Engineering Procedure

SAEP-348 09 September 2022

Chemical Cleaning, Disinfection, Post Treatment
and Storage of Reverse Osmosis Membranes
Document Responsibility: Process Utility System Standards Committee

Contents

1 Purpose.......................................................... 2
2 Scope............................................................. 2
3 Conflicts and Deviations................................. 3
4 References..................................................... 3
5 Definitions and Privations ……………………. 5
6 Responsibilities.............................................. 4
7 Safety............................................................. 5
8 Cleaning Equipment....................................... 6
9 Membranes Cleaning Frequency................... 7
10 Cleaning Effectiveness …………………………
11 Cleaning Polyamide SW Membranes............ 9
12 Disinfecting Polyamide SW Membranes...... 13
13 Storing Polyamide SW Membranes............. 14
14 Cleaning Polyamide HFF Membranes......... 15
15 Disinfecting Polyamide HFF Membranes..... 20
16 Post-Treating Polyamide HFF Membranes.. 21
17 Storing Polyamide HFF Membranes............ 23
18 Cleaning HFF Cellulose
Triacetate Membranes......................... 24
19 Storing HFF Cellulose
Triacetate Membranes.......................... 25
20 Disposal of Waste water
Appendix.............................................................. 27

Previous Revision: 12 May 2019 Next Revision: 26 April 2020

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 Document Responsibility: Process Utility System Standards Committee SAEP-348
Published: 07 September 2022 Chemical Cleaning, Disinfection, Post Treatment
Next Revision: 26 April 2020 and Storage of Reverse Osmosis Membranes

1 Purpose

For efficient Reverse Osmosis (RO) membranes operation, it is necessary to clean,

disinfect, post- treat, and store RO membranes as per this procedure. This can be
accomplished by one or more of the following steps:
1) Acid cleaning, e.g., citric acid
2) Alkaline cleaning, e.g., detergent cleaning
3) Enhanced sodium hypochlorite cleaning
4) PT-A (polyvinyl methyl ether) post-treatment
5) PT-B (tannic acid) post-treatment
6) Disinfection
7) Storage (short term and long term)

The cleaning frequency of RO membranes will be dictated by the efficiency of RO

pretreatment, antiscalant application, operating recovery, operating pH, bacterial
contamination, etc. This procedure does not override the membrane manufacturers'
cleaning recommendations especially where warranty rights are involved. Differences
shall be questioned and resolved by the proponent and Water Conservation Unit/ Water
Treatment & Conservation Division/EPD.

2 Scope

This procedure covers the following:

2.1 Defines when the RO membranes should be cleaned in order to restore their
productivity and salt rejection. It also defines how to choose the most
appropriate cleaning procedure for removing foulants and scalants from the
membranes.

2.2 Outlines the chemical cleaning equipment that should be used to carry out the
chemical cleaning, disinfection and post-treatment of the RO membranes.

2.3 Describes the low and high pH cleaning for spiral wound (SW) polyamide
membranes. It also outlines all steps that need to be taken for their disinfection
and storage.

2.4 Describes the chemical cleaning of hollow fine fiber (HFF) polyamide
membranes using citric acid, detergent cleaning and the enhanced pH
hypochlorite cleaning procedure for removing biofouling.

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Next Revision: 26 April 2020 and Storage of Reverse Osmosis Membranes

2.5 Describes the post-treatments (PT-A and PT-B) that need to be applied to HFF
polyamide membranes after chemical cleaning to enhance their salt rejection.
It also outlines all steps that need to be taken for their disinfection and storage.

2.6 Describes the chemical cleaning of HFF cellulose triacetate membranes and
their storage.

2.7 Supplements the membrane manufacturers' cleaning procedures. If warranty

rights are involved, the selected cleaning procedures are to be discussed with the
membrane manufacturer and differences to be resolved.

2.8 Appendix A-1 shows a detailed flow diagram of the RO cleaning, disinfecting
post-treatment and flushing equipment. Appendix A-2 provides general
guidelines for choosing the optimum cleaning chemical. Appendix A-3
provides a table for the recommended operating parameters and measurements
log sheet. Appendix A-4 provides a typical clean in place (CIP) log sheet,
Appendix A-5 describes the cleaning solutions for the SW polyamide
membranes, and Appendix A-6 outlines the quality testing procedure for tannic
acid to determine its suitability for membrane post-treatment application.

3 Conflicts and Deviations

Any conflicts between this document and other applicable Mandatory Saudi Aramco
Engineering Requirements (MSAERs) shall be addressed to the EK&RD Coordinator.

Any deviation from the requirements herein shall follow internal company procedure
SAEP-302.

4 References

The requirements contained in the following documents apply to the extent specified in
this procedure.

4.1 Saudi Aramco References

Saudi Aramco Engineering Procedures

SAEP-302 Waiver of a Mandatory Saudi Aramco
Engineering Requirement
SAEP-327 Disposal of Wastewater from Cleaning, Flushing,
and Dewatering Pipelines and Vessels

4.2 Industry Codes and Standards

American Water Works Association (AWWA):

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AWWA B110-09 Membrane Systems

American Membrane Technology Association (AMTA):

AMTA-10 Operation & Maintenance of Membrane Facilities

AMTA-16 Membrane Post Treatment

Technical Service Bulletins, Hydranautics Nitto Denko Company:

TSB -107 Foulants and Cleaning Procedures for composite

polyamide RO Membrane Elements

TSB-108 General Storage Procedures for Composite Polyamide and

Polyvinyl Derivative (PVD) RO Membrane Elements

TSB-110 Biocides for Disinfection and Storage of Hydranautics

Membrane Elements

TSB-118 Membrane Flushing Guidelines.

5 Definitions and Privations:

PT-A: Post treatment of RO membranes using polyvinyl methyl ether.

PT-B: Post treatment of RO membranes using tannic acid.

EDTA: Ethylene diamine tetra acetic acid

Hollow Fine Fiber (HFF) RO Membranes: One of four RO membrane configurations

(others are spiral wound, plate and frame, and tubular). Hollow fine fiber membranes
are made of extruded cellulose acetate or polyamide material. Pressurized feed water

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passes across the fiber (outside-inside). Pure water permeates the fibers and is collected
at the end of the element.

Spiral Wound RO Membranes: A membrane configuration, which is comprised of “flat

sheet membrane-permeate channel spacer - flat sheet membrane - feed channel spacer”
combinations rolled up around a product collection tube.

Polyamide (PA) Membrane (sometimes referred as thin film composite membrane): It is

a membrane that’s composed of three layers. The top layer is an ultra-thin asymmetric
aromatic polyamide polymer deposited on top of a micro porous layer made from
Polyethersulfone or polysulfone. The bottom layer is basically a polyester fabric support
base. The thin polyamide film is the salt rejecting layer where the two base layers
provide a porous structure support.

Cellulose Acetate (CA) Membrane: Asymmetric membrane made of cellulose diacetate

or triacetate (or a blend of both) that’s composed of three layers. The top dense surface
skin “membrane” and the thick, porous supporting under layers have exactly the same
polymer and chemical composition but are structurally dissimilar.

Membrane Element: Often referred to as a module or bundle, elements are the physical
devices that house the membrane. Spiral wound systems can have up to six elements per
pressure vessel. Hollow fiber RO systems usually have only one element per pressure
vessel.

Pressure Vessel: This is a tubular device, which contains the membrane elements. For
spiral wound elements the pressure vessel often is referred to as the pressure tube or
housing and can contain up to eight membrane elements (usually six). In hollow fiber
systems the pressure vessel is often referred to as the “Permeator.”

Permeate: Often referred to as “product,” permeate is the portion of the feedwater

stream which passes through the membrane.

Permeate = Feedwater – Concentrate

Osmotic Pressure: Is the pressure required to prevent the flow of water across a
semipermeable membrane separating two solutions having different ionic strengths. For
RO systems it is osmotic pressure that has to be overcome in order to produce permeate.

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A “rule of thumb” is for every 100 mg/L of TDS difference between feed and permeate,
1 psi of osmotic pressure exists.

Normalized Permeate Flow (NPF): is a calculation that allows the comparison of a

measured permeate flow rate to a standard (or start up) condition. Permeate flow is a
function of Net Driving Pressure (NDP), temperature and membrane condition.

Pressure Drop (psi) = Feed Pressure – Reject Pressure = FP - RP

Net Driving Pressure (NDP): the difference between the feed pressure, the osmotic
pressure and permeate back pressure. It is the measure of the actual driving pressure

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available to force the water through the membrane. As net driving pressure increases,
the flux increases proportionally (given all other factors remain constant).

Normalized Permeate Flow = NDPSU / NDPTODAY x TCF X PF

Net Driving Pressure = FP – Δπ - Pp

NDPSU = Average NDP at start up

NDPTODAY = Average NDP today

TCF = Temperature correction factor

PF = Permeate flow today

Δπ = Feed osmotic pressure – Permeate osmotic pressure

Recovery: Recovery is the percentage of the feed water, which passes through the
membranes into the permeate stream (sometimes referred to as conversion). It is usually
expressed in percentage.

Recovery (%) = (Permeate Flow rate / Feed flow rate) X 100 = (PF / FF) X 100

Salt Passage: The quantity of salt, as a percentage, which passes through the membrane
into to the permeate stream. Salt passage is a function of temperature, velocity and
concentration gradient (i.e., concentration of salt in the brine versus the permeate).

% Salt passage = [(TDS of permeate) / (TDS of feed)] x 100

Salt Rejection: The quantity of salt removed from the feed water stream as a percentage.

% Salt Rejection = [(TDS of feed – TDS of permeate) / (TDS of feed)] x 100

Note: Salt Rejection = 1 - Salt Passage

6 Responsibilities

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The facility operating department takes over the responsibilities for cleaning RO
membranes after the membranes are commissioned, and handed over to Operations.

6.1 Facility Operating Department

Has the overall responsibility for the operational chemical cleaning.

6.1.1 Maintenance
a) Provide maintenance support during the chemical cleaning
operation.
b) Coordinate chemical cleaning.

6.1.2 Operations Engineering

a) Advise and assist the foreman of the RO plant during all
chemical cleaning, disinfection, post-treatment and storage
activities involving the RO membranes and all associated
equipment.
b) During the chemical cleaning, disinfection, post-treatment and
storage of RO membranes, act as a technical representative to
facility operator.
c) Ensure adequate safety procedures and precautions are taken.
d) Coordinate and obtain the approval of chemical cleaning
procedures and formulations from the Materials Engineering and
Corrosion Water Conservation Unit/ Water Treatment &
Conservation Division/Consulting Services Department
(ME&CWCU/WT&CD/EPD), waste disposal plans per SAEP-
327 from Environmental Engineering Division/ Environment
Protection Department (EED/EPD) and the Research and
Development Center (R&DC). Maintain history of membranes
chemical cleaning, post-treatment and storage. Incorporate
relevant reports and data into permanent plant records.

6.2 Regional Laboratories

a) Perform chemical analysis, monitor and log chemical cleaning analyses
and foulant/scalant removal rates on-site during actual cleaning operations.
b) Verify the purity of solvents and chemicals used for chemical cleaning.

6.3 Environmental Protection Department/WT&CD/WCU

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a) Review and approve RO membranes cleaning, sanitization, post-treatment

and storage procedures
b) Provide specialist/consultant advice on request, during RO membrane
cleaning, disinfection, post-treatment and storage.

7 Safety

7.1 Wear all the necessary personal protective equipment and take all necessary
precautions when handling hazardous cleaning chemicals. These should
include: Eye and face protection from splashes (goggles and face shields),
hearing protection (ear plugs), head protection (hard hat), body protection,
(rubber gloves, rubber boots, proper personal clothing), and respiratory
protective equipment.

7.2 Have all the Material Safety Data Sheets (MSDS) available on site for all of the
cleaning chemicals to be used.

7.3 Add acids and caustic to water, not vice versa (apply continuous stirring to
dissipate the heat produced).

7.4 Have an eye wash and a safety shower in the vicinity of the chemical cleaning
area.

7.5 Mark dangerous chemicals and store them in designated areas.

7.6 Use cover on the chemical mixing tank to avoid splashes and a fan extractor for
produced fumes as indicated in figure 1 of Appendix A-1. If a procedure
produces fumes wear respiratory equipment such as Scott Air Pack or Self
Contained Breathing Apparatus (SCBA).

7.7 Be aware of chemical leaks during chemical cleaning (wear protective

equipment for eyes, face, hands and feet).

7.8 Follow work permit procedures when installing blinds

7.9 Pressure test to 1.5 x the recommended chemical cleaning pressure any
temporary connections to avoid chemical leaks during chemical solution
circulation.

7.10 To report emergencies ring 110 utilizing the following steps

a) Provide location of the emergency
b) Nature of the emergency
c) Name and badge number of caller
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d) Repeat the above three steps

e) Wait for further instructions before hanging up

8 Cleaning Equipment

The equipment for cleaning, disinfection, post-treatment and flushing of RO membranes

is shown in Figure 1 in Appendix A-1. The materials of construction of the cleaning
equipment must be chemically compatible with all chemicals used and corrosion
resistant.

8.1 The mixing tank shall be made of non-corrosive materials such as reinforced
plastic and should be sized for a minimum of three-minute retention time,
considering the number of membrane elements to be cleaned at one time and the
volume of the liquid in the cleaning pump and piping. It should be provided
with a cover, exhaust fan to outside of building, mixer, cooling coil, temperature
indicator and temperature alarm. A valve at the bottom of the mixing tank is
needed to assure that the tank can be completely drained and flushed of waste
chemical solutions.

8.2 The chemical cleaning skid can be placed on fixed foundation or it could be
mobile by being placed on railings so that it can easily be moved from one RO
unit to the next. Similarly, the piping can be hard piping or flexible hosing. For
a mobile CIP skid a flexible vent hose to fan will be required.

8.3 Temperature indicator and temperature alarm are required to ensure that the
temperature of the cleaning solution will not exceed the temperature limit set in
the procedures of this specification. Heat added by pumping and dilution of
chemicals will cause a rise in cleaning solution temperature.

8.4 The circulation pump should be 316 stainless steel (SS) or nonmetallic
compatible with the chemicals mentioned in Appendices A-5 and sized for the
flow and pressures that are required by the various procedures in this standard.
A centrifugal pump is most suitable for flexibility and safety.

8.5 If flexible hoses are to be used for supply and return lines, these should be of
adequate pressure ratings as required in the cleaning procedures of this
document. The use of quick lock connections makes flexible hose handling easy
and reliable.

8.6 Provisions should be made to send both the concentrate and permeate to drain
and back to the mixing tank during cleaning. During the initial recirculation of
the cleaning solution, it is sometimes desirable to allow the cleaning solution to
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run to drain if it is highly discolored with foulants or scalants which is removed

from the membranes. The cleaning solution return should not be throttled.
Permeate and concentrate streams should be returned below the liquid surface in
the mixing tank to minimize foaming. A flow recycle line should be installed
from the cleaning pump discharge to the mixing tank. This flow recycle is
needed to control the fluid velocity through the membranes so that it does not
exceed the membrane bundle pressure drop guideline during cleaning.

8.7 A strainer and a 5-10 micron cartridge filter should be installed to avoid
circulating sediment which may dislodge from the system during the cleaning
operation. The cartridge filtration should be located on the pump discharge and
not the return to the tank.

8.8 Flow meters are needed to establish proper flow rates through the membranes.
The flow requirements for effective membrane cleaning, disinfection, post-
treatment and flushing vary. These flow requirements are stated in the various
procedures of this specification. Sampling ports are needed for monitoring the
progress of the cleaning operation.

9 Membranes Cleaning Frequency

Membrane chemical cleaning is generally required when any of the following

conditions occur:
• A 10-15% decrease in normalized permeate flow (NPF)
• A 10-15% increase in salt passage (SP)
• A 10-15% increase in feed pressure to maintain normalized permeate flow.
• A 10-15% increase in differential pressure (DP) across all or part of a reverse
osmosis system. (This is what is recommended by membrane manufactures.
However, a maximum DP of 60 psi can be tolerated).

Knowing the nature of the membrane foulants will help in deciding the optimum
cleaning chemical or combination of chemicals (see Appendix A-2).

Adopt the following general precautions in selecting and using a cleaning chemical
1) Whether proprietary or generic chemicals are used, make sure that the chemical
has been qualified for use by the membrane manufacturer.
2) Use the least harsh cleaning regime to optimize the useful life of the membranes.
This includes the cleaning parameters of pH, temperature, and contact time.
3) Clean at the recommended temperature.

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Membrane foulants are typically mixtures of two or more of the following:

• Scale (e.g., CaCO3, CaSO4, and BaSO4)
• Bacteria and bacterial slime
• Organic debris (e.g., algae)
• Colloids (clays, silicates)
• Metal hydroxides
• Chemical precipitates

Clean RO systems sequentially, usually acidic cleaning followed by alkaline cleaning.

Foulants deposits are complex mixtures and do not always get removed by a single
cleaning. When the sequential technique is applied it is generally most effective to
begin with acid cleaning. An exception to this practice is when the foulant is organic.
For organic fouling alkaline cleaning should precede acid cleaning. The cleaning
procedure should be selected after determining if scaling, particulate fouling, or
biofouling are suspected (see Appendix A-2).

To determine the cause of fouling, operating records (see Appendix A-3) should be
reviewed and instruments checked. It is often very helpful to conduct complete water
analyses and microbiological assays on samples taken throughout the system. In the
event where an element has failed, it is very beneficial to have it opened and examined
(perform autopsy).

Scaling is suspected when there is decreased salt rejection, increased pressure drop in
the final stage, and decreased normalized permeate flow. Scaling first occurs in the
final stage, where the brine is more concentrated and the solubility of the scale forming
ions is exceeded. When scaling occurs in one element, it will always occur in the
following elements since the brine becomes more concentrated as it passes from one
element to the next.

Fouling by particulates or bacteria is suspected when there is increased pressure drop

and decreased normalized permeate flow.

The pH exposure time, flow rate, and temperature of the cleaning solution need to be
considered when planning the cleaning. Compatibility of the cleaner with the
membrane is also critical. Every membrane has limited pH and temperature ranges and
chemical reactivity vary for different membranes.

Acid or low pH cleaning is often the first step, especially when scaling is suspected.

Typical low pH cleaner is the 2% wt. ammoniated citric acid.

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The citric acid cleaning is effective for removing calcium carbonate and iron oxide
scales that must be removed before attempting to use a high pH cleaner since calcium
carbonate and iron are highly insoluble at high pH. A chelant such as EDTA can also
be used to remove metal salts. Iron and calcium carbonate can be successfully
removed, however, some inorganic compounds are very difficult to remove when they
have deposited on membrane surfaces. These include the following:
• Calcium sulfate
• Barium sulfate
• Strontium sulfate
• Silica
• Elemental sulfur

The most common high pH cleaners are:

• 1% Sodium tripolyphosphate
• 1% Trisodium phosphate
• 1% Sodium hydroxide
• Laundry detergents

These cleaners are effective in removing clay and silt particles, biofilms, and certain
organics. High cleaner flow rates are preferred when using these cleaners since the
mechanical action of the cleaner passing over the deposits helps to remove them.

When high and low pH cleaners have failed to restore performance and biofouling is
suspected, it may be necessary to disinfect the RO unit. Disinfection may be
accomplished by using a biocide such as sodium hypochlorite. Disinfection chemicals
are very reactive with membranes. Their application should be carried out only by
experienced personnel who will consider all the necessary parameters that need to be
taken care of, such as temperature, pH and contact time.

10 Cleaning Effectiveness

Effectiveness of cleaning RO membranes shall be determined after 24 hours of

operating the cleaned RO membranes. It can be measured by comparing the normalized
permeate flow (NPF) and normalized pressure drop (NPD) after cleaning with that
when the membranes are new or clean. The cleaning process is considered effective if
the following criteria is met:

• NPF after cleaning is equal or close to NPF when new or clean

• NPD after cleaning is equal or close to NPD when new or clean

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During the cleaning process, it’s better to continue cleaning as far as changes are seen in
the cleaning parameters. You can stop cleaning when you observe no changes in pH,
feed pressure, differential pressure and flow. Continue to clean until no changes occur
over 15-30 minutes period of time.

11 Cleaning Polyamide SW Membranes

11.1 Preparation for Membranes Cleaning

11.1.1 Ensure that all required chemicals are available and in sufficient
quantities.

11.1.2 Ensure that all instruments, e.g., conductivity, meters, pH meter, flow
meters, temperature meters are properly calibrated and working reliably.

11.1.3 Apply all safety procedures as per the safety Section 6, paragraphs 6.6
to 6.10.

11.1.4 Conduct conductivity and DP profile on the RO Module to be cleaned

and record the RO module operating data (feed pressure, product flow,
recovery, unit DP, salt passage, temperature, and product pressure).

11.1.5 Stop RO module to be cleaned and flush per the normal procedure
using chlorine free product (CFP) water. Normal procedure flush is a
once through flush with CFP water (brine and product to drain).
Do not exceed maximum allowed DP (0.7 bar per SW element in
housing). Use a flushing pressure of 100 psig.

11.1.6 If RO skid consists of two stages, install a blind flange (if there is no
isolation valve) between the stages to be cleaned and conduct the
cleaning on each stage separately.

11.1.7 Prepare the log book or cleaning log sheet to record all the chemical
cleaning parameters (e.g., flow, pressure, pH, conductivity, chemical
concentration, circulation time, temperature, etc.) during all steps [see
clean in place (CIP) log sheet in Appendix A-4].

11.2 Estimating the Cleaner Quantity for SW Membranes

The cleaner quantity in the tank should take into consideration the following:
• The water volume contained in the hoses or piping
• The water volume contained in the pressure vessels.
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11.2.1 The water contained in the hoses or piping can be determined by

following two ways:
a) Fill the cleaning tank to the desired level with water, e.g.,
200 gallons. Then fill the hoses or piping with the cleaning
pump. Loss in tank volume equals the hose or piping volume.
b) Hose volume may also be estimated mathematically from hose
diameter and length (see Table 1).

11.2.2 The volume of water contained within the elements in the pressure
vessels may be estimated from Table 2. The total volume of water may
be estimated by multiplying with the number of elements to be cleaned.

Table 1 – Calculation of Hose Volumes

Hose Diameter Hose Volume
Inches Gallons/Foot
2 0.16
3 0.37
4 0.65

Table 2 – Estimation of Element Volumes in Pressure Vessels

Element Diameter Element Length Gallons
Inches Inches Per SW Element
4 40 2
6 40 3.5
8 40 6

11.3 Ammoniated Citric Acid (pH 4.0 - 4.5) Cleaning for SW Membranes

11.3.1 Flush the membranes in the pressure vessels for 5 minutes (once
through flush reject and product to waste) by pumping chlorine free
product (CFP) water from the cleaning tank. Apply 60 psi (4 bars)
flushing pressure and flow rate of 6 gpm x number of 8-inch elements
to be cleaned. This flow rate is expected to be 24 to 40 gpm per
pressure vessel.

11.3.2 Fill cleaning tank to required level with CFP water (work out the total
volume including piping and housing vessels as per 8.2.1 and 8.2.2).
Ensure that there is sufficient water in the mix tank to permit
circulation through the piping and membranes without causing vortex
formation in the tank. Vortex formation can result in air being drawn
into the pump causing a loss of prime.
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11.3.3 Start stirrer and gradually add citric acid (C6H8O7) to prepare a
2 wt percent solution (Solution 1, see Appendix A-5). Add 7.6 kg of
citric acid (as 100% powder) per 100 gallons of water. Adjust the
temperature of the solution in the tank to about 104°F (40°C).
Citric acid may be pre-dissolved in a separate container before adding
it to the mix tank.
11.3.4 Allow mixing for 10 minutes and measure the solution pH from top
and bottom of the cleaning tank. Adjust pH of citric acid solution to
4.0 - 4.5 using small quantities of ammonium hydroxide (if required).
Wear protective equipment including a respirator to prevent inhalation
of ammonia fumes. Measure the total iron and calcium in the citric acid
solution and record it in the cleaning log sheet. 11.3.5 Check out
piping, valve positions, pump selection, etc. Open chemical tank
valves (pump suction, brine return and product return valves). Allow
few minutes priming by venting out air from all piping high points.

11.3.6 With chemical cleaning pump discharge valve partially closed, start
chemical cleaning pump. Adjust flow 6 gpm x number of 8-inch
elements and pressure of 60 psig. Send to drain the first 20% of
solution. Monitor DP and ensure it stays below 60 psi (4.0 bars) at all
times.

11.3.7 Ensure that the temperature of the solution is equal or less than 104°F
(40°C) and that the solution pH is 4.0 - 4.5.

11.3.8 Continue circulation of the cleaning solution for 5-6 hours. Monitor
iron levels, calcium levels, pH and DP drop. Check visual appearance
of solution.
Commentary Note:

As iron is removed from the membrane surfaces, it turns green and if excessive
quantities are removed, solution turns brownish.

11.3.9 If the color is brownish and iron concentration in the solution is

> 10 ppm, dump the solution and prepare another batch.

11.3.10 When iron and/or calcium levels in three consecutive samples taken 15
minutes apart are the same (within 10% difference) stop cleaning.
Divert brine return and product return to drain. Drain chemical tank.

11.3.11 Flush the membranes as per 10.3.1. If further rinsing is required fill
the cleaning tank and flush the membranes again.
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Commentary Note:

Step 9.3.8 can be replaced with an optional soak and recirculation sequence if
required. This involves stopping after 30 minutes of circulation and allow
soaking for 15 minutes. Continue with circulation/soaking whilst checking
pH, iron, calcium and DP drop.

11.4 Detergent Cleaning (pH 10) for Polyamide SW Membranes

11.4.1 Fill cleaning tank as per 10.3.2.

11.4.2 Start the stirrer and add sodium hydroxide to reach pH of 9.0.
Circulate the cleaning solution through the membranes for
10-15 minutes to neutralize any acidity in the membranes. Stop
membrane circulation and continue circulating within the tank.

11.4.3 Add more sodium hydroxide to reach pH of 10.0. Make up 2 wt

percent solution of sodium tripolyphosphate (Na5P3O10) and 0.8 wt
percent of Na-EDTA (sodium salt of ethylaminediaminetetraacetic
acid). This is known as Solution 2 (see Appendix A-5). The pH
adopted during the detergent cleaning will depend on the type of the
detergent used.

11.4.4 Circulate the cleaning solution through the permeators. Take the first
20% of the solution to drain via the brine return valve, and then recycle
the cleaning solution through the mix tank for 2 hours. Alternatively, a
circulate/soak method in 15 minutes cycles may be used. Use flow rate
of 6 gpm x number of 8-inch elements to be cleaned and pressure of
60 psig. Adjust the flow so as not to exceed 60 psi bundle pressure drop.

11.4.5 When cleaning is complete, stop circulation. Drain mix tank solution
to waste. Flush the mix tank and refill it with CFP water.

11.4.6 Add sodium hydroxide until the pH reaches 9.0. Flush the membranes
and piping with both brine and product going to drain.
At all time do not allow DP across the membrane bundle to exceed
60 psi. If DP across the membrane bundle reaches 60 psi then decrease
the feed water pressure.

11.4.7 Flush system again as per 9.3.1. If further rinsing is required fill the
cleaning tank and flush the membranes again. Feed water can also be
used for flushing. Flushing flow rate can increase to 9 gpm x the
number of elements to be flushed. Collect a sample of the brine in a
jar and shake it to test for any remaining detergent. If foaming occurs,

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continue the flushing until all the foaming stops. If no foaming occurs
then the detergent cleaning is complete.

11.4.8 Restart RO and place into service rinse. Divert the RO product to
drain until it meets the quality requirements (e.g., conductivity, pH,
etc.). It is not unusual for the system to take few hours to few days for
the RO permeate quality to stabilize, especially after high pH cleaning.

12 Disinfecting Polyamide SW RO Membranes

Solutions that may be used for disinfection and long term storage are:
a) Glutaraldehyde: A solution of 0.1 to 1.0% concentration may be used for
disinfection and long term storage. The membrane elements should be operated
for at least 24 hours before being exposed to glutaraldehyde.
b) Isothiazoline: The commercial solution contains 1.5% of active ingredient. The
recommended concentration of isothiazoline for disinfection and storage is 15 to
25 ppm.
c) Sodium bisulfite: It can be used as inhibitor for biological growth. To control
biological growth apply at a dosing rate of 500 ppm for 30 to 60 minutes daily.
It can also be used as a preservative during long term storage at 1% concentration.
Commentary Note:

Formaldehyde solution of 0.1 to 1.0% concentration may also be used for disinfection and
long term storage. However, it is not recommended because it is carcinogenic.

Hydrogen peroxide or solution of hydrogen peroxide with paracetic acid can be used for
disinfection. Special care must be taken that transition metals (Fe, Mn) are not present
in the feed water, since in the presence of transition metals, oxidation of the membrane
surface may occur resulting in membrane degradation. The concentration of hydrogen
peroxide for disinfection should not exceed 0.2% and the temperature should not exceed
77°F (25°C). Hydrogen peroxide should not be used as a preservative for long term
storage of membrane elements.

13 Storing Polyamide SW RO Membranes

13.1 Short-Term Storage of SW Membranes

13.1.1 Flush the RO unit with feed water while simultaneously venting any
gas from the system.

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13.1.2 When the pressure tubes are filled, close the appropriate valves to
prevent air from entering the system.

13.1.3 Re-flush as described above at 5-day intervals.

13.2 Long-Term Storage of SW RO Membranes

Long–term storage is for periods where the RO plant is out of service for more
than thirty days with the RO membrane elements in place.

13.2.1 Clean the RO membranes in place.

13.2.2 Flush the RO unit with an approved disinfecting solution

(see Section 9) prepared with CFP water.

13.2.3 When the RO unit is completely filled with this solution, close the
valves to retain the solution in the RO unit.

13.2.3 Repeat steps 2 and 3 with fresh solution every thirty days if the
temperature is below 80.6°F (27°C), or every fifteen days if the
temperature is above 80°F (27°C).

13.2.4 When the RO unit is ready to be returned to service, flush the system for
one hour using low pressure feed water with brine and product going to
waste. Flush for 5-10 minutes at high pressure with brine and product
going to waste. Before returning the RO system to service, make sure
that there is no residual disinfecting solution in the product.

13.3 Storage of SW RO Membranes Prior to Installation

When RO membrane elements are stored prior to installation, they should be

protected from direct sun light. Store the RO membrane elements in cool and
dry place with an ambient temperature range of 68°F to 95°F (20°C to 35°C).

14 Cleaning of Polyamide HFF RO Membranes

14.1 Preparation for Membranes Cleaning:

14.1.1 Ensure that all required chemicals are available and in sufficient
quantities.

14.1.2 Ensure that all instruments, e.g., conductivity, meters, pH meter, flow
meters, temperature meters are properly calibrated and working reliably.

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14.1.3 Apply the safety procedures as per the safety Section 6, paragraphs 6.6
to 6.10.

14.1.4 Conduct conductivity and DP profile on the RO Module to be cleaned

and record the RO module operating data (feed pressure, product flow,
recovery, unit DP, salt passage, temperature, and product pressure).

14.1.5 Stop RO module to be cleaned and flush per normal procedure using
chlorine free product (CFP) water Normal procedure flush is a once
through flush with CFP water (brine and product to drain) of 30 gallons
per 8-inch permeator. Do not exceed maximum allowed DP (60psi).
Use flushing pressure of 100 psig. The brine pH must be 6.0 or above.

14.1.6 If RO skid consists of two stages, install a blind between the RO stages
to be cleaned and conduct the cleaning on each stage separately.

14.1.7 Prepare the log book or cleaning log sheet yo record all of the chemical
cleaning parameters (e.g., flow, pressure, pH, conductivity, chemical
concentration, temperature, etc.) during all steps.

14.2 Estimating the Cleaner Quantity for HFF RO Membranes

14.2.1 The water contained in the hoses or piping can be determined in the
same way as per 9.2.1 (a) and (b) shown in Table 1.

14.2.2 The volume of water in the HFF permeators may be estimated from
Table 3. The total volume of water may be estimated by multiplying
with the number of permeators to be cleaned.

Table 3 - Estimation of HFF Permeators Volumes

Element Diameter Gallons
Inches Per Single HFF Element
4 2.5
8 7.5

14.3 Ammoniated Citric Acid (pH 4.0 – 4.5) Cleaning for Polyamide HFF
Membranes

14.3.1 Fill cleaning tank as per 10.3.2.

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14.3.2 Start the stirrer and gradually add citric acid to prepare a 2 wt percent
solution. Add 7.6 Kg of citric acid (as 100% powder) per 100 gallons
of water.

14.3.3 Allow mixing for 10 minutes and measure the solution pH from top
and bottom of the cleaning tank. Adjust the pH of citric acid solution
to 4.0 - 4.5 using small quantities of ammonium hydroxide (if
required).

14.3.4 Measure the total iron and calcium in the citric acid solution. Ensure
that the temperature of the solution is < 95°F (35°C).

14.3.5 Check out piping, valve positions, pump selection, etc. Open chemical
tank valves (pump suction, brine return and product return valves).
Allow few minutes priming by venting out air from all piping high
points.

14.3.6 With chemical pump discharge valve partially closed, start chemical
pump. Adjust flow 7.5 gpm x number of 8-inch single element /
permeator (minimum brine flow 6 gallons per 8 inch membrane) and
pressure to 90-125 psig. Send to drain the first 20% solution. Monitor
DP and ensure it stays within 60 psi (4.0 bars) at all times.

14.3.7 After 15 minutes, measure iron and calcium in brine return. Monitor
DP across the RO module/permeator. Check citric acid solution pH to
ensure it is 4.0 - 4.5.

14.3.8 Continue circulation of the cleaning solution for 5-6 hours. Monitor
iron levels, calcium levels, pH and DP drop. Check visual appearance
of solution.
Commentary Note:

As iron is removed from the membrane surfaces, it turns green and if excessive
quantities are removed, solution turns brownish.

14.3.9 If the color is brownish and iron concentration in the solution is

> 10 ppm, dump the solution and prepare another batch.

14.3.10 When iron and calcium levels in three consecutive samples taken 15
minutes apart are the same (within 10% difference) stop cleaning.
Divert brine return and product return to drain. Drain chemical tank.

14.3.11 Flush per normal procedure using CFP water.

14.4 Detergent Cleaning for Polyamide HFF Membranes

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14.4.1 Fill cleaning tank as per 10.3.2.

14.4.2 Start the stirrer and add sodium hydroxide to reach pH of 9.0.
Circulate in the cleaning solution the membranes for 10-15 minutes to
neutralize any acidity in the membranes. Stop membrane circulation
and continue circulating within the tank.

14.4.3 Add more sodium hydroxide to reach pH of 11.0. Add required

detergent amount to give the appropriate wt percentage which will
depend on the detergent chosen, e.g., if the PermaClean 67 is used, add
1 gallon for each 100 gallons of water.

14.4.4 Circulate the cleaning solution through the permeators. Take the first
20% of the solution to drain via the brine return valve, and then recycle
the cleaning solution through the mixing tank for 2 hours. Alternatively,
a circulate/soak method in 15 minutes cycles may be used. Use brine
flow of 9 gpm per 8-inch permeator and pressure of 50-150 psig. Adjust
the flow so as not to exceed 60 psi bundle pressure drop.

14.4.5 When cleaning is complete, stop circulation. Drain the mixing tank
solution to waste. Flush the mixing tank and refill it with CFP water.

14.4.6 Add sodium hydroxide until the pH reaches 9.0 to 10.0. Flush the
membranes and piping with both brine and product going to drain.
At all time do not allow DP across the membrane bundle to exceed
60 psi. If DP across the membrane bundle reaches 60 psi then decrease
the feed water pressure.

14.4.7 Flush the system again as per normal procedure using CFP water until
foaming stops. Collect a sample of the brine in a jar and shake it to test
for any remaining detergent. If foaming occurs, continue the flushing
until all the foaming stops. If no foaming occurs then the detergent
cleaning is complete.

14.5 Enhanced pH Hypochlorite Cleaning for Polyamide HFF Membranes

Important Note:

This cleaning procedure is very effective for removing membrane biofouling. However,
this procedure can harm the membranes irreversibly if it is not carried out correctly.
This procedure can only be carried out by experienced personnel; otherwise assistance
from a EPD specialist should be sought.

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14.5.1 Fill cleaning tank as per 10.3.2.

14.5.2 Start chiller to reduce cleaning tank temperature to < 86°F (30°C).

14.5.3 Start the stirrer and add sodium hydroxide gradually to adjust pH to
11.8-12.0 range.

14.5.4 Allow mixing for 5 minutes and measure the solution pH. Ensure that
the temperature is < 86°F (30°C).

14.5.5 Recheck piping, valve positions, pump selection, etc. Open chemical
tank valves (pump suction, brine return and product return valves).
Allow few minutes priming by venting out air from all piping high
points.

14.5.6 With the chemical pump discharge valve partially closed, start the
chemical pump. Adjust the flow to achieve a minimum brine flow of
6 gpm per permeators and pressure of 100-150 psig. Monitor DP and
ensure it stays within 60 psi (4.0 bars) at all times.

14.5.7 After 10 minutes, measure the pH in brine and product return. Ensure
it is 11.8-12.0. Monitor DP across the RO module/permeator.

14.5.8 Continue circulating the cleaning solution for 30 minutes. Monitor pH

and DP drop. Check the visual appearance of the solution.
(Note: As organic and biofoulants are released removed from the
membrane surfaces, the solution turns brownish).

14.5.9 At the end of the high pH treatment, drain the cleaning chemical tank.

14.5.10 DO NOT FLUSH. It is very important to allow the high pH solution

to remain in the RO module and to avoid damage to the permeators.

14.5.11 Fill the cleaning tank to the required level with CFP water.

14.5.12 Start the stirrer and add sodium hydroxide to adjust pH to 11.8-12.0.

14.5.13 After about 5 minutes of mixing, add about 2 liters sodium hypochlorite.

14.5.14 Allow mixing for 5 minutes and measure the solution chlorine and pH.
Adjust chlorine to 150 mg/L (as Cl2) using small quantities of sodium
hypochlorite.

14.5.15 Check pH and adjust it in the range of 11.8-12.0 using sodium

hydroxide (if required). Ensure that the temperature is < 86°F (30°C).

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14.5.16 Check out piping, valve positions, pump selection, etc. Open chemical
tank valves (pump suction, brine return and product return valves).
Allow few minutes priming by venting out air from all piping high
points.

14.5.17 With the chemical pump discharge valve partially closed, start the
chemical pump. Adjust the flow to 7.5 gpm x number of permeators to
be cleaned and pressure to 100-150 psig. Monitor DP and ensure it
stays < 60 psi (4.0 bars) at all times.

14.5.18 Monitor the chlorine level and DP across the RO module/permeator.

Check brine and product pH to ensure it is 11.8-12.0. (If pH decreases
to < 11.7, stop circulation, readjust pH and restart).

14.5.19 Continue circulating the cleaning solution for 30 minutes. Monitor

chlorine, pH, and DP change. If chlorine is consumed and its
concentration has been reduced to about 50 mg/l, add additional
sodium hypochlorite to bring the chlorine to 150 mg/l. Check visual
appearance of solution. (Note: As organic and biofoulants are
removed, the clear solution turns tan-brown color).

14.5.20 At the end of hypochlorite treatment, check Cl2 content of solution and
record. If the consumption of chlorine has stopped this means that the
treatment is complete. Stop the circulation and dump the cleaning tank
solution to drain.

14.5.21 Fill the cleaning tank to the required level with CFP water.

14.5.22 After about 5 min. of mixing, add 0.5 Kg of sodium bisulphite (SBS)
per 100 gallons of CFP water.

14.5.23 Start stirrer and add sodium hydroxide to adjust pH to 11.8-12.0.

14.5.24 Allow mixing for 5 minutes and measure the solution SBS content and
pH. SBS should be about 1,200-1,300 mg/l. If required, adjust SBS to
this level using small quantities of SBS.

14.5.25 Recheck the pH of the SBS solution to ensure that it is 11.8 to 12.0.
Add NaOH if needed to adjust the pH.

14.5.26 Recheck the piping, valve positions, pump selection, etc. Open the
chemical tank. Allow few minutes priming by venting out air from all
piping high points.

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14.5.27 With the chemical pump discharge valve partially closed, start the
chemical pump. Adjust the flow to 7.5 x number of permeators to be
cleaned and pressure to 100-150 psig.

14.5.28 After 10 minutes, measure the pH in brine and product return.

Monitor the chlorine of returning brine. The chlorine content must be
zero. Monitor the SBS level and DP across the RO module/permeator.
Check pH to ensure it is 11.8-12.0.

14.5.29 Continue circulating the cleaning solution for 30 minutes.

14.5.30 Check the chlorine residue to confirm it is zero. At the end of high pH
SBS circulation treatment, add SBS gradually as required to reduce
SBS solution pH to 7.5-8.5. Circulate for 10 minutes and divert the
brine and product return to the drain. Drain the cleaning chemical
tank.

15 Disinfecting Polyamide HFF RO Membranes

15.1 Fill cleaning tank as per 10.3.2.

15.2 Add the required quantity of disinfection chemical to the mixing tank and start
the stirrer. If PermaClean 55 is to be used, prepare a solution of 0.3% in the
mixing tank by adding 0.3 gallons of PermaClean 55 for each 100 gallons of
CFP water.

15.3 Circulate the disinfection solution through the RO module to be sterilized and
direct the first 20% of the solution to drain via the brine drain valve. Then,
recycle the brine through the mixing tank. Use a circulation pressure of
50-150 psig and a circulating flow rate of 7.5 gpm x number of permeators to be
sanitized. At all times do not allow DP across the membrane bundle to exceed
60 psi. If DP across the membrane bundle reaches 60 psi then decrease the feed
water pressure.

15.4 After 6 hours of circulation, stop circulation, direct brine to waste and drain the
mix tank.

15.5 Flush the system as per normal procedure using CFP water until foaming stops.
Collect a sample of the brine in a jar and shake it to test for any remaining
detergent. If foaming occurs, continue the flushing until all foaming stops.
If no foaming occurs then the disinfection is complete.

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16 Post-Treating Polyamide HFF RO Membranes

HFF polyamide membranes need to be post treated with PT-A (polyvinyl methyl ether)
and PT-B (tannic acid). PT-A increases the salt rejection by reducing the salt flow
through the membrane or fiber imperfections. PT-B works differently than PT-A. It is
absorbed on the membrane surface and enhances the salt rejection. Chlorine and iron
will react with PT-B and destroy its effect on salt rejection. Thus, all the water used to
prepare the solution must be free from chlorine and iron. PT-B and PT-A also react
between them and form precipitate. When both treatments are used, the membranes
must be thoroughly flushed between treatments. Polyvinyl methyl ether (PVME) can
be purchased from BASF directly and it is sold under the trade name “Lutanol 40” as a
50 wt percent aqueous solution. The tannic acid used for PT-B must be of good grade
(see Appendix A-6). Before using PT-A or PT-B post treatments, membranes should be
thoroughly cleaned.

16.1 PT-A Post-Treatment for Polyamide HFF Membranes (Off Line)

16.1.1 Flush the permeators with CFP water prior to post-treatment using a
once-through flush (brine and product to drain) of 30 gallons per
8-inch permeator.

16.1.2 In the mixing tank, prepare a well mixed solution containing 80 mg/l
Polyvinyl Methyl Ether (PT-A) active ingredient plus 530 mg/l iodine
free sodium chloride (NaCl) taking into account the volume of water in
the piping, hoses and permeators. Assume 7.5 gallons of water per 8-
inch permeator to be post treated. Use CFP water.
Allow mixing for 5 minutes and measure the solution pH.

16.1.3 Ensure that the temperature is <95°F (35°C) during treatment. Start
chiller to reduce cleaning tank temperature if necessary (Cloud point of
PT-A equals 98.6°F (37°C). Note: At higher concentrations, the cloud
point is lower; at 3 wt percent and above it is 86°F (30°C). Therefore,
these solutions should be stored at temperatures lower than 86°F (30°C).

16.1.4 Check out piping, valve positions, pump selection, etc. Open the
chemical tank valves (pump suction, brine return and product return
valves). Allow few minutes priming by venting out air from all piping
high points.

16.1.5 With the chemical pump discharge valve partially closed, start the
chemical pump. Adjust the flow to achieve a minimum brine flow of
6 gpm per permeator and pressure to 100-150 psig. Monitor DP at all
times and ensure it stays within 60 psi (4.0 bars).
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16.1.6 Monitor the product conductivity every 15 minutes. Terminate the

PT-A post-treatment when the product conductivity is constant for
30 minutes.

16.1.7 At the end of PT-A treatment, divert the brine return and product return
to the drain. Drain the chemical tank and clean with fresh water.

16.1.8 Flush (once through flush, both brine and product going to waste) the
residual PT-A solution from the permeators with CFP water by
operating at brine rate of 13.5 gpm for 5 minutes.

16.1.9 Repeat the flushing as per the normal procedure for 15 minutes.
Feed water may be used for this flushing.

16.2 PT-B Post-Treatment for Polyamide HFF Membranes (Off Line)

16.2.1 Flush the permeators with CFP water prior to post treatment using a
once-through flush (brine and product to drain) of 30 gallons per
8-inch permeator. Good flushing is very important to avoid PT-A
reaction with PT-B that results in precipitate formation.

16.2.2 In the mixing tank prepare a solution containing 1 wt percent citric

acid plus 80 mg/l of PT-B (tannic acid) taking into account the volume
of water in piping, hoses and permeators (assume 7.5 gallons per
permeator to be post treated. Use CFP water. Since the PT-B is a solid
which does not dissolve immediately, the PT-B may be added as a
dilute aqueous stock solution containing 3 wt. percent of PT-B.
The PT-B should be of good quality. Its suitability for membrane
post-treatment can be determined as per Appendix A-6.

16.2.3 Ensure that the temperature is 77°F to 86°F (25°C to 30°C). Never
should the temperature be over 90°F (32°C) during treatment. Start
chiller if necessary.

16.2.4 Allow 5 minutes of mixing and check pH to ensure that it is 4.0. If pH

is higher than 4.0, add more citric acid to obtain pH 4.0. Ensure that
the pH is the same by checking the top and bottom solution of the tank.

16.2.5 Check out the piping, valve positions, pump selection, etc. Open the
chemical tank valves (pump suction, brine return and product return
valves). Allow few minutes priming by venting out air from all piping
high points.

16.2.6 With the chemical pump discharge valve partially closed, start the
chemical pump. Adjust the flow to achieve a brine flow of 6 gpm per
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permeator and pressure to 100-150 psig. Monitor DP at all times and

ensure it stays within 60 psi (4.0 bars).

16.2.7 After 15 minutes, start monitoring the product conductivity.

Continue the treatment for the next 1 hour.

16.2.8 At the end of PT-B treatment, divert the brine return and product return
to the drain. Drain the chemical tank and clean with fresh water.

16.2.9 Flush (once through flush, both brine and product going to waste) the
residual PT-B solution from the permeators with CFP water by
operating at brine rate of 13.5 gpm for 5 minutes.

16.2.10 Repeat the flushing as per the normal procedure for 15 minutes.
Feed water may be used for this flushing.

16.2.11 Start up the RO unit and monitor data for normalization and evaluation
of cleaning effectiveness.

17 Storing Polyamide HFF RO Membranes

17.1 Storing New HFF Permeators

As shipped, HFF permeators contain a standard aqueous solution of

approximately 18 wt percent glycerin and 0.5 wt percent sodium metabisulfite
plus 200 to 350 mg/l as Mg++ MgCl2 to provide protection against freeze
damage and to maintain biostatic conditions. To avoid flux loss, membranes
should be stored at temperatures not exceeding 95°F (35°C) and not to be stored
under direct sunlight. Permeators stored as per 11.1 will retain their salt passage
performance for a period of at least two years. If storage for more than 2 years
is required then the pH of the solution should be checked periodically to ensure
that it has not dropped to a level below 4.0. If the pH of the preservative
solutions approaches 4.0 then the preservative solutions should be replaced.

17.2 Storing used HFF Permeators (preparing and adding storage solution)

17.2.1 Prepare 0.5 wt. percent sodium metabisulfite and 18 wt percent

glycerin in the mixing tank using CFP water. Use a hydrometer to
check the glycerin content. The specific gravity should be 1.045 to
1.050 for the temperature range of 15°C to 25°C. Adjust the specific
gravity by adding glycerin or water.

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17.2.2 Thoroughly mix the solution. Recirculate the solution in the feed
direction through the permeators at a pressure of 100 to 200 psig and
brine flow of 6 gpm for 8-inch single bundle permeators and 12 gpm
for 8-inch twin bundle permeators. Product and brine should be
recycled back to the mix tank. There will be very low permeate flow
due to high osmotic pressure.

17.2.3 Continue the circulation for 1.5 hours. After the first half hour check
the specific gravity of glycerin and add more glycerin if required.
At the end of 1.5 hours, stop the circulation, reduce the pressure to
zero, and disconnect the permeators.

17.2.4 Drain the permeators from excess solution. Seal all ports promptly to
prevent additional loss of solution. The permeators are now ready for
storage.

18 Cleaning HFF Cellulose Triacetate RO Membranes

Commentary Note:

For HFF Cellulose Triacetate Membranes (such as those that are used at Tanajib Seawater
Desalination Plant) only acid cleaning can be applied to these membranes, since under alkaline
conditions they hydrolyze. The membrane cleaning guideline at Tanajib RO plant is when one of
the following two criteria is reached:

a) When the differential pressure of the RO module reaches 54 psi

b) When the operating time of the RO module without cleaning reaches 4400 hours.

18.1 Preparation for Membranes Cleaning

As per Section 13, paragraphs 13.1.1 to 13.1.7.

18.2 Ammoniated Citric Acid (pH 4.0 – 4.5) Cleaning for Cellulose Triacetate
Membranes

18.2.1 Flush the membranes (once through flush, permeate and reject going to
waste) with product water for one hour.

18.2.2 Fill the cleaning tank as per 10.3.2.

18.2.3 Start the stirrer and gradually add citric acid to prepare a 2 wt percent
solution. Add 7.6 kg of citric acid per 100 gallons of water.

18.2.4 Allow mixing for 10 minutes and measure the solution pH from top
and bottom of the cleaning tank. Adjust the pH of citric acid solution

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to 4.0 - 4.5, using small quantities of ammonium hydroxide (NH4OH)

if required.

18.2.5 Measure the total iron and calcium in the citric acid solution. Ensure
that the temperature of the solution is <104°F (40°C).

18.2.6 Check out the piping, valve positions, pump selection, etc. Open the
chemical tank valves (pump suction, brine return and product return
valves). Allow few minutes priming by venting out air from all piping
high points.

18.2.7 With the chemical pump discharge valve partially closed, start the
chemical pump. Adjust the flow to 7.5-10.0 gpm x number of 8-inch
single element/permeator (minimum brine flow 6 gallons per 8 inch
membrane) and pressure of 90-125 psig. Send the first 20% solution to
the drain. Monitor DP and ensure it stays below 60 psi (4.0 bars) at all
times.

18.2.8 After 15 minutes, measure the iron and calcium in the brine return.
Monitor DP across the RO module/permeator. Check the citric acid
solution pH to ensure it is 4.0 - 4.5.

18.2.9 Continue circulating the cleaning solution for 2-3 hours. Monitor iron
levels, calcium levels, pH and DP drop. Check the visual appearance
of the solution.
Commentary Note:

As iron is removed from the membrane surfaces, it turns green and if excessive
quantities are removed, solution turns brownish.

18.2.10 If the color is brownish and iron concentration in the solution is

> 10 ppm, dump the solution and remake another batch.

18.2.11 When iron and calcium levels in three consecutive samples taken 15
minutes apart are the same (within 10% difference) stop cleaning.
Divert the brine return and product return to drain. Drain the chemical
tank.

18.2.12 Flush per the normal procedure using product water.

19 Storing HFF Cellulose Triacetate RO Membranes

19.1 Storing new HFF Cellulose Triacetate Membranes

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Shipped RO elements are filled with preservative solutions. Store these

elements prior to their installation satisfying the following conditions:
a) Store in well ventilated area.
b) Store away from direct sunlight.
c) Store at a temperature of less than 104°F (40°C). This temperature
specification should be adhered to for inland transportation, before
installation, at start up, standby and storage.
d) Avoid impact or severe vibration.
e) Do not store for more than 2 years.
f) Store RO elements horizontally.
g) Do not stack more than 4 stories for the elements in the packing style
delivered.
h) After element unpacking the element should be immediately installed and
put into service.

19.2 Storing used HFF Cellulose Triacetate Membranes

The preservative method for standby of the RO modules should be observed

according to the period of shutdown of the RO system as indicated in Table 4.

Table 4 – Guidelines for Preservation of

Used HFF Cellulose Triacetate Membranes

Shut-down Period Preservative Procedure

1) Operate with chlorinated feed water for more than 0.5 hour
Less than 3 days 2) Flush with permeate or feed water
3) Seal the RO system
1) Operate with chlorinated feed water for more than 0.5 hour
2) Flush with permeate or feed water
Less than 1 month
3) Fill with preservative solution (*)
4) Seal the RO system
1) Operate with chlorinated feed water for more than 0.5 hour
2) Flush with permeate or feed water
3) Perform chemical cleaning
More than 1 month
4) Flush with permeate or feed water
5) Fill with preservative solution (*)
6) Seal the RO system

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(*) Preservative solution is 0.25% sodium bisulfite. Formaldehyde of 0.5% can also be used but it is not
recommended because it is carcinogenic.

20 Disposal of Wastewater

Disposal of all wastewater and spent chemical cleaning solutions shall be in accordance with SAEP-327
and Saudi Aramco Hazardous Waste Code (SAHWC). The disposal of effluents outside Saudi Aramco
facilities shall be sent to an approved wastewater disposal facility provided by the Environmental
Protection Department (EPD), Dhahran.

Revision Summary
23 July 2011 Revised the “Next Planned Update.” Reaffirmed the contents of the document and
reissued with editorial revision to avoid ambiguity and to make clear and straight forward
cleaning steps.
16 March 2016 Editorial revision to transferred from CSD to the new consolidated entity of EPD.
27 April 2017 This document was revised as per the scheduled review cycle and updated to reflect
minor updates..
10 June 2018 Editorial revision to change standards committee from Environmental to Water
Treatment & Conservation
12 May 2019 Editorial revision to change Primary contact Person.
10 October 2019 Editorial revision to change responsible committee.
07 September 2022 Editorials revision to transfer this document to Process Utility System Standards Committee,
reference letter (ESD 000021.2022)

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Appendix

A-1 – Cleaning Equipment

Figure 1 - RO Cleaning, Disinfecting, Post-Treatment and Flushing Flow Diagram

LEGEND:
Mixing tank: Chemical tank, polypropylene or fiber reinforced plastic (FRP)
CCH Chemical charging hatch
TC Tank cover
PF Permeate fill
TI Temperature indicator
CC Cooling coil
STR Strainer
pHI pH indicator
RP Recirculation pump, 316 stainless steel (SS) or non-metallic composite
LLS Low level switch to shut off pump
DP Differential pressure gauge
CF Cartridge filter, 5-10 micron polypropylene with PVC, FRP or SS
housing
FI Flow indicator

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PI Pressure indicator
V1 Permeate inlet valve, CPVC
V2 Tank drain valve, PVC or CPVC
V3 Flow control valve
V4 Pump circulation valve
V5 Cartridge filter drain valve, PVC or CPVC
V6 Purge valve, SS, PVC or CPVC
V7 Concentrate return valve, CPVC 3 way valve
V8 Permeate valve, CPVC 3 way valve

A-2 – General Guidelines for Choosing Optimum Cleaning Chemical

Foulant General Symptoms Response

• Marked decrease in salt
Calcium precipitates rejection Moderate increase in Chemically clean the
(carbonates/phosphates found at DP RO system with
the tail end of the system) • Slight decrease in permeate Solution 1.(+)
flow.
• Rapid decrease in salt rejection
Chemically clean the
Hydrated Oxides (iron, nickel, • Rapid increase in DP.
RO system with
copper, etc.)
• Rapid decrease in permeate Solution 1.(+)
flow.
• Possible decrease in salt
rejection Chemically clean the
Organic Deposits • Gradual increase in DP. RO system with
Solution 2.(+)
• Gradual decrease in permeate
flow.
• Possible decrease in salt
rejection Chemically clean the
Bacterial Fouling • Marked increase in DP. RO system with
Solution 2.(+)
• Marked decrease in permeate
flow.

(+) For solution descriptions see Appendix A.5

A-3 – Operating Parameters and Measurements Log Sheet

Operating pH Temp. Feed Feed Permeate Feed Permeate
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Time Pressure Flow Flow Conductivity Conductivity

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A-4 – Clean In Place (CIP) Log Sheet

RO module:.....................
RO stage:……………….
Date:……………………
Operator:……………….

Item # Process Data Commissioning Data Pre-CIP Post-CIP

1 Feed temperature
2 Feed pressure (psi)
3 Reject pressure (psi)
4 DP pressure (psi)
5 Permeate pressure (psi)
6 Pressure–intermediate (psi)
7 Flow-permeate (gpm)
8 Flow concentrate (gpm)
9 Conductivity-Feed (µs/cm)
10 Conductivity-permeate (µs/cm)
11 Conductivity Conc. (µs/cm)
Key:
1) Pressure gauge directly downstream of Feed Control valve
2) Pressure gauge directly upstream of Concentrate Control Valve
3) Pressure gauge difference between 1and 2
4) Pressure gauge in permeate piping
5) Pressure gauge between stage 1 and stage 2
6) Flow meter reading in permeate piping
7) Flow meter reading in concentrate piping
8) Measurement with hand held conductivity meter from feed sample valve
9) Measurement from on line or hand held conductivity meter from permeate
10) Measurement with hand held conductivity meter from concentrate sample valve
Item # Chemical Data Units
1 Cleaner name N/A
2 Amount of cleaner used (neat) Kg
3 Tank dilution volume liters/gallons
4 pH of solution pH units
5 Recirculation begins time
6 Recirculation flow gpm
7 Recirculation ends time
8 Appearance N/A
9 Flush begins time
10 Flush flow rate gpm
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11 Flush ends time

12 Recirculation pressure psi

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A-5 – Description of Cleaning Solutions for SW Polyamide Membranes

Solution 1: This is a low pH cleaning solution (target pH 4.0 – 4.5) of 2.0% wt citric
acid (C6H8O7). It is useful in removing inorganic scales, e.g., calcium
carbonate, and metal oxides/hydroxides (e.g., iron, manganese, nickel,
copper, zinc), and inorganic-based colloidal materials.
Commentary Note:

Citric acid has chelating properties that function better when the upward pH
adjustment is done using ammonium hydroxide and not sodium hydroxide.

Solution 2: This is a high pH cleaning solution (target pH of 10.0) of 2.0% wt of

STPP (sodium tripolyphosphate) (Na5P3O10) and 0.8% wt of Na-EDTA
(sodium salt of ethylaminediaminetetraacetic acid). STPP functions as
an inorganic-based chelating agent and detergent, and it is effective in
removing calcium sulfate scale and light to moderate levels of organic
foulants. Na-EDTA is an organic based chelating agent that that aids in
the removal of divalent and trivalent metal ions.

Solution 3: This is a high pH cleaning solution (target pH of 10.0) of 2.0% wt of

STPP (sodium tripolyphosphate) (Na5P3O10) and 0.255 wt Na-DDBS
(C6H5(CH2)12-SO3Na) (sodium salt of dodecyl benzene sulfonate). It is
recommended for the removal of heavier levels of organic foulants.
STPP functions as an inorganic-based chelating agent and detergent.
Na-DDBS functions as an anionic detergent.

Solution 4: This is a low pH cleaning solution (target pH of 2.5) of 0.5% wt of HCl

(hydrochloric acid). It removes scales, metal oxides and foulants as per
solution 1. However, this cleaning solution is considered to be harsher
than solution 1. It is recommended to be used only in extreme cases of
scaled and fouled membranes.

Solution 5: This is a high pH cleaning solution (target pH of 11.5) of 1.0% wt of

Na2S2O4 (sodium hydrosulfite). It removes metal oxides and hydroxides,
and to a lesser extent calcium sulfate, barium sulfate and strontium
sulfate.

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Solution 6: This is a high pH cleaning solution (target pH of 11.5) of 0.1% wt of

NaOH (sodium hydroxide) and 0.03% wt of SDS (sodium dodecyl
sulfate). It removes organic foulants, organic and inorganic colloidal
foulants and biological material (fungi, mold, slimes and biofilm). SDS
is an anionic surfactant and will cause foaming.
This cleaning is considered a harsh cleaning regiment for the membranes
and it should only be used in extreme cases.

Solution 7: This is a high pH cleaning solution (target pH of 11.5) of 0.1% wt of

NaOH (sodium hydroxide). It removes polymerized silica.
This cleaning is considered a harsh cleaning regiment for the membranes
and it should only be used in extreme cases.

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A-6 – Tannic Acid (PT-B) Quality Testing

a) Specification for Tannic Acid

The suitability of tannic acid for membrane post-treatment can be determined by

titration with caustic (NaOH). If the % of the first acid (end point at a pH of
approximately 5) is ≤6.0 of the total acid titrated, the tannic acid is of acceptable
quality and can be used to PT-B the membranes.

Example: First acid = 0.11 m Eq/g of tannic acid

Total acid = 5.25 m Eq/g of tannic acid

0.11/5.25 x 100 = 2.1%, therefore, Quality is acceptable

b) Procedure for Titration of Tannic Acid

1. Weigh 1 g (to nearest 0.0001 g) sample of tannic acid into a 250 ml beaker

2. Add 100 ml water and a magnetic stirring bar

3. Stir the solution

4. Titrate with 1.0 n sodium hydroxide using a combination glass electrode

(Metrohm EA-120) and an automatic titrator (such as Metrom E-436).

5. Calculation:

Neutral Equivalent (m Eq/g) = Volume x Normality/Sample wt

Commentary Note:

When two end points are observed, they occur at pH 5 and 10, when only one end
point is observed, it occurs at pH 10.

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