Journal of Water Process Engineering 45 (2022) 102478
Contents lists available at ScienceDirect
Journal of Water Process Engineering
journal homepage: www.elsevier.com/locate/jwpe
Nanofiltration membrane processes for water recycling, reuse and product
recovery within various industries: A review
Nor Naimah Rosyadah Ahmad a, Wei Lun Ang a, b, Yeit Haan Teow a, b,
Abdul Wahab Mohammad a, b, *, Nidal Hilal c
a
Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
Centre for Sustainable Process Technology (CESPRO), Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor,
Malaysia
c
NYUAD Water Research Centre, New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, United Arab Emirates
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Nanofiltration
Membrane technology
Water recycling
Reuse
Industrial wastewater
Product recovery
Nanofiltration (NF) membrane has been applied for the treatment of wastewater owing to its unique features
such as higher selectivity towards divalent/polyvalent ions while allowing permeation for monovalent ions and
small molecules of less than 100 Da. Thus, the use of NF in wastewater treatment is promising for water recy­
cling, reuse, and recovery of other valuable products in industrial wastewater treatment. This review highlights
the current application of NF for water recycling, reuse, and product recovery within multiple industries such as
textile, food, oil and gas, mining, tannery, pharmaceutical as well as pulp and paper industry. The performance of
NF either as stand-alone or integrated with other processes for improving the overall treatment efficiency and
minimizing membrane issues is discussed. Finally, future perspectives for NF applications in industrial waste­
water treatment for water recycling, reuse, and product recovery are discussed.
1. Introduction
In this era of climate change which is very challenging for the global
population, the importance of water as a beneficial commodity for hu­
mankind is indisputable. The demand for water is expected to increase
annually and it has been estimated that by 2030, the water demand for
the whole world will be approximately 6900 billion m3. This amount is
approximately 64% more than the amount of water accessible to most
nations [1]. Thus, increasing the supply of clean water by alternative
means, such as desalination and water recycling and reuse should be one
of the main priorities of the world.
Towards this end, the United Nations (UN) through the Sustainable
Development Goals (SDG) initiative, has set the goal for water, namely
through Goal No 6 – “Ensure availability and sustainable management of
water and sanitation for all”. Under this goal, water recycling and reuse
have been seen as one of the important methods to achieve the goal. Two
specific targets that have been specifically mentioned are that by 2030,
the world should (i) improve water quality by minimizing release of
hazardous chemicals and materials, reducing pollution, halving the
proportion of untreated wastewater, eliminating dumping and sub­
stantially increasing recycling and safe reuse globally, and (ii) expand
capacity-building support and international cooperation to developing
countries in water and sanitation-related activities and programmes,
including water efficiency, water harvesting, wastewater treatment,
desalination, recycling and reuse technologies [2].
Over the last decade, data have shown that water recycling and reuse
activities have increased exponentially [3]. Various projects have been
initiated to treat wastewater from different industries, especially from
municipal sources, for either non-potable or potable applications. Mul­
tiple technologies for tertiary treatment of the effluent have been used,
including membrane technologies, adsorption, and advanced oxidation.
However, a recent report by the Global Water Market 2017 indicated
that there is still a vast potential for research and innovation as well as
the implementation of water recycling and reuse which can still be
explored [4]. Their data showed that up to 2017, the amount of water
that has been reused and recycled was only 1.2 billion m3 per year,
which constituted only about 4% of the total estimated wastewater.
The use of membrane technologies such as microfiltration (MF),
* Corresponding author at: Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia,
43600 Bangi, Selangor, Malaysia.
E-mail address: drawm@ukm.edu.my (A.W. Mohammad).
https://doi.org/10.1016/j.jwpe.2021.102478
Received 2 October 2021; Received in revised form 25 November 2021; Accepted 26 November 2021
Available online 9 December 2021
2214-7144/© 2021 Elsevier Ltd. All rights reserved.
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
relevant to the issues and were categorized as shown in Fig. 1.
ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) within
the tertiary processes for water recycling and reuse has also been
increasing over the years. Apart from that, membrane bioreactor (MBR)
has also been popular as part of the processes by combining biological
treatment with membrane separation capability. These membrane
technologies have been well received by many industries because of
their efficiencies, small footprint, high productivity, modular system,
and clean process. Yang et al. [3] have provided an excellent review on
the use of membrane technologies for water recycling and reuse,
focusing specifically on effluent from municipal sewage plants. Apart
from that, other reviews have also been published generally on the use of
membrane technologies in combination with other processes for water
recycling and reuse for different industries such as oil and gas [5], pulp
and paper [6], dairy and soy processing [7] and acid mine drainage [8].
This review is intended to focus only on the use of NF as one of the
membrane technologies that have been applied for water recycling and
reuse within various industries. Besides water recycling and reuse,
numerous published works have shown that NF is also promising for the
recovery of valuable products or by-products from wastewater. NF is
unique in comparison to UF since it demonstrates better retention of
small molecules such as peptides, sugars, and amino acids [9].
Compared to RO, NF has higher fluxes and greater selectivity towards
divalent/polyvalent ions while allowing permeation for monovalent
ions and small molecules of less than 100 Da. RO generally rejects
almost all ions and molecules and only allows water to pass through.
Thus, in terms of water recycling, reuse and product recovery, NF is
more suitable for the purpose.
Excellent reviews on NF have been published by quite a number of
authors on various aspects of NF membranes, including the overall NF
technology and development [10], NF membrane fabrication [11], NF
for water purification [12] and NF for removal of micropollutants [13].
However, there has not been any review specifically on the use of NF for
water recycling, reuse, and product recovery from various industries,
which is the primary purpose of this review paper. The industries that
will be focused upon will be the food, textile, oil and gas, mining,
pharmaceutical, pulp and paper and tannery industries. These are the
main industries upon which NF membranes have found widespread
applications. Fig. 1 shows the number of publications of NF application
in various industrial wastewater treatments that have been reported in
the Scopus database since the year 2000. The keywords “nanofiltration”
and specific industrial wastewater term such as “textile”, “food”,
“pharmaceutical”, “pulp and paper”, “mining”, “oil and gas”, “tannery”
were used for the data search. A total of 411 articles were found to be
2. Overview of nanofiltration and its separation mechanisms
The understanding on the NF membranes processes has been well
established over the last few decades since it was first recognized in the
early 90s. Commercially, NF is known as membranes with a pore size of
about 1 nm in addition to having a molecular weight cut-off (MWCO) of
300–500 Da and salt rejection that is low (10–30%) for monovalent salts
such as NaCl and very high (80–100%) for divalent salts such as Na2SO4.
These fundamental properties differentiate the NF membranes from RO
membranes, thus allowing NF to have greater selectivity for different
classes of small molecules and ions. This in turn enables NF to be applied
in niche applications in various industries, especially water and waste­
water treatment, pharmaceutical and biotechnology, and food engi­
neering [10]. Apart from NF with MWCO smaller than 500 Da (tight NF),
loose NF (MWCO 500–2000 Da) has also been introduced and applied in
numerous applications such as polyphenol fractionation and sugar
separation [14]. Its lower salt rejection, higher separation selectivity to
small molecules and higher permeability is promising for resource re­
covery, especially in textile wastewater treatment. Unlike tight NF,
which is widely available in the market due to its stable performance,
the competitive products of loose NF and its market demand are still
limited [14]. In terms of membrane materials, the polymeric NF has
widespread application in the wastewater treatment field, but its fouling
issue and long-term stability are the major concern [15]. On the other
hand, the ceramic membrane with high thermal and chemical stability,
good mechanical strength, ease of cleaning procedure and long mem­
brane lifetime, is a promising alternative to the polymeric membrane
[16]. However, its packing density and high investment cost require
further improvement. Table 1 provides descriptions of several
commercially available NF membranes made from various materials.
Over the last two decades, various studies have confirmed the sep­
aration mechanism of NF membranes, which basically consists of steric,
Donnan and dielectric effects, as shown in Fig. 2 [28–32]. The steric
effect, which is also a common rejection mechanism in MF and UF, is
basically due to the exclusion of molecular size by the membrane pores.
Solutes with larger molecular size in comparison to the membrane pore
size are effectively rejected by the membranes. Solutes smaller than the
membrane pore size will be able to permeate through depending on the
hindered diffusion transport phenomena across the membrane pores
[33]. For NF membranes, the steric effect will be influential for
permeation of small solutes such as saccharides (glucose, sucrose, and
Fig. 1. Total publications of NF application in various industrial wastewater treatment (based on Scopus database search).
2
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
Table 1
Description of commercial NF membranes available in the market.
Manufacturer/Supplier
NF membrane code
Membrane material
MWCO (Da)
Salt rejection
pH range
Hydranautics
Microdyn Nadirb
Microdyn Nadirb
GE Osmonicsb
GE Osmonicsb
GE Osmonicsb
GE Osmonicsb
GE Osmonicsc
Trisepb
Seprod
Hydracore50/NF-50
NP010
NP030
DK
Duracid
DL
HL
CK
TS 80
NF1
Sulfonated polyethersulfone
Polyethersulfone
Polyethersulfone
Polyamide
Polyamide
Polyamide
Polyamide
Cellulose acetate
Polyamide
Polyamide
1000
1000
500
150–300
150–200
150–300
150–300
150–300
150
150–300
2–11
0–14
0–14
2–10
0–9
2–10
3–9
2–8
2–11
3–10
Seprod
NF3
Polyamide
150–300
PCI Membranese
Dow Filmtechf
AFC-30
NF90
Polyamide
Polyamide
Not stated
257–330
Dow Filmtechf
NF200
Polyamide
~200
Dow Filmtechf
NF270
Polyamide
200–400
Kochg
Vontronh
Atechi
Inopork
MPS-34
VNF1
Type 19/3.3
Inopor® nano
Proprietary
Polyamide
TiO2
TiO2
200
260
1000
750,450, 200
50% NaCl
35–75% Na2SO4
80–95% Na2SO4
96% MgSO4
98% MgSO4
98% MgSO4
98% MgSO4
>94% MgSO4
99% MgSO4
90% NaCl,
99.5% MgSO4
60% NaCl,
98% MgSO4
75% CaCl2
>98% MgSO4,
90–96% NaCl
>98% MgSO4,
50% NaCl
>98% MgSO4,
50% NaCl
35% NaCl
>98% MgSO4
Not stated
Not stated
a
Data obtained from: a [17,18], b [19], c [18],
d
[20], e [21], f [10,22], g [23],
h
3–10
1.5–9.5
3–10
3–10
3–10
0–14
3–10
0–14
0–14
[24,25], i [26] and k [27].
Fig. 2. Schematic illustration of NF membrane separation mechanism.
raffinose) [30], polyethylene glycol (PEG) [34], hormones [35] and
phenolic compounds [36].
The Donnan effect or the electrostatic repulsion effect comes into
play due to the presence of charge on the membrane surface [31,33].
Small ions with either positive or negative charges will not be affected
by the steric exclusion effect but will be significantly affected by the
Donnan effect. The presence of a fixed charge on the membrane surface
will create a potential difference (called Donnan potential) at the
membrane-bulk interface. This potential will cause the counter ion
species to be repelled due to the electrostatic repulsion effect. To
maintain the electroneutrality condition of the solution, the co-ion will
also be simultaneously rejected. The higher the charge of the counterion, the higher the rejection that will take place. As a result of the
aforementioned events, electrostatic attraction or repulsion occurs in
accordance with the ion valence and the membrane's fixed charge,
which may evolve depending on the localized ionic environment.
The third effect, which is the dielectric effect, refers to the solvation
energy barrier formed when an ion passes from a solvent of one
dielectric constant to a solvent of a different dielectric constant [37,38].
Zhu et al. [38] demonstrated that electric field behavior and ion con­
centration distribution inside the nanopore reflect the variation of the
dielectric effect. Consequently, the dielectric effect affects the repulsive
force to co-ions and hence the rejection performance. The combination
of these separation mechanism effects has allowed NF membranes to be
effective for various types of applications that will be elucidated in this
review for different industries.
3. Application of nanofiltration for water recycling, reuse, and
product recovery
The presence of contaminants in industrial wastewaters is one of the
global environmental problems. Textile, food, oil and gas, mining,
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N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
tannery, pharmaceutical as well as pulp and paper industries are ex­
amples of industrial sectors that consume a huge amount of water in
their processes and generate wastewater that negatively influences the
ecosystem, water bodies, soil, and human health. Due to the increasing
freshwater scarcity and environmental protection concerns, water
recycling and reuse as well as other resource recovery have been pro­
moted in industries [39]. In this context, NF is one of the attractive
technologies for that purpose. This section discusses the application of
NF in the industries as mentioned earlier for water recycling, reuse, and
resource recovery.
(anionic) and MB (cationic) and various molecular weight (1136.3 and
319.8 Da, respectively). The slightly higher retention of RR195 (97.2%)
compared to MB (90.2%) could be attributed to its larger molecular size
and stronger electrostatic repulsion (Donnan exclusion) that repels
anionic RR195 dyes from the negatively charged membrane surface.
Despite the promising dyes rejection and dye/salt fractionation
performance of NF membrane, the process feasibility is hindered by one
challenge – fouling, which is a typical problem found in any membrane
operation. Fouling is a phenomenon whereby impurities are deposited
on a membrane surface or in membrane pores such that the membrane
performance is greatly affected and degraded [48]. The interactions
between the membrane surface and the foulants (especially dyes) in
textile effluent are the dominant factor affecting the severity of fouling
[49]. The positively charged dye molecules could be attracted and
accumulated on the surface of negatively charged membrane, which
subsequently adsorbed to the membrane through hydrophobic interac­
tion and blocked the membrane pores [50]. The integrated process
which combines the membrane unit with other processes in a treatment
train is one of the feasible strategies in fouling mitigation [51]. The aim
of integrated process is to achieve better performance than any of the
individual processes whereby the shortcomings of the stand-alone pro­
cess have been minimized or negated [52]. Previously, the NF process
has been integrated with numerous processes to minimize fouling pro­
pensity and achieve targeted permeate quality that can fulfil the water
reuse criteria in the textile industry (Table 2). For example, the inte­
gration of electrocoagulation as pre-treatment significantly enhanced
the steady membrane flux (~15 LMH) and flux recovery ratio (67.99%)
of NF as compared to stand-alone NF at ~2 LMH and 11.68% [45]. This
could be attributed to the reduction of pollutants (COD and suspended
solids) in textile wastewater by electrocoagulation pre-treatment, which
has also reduced the thickness of foulant cake layer on NF membrane
that enabled higher water permeation.
In another study, NF was employed to further polish the treated
effluent from MBR such that the treated water could be reused in fabric
dyeing [53]. The NF270 membrane was found to reduce the COD and
turbidity of MBR effluent to below 5 mg/L and 0.3 NTU, respectively,
which subsequently has been reclaimed for reuse in fabric dyeing test.
Surprisingly, the results showed that no adverse effects were observed
on the quality of the product in the dyeing experiment, indicating that
the integration of NF as post-treatment (polishing) process to MBR
enabled the recovery of water from textile effluent for reuse application.
Lebron et al. [54] combined the NF treatment with MF and advanced
oxidation process (AOP, photo-Fenton) to recover water from textile
industry effluent. In their work, two configurations, namely MF-NFAOP(c) and MF-AOP-NF (Fig. 3), were investigated and compared. The
NF permeate from both configurations complied with the water reuse
criteria for yarn washing-off and equipment washing down. Neverthe­
less, a higher fouling rate and lower permeate flux (19 LMH) was
observed for NF membrane in the second treatment train (MF-AOP-NF)
due to the high iron content in the effluent after being subjected to AOP
treatment which promoted the concentration polarization effect.
Meanwhile, the first configuration (MF-NF-AOP(c)) has achieved higher
NF permeate flux (38 LMH) and the application of AOP as posttreatment step for NF concentrate has effectively removed COD and
color about 70% and 98.5%, respectively. Even so, the effluent from
AOP post-treatment did not fulfil the standard for reuse in noble appli­
cation owing to its high iron content. The cost analysis revealed that the
MF-NF-AOP(c) treatment requires a lower operating cost ((0.421 US
$/m3) than that of MF-AOP-NF (0.736 US$/m3), suggesting that the first
configuration is more suitable for textile effluent treatment due to its
cost-effectiveness.
In the textile industry, the highly alkaline effluent from caustic main
bath discharges is a potential resource for NaOH recovery that can be
reused in the causticization process. For this type of effluent treatment,
the use of a ceramic membrane is promising since it has higher chemical
resistance than polymeric NF membrane [55]. Moreover, common
3.1. Textile industry
The textile industry, which is one of the most water-intensive sectors,
consumes a massive amount of water during the multiple production
stages and generates up to 200–350 m3 of wastewater per ton of finished
products [40]. The generated wastewater is usually rich in color (dyes),
chemical oxygen demand (COD), inorganic salts, suspended solids, and
trace heavy metals [41,42]. Dyes appear to be the most problematic
contaminant among these compounds due to their persistent, carcino­
genic, and poor biodegradability properties. The discharge of improp­
erly treated textile effluent will adversely affect flora and fauna present
in the water bodies, and at the same time, deplete the availability of
clean water resources for human consumption. Hence, advanced treat­
ment processes are required to handle the textile effluent containing
recalcitrant dyes and inorganic salts, where both could be potentially
recovered and reused in the textile industry.
The sustainable concept of recovering dyes and salt solutions from
textile effluent could be materialized with NF membrane, since the NF
process can separate the dyes and salts (particularly monovalent salts)
into two different streams. This approach not only recovers valuable
resources from textile effluent but also achieves multiple benefits such as
preventing the release of hazardous pollutants to the environment,
minimizing the consumption of resources (e.g., dyes, water, and salts),
and saving costs. For instance, Chu et al. [43] demonstrated the use of
hollow fiber loose polyethersulfone NF membrane that could attain high
fractionation efficiency of dye/salt mixtures, where the rejection of dye
(Congo red, 0.1 g/L) is as high as 99.9% while allowing more than 93%
of NaCl salt (1 g/L) to pass through the membrane. Their result high­
lights the potential of loose NF to recover dyes and salt solutions in
textile effluent treatment.
The NF process could also remove other impurities present in the
textile effluent [44]. This is reflected in the study of Tavangar et al. [45]
where real textile industry wastewater was used for NF filtration. The
textile effluent contained a wide range of reactive dyes with different
structures (monoazo, diazo, triazo, and multiazo) and molecular weights
(300–1200 g/mol), as well as high turbidity (1500 NTU), COD (2690
mg/L), and total dissolved solids (TDS) (7500 mg/L). Apart from sepa­
rating the color (rejection of 87%) and allowing most inorganic salts to
pass through (>96%), the use of loose NF membrane (NADIR® NP010)
also reduced 74% of COD and 99% of turbidity. This treatment produced
salt solution with good quality for reuse in the factory and eased the
handling of concentrated dye solution.
Generally, the separation mechanisms of NF in treating textile
wastewater could be attributed to size exclusion and Donnan exclusion
effects. In comparison to inorganic salt ions, dyes with larger molecular
weight tend to be rejected better by NF membrane, hence explaining the
high dye/salt fractionation efficiency of the membrane through size
exclusion mechanism. As an example, Ji et al. [46] observed that their
prepared NF membranes attained high rejection for large molecular
weight dyes, i.e., Congo red (>99.9%) and Direct yellow 24 (>97.7%).
In comparison, only about 78.5% of smaller molecular weight dye such
as Acid orange 10 was removed. Salahshoor et al. [47] described the
interplay between size exclusion and Donnan effect mechanisms of
negatively charged NF membrane (surface charge of − 9.4 to − 19.91 mV
and MWCO 789 Da) in rejecting two oppositely-charged dyes of RR195
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N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
Table 2
Application of NF in textile industry wastewater treatment for water/product recovery, recycling, and reuse.
Treatment process
NF membrane
Operating conditiona
Feed
Performance
Reuse application
Ref
NF-Electrochemical
process
(Pilot study)
Hydracore50
(H50)
Hydracore10
(H10)
NF90
P = 8 bar, Room
Temperature,
Dead end
Simulated textile
effluent
Dye removal H50:
98%
H10: 86%
Both NF permeate and electrochemicallydecolored concentrate were reused in new cotton
dyeing.
[17]
P = 8–15 bar,
T = 20–40 ◦ C,
Crossflow
Real textile effluent
Rejection by NF:
COD = 72%
Electrical
conductivity (EC)
= 98%
Color = 100%
Rejection by NF:
TDS = 40%
Turbidity = 99%
Color = 80%
COD = 97%
Overall removal:
COD = 97%
EC = 71%
Color = 97%
Total phosphorus
(TP) = 87%
The NF permeate
flux in:
MF-NF-AOP(c)
system = 38 LMH,
MF-AOP-NF
system = 19 LMHb
Overall removal:
COD = 89%
Color = 83.5%
TOC = 86.4%
Hardness = 68%
The NF permeate meets the reuse water quality in
textile industry.
-NF concentrate could be reused to wash
equipment and floors.
[62]
The NF permeate could be reused for fabric dyeing
process
[53]
The final effluent met requirement for water reuse
of various purpose including reclaimed water for
irrigation.
[63]
NF permeate fulfilled the recycled water quality
and could be considered for yarn washing-off and
equipment washing down.
[54]
The recovered caustic solution in NF permeate side
could be reused in caustic process again by mixing
with concentrated NaOH.
[26]
MF-MBR-NF
MBR-NF-UV
(Pilot study)
NF270
P = 5–7 bar
Woolen textile mill
wastewater
MBR-NF
(Pilot study)
NF90–2540
P = 6.4–8.1 bar, T =
26.3–26.9 ◦ C,
Crossflow
Biologically pretreated textile
wastewater
MF-NF-AOP(c) vs
MF-AOP-NF
NF90
P = 12 bar, T = 22 ◦ C,
Crossflow
Effluent from rinsing
stage of the dyeing
process
UF-NF
(Pilot study)
Ceramic NF
P = 2.5 bar, Crossflow
Caustic main bath
discharges from textile
factory
a
b
Operating condition for NF unit.
LMH unit represents L/m2⋅h.
Fig. 3. Illustration of (a) MF-NF-AOP(c) and (b) MF-AOP-NF integrated process for water recovery from textile industry wastewater [54].
polymeric NF membranes are only suitable for feed with low NaOH
content (0.1–0.4%) [56]. Therefore, recent work by Ağtaş et al. [26]
used the commercial ceramic NF (ATECH, 1000 Da) in the UF-NF inte­
grated process to recover caustic chemicals from caustic-containing
textile wastewater. It was found that installation of NF after UF treat­
ment has resulted in higher contaminant removal efficiency than that of
single UF treatment. The total organic carbon (TOC), COD, color, and
total hardness were removed by 67%, 71%, 92% and 42%, respectively,
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N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
while at least 50% sodium was recovered using the UF-NF treatment. It
was proposed that the recovered caustic solution could be reused in the
causticization process by mixing with some amount of concentrated
commercial caustic solution. The economic analysis estimated that the
application of ceramic UF-NF membrane treatment could achieve a
caustic recovery of 480 m3/year while caustic usage cost could be
reduced by 50% by reusing the caustic solution.
Besides integrated process, utilization of nanomaterials in NF
membrane modification or synthesis is another strategy that has been
proposed to address the membrane fouling issue and to enhance the
membrane performance [57,58]. Graphene oxide (GO) [58,59], TiO2
[60] and cellulose nanocrystals (CNC) [61] are examples of nano­
materials which have been applied to fabricate or modify NF for dye/salt
separation. Very recently, Seah et al. [58] prepared thin film nano­
composite (TFN) NF incorporated with surface-coated GO, aiming to
recover NaCl from textile wastewater which can be further reused. It was
found that the TFN containing acrylic acid (AA)-modified GO exhibited
24.9% improvement of pure water permeability over the control mem­
brane (without GO) due to enhanced hydrophilicity. Moreover, the TFNAA/GO successfully produced saline permeate with NaCl recovery of
79–86% and contained pigment less than 0.28%, suggesting potential
reuse in dyeing process. Even so, it shall be noted this promising result
was based on the performance test using simulated textile wastewater.
Despite extensive works in textile effluent treatment, challenges such
as membrane fouling, the economic feasibility of integrated NF process
(including investment in the system and savings from reclaimed water),
and the large-scale production of novel NF membrane still hinder the
widespread application of NF in textile wastewater treatment. More
pilot scale data and economic evaluation should be conducted to
convince the stakeholders of the benefits and possibility of reclaiming
water from textile effluent using an integrated NF process. Furthermore,
the loose NF membranes with high permeability, simple synthesis
procedure, exceptional antifouling properties and excellent dye/salt
separation efficiency should be further developed and explored for
textile wastewater treatment.
3.2. Food industry
Water is one of the intensively consumed resources in the food in­
dustry, where it is used in various aspects from being an ingredient in the
production processes and products, housekeeping and general cleaning,
and sanitation and disinfection purposes. The characteristics of the
wastewater generated from the agro-food industry can vary signifi­
cantly, depending on the operation processes and type of products.
Generally, the wastewater contains a few types of major pollutants such
as COD, total suspended solids (TSS), fats, oils, and nutrients [64]. Some
micropollutants (e.g., hormones, surfactants, antibiotics, and pesticides)
can also be found in certain types of food industry effluent. Hence, the
food industry effluents need to be treated before being discharged since
these pollutants will cause damage to the environment and ecosystem.
Rather than being used for treatment purposes, the NF membrane
could be utilized to reclaim treated water for reuse in the foodprocessing industry and recover value-added compounds found in the
effluents. The former strategy could help to reduce the water con­
sumption of the food industry, while the latter approach enables the
recovered compounds to be used in the food chain as functional addi­
tives in different products. Both these measures will help to progress the
food industry towards sustainable development. To achieve water and
resource recovery with desired reuse criteria, various integrated pro­
cesses equipped with NF as a post-treatment step have been proposed in
food industry wastewater treatment (Table 3). For instance, NF has been
employed as a tertiary treatment to further polish the dairy effluent
treated by MBR by removing the dissolved solids leftover in the MBR
permeate [65]. The integrated MBR-NF treatment process achieved
Table 3
Application of NF in food industry wastewater treatment for water/product recovery, recycling, and reuse.
Treatment process
NF
membrane
Operating
conditiona
Feed
Performance
Reuse application
Ref
NF
NF270
P = 3 bar,
T = 27 ◦ C,
Crossflow
Diluted aerobic
digested POME
NF permeate could be reused for
factory cleaning or machine
cleaning.
[74]
MBR-NF
NF90
P = 2.5–10
bar, Crossflow
Real dairy
industry
effluent
NF permeate could be reused as
cooling water and for low pressure
steam generation.
[65]
Fenton-like AOP,
flocculation–sedimentation and
olive stone filtration- NF
DK
P = 5–25 bar,
Crossflow
Real olive mill
wastewater
Purified effluent from NF could be
reused for irrigation purpose.
[67]
Pilot plant NF process
NF270
P = 5–15 bar,
T = 25 ◦ C,
Crossflow
Simulated olive
mill wastewater
DK
Two-phase
olive-oil
washing
wastewater
Isoelectric precipitation-NF
NF270, NF90
NF-column chromatographysolvent extraction
NF270,
NF200 and
NF90.
P = 25 bar, T
= 25 ◦ C,
Feed pH =
5.13,
Crossflow
TMP =
6.1–18.6 bar,
T = 25 ◦ C,
Dead end
P = 20 bar,
Crossflow
The recovered phenolic compound
(tyrosol) in permeate side has
potential application in cosmetic
and pharmaceutical industries.
Purified NF permeate (phenolic
free) suitable for irrigation reuse.
[69]
Centrifugation-NF
Removal:
COD = 95%
TDS = 93%
Color = 99%
Phosphorus = 80%
-Optimum permeate recovery =
45%.
- Overall removal efficiencies:
COD = 99.9%
TS = 93.1%
NF permeate flux = 69.9 LMH
Rejection:
EC = 55.5%
COD = 88.5%
Rejection:
Tyrosol=
12.3–23.9%
COD = 77.8–83.9%
NF permeate flux:160 LMH
a
Model dairy
wastewater
Industrial lupin
beans
wastewater
Operating condition for NF unit.
6
NF270 was more suitable than NF90
for dairy effluent concentration due
to its high antifouling, acceptable
permeate quality and lowest TMP.
NF270 membrane showed the
highest lupanine
rejection (99.5%) and total organic
matter removal (94%).
[70]
The lactose rich NF retentate could
be utilized as substrate for volatile
fatty acids production.
[71]
− 80% of the reclaimed wastewater
could be reused in the processing.
-Lupanine rich NF retentate could
be further purified for conversion to
spartein.
[22]
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
overall removal efficiencies of 99.9% for COD and 93.1% for total solids
(TS), where the NF permeate met all the standards for water reuse in
cooling and low-pressure steam generation. The minimization of water
consumption has also been applied to citric acid production wastewater
treatment where NF was utilized to remove the inhibitory compounds
(Na+ and Mg2+) in effluent (treated by anaerobic digestion and UF) such
that the reclaimed water could be reused in the fermentation of citric
acid production [66].
The capability of NF membrane to reject monovalent and divalent
ions (salinity) in wastewater has attracted the attention of olive mill
wastewater operators. The existing physicochemical processes, which
consists of natural precipitation, Fenton-like reaction, flocculationsedimentation, and olive stone filtration in series, could not remove
the dissolved ions in olive mill wastewater. This prohibited the treated
water from being reused or discharged to the environment. In this sce­
nario, the inclusion of NF at the end of the treatment train could help to
reduce the electroconductivity of the effluent, as in the case reported by
Ochando-Pulido et al. [67] where the EC value was reduced from
3.2–3.6 to 1.5 mS/cm. The final permeate possessed quality suitable to
be reused for irrigation.
In addition to a wide range of organic contaminants and dissolved
ions, the phenolic compounds in olive mill wastewater also pose a
challenge to the environment. Phenolic compounds are phytotoxic and
antimicrobial, resulting in difficult degradation under normal condi­
tions and adversely impacting the viability of microorganisms and
plants. However, their antioxidant and anti-inflammatory properties
have made it attractive to the food, pharmaceutical, and cosmetic in­
dustries. Hence, olive mill wastewater appears to be a feasible source for
the recovery of value-added phenolic compounds [68,69]. OchandoPulido et al. [70] have shown that NF membrane could be used to
treat the olive mill wastewater for water reclamation and phenols re­
covery. The NF process produced permeate stream with good quality for
irrigation reuse since it was practically free of phenolic content. The
interesting finding was that NF process managed to enrich the high
added-value phenols up to 75.7% (1315.7 mg/L) in retentate, which
could be a potential source to satisfy the demand in cosmetics, food,
pharmaceuticals, and biotechnological industries. The profit from phe­
nols recovery could help to convince the stakeholders to adopt the NF
treatment process since it can potentially offset a portion of the capital
and operation costs of the NF process. Nonetheless, pilot-scale study and
economic evaluation should be properly conducted to verify this benefit.
Direct filtration of NF with dairy wastewater is not feasible due to the
presence of impurities that will foul the membrane. To address this
issue, Chen et al. [71] demonstrated that the incorporation of isoelectric
precipitation as pre-treatment could control and minimize NF mem­
brane fouling. The isoelectric precipitation process removed caseins –
the main protein in dairy effluent that also appears to be the main
foulant for membrane operation. Consequently, the fouling severity has
been minimized, as reflected by the mild increase of transmembrane
pressure (TMP) (from 2 to 3 bar) as compared to without pre-treatment
(TMP rose from 2 to 34 bar). The NF permeate could be reused in the
plant while the retentate without caseins was found to be a better source
for anaerobic fermentation to produce a higher proportion of volatile
fatty acids and biogas for subsequent utilization. This integrated process
highlighted the potential of resource recovery from dairy wastewater
through the proper design of treatment technologies.
In a subsequent study, Chen et al. [72] modified the integrated
process for recovering water, proteins, cells, and lactic acid from model
dairy wastewater (Fig. 4). The isoelectric precipitation acted as pretreatment to minimize concentration polarization and fouling of
following UF and NF processes. The UF produced two useful streams –
permeate with reduced foulants for NF and retentate rich in whey pro­
tein for recovery. Apart from producing reusable water, NF also
concentrated the lactose in its reject stream which can be further posttreated using lactic acid fermentation process. It was found that use of
thermophilic Bacillus coagulans IPE22 in the fermentation process suc­
cessfully consumed lactose after 37 h, producing 37.6 g/L and 5.42 g/L
of lactic acid and cell mass, respectively. The cells and lactic acid
recovered from the fermentation step could be used as animal food and
raw material for bioplastic production, hence mitigating the retentate/
sludge disposal issue.
Besides olive mill and dairy wastewater, NF membranes also have
been used to treat the palm oil mill effluent (POME) [73–78]. Most of the
studies have focused on the integrated use of NF membranes and other
processes for tertiary treatment of the POME. In the palm oil industry, it
is estimated that 5–7.5 t of water are utilized to generate 1 t of crude
palm oil, with more than 50% of this water being discarded as POME
[79]. Even though the biological treatment process is commonly used to
treat the POME, this technique is ineffective in generating treated water
with reusable criteria [73]. Hence, a study conducted by Ghani et al.
[74] adapted the NF process as a polishing step to reclaim water from
diluted aerobic digested POME for recycling and reuse. This work
Fig. 4. Integrated process of isoelectric precipitation-UF-NF for water and resource recovery from dairy wastewater [72].
7
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
demonstrated that the POME treatment using commercial NF membrane
(NF270) was capable of removing the COD, TDS, color, phosphorus, and
turbidity by 95%, 93%, 99%, 80%, and 99%, respectively. Since the final
COD concentration in NF permeate was slightly higher than that of
boiler feed water criteria, the authors proposed that the permeate could
be reused for machine or factory cleaning activities. However, the severe
fouling issue in the NF membrane during long-term filtration of POME
needs to be addressed.
In lupin beans production, the processes to make these beans edible
by removing lupanine (toxic alkaloid) consume a huge amount of
freshwater. However, the lupanine in lupin beans wastewater is a
valuable resource since it can be used as starting material for the syn­
thesis of other alkaloids (such as sparteine) in the pharmaceutical in­
dustry. Esteves et al. [22] have developed an integrated process
consisted of NF, solvent extraction, and/or resin adsorption for the re­
covery of water and lupanine from the wastewater. The NF membrane
showed remarkable high rejections for lupanine (99.5%), allowing
around 80% of the wastewater to be reclaimed and reused in the pro­
cessing. However, the lupanine-rich retentate requires further purifica­
tion and isolation steps before subsequent use since the NF reject stream
also contained high amount of total organic species (94.1% rejection).
The post-treatment of NF retentate using several solvent extraction steps
(i.e., ethyl acetate as solvent) was found to be capable to isolate 95.4% of
lupanine with 78% purity, which could be further converted to sparteine
with a final purity above 95%. The finding signifies the role of NF as a
process to reclaim water and facilitate subsequent value-added com­
pound recovery in food wastewater handling.
The food industry wastewater typically contains organic impurities
that will easily foul the NF membrane. Thus, the NF membrane must be
integrated with other treatment processes to alleviate the fouling phe­
nomena by removing these impurities in the pre-treatment stage.
Furthermore, the integration of different technologies enables the whole
treatment process to recover water and valuable resources in the
effluent, such as phenols and lupanine. These strategies will minimize
the water consumption of the food industry and extract high addedvalue compounds from the wastewater.
3.3. Oil and gas industry
The effluent produced by the oil and gas industry is one of the main
contributors to environmental pollution. The extraction of oil and gas
using hydraulic fracturing generates a massive amount of waste stream,
namely produced water (PW). It is anticipated that more than 70 billion
barrels of PW have been produced annually [80–82]. Hydrocarbon,
corrosion inhibitor, salts, dissolved organic carbon, heavy metals, sus­
pended solids and dissolved gases (e.g., H2S and CO2) are typical con­
stituents of PW [5]. Besides oil and gas extraction, the oil refinery
process also consumes a huge amount of water during the cracking,
reforming, and topping activities. Each barrel of crude oil requires
246–340 L of water, resulting in the effluent that is 0.4–1.6 times the
volume of oil-treated [83]. To reduce the freshwater consumption in oil
and gas industry, the reuse of treated water has been promoted, which
requires the development of efficient technologies to reclaim water from
challenging wastewater such as PW and oil refinery effluent.
Numerous studies have been conducted to assess the effectiveness of
NF to treat the wastewater from the oil and gas industries for further
reuse (Table 4). Gamal Khedr [84] developed an integrated pilot-scale
system comprised of coagulation-sand filtration-NF to treat the PW
from the Suez Gulf region, which can be reused for injection purposes in
the oil formation to increase oil production. Conventional coagulation/
sand filtration system applied in Suez Gulf PW treatment is not efficient
to remove the TDS, hardness components and metal ions (e.g., uranium)
from the PW, resulting in biofilm and solid scale formation as well as
microbial-corrosion phenomenon in the injection pipelines. Moreover,
the injection of poorly treated PW, which contain high SO42− content,
would destroy the porous structure of the oil formation. To overcome
these issues, Gamal Khedr [84] installed the polyamide thin-film com­
posite NF membrane after the coagulation/filtration during the PW
treatment. It was found that the integrated system was highly efficient in
removing SO42-, uranium, and other cations such as Cu2+, Pb2+, Cr3+
and Ra2+ from PW. Unlike single coagulation treatment which possessed
lower uranium rejection (15–45% removal) at pH 4–6, the adoption of
NF membrane as the post-treatment step has successfully achieved more
than 80% uranium removal efficiency across the pH range. The coagu­
lation/NF integrated system also completely removed the SO42− ions
Table 4
Application of NF in oil and gas industry wastewater treatment for water/product recovery, recycling, and reuse.
Treatment
process
NF
membrane
Operating
conditiona
Feed
Performance
Reuse application
Ref
Coagulationfiltration-NF
(Pilot study)
HL 4040F
T = 25 ◦ C, Feed
pH = 7.5–8.5,
Crossflow
PW from Suez Gulf
The treated PW could be reused for injection
purpose in the oil formation to increase the oil
production.
[84]
Coagulation-UFNF
VNF1
P = 100–400 psi,
T = 25 ◦ C, Dead
end
Flowback PW
Treated PW for internal reuse of hydraulic
fracturing
[24]
BAF-UF-NF
NF90
Piceance basin PW
The final effluent suitable for livestock watering
and hydraulic fracturing.
[87]
NF-Ion exchange
sorbent
MBR-H2O2/UVNF
NFS
P = 150–300 psi,
T = 20 ◦ C,
Crossflow
P = 5 bar,
Dead end
P = 10 bar, T =
25 ◦ C,
Crossflow
The recovered lithium has potential application
in industries.
The NF permeate could be reused in cooling
system.
[89]
P = 15 bar,
Crossflow
Spent caustic effluent
from refinery plant.
Overall removal:
SO42− ~ 100%
TDS = 34%
Hardness cations = 76–80%
-NF permeate flux enhanced by
23% using coagulation-UF pretreatment.
-NF rejection:
COD>96%
SO42− ~ 100%
EC = 26–34%
Overall removal:
TDS = 94%
Turbidity = 98%
Removal efficiency:
NPOC = 53%
Overall removal:
TDS = 98.2% Calcium = 100%
Ammonia = 99.1%
Chloride = 98.8%
COD = 100%
Toxicity = 100%
Removal efficiency:
Polar oil and grease = 99.9%
COD = 97.7%
The purified permeate caustic solution (sodium
rich) could be recycled back for further reuse in
refinery process.
[91]
NF process
(Pilot study)
a
NF90
MPS342540
Flowback PW
Petroleum refinery
wastewater
Operating condition for NF unit.
8
[90]
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
and material of bacteria growth while the TDS, other hardness cations
and monovalent cations were rejected by approximately 34%, 76–80%
and 35–37%, respectively. Thus, the use of NF membrane was capable to
upgrade the quality of treated PW for injection purposes, which is
important to inhibit the scale and corrosion formation in the pipelines.
Internal reuse of PW for hydraulic fracturing operation is now the
most prevalent and cost-effective alternative in the shale gas industry.
However, the PW needs to be properly treated where removal of divalent
ions is necessary prior to recycling for internal reuse. The presence of
divalent cations in the recycled PW may have a detrimental effect on
shale gas production by precipitating sulfate and the formation of stable
carbonate [24,85]. Thus, the application of the NF membrane is bene­
ficial to treat the PW since it can remove divalent ions. However,
adopting a proper pre-treatment is essential during the wastewater
treatment to prolong the lifetime of the NF membrane. In this context,
Chang et al. [24] used the coagulation-UF configuration to pre-treat the
PW before NF process for internal reuse. Unlike common filtration
techniques such as sand filtration, the UF is more promising to reduce
turbidity. It was found that the use of iron coagulation-UF as the pretreatment unit has enhanced the NF permeate flux up to 23%. The in­
tegrated iron coagulation-UF-NF (200 psi) system has successfully pro­
duced the permeate that fulfils the flowback PW reuse specification in
Marcellus shale play [24,86]. The final concentration of SO42− , Mg2+,
Ca2+, Sr2+, Ba2+ in the treated water were 1.0 mg/L, 3.7 mg/L, 63.4 mg/
L, 14.5 mg/L and 23.2 mg/L, respectively, which represents the
72.8–91.7% removal efficiency.
Besides coagulation, biological pre-treatment such as biologically
active filtration (BAF) has also been proposed to be coupled with UF-NF
for treating PW for hydraulic fracturing reuse [87,88]. The BAF unit,
which contains the biofilm supported on filter media can effectively
degrade organic matter from the oil and gas industry wastewater. Riley
et al. [87] reported that the BAF-UF-NF configuration (Fig. 5) had
reduced the TDS level in PW feed from 12,615 mg/L to 685 mg/L (94%
removal) by increasing the pressure up to 300 psi. The installation of
BAF-UF pre-treatment has also mitigated the fouling in the NF mem­
brane. However, this result may not be indicative of long-term fouling
since this water treatment was only conducted under short term oper­
ation (60 h).
Recently, attempts have been made to explore the potential of
flowback PW as a resource for lithium recovery. Increasing global de­
mand for lithium supply, particularly for lithium-based battery pro­
duction, has promoted the exploration of potential lithium resources. A
study conducted by Seip et al. [89] proposed the integration of NF with
manganese-based ion-exchange sorbents for lithium recovery from
flowback PW. The presence of small organic molecules (<250 Da) in
untreated flowback PW can reduce the manganese in the sorbent during
the lithium recovery, causing the sorbent loss via reductive dissolution.
Thus, the PW was subjected to NF treatment using Da Synder Filtration
Fig. 5. Integrated process of BAF-UF-NF in PW treatment for water reuse application [87].
9
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
NFS membrane (100–250 Da) to remove the small organic molecules
before the lithium recovery step. The removal of non-purgeable organic
carbon (NPOC) content from 180 ppm to 85 ppm after NF treatment has
minimized the sorbent loss in acid desorption of lithium, signifying the
importance of NF in improving the efficiency of the integrated process
for lithium recovery.
In the petroleum refinery wastewater treatment, NF has been inte­
grated with MBR and AOP to produce permeate water that can be reused
in the cooling systems [90]. In a recent study, Moser et al. [90] inves­
tigated the effect of AOP (i.e., UV/H2O2 process) pre-treatment on the
NF (Dow FilmTec NF90) performance and assessed the overall efficiency
of the integrated system in treating petrochemical effluent taken from a
refinery plant in Brazil. It was observed that the NF permeate flux was
enhanced since the fouling potential in NF was reduced. The UV/H2O2
pre-treatment has altered the fouling characteristics, which make it
easily removed, and thus less NF cleaning frequency was required.
Moreover, the use of NF as post-treatment was found to effectively
remove the toxic intermediate substance produced by the UV/H2O2
process. The integrated treatment has successfully removed the TDS,
calcium, ammonia, chloride, COD, TOC, and toxicity level by more than
98%. The final NF permeate contained 28 mg/L of TDS, 0.3 mg/L of
ammonia, 7.2 mg/L of chloride and 0.96 mg/L of TOC, complying with
the water standard quality for cooling system.
The potential of NF to treat the spent caustic solution for reuse in
crude oil refinery was explored by Santos et al. [91]. The commercial
composite polymeric NF (SeIRO® MPS-34) with the alkaline resistant
feature was installed in a pilot plant to treat spent caustic with a con­
ductivity of 110 mS/cm, pH 13.7, polar oil and grease content of 11,300
mg/L and COD of 81,571 mg/L. The crossflow operation mode was
applied in that study and the performance of ceramic UF membrane
(Carbosep M2, 15 kDa) was also evaluated separately for comparison
purposes. Unlike ceramic UF membrane which failed to reduce the polar
oil and grease content in the permeate side to below 20 ppm, the per­
formance of NF membrane seems more promising since it can attain the
polar oil and grease and COD removal efficiency of 99.9% and 97.7%,
respectively, at 15 bar operating pressure. A restorable and stable NF
permeate flux was observed until the volume concentration factor of 3.
Also, the NF operation under this condition was capable of recovering
the sodium, resulting in a purified permeate caustic solution that can be
recycled back for further reuse in the refinery process. The economic
analysis revealed that the reuse of the purified permeate could benefit
the oil refinery by offering a significant saving of 1.5 M€ per year.
Overall, most of the studies related to NF application in oil and gas
industry wastewater treatment have focused on water recovery and
reuse. However, limited studies related to by-products recovery such as
lithium recovery from PW has been reported in the literature. Thus,
further investigation is required in the future to explore the potential of
membrane-based technologies such as NF in the integrated process for
resource recovery in oil and gas industry wastewater treatment.
reuse and allow the recovery of acid and valuable metals from mining
industrial effluent as reported in several studies [93,96–102] and sum­
marized in Table 5.
Mullett et al. [96] compared the performance of two types of com­
mercial polyamide NF membranes, namely Dow NF270 and TriSep TS
80, in treating the AMD for recovering valuable metals such as copper.
The NF270 membrane demonstrated 95% removal efficiency for all
multivalent ions (i.e., Ca2+, Cu2+, Mg2+, Mn3+) at feed pH less than 3,
while higher sulfur rejection (95–97%) was achieved at high pH con­
ditions (pH > 3). Unlike the NF270 membrane, the TS 80 membrane
showed that the removal efficiency for sulfur and all multivalent ions
was less affected by the feed pH. Higher rejection (>95%) can be
attained by the TS 80 membrane across the studied pH range. Despite its
promising performance for mine water treatment, TS 80 membrane
required higher operating pressure than NF270 membrane, which thus
consumed more energy. The recovery test of the TS 80 membrane
revealed that increasing the feed pH higher than the membrane iso­
electric point (IEP) would result in 2.4 kg/h of the copper loss in
permeate, which corresponded to copper loss of around $69,000/year.
Such findings highlighted the necessity of understanding the relation­
ship between solution chemistry and membrane properties to achieve
optimal recovery and avoid significant loss in capital and operating cost.
The potential of NF for AMD reclamation in both lab-scale and pilotscale studies was further investigated by Wadekar et al. [93]. Initial
screening in a lab-scale study using cross-flow module showed that the
use of polyamide NF membrane (NF90) would be preferable to poly­
piperazine amide NF membrane (NF270) for treating actual AMD. The
NF90 membrane, which possessed a smaller pore size, has demonstrated
better rejection for all ions (>97%) with sulfate removal in excess of
99%. The performance of the NF90 membrane was further assessed in a
pilot plant where the real AMD feed was pre-treated first using aeration,
sedimentation, bag filtration and UF process prior to NF filtration at 10
bar. These pre-treatment steps have efficiently removed iron from the
AMD feed, and thus prevented the fouling due to inorganic or iron
scales, resulting in long term stability of NF system. The long-term
operation (208 h) of the integrated system indicated that the NF mem­
brane successfully achieved stable water recovery of 57% with TDS
rejection of more than 98%. Besides high removal of magnesium, cal­
cium, and sulfate ions (>99%), the tight NF90 membrane also was able
to reject about 90% of monovalent ion (chloride) from the AMD. The
final NF permeate which is comprised of low TDS content (<50 mg/L),
sulfate (<10 mg/L), calcium (1 mg/L) and magnesium (0.3 mg/L) could
be reused for industrial applications such as for the cooling system.
Meanwhile, it has been proposed that the NF concentrate with high
sulfate content (~4000 mg/L) could be used to treat the flowback and
PW. The mixing of flowback water and sulfate-rich AMD concentrate has
the potential to remove the barium and strontium ions from flowback
water via sulfate precipitation process, as reported by others [103].
Besides AMD treatment, the polyamide NF90 membrane has also
been applied in gold mining effluent reclamation. Reis et al. [99]
assessed the performance NF90 to recover water from the gas scrubber
effluent taken from a gold mining plant in Brazil, which mainly con­
tained TDS (7085 mg/L), sulfate (4852 mg/L), calcium (258 mg/L),
magnesium (134 mg/L) and some arsenic (As(V) and As(III)). Unlike
Wadekar et al.'s finding [93], which showed high TDS rejection (>98%)
for AMD reclamation, Reis et al. [99] found that the NF90 membrane
demonstrated a lower TDS rejection (86%) during water recovery from
gold mining wastewater at 10 bar pressure. Such discrepancy could be
attributed to the higher contaminant concentration in gold mining
effluent, where its TDS and sulfate content level is five times higher than
that of AMD. Moreover, the gold mining effluent in Reis et al.'s study
[99] was just pre-treated using MF filtration to remove the suspended
solids. Even though the NF permeate did not fulfil the water quality
standard for reuse in boilers or cooling systems, the authors proposed
that it can be reused in other mining processes that employ water with a
low pH value, hence decreasing the expense of pH adjustment.
3.4. Mining industry
The mining industry generates several types of effluents during
mining activities and processing. One of the major mining effluents is
acid mine drainage (AMD), which was formed due to the exposure of
rocks containing sulfur to water and air [16,92]. AMD commonly shows
a high level of sulfate content (1–20 g/L), low pH value (pH 2–4), high
concentration of heavy metals and toxic components [16,93]. In gold
mining activity, a large volume of acidic effluent containing substantial
metal concentration is generated by the pressure-oxidation process.
Conventional mining effluent treatment involves the use of lime
neutralization technique that can precipitate the sulfate and metals
[94,95]. Nevertheless, this method produces a tremendous amount of
sludge which presents an environmental threat and requires proper
disposal [93,96]. Therefore, the application of membrane technologies
such as NF is a promising alternative that can produce permeate for
10
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
Table 5
Application of NF in mining industry wastewater treatment for water/product recovery, recycling, and reuse.
Treatment process
NF membrane
Operating
conditiona
Feed
Performance
Reuse application
Ref
NF
NF 270
TS 80
Simulated mine
water
NF90
TS 80:
Rejection for Ca2+, Cu2+, Mg2+, Mn3+ >
95%
Removal:
-TDS > 98%.
magnesium, calcium, and sulfate ions
>99%
Filtration-NF
NF90
TMP = 10 bar, T =
25 ◦ C, Crossflow
Gas scrubber
effluent from gold
mining plant
The recovered copper in NF reject
stream has potential application in
industries.
The final NF permeate could be
reused for cooling system.
The sulfate-rich AMD concentrate
has potential to treat flowback
water via sulfate precipitation.
NF permeate can be reused in other
mining processes that employ
water with a low pH value.
[96]
Aeration and
sedimentationbag filter-UF-NF
(Pilot study)
P = 5–20 bar,
T = 25 ◦ C,
Crossflow
P = 10 bar, T =
20 ◦ C, Feed pH =
5.6, Dead end and
crossflow
MF-NF-RO
MPF-34
P = 10 bar, T =
25–35 ◦ C,
Crossflow
Gold mining
effluent that
generated by
pressure oxidation
process
UF-NF-RO
DK, Duracid,
NF90, NF270
and MPF-34
P = 10 bar, T =
25 ◦ C, Crossflow
Gold mining
effluent that
generated by
pressure oxidation
process
a
Real AMD
Rejection by NF:
TDS = 86%
EC = 85%
SO42− = 95%
Ca2+ = 99%
Mg2+ = 99%
Acid permeation through NF =82%
MF-NF-RO rejection:
TDS = 99.2%
TSS = 100%
TS = 99.2%
EC = 97.2%
DK is more suitable for gold mining
effluent treatment due to its higher
chemical stability than MPF-34, high
permeate flux (25 LMH), high noble
metals rejection (>94%).
-The recovered sulfuric acid in NF
permeate was concentrated by RO
for further reuse in gold mining
processing (pressure oxidation
stage).
-The final permeate could be reused
in boilers system.
-The final permeate could be reused
in gold mining process which do
not requires pH adjustment.
-The recovered sulfuric acid could
be reused in mining production
process.
[93]
[99]
[97]
[100]
Operating condition for NF unit.
Ricci et al. [97] combined the MF-NF with the RO process to improve
the permeate quality and recover noble metals and sulfuric acid during
the treatment of gold mining effluent generated by pressure oxidation
process (Fig. 6). The role of NF in the integrated system was to produce
metal-enriched retentate and obtain sulfuric acid-enriched permeate for
further separation in the RO unit. It was found that the combination of
NF membrane (MPF-34) and MF has successfully retained more than
95% valuable metals such as copper, cobalt, and nickel in the retentate
streams, enabling further treatment in the metal recovery process. Since
the post-treatment stage of the metal-enriched retentate was not covered
in their study, the potential of integrating MF-NF system with bio­
electrochemical technology such as microbial fuel cell which is prom­
ising for heavy metal-recovery [104] can be further explored in future.
Basically, the MPF-34 NF membrane (IEP 4.5) was positively charged
under exposure to acidic gold mining effluent (pH 1.46) [97]. So, it
possessed high metal cations rejection but low HSO4− anion rejection.
This NF property allowed 82% acid permeation, resulting in a high
sulfuric acid recovery in the NF permeate stream which was further
concentrated up to 99% by RO (TFC-HR) membrane. It was proposed
that the recovered acid could be recycled and reused to control the
acidity in the pressure oxidation stage in gold mining processing.
Meanwhile, the integrated system also has reduced the TDS level in the
gold mining effluent from 23,973 to 192 mg/L (>99% removal), pro­
ducing final permeate with quality that was suitable for reuse in boilers
system. Despite these promising results, further investigation by Ricci
et al. [98] revealed that the nickel and cobalt rejection of MPF-34 NF
membrane was reduced by 33% upon continuous exposure to the gold
mining effluent for eight weeks. Based on this finding, it can be sug­
gested that a more stable NF membrane shall be applied in gold mining
effluent treatment to prevent the noble metal loss in permeate side under
long term operation mode.
In a recent work by Ramos et al. [100], the performances and
chemical stability of various commercial NF membranes, including DK,
Duracid, NF90, NF270 and MPF-34, were compared to seek a more
chemically stable NF that can stand the acidic gold mining effluent in
integrated UF-NF-RO system. Among the investigated NF membranes,
DK appeared as the most promising NF membrane for gold mining
effluent treatment due to its high permeate flux (25 LMH), low fouling
tendency and high noble metals rejection (>94% for copper, cobalt, and
nickel). Unlike MPF-34 performance in previous work [98], the DK
Fig. 6. Integrated process of MF-NF-RO for water and resource recovery in gold mining effluent treatment (source: redrawn from [97]).
11
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
membrane possessed higher chemical stability under long term exposure
(180 days) to gold mining effluent with a conductivity of 18.64 mS/cm
and pH 1.53. The final permeate water from the integrated UF-NF-RO
system contained low acid concentration (pH ~2.5) that could be
reused in the gold mining process, which does not require pH adjust­
ment. Moreover, the integrated system was capable of recovering sul­
furic acid with high purity for further reuse in the mining production
process. Their findings indicate that proper membrane selection is a vital
component in designing process to recover water and valuable resources
from challenging wastewater. Overall, it can be observed that polymeric
NF membrane has been commonly applied for water recycling and reuse
and product recovery from mining wastewater. Despite the excellent
separation performance of polymeric NF, its long-term stability issue in
highly acidic mining effluent remains a significant concern. Thus, to
overcome the limitation of polymeric NF, future studies can explore the
performance of ceramic NF membrane for water recycling and reuse as
well as product recovery in the mining industry.
membranes allowed the tannins recovery due to the charge repulsion
and molecular sieving mechanism where the highest tannins rejection
(97.6%) was achieved by the MPF-34 membrane. It was proposed that
the tannin-rich retentate stream could be reused in the production of a
new liquor tannin solution. Despite its high tannin recovery, MPF-34
showed a significant drop in permeate flux. In contrast, the DK mem­
brane showed the highest permeate flux (17.17 LMH) and a low fouling
tendency, but its tannin recovery rate is not sufficient compared to the
other NF membranes.
The tannery industry produces sulfate-rich effluent due to the usage
of abundant amounts of sulfuric acid and sulfide application in the
unhairing stage, which was further oxidized into sulfate. Therefore,
Galiana-Aleixandre et al. [109] applied the NF process as a pollution
prevention technique in reducing sulfate concentration in the tannery
effluent. Sulfate retention of 97% was achieved in the NF treatment of
the tanning washing wastewater, where the sulfate-rich concentrate
could be reused in the tanning drums. The high sulfate rejection was due
to the size exclusion mechanism since there was no charge interaction as
the pH of the tanning washing effluent (pH 4) was equal to the IEP of the
applied NF membrane (Desal 5DL). It was estimated that the imple­
mentation of NF membrane with 97% sulfate retention for treating 50
m3 tanning washing effluent would be able to recover 61.63 t of sulfate
per year for recycling and reuse in tanning drums.
Religa et al. [110] applied NF membrane for recirculation of Cr(III)
from tannery wastewater-concentrate salt mixture solution at very low
pH. Four types of commercial NF membranes, namely HL, DK, DL and
CK, were tested to compare their performance upon exposure to syn­
thetic chromium tannery wastewater with a pH range of 3.6–3.9. The
thin, selective skin layer of DL membrane ensures both low chlorine
retention (7–11%) in conjunction with high Cr(III) retention (94–97%)
and a high permeate flux. They concluded that the use of NF membrane
with low IEP value, such as DL (IEP 3), was more preferred for the
treatment of tannery wastewater at pH below 4. In that condition, the
negatively charged NF membrane could facilitate the chloride ions
permeation, minimizing the concentration polarization phenomenon
and increasing the permeate flux. The obtained chromium-rich
concentrate and chloride-rich permeate from the NF process could be
reused as tanning and pickling baths, respectively.
3.5. Tannery industry
The tannery industry releases very high volumes of toxic effluent,
including numerous recalcitrant pollutants which have a devastating
effect on surface water. It has been estimated that global leather pro­
duction generates about 600 million m3 of wastewater annually [105].
The pre-tanning and tanning activities in skin/hides processing are the
major sources of pollution in the tannery industry [106]. These pro­
cesses discharged wastewater containing high levels of chromium,
chloride, sulfate, sulfide and suspended solids [105,106]. Among tan­
nery effluent pollutants, chromium (Cr) is the contaminant of primary
concern due to its toxic and carcinogenic properties [20,107]. Given the
toxicity of the tannery wastewater, an efficient technique is required to
treat this effluent prior to discharge or reuse.
Several investigations have been carried out to study the perfor­
mance of the NF process in the treatment of tannery effluent for water
and resource recovery as well as reuse applications (Table 6). RomeroDondiz et al. [108] compared the performance of various types of
commercial NF membranes, namely DK, CK, TFC-SR3 and MPF-34, for
tannins and water recovery from real vegetable tannin liquor. The NF
Table 6
Application of NF in tannery industry wastewater treatment for water/product recovery, recycling, and reuse.
Treatment
process
NF membrane
Operating
conditiona
Feed
Performance
Reuse application
Ref
NF
DK, CK
TFC-SR3 and MPF34
P = 20 bar, T =
25 ◦ C,
Crossflow
Pre-treated vegetable
tannin liquor from
tanning industry
-The retentate stream could be reused to
formulate a new liquor tannin solution.
-The permeate could be used as process
water in the industry.
[108]
NF
(Pilot study)
Desal5 DL
Tanning washing
wastewater
Sulfate-rich concentrate could be reused
in the tanning drums.
[109]
NF
HL, DK, DL and CK
TMP = 5 bar,
T = 26 ◦ C,
Crossflow
TMP = 10–24
bar,
T = 25/40 ◦ C,
Crossflow
-MPF-34 showed the highest
tannins rejection (97.6%).
-DK presented the highest
permeate flux (17.17 LMH) and a
low fouling index.
Sulfate retention = 97%
The chromium-rich concentrate and
chloride-rich permeate from NF process
could be reused as tanning and pickling
baths, respectively.
[110]
Ion-exchange-NF
TS80
Synthetic tannery
wastewater
NF1 and NF3
The retentate stream enriched in
chromium (III) salt could be reused in the
tanning process.
The NF permeate could be reused in
primary tannery operations.
[111]
Coagulation-NF
AOP (Fenton's
oxidation)-MFNF
GO-based
nanocomposite
membrane
TMP = 10 bar,
T = 25 ◦ C,
Crossflow
TMP = 10 bar,
T = 32 ◦ C,
Crossflow
P = 6–16 bar, T
= 30 ◦ C, pH =
7,
Crossflow
-DL is more suitable for the
tannery effluent with pH < 4.
-DL performance: chlorine
retention (7–11%), Cr(III)
retention (94–97%) and a high
permeate flux.
NF rejection:
Cr(III) = 90%,
SO42− = 77%
Removal of Cr(IV) > 98%
a
Model chromium
tannery wastewater
Real tannery effluent
Real tannery
wastewater
Flux = 210–220 LMH,
Rejection efficiency:
Chromium = 99.5%
COD>99%
TDS > 96%
Operating condition for NF unit.
12
The treated effluent met the reusable
water criteria.
[20]
[105]
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
To improve the efficiency of tannery wastewater treatment, NF has
been integrated with other technologies in several works. For instance,
Gando-Ferreira et al. [111] integrated NF with ion-exchange pre-treat­
ment processes to recover Cr(III) salts from simulated tannery waste­
water containing a typical concentration range of Cl− , Cr(III) and SO42−
in industrial effluents of tanneries. The ion-exchange pre-treatment unit
was installed for uptaking the chloride ions from the tannery effluent,
enabling the generation of Cr (III)-rich retentate by NF. Their results
demonstrated that the NF performance was affected by the Cl− /SO42−
ratio. The ratio of 0.082 led to the best operating conditions for the
integrated process, producing 90% Cr (III) enriching retentate for reuse
in the tanning process. In another work, Dasgupta et al. [20] employed
the coagulation-NF based integrated treatment scheme to achieve
maximum removal of toxic Cr(VI) species from tannery wastewater. The
coagulation pre-treatment has successfully mitigated the fouling in NF
membrane, and high Cr(VI) removal efficiency (>98%) was achieved by
the hybrid process. The installation of NF after coagulation pretreatment has successfully improved the permeate quality up to the
standard criteria for water reuse in tannery operation.
A new GO-based nanocomposite membrane was developed by Pal
et al. [105] for the application in an AOP-NF integrated process that was
specifically designed to recover water from real tannery wastewater for
recycling and reuse. The surface of the freshly casted polyethersulfone
membrane was modified using GO nanomaterials in a layer-by-layer (LB-L) assembly method. Trimesoyl chloride (TMC) acted as a crosslinking reagent that helps the GO layer to adhere firmly onto the
membrane surface, as illustrated in Fig. 7. High rejection efficiency of
99% COD, > 96% TDS, and > 99% chromium with high flux at 210–220
LMH under operating pressure of 16 bar indicated the effectiveness of
the AOP-NF system for water reclamation from leather industry
wastewater.
A pilot-scale forward osmosis (FO) and NF integrated closed-loop
system was developed by Pal et al. [112] for continuous reclamation
of clean water from tannery wastewater at a rate of 52–55 LMH at 1.6
bar pressure. Continuous recovery for recycling the draw solute was
done by NF of diluted draw solution at an operating pressure of 12 bar
and volumetric crossflow rate of 700 L/h. The work of Pal et al. [112]
culminated in the development of a compact, efficient, and low-cost
tannery industrial wastewater treatment and reclamation technology
with the maximum COD rejection of 98.5%, chloride rejection of 97.2%,
and sulfate rejection of 98.2%. The treatment cost of 1 m3 tannery
wastewater was calculated to be $ 0.72. These findings are useful in the
design and operation of an industrial-scale tannery wastewater treat­
ment plant as the cost analysis is likely to raise the confidence level in
scale-up installation. Subsequently, Pal et al. [113] developed a model
for the FO-NF closed-loop system in validating the context of real tan­
nery wastewater. The developed mathematical model for the proposed
system showed low relative error (< 0.1), high overall correlation co­
efficient (R2 > 0.98), and high Wilmot d-index (> 0.95), thereby indi­
cating reasonably high-performance prediction capability. The findings
from these studies [112,113] demonstrated that the integrated FO-NF
system is promising for clean water recovery from tannery effluent.
3.6. Pulp and paper industry
The wastewater generated by the pulp and paper industry is one of
the common sources of industrial water pollution. The pulp and paper
industry consumes a lot of freshwater (273–455 m3 per tonne paper) and
generates significant amounts of contaminated wastewater (220–380 m3
per tonne paper) [114,115]. The wastewater generated by the pulp and
paper industry contains various types of contaminants and composition,
depending on the substrate type (e.g., recycled paper, softwood, and
hardwood) and the manufacturing process (i.e., pulping, bleaching and
papermaking) [116,117]. For instance, pulping process discharges
effluent with COD of 500–115,000 mg/L, pH range of 6.3–6.8 and high
lignin concentration (11,000–25,000 mg/L). The bleaching process
generates effluent containing toxic pollutants such as phenols, organic
halogen and chlorinated organic compounds that can harm living or­
ganisms. Meanwhile, the wastewater from the papermaking process
contains high COD, TDS, phosphates, sulfate and chloride [117].
To reduce freshwater consumption in the pulp and paper industry,
advanced water treatment such as membrane technology has been
developed to recover water for recycling and reuse in the manufacturing
process. In this scenario, NF is one of the promising membrane
Fig. 7. Illustration of GO-based nanocomposite membrane [105].
13
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
treatments since it that can reject multivalent ions from pulp and paper
industrial effluent. For instance, Lee et al. [118] used the commercial
NF90 membranes to study the phosphorus ions removal from simulated
wastewater comprising 14.5 mg/L phosphorus, which corresponded to
typical concentration in the pulp and paper industrial effluent. The
phosphorus rejection of 99.77% and permeate flux of 88.74 LMH were
recorded under optimized conditions at pH of 7.2, 9.3 bar and 34 ◦ C.
Previously, the NF process has been used either as stand-alone or
integrated with numerous processes to achieve targeted permeate
quality that can fulfil the reuse criteria in the pulp and paper industry
(Table 7). Although most of the paper mills use the biological treatments
such as activated sludge process to pre-treat their effluents, the treated
water is not clean enough to enable the reuse of water in producing most
of paper grades [119]. Thus, desalting process using membrane tech­
nologies such as NF is required to polish the water quality for reuse in
the manufacturing processes. In a recent work conducted by Caldeira
et al. [120], NF was applied after pre-treatments comprised of flotation,
up flow anaerobic sludge blanket bioreactor (UASB) and activated
sludge process during water recovery from simulated thermomechanical pulp mill effluent for internal reuse. The NF membrane
attained rejection of 89%, 99%, 82%, 74% and 57% for Cu2+, Mn2+,
Fe2+, Ca2+ and Mg2+ ions, respectively, while the overall permeate
quality was suitable for industrial processes. It was found that the reuse
of 100% of the treated effluent in the bleaching process did not signif­
icantly affect the pulp quality in terms of brightness and brightness
reversion. Despite this promising result, it should be noted that the
membrane performance was based on exposure to synthetic wastewater.
A study reported by Gönder et al. [121] further revealed the poten­
tial of NF in pulp and paper industry wastewater reclamation. In their
work, the real pulp and paper wastewater pre-treated using biological
treatment was subjected to two-step NF process to recover water with
quality up to water reuse standard. The use of FM NP010 membrane in
the first step of the NF process has rejected 92% total hardness, 91%
COD and 98% sulfate under optimized conditions. The FM NP030
membrane was further used as the second step in the NF treatment
system and successfully produced permeate with quality that meets the
actual process water. A minimal fouling effect was observed by
increasing the feed pH up to pH 10. Under this condition, the negatively
charged membrane could repel the negatively charged contaminants in
the pulp wastewater, reducing the solutes adsorption onto the
membrane.
The treatment of paper machine circulation wastewater (white­
water) by a two-step NF process was carried out by Kaya et al. [122].
Like Gonder et al.'s study, the FM NP010 membrane (loose NF) and FM
NP030 (tight NF) were used in the first and second stage NF, respec­
tively. The results showed that the combination of loose and tight NF
membranes successfully recovered water that can be reused as shower
water for paper machines. The best performance was observed at the
pressure of 32 bar and pH of 5.6, where all the contaminants with the
exception of chloride ions were efficiently removed. Suspended solids,
TP, sulfate, and color were removed more than 99% after passing
through the tight NF, resulting in sufficient permeate quality for shower
water application.
Khosravi et al. [119] evaluated the NF and low-pressure RO mem­
branes in MBR for Mazandaran pulp and paper industry wastewater
treatment. The measured parameters such as color, organic carbon and
UV absorption were almost completely rejected by the NF270 mem­
brane but monovalent ions (especially nitrate and chloride ions) and
inorganic carbon permeated easily through the membrane. Therefore,
NF is attractive in purifying discharge water for reuse in the paper
manufacturing process as long as the discharge water does not contain
too high amounts of monovalent ions.
Bleached sulfite pulp mills generate a considerable amount of browncolored effluents rich in COD and valuable waste products such as lignin
derivatives [123]. The recovery of lignin derivatives is advantageous
since these materials can be further used in the production of biobased
Table 7
Application of NF in pulp and paper industry wastewater treatment for water/product recovery, recycling, and reuse.
Treatment process
NF membrane
Operating
conditiona
Feed
Performance
Reuse application
Ref
Flotation-up flow anaerobic
sludge blanket reactor
(UASB)-activated sludge
reactor-NF
AFC30
P = 10–20 bar,
Crossflow
Simulated thermomechanical pulp mill
effluent
The treated effluent could be recycled and
reused in the bleaching process without
affecting the pulp brightness.
[120]
Two steps NF
(Loose NF-Tight NF)
FM NP010
(loose NF)
FM NP030
(tight NF)
TMP = 12–36
bar,
T = 25–45 ◦ C,
pH = 4–10,
Crossflow
Biologically treated
pulp and paper mill
wastewater
The final permeate met the actual process
water quality.
[121]
Two steps NF
(Loose NF-Tight NF)
FM NP010
(loose NF)
FM NP030
(tight NF)
TMP = 8–32
bar,
T = 25 ◦ C,
Crossflow
Paper machine
circulation wastewater
(whitewater)
The recovered water can be reused as
shower water of paper machine.
[122]
NF
NF270
P = 8 bar,
T = 40 ◦ C,
Crossflow
Pre-treated paper mill
effluent
NF permeate could be reused in the paper
manufacturing process.
[119]
UF-NF
Commercial
ceramic NF
TMP = 1–5
bar,
T = 60 ◦ C,
Crossflow
Bleached sulfite pulp
mills effluent
Removal efficiency of
NF:
COD = 81%
Color = 100%
TDS = 27%
TSS = 70%
Removal efficiency:
COD>97%
Total hardness =
100%
Chloride = 82%
Sulfate = 99%
EC = 87%
Removal efficiency:
COD = 97.9%
Total hardness =
92.7%
Chloride = 64.2%
Sulfate = 99.3%
Color>99%
TP = 100%
Flux = 100–150 LMH
Conductivity
retention = 80%
Dissolved inorganic
carbon retention =
76%
COD retention =
35–40%
Lignin retention =
45–66%
Lignin recovery for conversion into
biobased products.
[123]
a
Operating condition for NF unit.
14
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
products, including resins, biofuels, and fine chemicals. In this context,
Ebrahimi et al. [123] investigated the possibility of recovering lignin
from pulp and paper industry wastewater using ceramic tubular mem­
brane technology. The average COD and lignin retention efficiencies
achieved by the two-stage UF-NF treatment were 35–40% and 45–66%,
respectively. However, the two-stage process of MF-UF configuration
showed better treatment efficiency for alkaline bleaching effluent,
lowering the overall COD by 35–45% and residual lignin concentration
by 60–73%.
Shukla et al. [124] designed an integrated membrane filtration sys­
tem comprised of UF, NF, and RO membranes in series to treat the
effluent generated by extraction stages and chlorination (C-stage) in a
bleach plant at an Indian pulp and paper mill. The majority of the
constituents in the C-stage effluent were too small to be rejected, even by
a very dense UF membrane. However, significant removal of the pol­
lutants was obtained via the NF process with 45.18–81.48% TDS,
46.27–80.78% COD, 100% color, and 47.90–68.34% adsorbable organic
halides (AOX). On the other hand, comparative removal was observed
for the treatment of effluent from the extraction stage. During the NF
process, removals ranging from 40.53–48.78% for TDS, 25.04–54.20%
for COD, 75.30–96.51% for color, and 43.27–81.98% for AOX were
observed at different pressure. Excellent removals of all pollutants were
achieved by RO where the overall removal of the lab-scale membrane
treatment plant was 100% TDS, 75–98% COD, 100% color, and 91–98%
AOX for C-stage effluent and 100% TDS, 90–100% COD, 100% color,
and 93–99% AOX for extraction stage effluent. The installation of NF
prior to RO has enhanced the pollutants removal efficiencies of RO,
signifying the importance of an integrated membrane system in clean
water recovery from pulp and paper industry wastewater.
wastewater has emerged as one of the most pressing issues since these
compounds are harmful to human health and environment. Besides,
there has been an increased emphasis on water reuse in pharmaceutical
sector in recent years [127]. Thus, the development of efficient methods
for pharmaceutical wastewater treatment is mandatory.
The effective removal of PhACs can be achieved via membrane
technologies such as NF since most of the PhACs possess molecular
weight greater than 250 Da [128]. It is expected that the PhACs can be
well retained by the membrane through molecular sieving if the mem­
brane MWCO is greater than the molecular weights of PhACs. In this
scenario, the application of tight NF with small MWCO (<500 Da) is a
promising option and has been frequently applied for the removal of
PhACs (Table 8) [129–131]. For example, Yangali-Quintanilla et al.
[131] examined the performance of tight NF membranes namely NF-90
and NF-200 membranes for treating synthetic water solution containing
17 compounds including various PhACs and EDCs. The performance of
RO membrane ((BW30 LE and ESPA2) was also studied for comparison
purpose and the filtration test was conducted in bench, pilot, and full
scale to generate reusable water. It was revealed the NF-90 had higher
rejections than NF-200 due to a combination of electrostatic repulsion
and size exclusion. Furthermore, NF and RO attained 97% and 99%
average rejection of ionic compounds, respectively, and the removal of
neutral compounds was approximately 82% and 85%, respectively.
Thus, they concluded that the tight NF membranes were a viable option
to RO since NF can also achieve effective removal of PhACs or EDCs at
lower operating cost.
In another work, Azaïs et al. [130] investigated the performance of
NF-90 and NF-270 membranes during the treatment of pre-treated
effluent from a wastewater treatment plant (spiked with PhACs). The
influences of solute-solute interaction and fouling on the PhACs rejec­
tion (i.e., acetaminophen (ACT), atenolol (ATL), carbamazepine (CBZ)
and diatrizoic acid (DTZ)) was studied and the NF permeate quality was
assessed to explore its suitability for reuse. In terms of PhACs removal,
excellent rejection (>90%) was achieved by NF-90 membrane which
contained smaller pores than NF-270. Unlike NF-270 membrane which
possessed lower removal of PhACs due to cake enhanced concentration
polarization, it was found that the solute-solute interaction (PhACs
binding) and fouling has less effect on the PhACs rejection of NF-90
membrane. Moreover, the permeate quality analysis revealed that the
recovered water using NF-90 membrane has fulfilled the irrigation water
standard, suggesting that a tight NF membrane such as NF-90 is prom­
ising for wastewater reuse.
3.7. Pharmaceutical industry
The pharmaceutical industry is one of the fastest growth industries
and its global market size is predicted to increase at a compound annual
growth rate of 11.34% from 2021 to 2028 [125]. Hence, it is expected
that more pharmaceutical wastewater will be produced in the coming
years since water is mainly used in pharmaceutical manufacturing
process such as chemical synthesis and fermentation stages. Pharma­
ceutical effluent may contain organic and inorganic pollutants, phar­
maceutical active compounds (PhACs) (e.g., tranquilizers, antibiotics,
diuretics, and psychiatric drug) and endocrine disrupting compounds
(EDCs) [126]. The removal of PhACs and EDCs from pharmaceutical
Table 8
Application of NF in pharmaceutical industry wastewater treatment for water/product recovery, recycling, and reuse.
Treatment
process
NF
membrane
Operating conditiona
Feed
Performance
Reuse application
Ref
NF process
NF-90 and
NF-270
Pre-treated real effluent spiked
with PhACs
NF-90 rejection:
PhACs>90%
The NF-90 permeate fulfilled
the water irrigation standard.
[130]
NF process
(Pilot
study)
NF-50 (loose
NF)
P = 800 kPa, T =
20 ◦ C, pH = 7,
Crossflow
P = 8 bar, T = 25 ◦ C,
Dead end
Synthetic effluent containing
model drugs
Not specified
[132]
MF-FO-NF
NF-1 and NF2
Real pharmaceutical industry
wastewater
NF permeate could be reused in
industry
[135]
MBR-NF
(Pilot
study)
MBROzonationNF
(Pilot
study)
NF-90
P = 10–14 bar,
T = 35 ◦ C, pH = 7
Crossflow
TMP = 5–7.5 bar, pH
= 6.23–8.07,
Crossflow
TMP = 10 bar,
Crossflow
Removal of drugs:
DIC = 99.7%
IBU = 80.5%
PARA = 36.2%
NF permeate flux = 58–60 LMH,
Salt removal efficiency for draw
solutes 98–99%.
Water yield = 92%,
Antibiotic (spiramycin and new
spiramycin) removal rates >95%.
Rejection for
TOC = 92–98%,
Cl− , Na+, K+
=
83–97%,
SO42− , Mg2+, Ca2+ = 93–100%,
Organic micropollutants =
84–98%
NF permeate fulfilled the water
quality standard for industrial
reuse
Not specified
[133]
a
NF-90
Antibiotic production wastewater
from pharmaceutical company
Real effluent spiked with four
types of PhACs
Operating condition for NF unit.
15
[134]
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
Tight NF has demonstrated good PhACs removal efficiency but
irreversible fouling is the main issue in tight NF with low MWCO.
Therefore, Maryam et al. [132] proposed the use of loose NF (HYDRA­
CoRe, NF-50) with MWCO of 1000 Da for the removal of three types of
PhACs namely Ibuprofen (IBU), Diclofenac (DIC) and Paracetamol
(PARA) from synthetic wastewater. In their work, the efficiency and
behavior of loose NF was assessed under extreme pH condition using
pilot plant dead-end system at 8 bar. It was found that loose NF removed
99.7% DIC at pH 3, 80.5% IBU at neutral pH and 36.2% PARA at pH 12.
Even though the permeate flux changed due to drugs chemical proper­
ties, no apparent fouling was observed for NF-50 since this negatively
charged membrane surface could repel the negatively charged drug
molecules. Thus, they suggested that the application of loose NF with
large MWCO can also be a promising alternative technique for removal
of PhACs from effluent. Nevertheless, the low rejection of Paracetamol
needs to be addressed.
The limitation of biological treatment to remove inorganic com­
pounds and salt in pharmaceutical wastewater requires installation of
post-treatment unit to polish the effluent quality up to water reuse
criteria. In the case of MBR, low removal efficiency of some micro­
pollutants has been reported [133,134]. Therefore, the application of
integrated process comprised of NF as polishing step can be used to
enhance the efficiency of pharmaceutical wastewater treatment for
recycling and reuse. In a study conducted by Wang et al. [133], a pilot
scale membrane system comprised of MBR-NF was installed at a phar­
maceutical company in Wuxi, China, to recover water from antibiotic
production effluent for industrial reuse. Two commercial polyimide NF
membranes (Filmtec™ NF-90 and NF-2540) were installed in parallel
and operated at TMP of 5.0–7.5 bar at a cross-flowrate of 2.0 m3/h. The
performance of integrated system was assessed over three-month period
and part of the NF concentrate was recycled to the MBR on the day-62.
During the process, the organic pollutants (e.g., protein, humid sub­
stances and polysaccharides) were accumulated and further bio­
degraded in MBR by recycling the NF retentate. Their result
demonstrated that the strategy of NF concentrate recycling has resulted
in effective antibiotic wastewater treatment with high water yield
(92%). The integrated process successfully generated final permeate
with turbidity of 0.15 NTU, conductivity of 2.5 mS/cm, TOC of 5.52 mg/
L and TP of 0.34 mg/L, complying with China's water quality standard
for industrial usage. Moreover, it shall be noted that the application of
NF as post-treatment step not only improve the antibiotic removal
(>95%), but it also helps to reduce the acute toxicity of the effluent.
Despite this promising result, further economic evaluation is required to
analyse the cost of the membrane treatment system, including the cost
saving after water reuse implementation.
To mitigate the fouling in NF membrane, Amadou Yacouba et al.
[134] proposed the application of ozone-based AOP to pre-treat the MBR
effluent prior to NF process. In their study, the real MBR-effluent from a
wastewater treatment plant spiked with four pharmaceuticals (i.e.,
acetaminophen (ACT), carbamazepine (CBZ), sulfamethoxazole (SUL)
and tetracyclin (TET) and herbicide was used as the feed. It was found
that the NF-90 membrane operated using crossflow system at 10 bar
successfully removed the organic micropollutants with rejection of
84–98%. Moreover, the pre-ozonation has reduced the fouling resistance
by about 40% due to degradation of dissolved organic matters which
consequently turned them into more hydrophilic constituents with less
tendency for irreversible fouling. However, it shall be noted that the
efficiency of NF-90 membrane to remove ozonation-by products was not
evaluated in this work, and thus remains questionable.
Besides MBR, the NF also has been paired with other membrane
technologies such FO during pharmaceutical wastewater reclamation.
For instance, Thakura et al. [135] applied the NF after FO process for
draw solution regeneration/reconcentration and recycling while at the
same time extracting the clean water trapped inside the draw solution
during the treatment of real pharmaceutical wastewater. The installa­
tion of downstream NF module at 12 bar TMP achieved the draw
solution recovery and recycle of 99% while generating high permeate
flux (58–60 LMH) which can be reused in industry. Besides the prom­
ising water treatment performance, the cost analysis is important to
enhance the confidence level in scale-up installation. Thus, economic
analysis was also evaluated in their work for a wastewater plant with
plant capacity of 50,000 L/day. It was found that the total operational
cost was $17,800/year, but this cost could be further reduced to
$13,300/year by implementing the water reutilization.
In terms of resource recovery, the potential of NF to recover organic
solvent and PhACs from waste stream generated by pharmaceutical
production process has been reported in previous studies [136,137]. The
recovery of pharmaceutical compound namely 1-(5-bromo-fur-2-il)-2bromo-2-nitroethane (G-1) from residual ethanol stream generated by
G-1 purification stage was investigated by Brito Martínez et al. [137].
Commercial NF membranes namely Duramem 150 and NF-90 have
attained high G-1 retention (>60%) via one step separation, high­
lighting the potential of NF for valuable PhACs recovery. Moreover,
heavy metals such as nickel are another by-product that can be found in
pharmaceutical industry effluent [128]. However, limited studies have
been focused on the valuable metal recovery from pharmaceutical
wastewater. Thus, there should be more emphasis on this resource re­
covery aspect using NF-based integrated process for pharmaceutical
effluent treatment in future work. Even though the by-product reuse
application within pharmaceutical industry is often restricted by the
stringent quality control requirement, the waste exchange which in­
volves the transfer of the recovered products to another industry or
company can be done as alternative to promote recycling and reuse
[128].
4. Outlook and future perspective
The unique feature of NF which allows selective separation of tar­
geted species is promising for water and resource recovery from indus­
trial effluent. The reclaimed water and valuable products from
wastewater via integrated NF process fulfilled certain standard criteria
that enable resource recovery and water recycling and reuse. Never­
theless, more studies need to be conducted in the future to promote
resource recovery as well as water recycling and reuse practice in in­
dustrial wastewater treatment using membrane technologies, especially
the NF. The aspects that need to be considered in future research are
summarized as follow:
4.1. Membrane materials and design
For industrial effluents that are highly acidic or alkaline such as gold
mining effluent and caustic-containing wastewater in the textile and oil
refinery industry, few studies involving the use of NF for resource re­
covery and reuse application have been reported. Hence, the develop­
ment of polymeric NF that possesses highly acidic or alkaline resistant
feature can be investigated more in the future to explore the potential of
NF for product recovery from these industrial effluents. The utilization
of nanomaterials/nanotechnology to fabricate higher resistance NF
membranes should be explored further in this direction. Meanwhile,
ceramic NF is a promising alternative for industrial wastewater treat­
ment involving extreme pH or high-temperature condition. Neverthe­
less, the application of ceramic NF for industrial wastewater treatment is
still limited compared to polymeric NF, probably due to its high capital
cost. Thus, it is essential to find strategies for reducing the cost of the
ceramic membrane to make it economically viable in comparison to the
polymeric membrane. For instance, future studies can explore wastederived materials, inexpensive precursors, or new technique to fabri­
cate cost-efficient ceramic NF. In the context of textile industrial effluent
treatment, the development of loose NF membranes with high perme­
ability, superior antifouling property, and excellent dye/salt separation
efficiency that can be easily synthesized and mass-produced can also be
explored.
16
N.N.R. Ahmad et al.
Journal of Water Process Engineering 45 (2022) 102478
4.2. Pre-treatment processes
reclaimed water via NF or integrated NF process for external reuse,
including irrigation purposes. In the context of produced water treat­
ment, many governments have expressed interest in reusing produced
water for purposes outside the internal industry due to the increasing
global water demand [5,139]. For irrigation application, the effect of
treated industrial wastewater on plant growth and soil quality must be
investigated comprehensively in the future to provide supporting data
that enable more reuse applications of treated industrial wastewater.
Most of the works reported have also highlighted the issues with
membrane fouling due to the complexity of the wastewater from these
various industries. Effective pre-treatment processes are vital to mini­
mize the issues with NF membranes and allow for a more sustainable
and long-term operation of membranes. Various pre-treatment processes
have been reported, such as coagulation/flocculation, precipitation,
adsorption, membrane-based processes and AOP. More studies should
be conducted to determine the most optimum configuration and its
impact on the NF membrane as well as the overall performance.
4.7. Large scale process
The promising performance demonstrated by the integrated NF
process in the lab-scale study should be further studied in the context of
pilot-scale. In this way, a full assessment of the feasibility and viability of
the water treatment process (e.g., technical aspects, cost, and perfor­
mance) in industrial wastewater reclamation can be done. The data will
provide a more thorough understanding of the potential of integrated NF
process for recycling and reuse. Moreover, the development of predic­
tive models for scaling up from laboratory scale to large scale applica­
tion as well as cost assessment is helpful to explore the profitability of
the integrated NF treatment in industrial operation.
4.3. Retentate post-treatment processes
Besides the concern on NF permeate quality for reuse, the retentate
or brine management is also a vital issue. Common disposal techniques
(i.e., evaporation ponds, surface water discharge, land application and
deep-well injection) could impart negative influences on soil, ground­
water, and marine environment [138]. Rather than being disposed, the
retentate could be post-treated if it contains value-added compounds.
Numerous techniques such as resin adsorption, solvent extraction, mi­
crobial fuel cell and membrane crystallization unit are promising for
treating the NF retentate, depending on the nature of the by-products to
be recovered. There should be extensive research to investigate the ef­
fect of these post-treatment techniques on the purity of the recovered byproducts to unlock their potential for reuse application, and thus
achieving zero liquid discharge.
5. Conclusions
NF has drawn a lot of attention in industrial wastewater reclamation,
recycling, reuse, and resource recovery applications due to its capability
to separate the divalent/polyvalent ions from monovalent ions and small
molecules. In this review, the application of NF within various industrial
wastewater treatments for water recycling, reuse and product recovery
targets has been highlighted. The NF treatment can be integrated with
other membrane technologies or processes to mitigate the fouling,
prolong the membrane lifespan, and enhance the membrane perfor­
mance upon exposure to real industrial wastewater. In most integrated
processes, NF has been commonly adopted as a post-treatment step to
polish the treated effluent quality up to the standard reuse criteria and
recover other by-products that can be recycled. Most of the studies found
that NF is promising to remove a wide range of pollutants in various
industries, and thus capable to generate reusable water. Nevertheless,
less attention has been paid on the NF retentate or concentrate treat­
ment. More aspects associated with NF concentrate treatment, long term
membrane stability and fouling, cost assessment, membrane materials
and design, process configuration, process scaling up and reuse appli­
cation can be further explored in the future to promote the imple­
mentation of NF technology for water recycling, reuse, and resource
recovery.
4.4. Long term assessment
The separation performance from most of the published works so far
were based on short-term assessment. Future works shall focus on
investigating the long-term performance upon exposure to real indus­
trial wastewater in order to investigate the fouling propensity behavior,
membrane stability and its performance in challenging conditions. The
installation of a suitable NF membrane based on the consideration of
long-term chemical stability, real separation performance and less
fouling propensity will increase the process sustainability during the
water or by-products recovery from the industrial wastewater.
4.5. Economic analysis
To mitigate the membrane fouling and to improve the permeate
characteristics up to a certain standard that enables the reuse within the
industrial process, the NF has been commonly integrated with other
processes during the industrial wastewater treatment. Despite the good
water or by-products recovery performance of the integrated process,
most studies did not report the economic analysis, including the overall
cost treatment. In addition, the analysis on water or chemical saving cost
after reuse implementation is essential to convince the industries to
invest in the integrated water treatment process for recycling and reuse.
Therefore, future studies should also analyse the practicability of the
treatment process from the economic perspective.
Declaration of competing interest
The authors have no affiliation with any organization with a direct or
indirect financial interest in the subject matter discussed in the
manuscript.
Acknowledgement
4.6. Reuse application
The authors gladly acknowledge the financial support from the
MRUN research grant (grant number: KK-2019-001) and Modal Insan
Scheme (RGA1). Prof Hilal would like to thank New York University Abu
Dhabi (NYUAD) and Tamkeen for funding NYUAD Water Research
Center. (Project CG007).
Most of the studies related to the application of NF in the industrial
effluent treatment reported that the treated water fulfilled the standard
quality for internal reuse application such as for the manufacturing
process. In the case of reuse applications involving product fabrication,
limited data on the effect of recycled water or other recovered compo­
nents from NF-based treatments on the product quality has been re­
ported. Such data is essential to explore the potential of reclaimed water
or other by-products for recycling and reuse within industries. Thus,
future studies can also consider this aspect of investigation. Moreover, it
shall be noted that little attention has been paid on the application of the
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