Vol. 7(1), 23-32 (2012)
Current World Environment
Reverse Osmosis Pretreatment: Removal
of Iron in Groundwater Desalination Plant in
Shupramant-Giza - A Case Study
AL-SAYED M. ALY¹, MAHMOUD M. KAMEL², A. HAMDY¹*,
KHALED Z. MOHAMMED¹ and MOHAMED A. ABBAS¹
¹Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo (Egypt).
²Chemistry Department, Al-Azhar University (Assuit Branch) (Egypt).
(Received: March 18, 2012; Accepted: May 20, 2012)
ABSTRACT
Reverse osmosis (RO) is being increasingly utilized throughout the world for desalination
due to the latest improvements in RO membrane performance and its reduced cost compared to
thermal desalination. In this paper, Different media and chemicals have been used for Iron removal
to prevent membrane fouling of groundwater reverse osmosis plant located in Shupramant-Giza.
The objective is to present field results of the reverse osmosis plant operation in order to evaluate
the reliability of this technology. The operating pressure and pressure drop increased significantly
without an increase in the production capacity. Frequent shutdowns of the plant were observed
due to severe membrane fouling. The membrane was cleaned with different chemical solutions to
dissolve the deposits from the membrane surface. To achieve high cleaning efficiency, the flow
rate of desalinated water and total dissolved salts (TDS) were studied.
Key Words: Reverse osmosis (RO); desalination; groundwater; fouling.
INTRODUCTION
Due to recent developments in membrane
technology, the trend in the desalination industry is
to use reverse osmosis (RO) for desalting seawater.
Brackish water (BW) desalination using membrane
technology is also expanding as the salinity of
groundwater increases. Selecting an appropriate
process to meet specific needs at specific locations
is essential though the biggest challenge remains
in the capability to successfully operate these plants
once installed due to peculiarities of sea and
brackish waters in the region1. Membrane filtration
in general and reverse osmosis (RO) in particular
is applied in a wide range of fields, such as
chemical, medical, textile, petrochemical,
electrochemical, water treatment, biotechnology
and environmental industries2.
Fouling and scaling are the most serious
problems in membrane processes. In sea/brackish
water applications, pretreatment of RO feed water
is the key step in designing the plants to avoid
membrane fouling and scaling1. At the present time,
pretreatment technology is divided into
conventional pre-treatment and non-conventional
pre-treatment. Conventional RO pre-treatment has
been widely applied for sea and ground water RO
plants to achieve the expected quality of feed water
to the RO membrane. But with the deterioration of
feed waters and the consideration of the less
efficient conventional system, an increasing number
of plant owners were considering the use of
membrane based pretreatments3.
Iron is found in surface and ground waters
at varying concentration levels, usually up to 3–4
mg/l and in some cases up to 15 mg/l4. Sharma ; et
al., found that when present, even at low
concentrations it can be linked to aesthetic and
operational problems such as bad taste and color,
staining, as well as deposition in the water
distribution system leading to incidence of high
turbidity5. Also, iron promotes the growth of certain
24
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
types of chlorine-tolerant microorganisms in water
distribution systems, thus causing increased costs
for cleaning and sterilizing systems in addition to
odor and taste problems. The highest permitted limit
of iron concentration for drinking water is 0.2 mg/l6.
Chemical cleaning of membrane means
removing impurities by means of chemical agents.
The first step of chemical washing is finding
appropriate materials as cleaning agents. This
depends on feed composition and precipitated
layers on the membrane surface and in most cases
is performed using a trial and error method7. The
cleaning agents must be able to dissolve most of
the precipitated materials and remove them from
the surface of membrane with no surface damage8.
The
FilmTec
Cor poration
was
established in 1977 with the introduction of the
FILMTEC FT30 reverse osmosis membranes
which was the first commercially viable thin-film
composite polyamide membrane for brackish
water treatment. The FilmTec Corporation was
purchased by the Dow chemical company in 1985,
a move that merged Dow’s sales and marketing
strength and expertise in polymer and membrane
research with FilmTec’s membrane research,
manufacturing and technical service resources9.
This paper includes evaluation to compare
performance results during operation and
operating cost of conventional media filtration,
which is one of the most important decision-making
bases for choosing feasible pretreatment methods.
Raw Water Characteristics
The raw water coming from two wells
contains ca. 2 g/l total dissolved solids,
predominantly chloride and sodium ions. The
increase in the salinity represents only dissolved
salts. Iron and manganese often occur together in
groundwater but manganese usually occurs in
much lower concentration than iron. Both iron and
manganese are readily apparent in drinking water
supplies. The highest permitted limit of iron
concentration for drinking water is 0.2 mg/l6. The
feed water temperature is almost ranged in all
seasons between 20 and 42°C. Raw water analysis
by an Atomic Absorption Spectrometer (Perkine
Elmer Flame AAS 3110) is presented in Table1.
RO Plant Characteristics
The feed water is supplied with two feed
pumps with a specification: stainless steel 304, 20
m3/h – 5 bar max, kw 5.5, IP 55, class F. Feed water
pumps are followed by dual media filter vessel. This
vessel constructed of a fiberglass reinforced
polyester resin for standard water conditioning use
with specific size (diameter 13 inches (330 mm)
and height 54 inches (1372 mm)), maximum
operating pressure 150psi (10.34 bars), maximum
operating temperature 120o F (48o C), bed capacity
in liters is 105 and the top opening of this vessel is
2½ inches. Dual media filter vessel has two layers
of filtration media – typical design includes
anthracite10, with effective size: 0.6-0.8 mm, sand11,
0.45-0.55 mm, and/or gravel, 2.0-3.0 mm, Table 2.
The vessel which used as media filter is
controlled by automatic head conditioning controller
that is a simple mechanical design, two valve body
designs, one for downflow regeneration and one
for upflow. Head controller has a choice of 7 or 12day time clock or demand regeneration with either
mechanical or electronic meter. The continues flow
rate up to 20 gpm with regeneration time available
up to 120 minutes and mounting base 2½ inches.
The high pressure pump with a
specification: stainless steel 304, 20 m3/h – 17 bar
max, k w15, IP 55, HP 20 and class F, supplies the
pretreated water to the three membrane pressure
vessels (housings) of the RO plant. Each housing
contains one spiral wound polyamide membranes
(Filmtec BW30-4040), Table 3. The membrane
nominal active surface area is 7.6 m2; its permeate
flow rate is 9.1 m3/d and the minimum salt rejection
is 99.5%. Two flow meters are present to measure
the in-and-out water of RO plant. Finally, the RO
plant was controlled by electrical control panel.
Pretreatment Methods
Granular Media Filtration
Direct filtration, using mono, dual-media
or mixed-media filtration, is the most common
technology used for the filtration of seawater prior
to the RO system. Filtration depends primarily on a
combination of complex physical and chemical
mechanisms, the most important being adsorption.
As water passes through the filter bed, the
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
suspended particles contact and adsorb (stick) onto
the surface of the individual media grains or onto
previously deposited material 13 . To reach the
expected quality of filtrate, the size, surface charge,
and geometry of both suspended solids and filter
media are the most important parameters that need
to be well designed.
Water Desalination Technical Manual
(WDTM), Department of the U.S. Army 14, gave the
following design parameters for single, dual and
mixed-media filtration: 1. Single-media filtration.
Single-media filtration consists of one media. This
media is often small-grained silica sand; however,
anthracite may be used after lime and lime-soda
softening. Some desalination pretreatment systems
use an alternate media such as greensand to
remove iron and manganese compounds.
Diatomaceous earth media is not recommended
for primary filtration because of its characteristic
high head loss and short run times. 2. Dual media
filtration. Dual media filtration consists of two media
with different specific gravities. The difference
creates a two-layer separation effect: The use of
silica sand or greensand for one layer; or the use of
anthracite for the other layer. The use of dual media
will allow larger quantities of material to be filtered
and will reduce head loss during operation. The
use of two media types will provide a good coarseto-fine filtration process for desalination facilities. 3.
Mixed-media filtration. When three media are used
in filters, a better coarse-to-fine filtration pattern can
be obtained. High density silica sand, garnet, and
anthracite are commonly used to provide the filter
bed. The different media do not stratify completely.
Instead, there is a small amount of intermixing
among the different layers. This gradual change in
media size provides a gradient from coarse to fine
and creates a media flow pattern necessary to
achieve a very low silt density index.
In this case, Dual media filter have two
layers of filtration media – typical design includes
anthracite, sand and/or gravel, Table3. The depth
of the filter bed is typically a function of the media
size and follows the general rule-of-thumb that the
ratio between the depth of the filter bed (l - in
millimeters) and the effective size of the filter media
(de - in millimeters), l/de, should be higher than 1500.
For example, if the effective size of the anthracite
25
media is selected to be 0.6 to 0.8 mm, the depth of
the anthracite bed should be at least (0.6 mm ×
1500= 900 mm to 0.8 mm × 1500= 1200 mm, i.e.,
0.9-1.2 m)15.
In comparison to single sand filter media,
dual filter media with anthracite over sand permit
more penetration of the suspended matter into the
filter bed, thus resulting in more efficient filtration
and longer runs between cleaning. Periodically,
when the differential pressure increase between
the inlet and outlet of the pressure filter is 0.3–0.6
bar, and about 1.4 m for the gravity filter, the filter is
backwashed and rinsed to carry away the deposited
matter. Backwash time is normally about 10-120
min. Before a backwashed filter is placed back into
service, it must be rinsed to drain until the filtrate
meets the specification16.
Last, to protect the RO membrane from
the breakthrough particles from media filtration,
cartridge filters are usually recommended in the
last step of a pre-treatment sequence. The pore size
from 1 to 20 µm can be used based on different
produced water quality from media filtration14.
In this case, we used cartridge filter with pore size 5
µm and length 20 inches. After filtration through
these filters, the turbidity reduced from 3.87 NTU to
0.24 NTU.
Scale Inhibition
Scale inhibitors (antiscalants) can be used
to prevent or control scaling. There are generally
three different types of scale inhibitors: sodium hexametaphosphate (SHMP), organophosphonates and
polyacrylates. According to FILMTEC Reverse
Osmosis Membranes Technical Manual 17, SHMP
is inexpensive but unstable compared to polymeric
organic scale inhibitors. Hydrolysis of SHMP will
not only decrease the scale inhibition efficiency,
but also create a calcium phosphate scaling risk.
Therefore, SHMP is generally not recommended.
Organo-phosphonates are more effective and
stable than SHMP. They act as anti- foulants for
insoluble iron, keeping them in solution.
Polyacrylates (high molecular weight) are generally
known for reducing silica scale formation via a
dispersion mechanism. Dosage rates on all
antiscalants should be based on the antiscalant
manufacturers. Overdosing should be avoided to
26
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
make certain that no significant amounts of cationic
polymers are present when adding an anionic scale
inhibitor18.
In this case study, injection of antiscalant
has done by chemical dosing pump (5 liters/7bars).
Feed water pH was reduced from 6.78 to 6.52 by the
effect of Permatreat 510 antiscalant which is a
mixture of polymers and phosphonates. This
antiscalant is specifically developed for groundwater
with a high content of silica, and it is also effective
with respect to precipitation of calcium salts
(carbonate, sulfate and fluoride) and the fouling of
iron (iron reduced from 3.8 mg/l to 3.12 mg/l).
pH Adjustment
Acidity (pH) adjustment is an efficient way
to control scaling. By adding H + as acid, the
equilibrium can be shifted to keep salts dissolved.
Adjustment chemicals to the pH include carbon
dioxide, sulfuric acid, and hydrochloric acid. Carbon
dioxide should not be used for pH adjustment of
lime addition systems due to scaling problem
associated with lime pretreatment. Sulfuric acid is
easier to handle and in many countries more
readily available than hydrochloric acid; however,
additional sulfate is added to the feed stream,
potentially causing sulfate scaling13.
In this case, it should be known that the
pH is always changed significantly and the pH must
be returned to a neutral state for the final produced
water. At the beginning of the study, sulfuric acid is
used. However, membrane fouling was observed.
In order to stopping this fouling, the acid was then
switched to hydrochloric for the remainder of the
study. After the switch from sulfuric to hydrochloric
acid, the plant worked very well, and the fouling is
not observed according to standard permeate flow
rate (27.3 m3/d) and TDS (50 mg/l).
Iron Removal Strategies
Iron, usually presents in groundwater as
divalent ion (Fe2+) and is considered as source of
membrane scaling. The main target in our case
study is the removal of iron in groundwater before
passing through reverse osmosis membranes as
pretreatment technique to avoid membrane fouling.
Take in account that the antiscalant feeding before
membranes is effective with respect to precipitation.
It reduces iron concentration from 3.8 mg/l to 3.12
mg/l, but this iron level is still the main source of
membrane problems.
In this case, various treatment methods
have been employed to enhance water quality by
removing iron.
Oxidation Processes
Alternative processes have been
proposed in order to facilitate the operation and to
allow the removal of high amounts of iron in the
presence, or absence, of dissolved organic matter.
In both cases, a pH adjustment is necessary to
maintain iron in the dissolved state to avoid
membrane fouling.Ferrous iron is oxidized in air
according to the following reaction:
Fe2+ + (1/4) O2 + H+ ”! Fe3+ + (1/2) H2O
...(1)
Potassium Permanganate and Depth Filtration
Conventional treatment for iron removal
from groundwater consists of oxidation and depth
filtration. Oxygen or stronger oxidants, such as
potassium permanganate (KMnO4), are generally
used for Fe 2+ oxidation. The solid products of
oxidation (FeOOH.H2O) are then filtered through a
granular bed, commonly green sand 19 . The
potassium permanganate dose applied must be
carefully controlled to minimize any excess passing
into supply which could give a pink color to the
water. Potassium permanganate oxidation tends to
form a colloidal precipitates which may not be well
retained by the filters.
Chlorine and Depth Filtration
The removal of iron along with chlorination
step and appropriate dose of chlorine will be
discussed. In particular membrane fouling caused
by oxidized particles, was assessed in depth with
visualization of the membrane surfaces. As shown
in Fig.1, the removal efficiency of dissolved iron
increased very rapidly and reached nearly 100%
within 20 minutes with the appropriate dose of
chlorine, 2.75 mg/L. With a higher dosage of
chlorine 2.75 mg/L, there was no significant
increase in the removal of metal ions but more
serious membrane fouling occurred. The use of
chlorine may be inadvisable when treating waters
containing organic substances due to the possibility
of disinfection byproducts (DBPs) formation.
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
Manganese Greensand
An alternative filter media is manganese
greensand 20 , formed by treating greensand
(glauconite), which is a sodium zeolite, with
manganous sulphate followed by potassium
permanganate. Mn-greensand removes soluble
iron by a process of ion exchange, frequently with
the release of hydrogen ions. The process is
therefore pH dependent, being virtually ineffective
Table 1. Groundwater Composition
Ca++, mg/l
Mg++, mg/l
Na+ , mg/l
K+, mg/l
Mn++, mg/l
Fe++, mg/l
SiO2, mg/l
HCO3, mg/l
Cl–, mg/l
SO42–, mg/l
NO3–, mg/l
F–, mg/l
pH
Turbidity, NTU
Temperature, ºC
Conductivity, µS/cm
TDS, mg/l
107
72
406
8
0.62
3.8
8.33
199
737
297
7.66
0.04
6.78
3.87
20-42
2677
1938
27
below pH 6.0 and very rapid at pH values above
7.5. When the Mn-greensand is saturated it is
regenerated by soaking the filter bed with weak
potassium permanganate solution. This procedure
oxidizes iron on the surface of Mn-greensand
thereby reactivating the exchange sites. It is
reported that the exchange capacity is 1.45 g of Fe
/l of Mn-greensand and that 2.9 g of potassium
permanganate (as a 1% w/v solution) per liter of
Mn-greensand is required for regeneration 21 .
Alternatively, potassium permanganate is
continuously applied to the bed by dosing it at the
filter inlet, which maintains Mn-greensand active
and catalyses the oxidation reaction. Mn-greensand
then acts as a filter medium in addition to catalytic
oxidation of any residual soluble manganese and
is usually capped with a layer of anthracite to achieve
longer filter runs. Operating the bed after oxidation
capacity is exhausted will reduce its service life
and may cause stain.
Oxidation and Microfiltration
This treatment is similar to the conventional
one except that depth filtration is replaced by
microfiltration (MF). The expected advantage of this
treatment is to have a compact separation unit which
produces high quality water from a wide range of
raw water quality. In the present study the MF of
iron oxide suspensions is removed22,23.
Table 2. Pretreatment Media Specifications
Color
Mesh size
Effective size, mm
Bulk Density, lbs./cu. Ft.
Bed depth, inch
Freeboard of bed depth,%
Backwash flow rate,
gpm/sq. ft.
Backwash bed xpansion
of bed depth, %
Service flow rate, gpm/sq.ft.
Sand and
gravel
Light tan
to reddish
brown
Anthracite
Black
Activated
carbon
Black
Manganese
greensand
Black
18x35
0.45-0.55
100
18-30
50
15-20
14x30
0.6-0.8
50
24-36
50
12-18
12x40
0.55-0.75
31
26-30
50
10-12
16x60
0.30-0.35
85
30
50
10-12
20
20-40
30-40
40
1.5-2
5
5
3-5
28
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
Table 3. Filmtec BW30-4040 Specifications 12.
Membrane type
Max. operating temperature, oF (oC)
Max. operating pressure, psi (bar)
Max. feed flow rate, gpm (m3/h)
Active area, ft2 (m2)
Applied pressure, psig (bar)
Permeate flow rate, gpd (m3/d)
Stabilized salt rejection, %
Pressure vessel diameter, inch
Pressure vessel length, inch
Free Chlorine Tolerance, ppm
Polyamide thin film composite
113 (45)
600 (41)
16 (3.6)
82 (7.6)
225 (15.5)
2400 (9.1)
99.5
4
40
<0.1
Table 4. Amberlite IR120Na Data Sheet 25.
Matrix
Functional groups
Ionic form
Total exchange capacity
Harmonic mean size
Minimum bed depth
Service flow rate
Regenerant
Level (g/L)
Concentration (%)
Minimum contact time
Styrene divinylbenzene copolymer
Sulphonates
Na+
≥ 2.0 eq/L
600-800 µm
700 mm
5 to 40 BV/h
NaCl
80-250
10
30 minutes
Fig. 1. Removal efficiency of iron through 60 min. at different chlorine dosages.
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
Finally, under certain conditions, the
presence of free chlorine and other oxidizing
agents, in the oxidation processes, will cause
premature membrane failure. Since oxidation
damage is not covered under warranty, FilmTec
recommends removing residual free chlorine and
other oxidizing agents by another suitable
pretreatment prior to membrane exposure24.
Ion exchange resin
Ion exchange resins are able to remove
many inorganic metal ions from groundwater
including iron. In this case, Amberlite IR120Na,
strong acid cation exchanger was used, Table 4.
Ion exchanger was carried out in a vessel
constructed of a fiberglass reinforced vinylester
resin for standard water de-ionizing use with
specific size (diameter 13 inches and height 54
inches), maximum operating pressure 150psi
(10.34 bars), maximum operating temperature 150o
F (66oC), bed capacity in liters is 105 and the top
opening of this vessel is 2½ inches. The total
hardness concentration averaging 528 mg/L was
passed through sodium charged strong acid cation
exchange resin to reduce the hardness to less than
5 mg/L. Amberlite IR120Na, also treat with other
metal ions like iron and so, the total exchange
capacity is become smaller. The resin was then
regenerated using commercially available extra
coarse water-softening salt (NaCl). This process
was repeated several times to demonstrate that no
irreversible fouling had occurred to resin.
Granular activated carbon
Activated carbon 26 is prepared from a
char form material such as almond, coconut, and
walnut hulls, other woods, and coal. Activated
carbon has the strongest physical adsorption forces
or the highest volume of adsorbing porosity of any
material known to mankind. It is a highly porous
material; therefore, it has an extremely high surface
area for contaminant adsorption27. The objective of
this topic was to determine the effectiveness of
granular activated carbon (GAC) in removing iron
from the groundwater. From these advantages for
granular activated carbon, in this case study, we
used a single-media filter, Table3. The depth of the
GAC media is estimated based on the average
contact time in this media, which is recommended
29
to be 10 to 12 min. For example, if a filter is designed
for a surface loading rate of 4 m3/m2 h, the depth of
the GAC media should be at least 0.66 m (4 m3/m2
h ×10 min/60 min per h=0.66 m to 4 m3/m2 h ×12
min/60 min per h=0.8 m, i.e., 0.66 0.8 m)15. For the
following reasons28, we used the granular activated
carbon in the adsorption of ferrous.
The van der Waals force that forms
multilayer adsorption was overcome by the
adsorbate due to the high ambient temperature 29.
With relatively high room temperature of about 30oC
where the adsorption process occurs, the
chemisorption was more dominant as compared to
the physisorption. The relatively high room
temperature cause the chemical bond to occurs
between the metal ions. Furthermore desorption
will also occur between adsorbate and activated
carbon at high temperature which physically
bonded by the van der Waals force. Adsorbates
which are physically adsorbed onto activated
carbon receive sufficient energy from such high
temperature to overcome the van der Waals force.
Activated carbon has high adsorption
capacity for Fe(II) as compared to others. This may
relate to adsorbate characteristics in terms of
electronegativity. The electronegativity of Fe(II) is
1.8 . In fact, electronegativity is a measure of strength
for element to attract electron. In this case, it would
measure the strength of Fe(II) attach to negative
charge at activated carbon surface. According to
previous literature 30, higher electronegativities
corresponded to the higher adsorption levels of
metal ions onto the GAC.
Another factor that contributes to different
GAC adsorption capacity on metal ion is ionic
radius. Fe(II) has relatively smaller ionic radius than
that of the others since Fe(II) has the higher attractive
charge in nucleus on the electron orbital 29. The
smaller ionic radius of Fe(II) makes it easier to
penetrate into the micropores of the GAC.
There were four major functional groups
on the surface of activated carbon which are
carboxyl, carbonyl, hydroxyl, and lactonized
carboxyl31. All these four functional groups were
promoted to attract cation to it and ion exchange
would occur. Therefore, the Fe(II) which has positive
30
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
charge would react and attach onto GAC surface’s
functional groups with chemically bonded. However,
the actual chemical reaction between the metal ion
and functional groups on the activated carbon
surface was complex and difficult to understand.
In the case of iron, oxidation is followed
by settling and filtration or filtration alone,
depending on the concentration of iron in the water.
In the presence of turbidity (and color) and when
the Fe(II) concentration is greater than about 5 mg/
l, settling or flotation would be assisted by a
coagulant and/or a coagulant aid. Direct filtration is
used when the iron concentration is less than about
5 mg/l 32.
Post-treatment strategies
Post-treatment1 is limited to injection of
lime to increase the pH from 6.52 to 8.0 and chlorine
for disinfection.
Lime Post-treatment
Lime has been added to neutralize the
final produced water. For excess lime injection, it is
necessary to raise pH to approximately 8. The high
pH level produces good disinfection as a by-product
and thus chlorination might be unnecessary after
such injection except for a small dose to provide
residual chlorine in the distribution system.
Carbonation is necessary to remove the excess
lime and reduce the pH after treatment.
Disinfection
Groundwater
may
be
contains
microorganisms such as bacteria, algae, fungi, and
viruses, which can cause serious biological fouling.
There are various methods to prevent and control
biological fouling such as the addition of chemical
oxidants (chlorine, bromine, iodine, or ozone),
ultraviolet irradiation, biofiltration to remove
nutrients, and the addition of biocide. Because of
the risk of oxidation of the membrane, the use of
oxidants must be monitored carefully to keep the
chlorine well below 0.1 mg/L of free chlorine
residual. Sometime dechlorination upstream of the
membranes is required through sulfite compound
addition or passage through granular-activated
carbon 18.
World Health Organization (WHO) 33
considers: ‘it has been demonstrated that virus-free
water can be obtained from faecally polluted source
waters’ if the following chlorine disinfection
conditions are met.
The water has a turbidity of 1
Nephelometric turbidity unit ( NTU) or less, Its pH is
below 8.0, A contact period of at least 30 minutes is
given; and, The chlorine dose applied is sufficient
to achieve at least 0.5 mg/l free residual chlorine
during the whole contact period.
Sodium hypochlorite (NaOCl) was used
in our case study and the injection of hypochlorite
has done by chemical dosing pump (5 liters/7bars)
in dosage 1 mg/l. Typically iron should be less than
0.2 mg/l. If at the point of chlorine application, their
levels are too low to justify disinfection, the dose
must take their demand into account.
Membrane cleaning
The fouling of RO elements is unavoidable
with long-term operation. They can be fouled by
biological matter, colloidal particles, mineral scale,
and insoluble organic constituents. Deposits build
up on the membrane surfaces during operation until
they are causing loss in normalized permeate flow
(product flow rate) and/or loss of normalized salt
rejection [total dissolved salts (TDS)]. Elements
should be cleaned whenever the normalized
permeate flow drops by ≥10%, or the normalized
salt passage increases by ≥10%, or the normalized
differential pressure (feed pressure minus
concentrate pressure) increases by ≥15% from the
reference condition established during the first 48
h of operation. Cleaning procedures are usually
given by the membrane manufacturers17.
In this case, the maximum operating
pressure required is 15.5 bar and maximum
pressure drop is 1 bar increased to 16.5 and 1.5bar,
respectively, without an increase in the standard
permeate (flow rate 27.3 m3/d and TDS 50 mg/l).
Frequent shutdowns of the plant were observed
due to membrane fouling (permeate flow rate is
18.7 m3/d and TDS is 580 mg/l).
In this case, both acidic and alkaline
cleaners can be used. Acid cleaning to remove
mineral scale was done at pH 2 or lower with 0.2%
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
31
(W) hydrochloric. Citric acid can also be used in the
same concentration. Alkaline cleaning to remove
organic fouling was done at pH 12, generally done
with 0.1% (W) sodium hydroxide 24,34. After resolving
the fouling problem, membranes are cleaned with
the first option given by the manufacturer every six
months and the cartridge filters are replaced every
three months1.
conventional and specific pre-treatment methods,
we concluded that, every applied method has
advantages and disadvantages in application. The
most suitable pretreatment technique for iron
removal (concentration less than 5 mg/l) is a
granular activated carbon (GAC) filter which has
higher adsorption capacity and leads to low
operating cost.
CONCLUSIONS
ACKNOWLEDGMENTS
In our case study iron was removed in
groundwater before passing through reverse
osmosis membranes as pretreatment technique to
avoid membrane fouling. Different pretreatment
techniques are done to remove iron and save the
membrane.
The authors express their appreciation to
Prof. Dr. Naglaa Ali and Prof. Dr. Yasser Moustafa,
Egyptian Petroleum Research Institute (EPRI), for
their assistance and revision of this paper. Also, the
authors wish to acknowledge the assistance and
support of this study by Eng. Mohamed Amer,
General Manager of Water Engineering Technology
Co. (WETCO), which agent for each products of
Jacobi Carbon, Clack and DOW.
Many processes affecting the iron removal
from the groundwater are applied in this case study.
From the performance comparison between
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Arras W., Ghaffour N., Hamou A.,
Desalination 235: 170, (2009).
Bodalo-Santoyo A., Gomez-Carrasco J.L.,
Gomez-Gomez E. and Montesinos A.M., ,
Desalination ,160 : 151, (2004).
Wolf P.H., Siverns S.and Monti S.,
Desalination, 182: 293, (2005).
Ellis D., Bouchard C. and Lantagne G.,
Desalination . 130: 255, (2000).
Sharma S.K., Kappelhof J., Groenendijk
M.and Schippers J.C., J. Water Supply Res.
Technol., 50: 187, (2001).
EC-Official Journal of the European
Communities Council Directive 98/83/EC L.
330: 32, (1998).
Madaeni S.S., Mohammadi T. and
Moghadam M.K., Desalination 134: 77,
(2001).
Lindau J.and Jonsson A.S., J. of Membrane
Science 87: 71, (1994).
Redondo J.A. and Lomax I., Desalination,
110 : 167, (1997).
Clack Corporation, Anthracite data sheet
11.
12.
13.
14.
15.
16.
17.
form no. 2354, replaces form 1785, Part no.
A8029, 3 (2011).
Clack Corporation, Filter sand and gravel
data sheet form no. 2352, replaces form 1824,
Part no. A8071, 3 (2011).
Filmtec Reverse Osmosis Membranes,
BW30-4040, Technical bulletin 609-00350804
Chua K.T., Hawlader M.N.A. and Malek A.,
Desalination , 159: 225, (2003).
Headquarters, Department of the Army,
Washington, D.C., Water Desalination
Technical Manual, (1986).
Voutchkov N., Desalination , 261: 354,
(2010).
Voutchkov N.and Dietrich J., Pilot testing
alternative pretreatment systems for
seawater desalination in Carlsbad,
California, Proceedings of World Congress
in Desalination and Reuse, International
Desalination Association, SP05-095,
Singapore, 11-16, (2005).
Filmtec Reverse Osmosis Membranes
32
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
ALY et al., Curr. World Environ., Vol. 7(1), 23-32 (2012)
Technical Manual,( 2004).
Prihasto N., Liu Qi. and Hyun Kim S.,
Desalination, 249: 308, (2009).
Lessard C., Ellis D., J. S &odes and C.
Bouchard, Environment, 32, (1999).
Clack Corporation, manganese greensand
data sheet form no. 2349, replaces form 1564,
Part no. A8041, 3, (2011).
Benefield, L. D. and Judkins, J. F. ,Process
Chemistry for Water and Wastewater
Treatment. Prentice-Hall (1982).
Mourato D. and Smith C., Proc., 6th Workshop
on Drinking Water, AQTE, Montr6al, 705-716,
( 1994).
Cote P., Mourato D. , C.Gungerich, Russell J.
and Houghton E., ISWA Conference,
Membranes in Drinking and Industrial Water
Production, Amsterdam ( 1998).
Filmtec Reverse Osmosis Membranes
Technical bulletin 609-22010/CH172-086-E.
Rohm and Haas Amberlite IR120Na, PDS
0210 A.1997.
Clack Corporation, Activated carbon data
sheet form no. 2348, replaces form 1795 &
1564, Part no. A8009-12, 3, (2011).
Cheremisinoff N.P., Handbook of Water and
Wastewater Treatment Technologies,
Butterworth-Heinemann, Boston, USA, 138:
28.
29.
30.
31.
32.
33.
34.
140, ( 2002).
Ahmad bin Jusoh, Cheng W.H., Low W.M. ,
Ali Nora’aini and Megat Mohd Noor M.J.,
Desalination, 182: 347, (2005) .
Tam Y.K., Studying on Removal of Dye Using
Granular Activated Carbon, Science
Engineering Department, Kolej University of
Science and Teknology Malaysia ( 2003).
Rockstraw D.A. and Dastgheib S.A., Carbon,
40: 1843 (2002).
Keneth E.N. and Chang H.T., Effect of
Surface Functional Groups on the Coefficient
of Freundlich Isotherm, Depar tment of
Chemical and Environmental Engineering,
Illinois Institute of Technology, 1999, http://
www.chee.lit.edu/
chang/index.html,
Accessed 18 April ( 2004).
Ratnayaka Don D., Malcolm J. Brandt and
Michael Johnson K., Water Supply (Sixth
Edition), CHAPTER 10: Specialized and
Advanced Water Treatment Processes, 365:
423, (2009).
WHO ,Guidelines for Drinking-Water Quality,
Vol. 1, Recommendations. 2nd Edn (1993).
Filmtec Reverse Osmosis Membranes
Technical bulletin 609-24010/CH172-120E.