the requirements for the recovery, purification and concentration of phenolic compounds
with the production of concentrated fractions of potential applications in the food, pharmaceutical and cosmetic
industries. New perspectives and potentialities in this field are expected from the development of superior
membranes and process engineering breakthroughs as well as through the combination of membrane
operations and conventional separation technologies (i.e. adsorption, centrifugation, evaporation).
References
Arboleda Mejia J.A., Parpinello G.P., Versari A., Conidi C., Cassano A., 2019, Microwave-assisted extraction and
membrane-based separation of biophenols from red wine lees, Food and Bioproducts Processing, 117, 74-83.
Arboleda Mejia J.A., Ricci A., Figueiredo A.S., Versari A., Cassano A., Parpinello G.P., de Pinho M.N., 2020,
Recovery of phenolic compounds from red grape pomace extract by nanofiltration membranes, Foods, 9, 1649.
Bazzarelli F., Piacentini E., Poerio T., Mazzei R., Cassano A., Giorno L., 2016, Advances in membrane operations
for water purification and biophenols recovery/valorization from OMWWs, Journal of Membrane Science, 497,
402-409.
Cassano A., Conidi C., Drioli E., 2011, Comparison of the performance of UF membranes in olive mill wastewaters
treatment, Water Research, 45, 3197-3204.
Cassano A., Conidi C., Giorno L., Drioli E., 2013, Fractionation of olive mill wastewaters by membrane separation
techniques, Journal of Hazardous Materials, 248, 185-193.
Cassano A., Conidi C., Ruby-Figueroa R., 2014, Recovery of flavonoids from orange press liquor by an integrated
membrane process, Membranes, 4, 509-524.
Federici F., Fava F., Kalogerakis N., Mantzavinos D., 2009, Valorisation of agro-industrial by-products, effluents and
waste: concept, opportunities and the case of olive mill wastewaters, Journal of Chemical Technology and
Biotechnology, 84, 895-900.
Mirabella N., Castellani V., Sala S., 2014, Current options for the valorization of food manufacturing waste: a review,
Journal of Cleaner Production, 65, 28-41.
Obied H.K., Allen M.S., Bedgood D.R., Prenzler P.D., Robards K., Stockmann, R., 2005, Bioactivity and analysis of
biophenols recovered from olive mill waste, Journal of Agricultural and Food Chemistry, 53, 823-837.
Ruby-Figueroa R., Cassano A., Drioli E., 2012, Ultrafiltration of orange press liquor: optimization of operating
conditions for the recovery of antioxidant compounds by response surface methodology, Separation and
Purification Technology, 98, 255-261.
Teixeira A., Baenas N., Dominguez-Perles R., Barros A., Rosa E., Moreno D.A., Garcia-Viguera, C., 2014, Natural
bioactive compounds from winery by-products as health promoters: a review, International Journal of Molecular
Sciences, 15, 15638-15678.
Tundis R., Conidi C., Loizzo M.R., Sicari V., Cassano A., 2020, Olive mill wastewater polyphenol-enriched fractions
by integrated membrane process: a promising source of antioxidant, hypolipidemic and hypoglycaemic
compounds, Antioxidants, 9, 602.
Zagklis D.P., Arvaniti E.C., Papadakis V.G., Paraskeva C.A. 2013, Sustainability analysis and benchmarking of olive
mill wastewater treatment methods, Journal of Chemical Technology and Biotechnology, 88, 742-750.
366