S. AL-JLIL: PERFORMANCE OF NANO-FILTRATION AND REVERSE OSMOSIS PROCESSES ...
541–548
PERFORMANCE OF NANO-FILTRATION AND REVERSE
OSMOSIS PROCESSES FOR WASTEWATER TREATMENT
OCENA ZMOGLJIVOSTI POSTOPKOV NANOFILTRACIJE IN
POVRATNE OSMOZE PRI OBDELAVI ODPADNE VODE
Saad Al-Jlil
National Center for Membrane Technology (NCMT), King Abdulaziz City for Science and Technology (KACST),
P. O. Box 6086 Riyadh, Saudi Arabia
saljlil@kacst.edu.sa
Prejem rokopisa – received: 2015-08-09; sprejem za objavo – accepted for publication: 2016-06-30
doi:10.17222/mit.2015.250
This study was carried out to evaluate the performance of nano-filtration (NF) and reverse osmosis (RO) technology for
reducing the total salt concentration from waste water. The nano-filtration proved very effective in removing the polyvalent
cations and anions, such as SO4–, whereas the removal efficiency was 97.22 %. It is well known that a RO water-treatment
process removes all the cations and anions from waste water or brine or sea water, especially removing the monovalent ions
such as Cl– where the removal efficiency was 94.4 %. The performance efficiency of RO and NF water-treatment processes
declined significantly during the first 3 years of operation due to fouling and biofouling of the membrane. The research findings
provided a concrete clue for the important issue of water treatment as an alternative to existing water use methods on a
cost-effective basis. The research also highlighted the potential to replace the NF and RO membranes used in these two
water-treatment techniques.
Keywords: desalination of waste water, reverse osmosis, nano-filtration
Izvedena je bila {tudija ocene zmogljivosti tehnologije nanofiltracije (angl. NF) in povratne osmoze (angl. RO) za zmanj{anje
skupne vsebnosti soli v odpadni vodi. Nanofiltracija je zelo u~inkovita pri odpravljanju polivalentnih kationov in anionov, kot so
SO4–, kjer je bila u~inkovitost odstranitve 97,22 %. Dobro je poznano, da RO postopek obdelave vode odstrani vse katione in
anione iz odpadne vode, slanice ali morske vode, {e posebno monovalentni Cl–, kjer je bila u~inkovitost odstranitve 94,4 %.
Zmogljivost RO in NF procesov pri obdelavi vode se ob~utno zmanj{a med prvim 3-letnim obratovanjem zaradi ma{enja in
biolo{kega nalaganja na membrane. Ugotovitve raziskave omogo~ajo konkreten namig za pomembno vpra{anje obdelave vode,
kot cenovno u~inkovita alternativa sedanjim metodam. Raziskava je pokazala tudi mo`nost za zamenjavo NF in RO membran,
ki se jih uporablja v teh dveh na~inih obdelave vode.
Klju~ne besede: razsoljevanje odpadne vode, povratna osmoza, nanofiltracija
1 INTRODUCTION
Water uses are manifold, ranging from domestic,
agriculture to industries. Among these, the chemical
industry uses water as a coolant and to generate steam
from boilers for use in different industrial processes for
the production of different types of products. In boilers,
water evaporates continuously and the dissolved salts
precipitate after reaching the saturation stage at
equilibrium, thus forming a hard scale that deposits on
the inner walls of the boiler. There are several dis-
advantages of these deposits. Among them, the most
important is corrosion, which decreases the efficiency of
the boiler unit through the clogging of pipes, valves and
condensers, decreases the heat-transfer rate, causes the
excessive use of fuel and a danger of explosion. There-
fore, wastewater treatment is important for the safe
operation of boilers. Among the traditional methods of
water softening, the addition of lime-soda is one process.
But this process has some disadvantages i.e., it leaves
more sodium chloride as residue in the raw water and the
need for reaction tanks equipped with mechanical stirrers
in addition of course to the main chemicals used by the
process and the coagulant to facilitate filtration of the
formed precipitates.
Presently, among the various techniques for softening
high-hardness waters, membrane separation is a new
approach. The membrane-separation processes have the
unique advantage of not requiring energy to affect phase
changes compared to distillation or crystallization. Hen-
ce, it is an economically attractive alternative as com-
pared to costly methods due to low energy requirements.
The objective of this work was to investigate the
possibility of using reverse osmosis and nano-filtration
processes to improve the water quality by removing the
major cations and anions, such as calcium, magnesium
and chloride, from wastewater. We also wanted to
determine the decline in the performance of RO and NF
processes due to membrane fouling.
2 REVIEW OF LITERATURE
2.1 RO – Technology application
Membrane technology is playing an important role in
the reclamation of municipal wastewater. In particular,
high-quality reclaimed wastewater can be used by
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UDK 621.6.031:66.081.63:628.16:66.067.1 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 51(3)541(2017)
industrial customers. Currently, many large-scale
commercial membrane plants are in use for the treatment
of municipal wastewater. These plants include the
270,000 m3/day plant in Orange County, California and
the 380,000 m3/day plant for Sulayabia, Kuwait.1
A typical municipal wastewater treatment process
consists of primary, secondary and tertiary treatments.
When tertiary effluent from a conventional treatment
process is supplied to a RO system, it encounters all
forms of fouling, i.e., colloidal, biological, scaling and
organic fouling. The coatings of foulant will impede the
water transport through the membranes, thus resulting in
short membrane life and increased operational cost.
Since the development of practical cellulose acetate
membranes in the early 1960s and the subsequent
development of thin-film, composite membranes, the use
of reverse osmosis technology expanded to include not
only the traditional desalination process but also a wide
range of wastewater treatment applications. Several
advantages of the RO process that make it particularly
attractive for dilute aqueous wastewater treatment have
been widely advocated by many investigators.2–4 The
applications reported for RO processes include the
treatment of organic-containing wastewater, wastewater
from electroplating and metal finishing, pulp and paper,
mining and petrochemical, textile, and food processing
industries, radioactive wastewater, municipal wastewater,
and contaminated groundwater.2,4,5
2.2 Contaminated drinking water
Reverse osmosis processes can simultaneously
remove hardness, color, many kinds of bacteria and
viruses, and organic contaminants such as agricultural
chemicals and trihalomethane precursors. T. Eisenberg
and E. Middle Brooks6 reviewed the RO treatment of
drinking-water sources, and they indicated that RO can
successfully remove a wide variety of contaminants.
E. Chian et al.7 studied several agricultural chemicals
contaminating water supplies and found their removal
was good by adsorption on the membranes. H. Odegaard
and S. Koottatep8 reported that humic and fulvic ma-
terials, which are THM precursors, were largely removed
by RO membranes. T. Clair et al.9 found the excellent
removal (>95 %) of dissolved organic carbon from natu-
ral waters using FT30 membranes. T. Sorg et al.10
showed that the RO system can effectively remove ra-
dium from contaminated water. J. Baier et al.11 reported
the removal of several agricultural chemicals from
groundwater from 0 % to >94 % using different mem-
branes. J. Taylor et al.12 found that RO membranes could
be used to remove 96 % of DOC, 97 % of color, 97 % of
trihalomethane formation potential (THMFP), and 96 %
of total hardness. L. Tan and R. Sudak13 examined seve-
ral RO membranes and found that all were capable of
acceptably removing color from groundwater, even over
long operating periods.
2. 3 Municipal wastewater
Reverse osmosis (RO) can remove dissolved solids
from municipal wastewaters, which cannot be removed
by biological or other conventional water-treatment pro-
cesses. However, extensive pretreatment and periodic
cleaning are usually needed to maintain acceptable
membrane water fluxes. Early studies14,15 showed that the
high removal of TDS and the moderate removal of
organics can be achieved. H. Tsuge and R. Mori16
showed that tubular membranes (with a substantial pre-
treatment system) can remove both the inorganic and
organic pollutants from municipal secondary effluent and
produce water that meets drinking-water standards. Pre-
viously, N. Richardson and D. Argo17, P. Allen and
G. Elser18 and I. Nusbaum and D. Argo19 discussed mu-
nicipal wastewater treatment at a large scale plant (Water
Factory 21, Orange County, California). The feed water
to the plant consisted of secondary effluent, and the
process was composed of a variety of treatment systems,
including RO membranes (several different types) with a
5 MGD capacity. The process reduced TDS and organics
to levels that allowed the effluent to be injected into
groundwater aquifers used for water supplies.
E. Cséfalvay et al.20 stated that membrane separations
are gaining increasing interest in wastewater treatment
due to their efficiency. Nano-filtration and reverse-osmo-
sis membranes were tested under different conditions to
reduce the chemical oxygen demands (COD) of waste-
waters. However, none of the membranes decreased the
COD to the release limit in one step. Gholami et al.
found that the range of rejection was 73.52 % to 99.36 %
and 75.1 % to 98.8 %, for amoxicillin and ampicillin,
respectively. Also, the application of the RO membrane
was recommended for the removal of selected antibiotics
up to 95 % from synthetic waste effluent.21 In addition
pressure-driven membrane processes, particularly nano-
filtration (NF) and reverse osmosis (RO) have also been
gaining attention in the past decade and their application
in drinking-water treatment has been the focus of many
researchers.22
2.4 Nano-filtration applications
Recently, nano-filtration membranes, having high
water fluxes at low pressures, were developed as new
applications in wastewater treatment. These membranes
also reject organic compounds with molecular weights
above 200 to 500. These properties have made possible
some interesting new applications in wastewater treat-
ment, such as selective separation and the recovery of
pollutants that have charge differences, the separation of
hazardous organics from monovalent salt solutions, and
membrane softening to reduce hardness and trihalo-
methane precursors in drinking-water sources.23, 24
2.5 Contaminated drinking-water supplies
Nano-filtration membranes have attracted a great deal
of attention for use in water softening and the removal of
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various contaminants from drinking-water sources.
Nano-filtration (NF) processes can reduce or remove
TDS, hardness, color, agricultural chemicals, and high-
molecular-weight humic and fulvic materials (which can
form trihalomethanes when chlorinated). In addition, NF
membranes typically have much higher water fluxes at
low pressures than traditional RO membranes used for
this application. W. Conlon 25 reported that FilmTec
NF50 membranes can effectively remove color (96 %)
and TOC (84 %), reduce hardness and TDS, and lower
trihalomethane formation potential (THMFP) to below
regulatory levels. P. Eriksson23 and J. Cadotte et al.24 also
indicated that NF membranes (such as FilmTec NF40,
NF50, and NF70) can be used to reduce TDS, hardness,
color, and organics. B. Watson and C. Hornburg26, and
W. Conlon et al.27 have also identified NF as an emerging
technology for compliance with THM regulations and
for the control of TDS, TOC, color, and THM precur-
sors. P. Lange et al.28 also suggested that NF treatment
would be a reliable method of meeting existing and
future THM limits compared to chemical treatment
alternatives. G. Amy et al.29 used NF70 membranes to
remove dissolved organic matter from both groundwater
(recharged from secondary effluent) and surface water in
order to reduce THM precursors. They found that the
process was effective in reducing the organics as well as
the conductivity in both water sources. S. Duranceau et
al.30 also reported on the use of NF70 membrane
separation for several agricultural chemicals spiked in
groundwater. Ethylene dibromide and
dibromochloropropane removals averaged 0 % and 32
%, respectively, while the remaining organics (chlordane,
heptachlor, methoxychlor, and alachlor) were 100 %
removed. Rejections of TDS were 85 % and THMFP
were 95 %. However, it was also indicated that some of
the organics adsorbed on the membrane.
2.6 Wastewater
Nano-filtration is also used to remove both the
organics and inorganics from different wastewaters.
A. Bindoff et al.31 reported that using NF membranes,
the color removal was >98 % at water recoveries up to
95 %, while the in-organics were poorly rejected. K.
Ikeda et al.32 indicated NF could give high separations of
color-causing compounds such as lignin sulphonates in
paper pulping wastewaters. M. Afonso et al.33 found NF
removal (>95 %) of chlorinated organic compounds from
alkaline pulp and paper bleaching effluents with high
water fluxes. M. Simpson et al.34 reported the use of NF
membranes to remove hardness and organics in textile
mill effluents. S. Gaeta and U. Fedele35 also indicated
high water recoveries (up to 90 %) from textile dye
house effluent could be achieved with NF membranes.
M. Perry and C. Linder36 discussed the recovery of low-
molecular-weight dyes from high salt concentration
effluent. K. Ikeda et al.32 and J. Cadotte et al.24 reported
the use of NF membranes in the treatment of food-pro-
cessing wastewaters. Some specific uses included the
desalting of whey and the reduction of high BOD and
nitrate levels in potato processing waters (Anonymous,
1988b). D. Bhattacharyya et al.37 used NF40 membranes
to selectively separate mixtures of cadmium and nickel.
M. Williams et al.38 examined NF40 membranes with
and without pretreatment by feed preozonation to study
the removal of various chlorophenols and chloroethanes.
TOC rejections up to 90 % were possible with ozonation
pretreatment. R. Rautenbach and A. Gröschl39 discussed
the separation results of several organics (ranging from
methanol to ethylene glycol) by various NF membranes.
M. Chu et al.40 detailed the use of NF in a process for
treating uranium wastewater; NF40 uranium rejections
were 97 % to 99.9 %. C. Dyke and Bartels41 discussed
the use of NF membranes to replace activated carbon
filters for the removal of organics from off-shore pro-
duced water containing residual oils. The produced
waters contained ~1000 mg L–1 soluble organics (mostly
carboxylic acids) and high inorganic concentrations
(~15,000 mg L–1 Na+ and ~25,000 mg L–1 Cl– as well as
other dissolved ions). Organic rejections were suitable to
meet discharge standards, while inorganic rejections
were low (<20 %), allowing operation at low pressures.
Andrade et al. observed that the MBR efficiently
removed the organic matter and color of the feed effluent
followed by nano-filtration as a polishing step for the
removal of high contents of solids.42 While the mem-
brane separation systems and the combination of these
systems with other technologies, such as membrane
bioreactors (MBR), are the most promising treatment
technologies for effluent reuse.43 Also, studies show that
NF is an efficient treatment system for secondary or
tertiary effluents aiming at the generation of water for
industrial, agricultural, or indirect potable reuse.44,45
3 MATERIALS AND METHODS
The experiment was carried at the Wastewater
Treatment Plant (WTP), National Center for Water tech-
nology (NCWT), King Abdulaziz City for Science and
Technology (KACST) during 2012-2013.
3.1 Analysis of wastewater samples
The water samples were analyzed for pH, cations and
anions. Cations and anions such as chloride, sulphate
were determined by using Dionex 300 Ion chromato-
graphy. The requirements for this analysis are Dionex
ion chromatography with column As-14 (4mm), guard
column AS-12, suppressor-ASR-1, fluent mixture of
carbonate and bicarbonate, deionized water and nitrogen
gas. The total dissolved solids (TDS) were estimated
using Oven Heraeus Instruments. The pH was measured
by using Hach HQ D40.
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3.2 Experimental set-up
3.2.1 Advanced waste water treatment units (AWWTU)
The AWWTU at KACST consists of two parts repre-
senting two different water treatment technologies such
as a Reverse Osmosis Unit (RO-Unit) and Nano-filtra-
tion (NF).
3.2.2 RO-Unit
The pre-treated water from the biological unit is de-
salinized using the RO-technology. Its water production
capacity is 0.12 m3/h (Figure 1).
3.2.3 NF-Unit
The pre-treated water from the biological unit is de-
salinized by applying NF technology. Its water produc-
tion capacity is 0.12 m3/h (Figure 2).
4 RESULTS AND DISCUSSION
The results of the RO and NF wastewater treatment
technologies containing cations and anions are presented
in Figure 3. Only moderate rejection was observed for
the monovalent species, as expected with NF. However,
the rejection of polyvalent cations and anions was high.
On the other hand, strong rejection was observed for
monovalent cations and anions by RO.46 The percentage
rejection of species ions (rej. %) was calculated as
follows in Equation (1):
rej %=
a b
a
−
× 100 (1)
a – concentration of species in the feed,
b – concentration of species in the permate.
The data in Figure 4 shows the results of the
advanced treatment RO and NF of waste water contain-
ing cations and anions using old RO and NF membranes
(worked for 3 years). It was found that the rejection of
the cations and anions decreased for monovalent species.
This behavior is expected with old membranes. Also,
modest rejection was observed for polyvalent cations and
anions. On the other hand, moderate rejection was
observed for monovalent cations and anions by RO due
to membrane fouling and biofouling. This reason is
definitely right, because the wastewater has different
types of bacteria and pathogens and organic material.
The organic material adsorbed onto the membrane
surface and increased the fouling problem.
Figure 5 shows the performance of NF and RO for
the rejection of TDS. In general, the TDS rejection
decreases with an increase in the feed concentration due
to increased concentration polarization at the membrane
solution interface.47 It was observed that TDS rejection
was less by NF than RO membrane. This could be
attributed to the monovalent ions such as Na+, which
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Figure 4: Comparison of the performance of old RO and NF mem-
branes
Slika 4: Primerjava zmogljivosti starih RO in NF membran
Figure 2: Layout of nano-filtration unit
Slika 2: Postavitev nanofiltracijske naprave
Figure 3: Comparison of the performance of new RO and NF mem-
branes
Slika 3: Primerjava zmogljivosti novih RO in NF membran
Figure 1: Layout of reverse osmosis (RO) unit
Slika 1: Postavitev naprave za reverzibilno osmozo (RO)
represents the main component in the feed water; there-
fore, the ability of NF in rejection of the monovalent ions
is weak.
Figure 6 shows the performance of the NF and RO
membranes for the rejection of TDS at the same pH of
feed water. The percentage rejection of the Na+ ion by
RO membrane was higher than the NF membrane. This
could be attributed to the fact that the rejection of mono-
valent ions such as Na+ by NF is weak.42,43 In addition,
the pH did not affect the membrane rejection when the
polyamide membrane pH operating range is 4–11.
Figure 7 shows the results of RO for waste water
treatment containing cations and anions using the old RO
and new RO membranes. The old membrane was 3 years
old. It was found that the percent rejection decreased for
all the ion species. For example, the percent rejection of
Cl– ion was 94.4 % using the new membranes and the
membrane percent rejection was 43.9 after three years.
This would mean that the membrane performance
declined due to fouling and biofouling. The study results
agree with those of Gholami et al., and Sahar et al. who
reported the significant rejection of pollutants from
waste effluents.21,22
Figure 8 shows the results of NF for wastewater
treatment containing cations and anions using the old NF
and new NF membranes. The old membrane worked for
3 years. It was found that the rejection decreased for
polyvalent cations and anions. This behavior was
expected with the old membranes. On the other hand, the
percent rejection of monovalent cations and anions by
NF was not affected. For example, the percentage
rejection of Cl– ion was 11.6 %, while after three years,
the membrane rejection was 9.62 %. The rejection of
SO4– ions was 97.22 % with the new membrane, while
after 3 years the membrane rejection was 61.43 %. A
strong rejection was observed for polyvalent cations and
anions by NF.46
Figure 9 and Table 1 show the percent decline of RO
for the treatment of waste water containing cations and
anions. It is clear that the decline in the performance of
RO was higher during 3 years operation. This decline in
performance could be attributed to fouling and bio-
fouling on the surface of the membrane. In conclusion,
this promising method, based on these results, suggests
replacing the old membrane by a new product. Where
the % decline of performance of membrane (decline %)
can be calculate as follows in Equation (2):
decline % =
c d
c
−
× 100 (2)
c – rejection of new membrane, d – rejection of old
membrane
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MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 7: Comparison of the performance of RO membranes during 3
years of operation
Slika 7: Primerjava zmogljivosti RO-membran med triletnim obrato-
vanjem
Figure 5: Percentage rejection of TDS versus feed concentration for
RO and NF membranes
Slika 5: Odstotek zavrnitev TDS v odvisnosti od vstopne koncentra-
cije pri RO- in NF-membranah
Figure 8: Comparison of the performance of NF membranes during 3
years operation
Slika 8: Primerjava zmogljivosti NF membrane med triletnim obrato-
vanjem
Figure 6: Effect of pH on removing sodium ions using RO and NF
membranes
Slika 6: Vpliv pH na odstranitev ionov natrija, z uporabo RO in NF
membran
Table 1: Percentage decline of the performance of RO
Tabela 1: Odstotek zmanj{anja zmogljivosti RO
Species % decline of performance of RO
Ca2+ 28.38
Mg2+ 20.39
Na+ 21.98
Cl– 53.45
SO42– 31.73
Figure 10 and Table 2 show the percent decline in
the performance of NF for the treatment of wastewater
containing cations and anions. It is clear that the decline
in the performance of NF was higher during 3 years
operation, which might be due to fouling and biofouling
on the surface of the membrane. The results of this
investigation suggest that the old membrane should be
replaced with the new product.
Table 2: Percentage decline of the performance of NF
Tabela 2: Odstotek padanja zmogljivosti pri NF
Species % decline of performance of NF
Ca2+ 37.67
Mg2+ 12.72
Na+ 9.37
Cl– 16.97
SO42– 36.81
4.1 Factors affecting the decline performance of the
membrane
There are many factors that affect the performance of
membranes, such as membrane fouling and biofouling,
membrane degradation by oxidation and hydrolysis,
mechanical damage, inorganic colloids, adsorbed orga-
nics, coagulants, silica scale and other inorganic scale
and fouling with waste water. In general, biofouling and
fouling are the major constraints that cause a decline in
the performance of membranes. In order to find the pos-
sible reasons causing a decline in membrane perfor-
mance, membrane autopsy was conducted to collect
sheet membrane samples for examination by using
energy-dispersive x-ray to analyze the fouling deposit.
Also, Fourier-transform infrared spectroscopy was used
to identify the components of the deposition that deposit
on the membrane. In addition, SEM can be used with the
membrane samples to show the advanced fouling on the
membrane surface
4.2 Factors to control membrane fouling
Many factors can be used to control the membrane
fouling, these are:
1. Pretreatment for the water.
2. Membrane cleaning in the early stages of fouling.
3. Control of bacterial growth by depriving bacteria
from nutrition by controlling the organic content in
the feed water.
4. Efficient control of membrane fouling by proper sani-
tization of membrane system by using chlorination or
UV.
5 CONCLUSIONS
Nano-filtration (NF) is very effective in removing
polyvalent cations and anions such as SO4– (where the
percent rejection of SO4– ions was 97.22 %). While the
RO membrane is very effective in removing all ions,
especially the monovalent cations and anions such as Cl–,
where the percent rejection of Cl– ions was 94.4 %. The
decline in the performance of RO and NF was very
significant after 3 years of operation, attributed mainly to
fouling and biofouling on the surface of the membrane.
The study results suggested strongly to replace the old
membranes with new ones to improve the system
performance and efficiency for wastewater treatment on
a cost-effective basis.
5.1 Recommendations and suggestions
1. Change the membrane for a new one.
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Figure 10: Percentage decline of the performance of NF during 3
years operation
Slika 10: Odstotek padanja zmogljivosti NF med triletnim obrato-
vanjem
Figure 9: Percentage decline of the performance of RO during 3 years
operation
Slika 9: Odstotek zmanj{anja zmogljivosti RO med triletnim obrato-
vanjem
2. Observe the performance after fixing a new mem-
brane and backwash after 10 % of decline in perfor-
mance.
3. Conduct training for the technicians in RO and NF
systems maintenance, including the backwash and
fouling problems.
4. Regular cleaning of the membrane to improve reco-
very of the membrane.
5. Conduct autopsy of the membrane to know the exact
reason for the decline of performance.
6. Use an alternate membrane, such as a ceramic mem-
brane.
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