ro systems operationc - best practice guidelines

GEWater & Process Technologies

CONFIDENTIAL INFORMATION

RO Systems OperationBest Practice Guidelines

Second Edition


CONFIDENTIAL INFORMATION i

CONFIDENTIAL AND SENSITIVE MATERIAL—

This is an internal and CONFIDENTIAL GE Water & Process Technologies manual and is not for distribution or release to non-GE entities. Contact Ed Habayeb or Technical Marketing Management with any questions about usage and restrictions.

This is an evolving document that is continually updated based on formal workshops, meetings, and discussions with many global experts. Thanks to all of those who have contributed.

Second Edition: January 2008

Second Edition Authored by: Matthew Hunter, Anna Bandick, and Ed Habayeb


CONFIDENTIAL INFORMATION iii

Table of Contents 1. Membrane Elements ........................................................................................................12. Site Survey Data Required.............................................................................................33. Feed Water Quality Guidelines....................................................................................54. Water Source Characterization and Filtration Pretreatment

Requirements ...................................................................................................................75. SDI Determination .............................................................................................................96. Media Filter Typical Operating Parameters (Carbon, Multimedia, Greensand)..............................................................................................................................117. Multi Media Backwash Practices.............................................................................158. Cartridge/Depth Filter Replacement .....................................................................179. Chemical Feeding Sequence.....................................................................................1910. Coagulant Feed and Selection...............................................................................2111. Feed Water pH Control..............................................................................................2512. Antiscalant Selection..................................................................................................2713. Argo Analyzer Software Program ........................................................................2914. Bisulfite Feed and Dechlorination ........................................................................3115. Microbiological Control .............................................................................................3316. RO Normalization Data Collection/Interpretation........................................3717. RO Troubleshooting Guidelines .............................................................................4118. RO CIP Cleaning ............................................................................................................4319. Calcium Carbonate Scale.........................................................................................4720. Sulfate-Based Scale....................................................................................................4921. Iron and Manganese Fouling .................................................................................5122. Aluminum Fouling........................................................................................................5323. Silica Scaling and Fouling.........................................................................................5524. Colloidal Fouling ...........................................................................................................5725. Microbiological Fouling .............................................................................................5926. Organic and Chemical Fouling ..............................................................................6127. Membrane Autopsy Results and Interpretation............................................6328. RO Storage Practices and Procedures...............................................................6529. Membrane Element Installation............................................................................6730. Pressure Vessel Probing............................................................................................69Appendix 1. Temperature Correction Factors (TCF) ...........................................71Appendix 2. Sample Cleaning Procedure................................................................73Appendix 3. Spacer Tube Installation .......................................................................77


CONFIDENTIAL INFORMATION v

ForwardGE Water & Process Technologies has the unique position in the industry of being an OEM of RO systems, RO membranes, and cartridge filters, as well as a service provider of RO chemistries. This broad product and service offering has been achieved through the integration of various services and manufacturing entities. This allows us to offer a wide spectrum of solutions to meet our customers needs.

A word of caution from the authors of this manual: Each of the organizations integrated into GE has brought with them unique design and operational philosophies. It is in our best interest and the interest of our customers to be accurate in our appraisal of their current systems for functionality and operational readiness. Part of that evaluation means understanding the original specifications and design intent under which the systems were sold and installed. We encourage you to familiarize yourselves with the equipment from all our heritage businesses and to understand that multiple system designs and operation philosophies are acceptable and optimal. We have put to paper the best practices as we see them. These are not the only way or last word in how to accomplish a given task, just the recommendations of where to start.


CONFIDENTIAL INFORMATION 1

1. Membrane Elements Two types of commercial membranes are most commonly used in NF/RO membrane equipment: cellulose acetate (CA) and a family of polyamide (PA) thin film composite (TFC) membranes.

Comparative Properties Commercial RO Membranes Note: These are typical ranges and limits; always consult membrane manufacturers’ specifications for actual tolerance limits.

CA Membranes PA (TFC) Membranes Surface Charge Uncharged Negative Pressure 300 – 600 psi 150 – 450 psi Temperature (Max) 35o C (95o F) 50o C (122o F) pH (Operating) 4 – 6 3 – 11 Chlorine Free Up to 1.0 ppm None†

† Maximum 1000 ppm-hours exposure to free chlorine.

Note:1. CA Membranes are typically used in municipal drinking water or

beverage applications due to their tolerance for chlorine. 2. CA membrane cleaning: do not exceed pH 7.5 due to potential

damage to membranes from higher pH (hydrolysis).

PA Advantages 1. Overall lower operational cost 2. Lower operating pressure 3. Improved salt rejection 4. Significantly lower energy consumption.

CA Advantages 1. Chlorine and oxidizer tolerant- CA membranes can tolerate up to

1 ppm free chlorine. Chlorine and oxidizers destroy PA membranes.

2. Good for high MB potential applications- oxidizer tolerance makes CA membranes a good choice for applications with potential for MB problems. An oxidizing biocide such as chlorine can be continuously fed without damaging the membrane.

3. Attractive for potable applications due to chlorine tolerance.


2 CONFIDENTIAL INFORMATION

4. Less likely to foul- the relatively smooth, uncharged surface of a CA membrane is less likely to attract foulants compared to charged PA and polysulfone (PS) surfaces.

CA Disadvantages 1. Hydrolysis- the acetyl groups on the polymer in the CA

membrane will hydrolyze over time. The pH dependency of the hydrolysis mechanism limits the operational pH to the range of 4.0 to 6.0. As hydrolysis occurs, the membrane will lose salt rejection performance.

2. Potentially shorter life due to hydrolysis. Three years is a good estimate for the membrane life of both PA and CA membranes. CA membranes that are run outside of the recommended pH range will not last as long. Both types are capable of lasting up to 7 or 8 years.

3. Higher operating pressures- Must operate at ~400 psi to get reasonable permeate flow and salt rejection

4. Capital Equipment costs- higher equipment costs compared to PA membranes since the higher pressure requires bigger pumps. CA membranes are often more expensive.

Salt Rejection The percentage of any individual ion rejected by a membrane depends on the size and electrical characteristics of the ion, with the following percentages typical for the general range of ions found in treated water. Note that gases are generally not rejected by RO membranes (e.g. CO2,NH3, etc.).

Typical Salt Rejection for Membrane Performance Ion CA Membrane PA Membrane Sodium 85 – 99% 96 – 99% Chloride 85 – 99% 96 – 99% Calcium 90 – 99+% 98 – 99+% Magnesium 90 – 99+% 98 – 99+% Sulfate 90 – 99+% 98 – 99+% Bicarbonate 85 – 99+% 96 – 99+% Conductivity 85 – 99% 97 – 99+% Silica 85 – 95% 98%



2. Site Survey Data Required The following information is the minimum that should be obtained and used in the proposal generation phase, start-up planning, as well as in surveys of existing installations. This ensures new equipment installation, start-up, and ongoing operation requires minimal maintenance and meets the customer’s expectations.

Project Scoping Details 1. Flow rates

a. Daily flow b. Peak flow

2. Identify all water sources and seasonal variations a. Well water b. City/municipal supply c. Surface water d. Process water/waste water

3. Current treatment process a. Technology used, process flow details b. Cost of current treatment process c. Operator time to cover d. Chlorine present in feed water?

4. Projected running style, 24/7 or on/off a. 24/7 or on/off b. Existing tanks available for post pretreatment break and

for permeate product storage

Makeup Water Quality Details 1. Detailed feed water analysis (i.e. Grid 40) 2. Free and total chlorine analysis 3. SDI for projected makeup water 4. Turbidity for projected makeup water 5. Particle size analysis for projected makeup water 6. Temperature for feed water; average and range 7. Grid 48 for process water reuse applications 8. Argo Analyzer projections 9. Pretreatment and cleaning chemicals required

Target Product Quality Details 1. Customer target product quality parameters and flows.



3. Feed Water Quality Guidelines The RO feed water guidelines provided in the table below are recommended to provide efficient RO performance. The expected cleaning frequency would be quarterly when these guidelines are met.

Parameter Typical Limits Turbidity Preferably < 0.2 NTU, 1.0 max SDI15 Preferably 3 or less, up to 5 acceptable Iron < 0.05 ppm Manganese < 0.05 ppm Aluminum < 0.1 ppm Boron < 0.05 ppm TOC < 3 ppm Silica < 40 ppm pH TFC 5.0 to 9.0

CA 4.0 to 6.0 Temp, °F (°C) 55-85 (12.7 to 29.4) LSI Run Argo Analyzer Barium Run Argo Analyzer Strontium Run Argo Analyzer Phosphate Run Argo Analyzer

Notes:1. If RO feed water values are above the targets, or in the case of

temperature, above or below the targets, additional engineering evaluation or design changes should be considered. In addition, pretreatment equipment will be needed. See section on water source and pretreatment equipment requirements.

2. Silica limits: The above silica limit was set so that the max silica concentration in the brine solution does not exceed 160 ppm at 75% recovery. New antiscalants have been developed that allow for running the RO at higher brine silica levels in excess of 300 ppm. In addition, HERO is a patented process that allows an RO to be run with much higher silica levels. GEWPT has rights for the patent in certain markets and geographies. Consult with GE Engineers for operating guidelines and antiscalant recommendations.

3. Parameters show “ Run Argo Analyzer” because their effect on RO performance is determined by operating conditions such as pH, recovery, temperature, and the overall ionic make up of the water. All feed waters should be evaluated by running Argo Analyzer.Contact GE Technical Marketing if there are any questions.



4. Water Source Characterization and Filtration Pretreatment Requirements

In order to properly determine the types and extent of pretreatment, the end-user must be aware of the water sources involved. Following these tables are typical equipment recommendations etc.

Typical Properties of Source Waters

Source Turbidity NTU Color TOC TDS SDI

RiverHigh with seasonalvariation

Moderate Moderate to High Low >5

Lake/Pond Low, with seasonalvariation

High with seasonalvariation

High Low >5

Well Low Low Moderate Low to High <5

Municipal Low to Moderate Low Low to

Moderate Low to

Moderate >5 or <5

Brackish Low Low Low to Moderate

Moderate to high >5

Seawater Low to Moderate Low Low High >5

Definition of Characterization

Parameter/Values Low Moderate High Turbidity –NTU 1-10 10-25 >25 Color –PtCO <10 15-30 >30 TOC –ppm <1 2-10 >10 TDS-ppm 10-150 150-2,500 > 2500 – Brackish



Pretreatment Equipment Selection is based on water source and turbidity.

Pretreatment Equipment Selection Based on Water Source and Turbidity

WaterSource

Critical Water Parameter

Suggested Treatment Equipment

NTU > 25† Clarifier† + MMF or UF/MF NTU 10-25 MMF or UF or MF with Coagulant RiverNTU <10 MMF or UF or MF (Coagulant may

be needed) Hard water and TOC Lime softener + Clarifier MMF NTU >25† Clarifier† + MMF or UF/MF

SurfacewaterLake NTU<25 MMF or UF/MF

Chlorination + MMF Iron and manganese

Greensand Filter Well Water NTU < 10 MMF or UF/MF NTU >10 MMF Brackish

Water NTU <10 UF/MF or MMF Sea or Ocean NTU >50 Clarifier† + MMF

NTU < 50 UF or MF – Check with MF supplier

NTU <25 UF/MF TOC= Organics, MF= Micro filtration, UF= Ultrafiltration, MMF= Multimedia Filters †Total suspended solids greater than 100 mg/L require clarification.



5. SDI Determination Silt Density Index (SDI) is a critical RO feed water parameter. It provides an indication of fouling potential caused by particulate matter. It is desired to have feed water that has SDI15 readings less than 3 to insure long membrane life, but less than 5 is acceptable. Readings higher than 3 indicate that improved pretreatment should be considered or that frequent cleaning may be required.

SDI Measurement involves measuring the number of seconds it takes for 500 mLs of water at 30 psi to pass through a 0.45 micron filter at 0 (initial) minutes, 5 minutes, 10 minutes and 15 minutes. SDI is calculated with the following equation.

SDITimex = [1-(initial T0 sec)/(Timex Seconds)] x 100 Timex

Where TimeX can be 5, 10 or 15 minutes.

Sample Calculation: The table below shows an example of the data that would be collected while running an SDI test.

Measurement Time Interval

Time to pass500 mL (sec)

Initial (T0) 31 5 minutes (T5) 45

10 minutes (T10) 67 15 minutes (T15) 106

The SDI for each time interval can be calculated using the equation above. The convention is to report the 15-minute SDI value.

SDI5 = [1 – (31/45)] x 100 = 6.22 5

SDI10 = [1 – (31/67)] x 100 = 5.37 10

SDI15 = [1 – (31/106)] x 100 = 4.72 15



SDI Equipment There are two devices that are commonly used to measure SDI:

1. Auto SDI Auto SDI is initially calibrated to a 500 mL flow. It has the convenience of automatically measuring the amount of time required for 500 mL flows at T = 0, 5, 10, and 15 minutes and calculating the individual SDI reading for each time interval. It has the disadvantage of shutting off once the flow through the instrument falls below 1.5 mLs per second. Of course, water with this low a flow level has a very high SDI reading.

2. Manual SDI Manual SDI is simply a pressure regulator and filter holder. It has the advantage of not shutting off. A disadvantage is that the 500 mL flow must be physically measured and timed for each time interval.

Feed water source must be constant 30 psi for the test and the SDI test equipment should include a pressure regulator capable of maintaining 30 psi during the test. Use the SDI booster pump kit if the feed pressure is inadequate.



6. Media Filter Typical Operating Parameters (Carbon, Multimedia, Greensand)

Feed water pretreatment for RO machines may consist of activated carbon filters, sand filters, multimedia filters, greensand filters, water softeners, and other means of solids removal. This section provides typical operational ranges. Always follow manufacturer’s written Operating Manual instructions and design specifications.

Activated Carbon Filters are specially prepared carbon beds that are designed to remove organics and chlorine from RO feed waters. The source and grade of the carbon media is critical for RO applications. Lignite and coconut-shell carbons are recommended (Hardness 95).Coal and soft-wood carbons generate fines that can cause downstream problems in the RO.

Activated Carbon Filter

Operating Pressure 25-100 psi Operating Temperature 35-120 F Turbidity <2 NTU Chlorine Removal limits 440,000 ppm per ft3 of carbon OperationLoading Flow rate For Chlorine Removal For Removal of Soluble Organics

3-5 gpm/ ft2 (120-205 L/min/m2)1-3 gpm/ft2 (40-125 L/min/m2)

Clean Bed pressure drop (delta P) 2-3 psi Max allowable pressure drop 15 psi Backwash Cycle Backwash flow rate 8-10 gpm/ft2 (325-410 L/min/m2)Backwash filter Source Filtered Feed water Rinse Cycle Fast rinse for 5 minutes, 2-3 bed volume Backwash frequency Breakthrough, volume or time

Note: Activated carbon removes incoming chlorine in the first several inches of media. This may result in the microbiological activity in the remainder of the bed. Periodic sanitizing is recommended.



Multimedia Filters are a combination, in descending layer order, of anthracite, sand and garnet. The density of the material determines the position in the layer. The combination of the three layers acts to remove a wide range of incoming solid contaminant particle sizes as small as 10-15 micron.

MMF – Multi Media (Anthracite, Sand, Garnet)

Parameter Max Inlet Limit Turbidity 50 NTU TSS 50 mg/L OperationLoading flow rate 4-7 gpm/ft2 (160-290 L/min/m2)Max allowable pressure drop 15 psi Clean bed pressure drop 5 psi Air scour (if equipped) 3 SCFM/ft2

Filter Backwash Backwash rate 15-20 gpm/ft2 (610-820 L/min/m2)Backwash source Feed or filtered RO brine Rinse source Feed Backwash frequency Delta P, Breakthrough on Turbidity

Multimedia filters can be used in concert with chlorine feed in front to oxidize and remove certain metals. Required chlorine dosages are in the following table:

Chlorine required for oxidation (ppm Cl2) Iron, Fe 0.6 Manganese, Mn 3.5 Hydrogen Sulfide, HS 8.5

Note: For polyamide (PA) membrane applications, all chlorine must be removed from RO feed water prior to contacting the membranes.



Greensand Filters are used to remove iron and manganese from RO feed waters. They function by oxidizing the iron and manganese to insoluble forms that are easily removed and held by the greensand media. Greensand filters require accompanying feed of potassium permanganate either with the feed or with the backwash. Chlorine is also use alone or in conjunction with permanganate in continuous feed applications.How they work: The surface of the sand is treated and coated with MnO2 groups that can change valence states. Upon contact, soluble Fe, Mn, and H2S are oxidized to an insoluble form. For example: 2(Z:MnO2) + 2Fe(OH)2 Z:Mn2O3 + Fe2O3 + 2H2O [Fe2+ ferrous] [Fe3+ ferric] The media bed serves to capture and filter insoluble particles.

Greensand Filter

Parameter Max Spec Iron (Ferrous) 15 ppm Manganese 2 ppm H2S 5 ppm Alkalinity 125 ppm OperationLoading flow rate 2-5 gpm/ft2 (80-205 L/min/m2)Bed depth based on Iron levels < 5 ppm Iron < 8 ppm Iron <15 ppm Iron

30” Greensand 36” Greensand 42” Greensand

Clean bed pressure drop (delta P) 3-5 psi Max allowable pressure drop (delta P)

15 psi

KMnO4 demand rate (3% KMnO4) 1 ppm /ppm of Fe+

2 ppm/ppm of Mn+

5 ppm / ppm of H2SGreenSand Filter BackwashBackwash flow rate 12-15 gpm/ft2 (485-615 L/min/m2)Backwash water source Filtered feed water Rinse volume 2-3 bed volume Backwash Frequency Time or water flow or pressure drop



7. Multi Media Backwash Practices Progressively finer layers of filter media trap increasingly smaller particles. The arrangement of the media (coarse and less dense on top grading to finer, higher density placed deeper in the bed) utilizes the entire bed and enables the filter to run for longer periods of time before backwashing is necessary. Dual-media filters remove suspended solids to as low as 10-20 microns in size, but no dissolved solids. The top layer is typically coarse anthracite followed by fine sand.

Multi Media Filters Turbidity is an excellent measure of MMF performance. Turbidity of < 0.2 NTU is a good output of the MMF. On-line turbidity instrumentation is recommended.

Backwash is recommended when pressure drop reaches 8 to 10 psi from a clean condition or from a previous backwash condition. To determine if the current back wash cycle is adequate, it is desirable to run a Turbidity Profile on the MMF backwash cycle. Turbidity measurements are taken periodically; i.e. every one or two minutes, and graphed turbidity vs. time. The graph will demonstrate whether the duration of the backwash was sufficient to remove the filtered solids.

Typically, if the turbidity at the end of wash cycle is <20 NTU, then the backwash cycle can be considered to be of sufficient duration and flow to have removed the majority of the particulates in the filter. If not, the backwash cycle needs to be lengthened.

Caution 1. Do not backwash based on time of operation alone, unless a

study has been completed that indicates that the time interval correlates to an 8 to 10 psi drop.

2. Backwashing too often can increase the possibility of channeling and insufficient time for filtration media conditioning (cake) to sufficiently form.



8. Cartridge/Depth Filter Replacement

Cartridge Filter Changing Cartridge filters were once considered only as a point-of-use water treatment method for removal of larger particles. However, breakthroughs in filter design, such as the controlled use of blown micro fiber filters (as opposed to wrapped fabric or yarn-wound filters), have tremendously broadened cartridge filter utilization.

Best Practice Change filters based on the pressure drop (delta P) across the filter housing. Cartridge filters are typically changed out after an increase of 10 psi delta P develops. The delta P needs to include temperature correction.

Filters can be changed based on scheduled time frequency. This can be dictated by the type of application or the end user requirement. Filters used for drinking water may be changed once per month regardless of the pressure drop.

Special industries like pharmaceutical and drinking water commonly change filters based on time where differential pressure does not build to an unacceptable level in order to avoid biological growth.

Newer filter technologies allow change-outs greater than 30 days before delta P is reached. Microbiological growth should be checked on change-outs greater than 30 days.

Types of Cartridge Filters Cartridge filters fall into two categories: depth filters or surface filters. One, 5, or 10 micron depth cartridge filters are commonly supplied ahead of RO systems. Most GEWPT RO machines come standard with 1 micron cartridge filters.



9. Chemical Feeding Sequence Due to the interaction and mixing requirements of pretreatment chemicals, the following order of application is generally followed. See a typical process flow diagram on the following page for feed points.

Acid (pH adjust) CoagulantMMFAntiscalantBiocide (intermittent, continuous) Bisulfite for Cl2 destruction Cartridge Filters

Note: Every system is different and individual system configurations may favor alternative feed points. For example, the chemical injection points on PRO-series machines are generally always upstream of the cartridge filter housing to maximize mixing and contact time and due to the proximity of other components.

Acid: Feed point can vary greatly depending upon its primary function. It may be fed ahead of the multimedia filter to aid in coagulation and precipitation, or it may be fed in conjunction with the antiscalant for improved scale control in the RO machine.

Antiscalant: Can be fed either upstream or downstream of the cartridge filters. On most machines, the injection point is upstream of the filters.

Biocide: Can be fed either upstream or downstream of the cartridge filters when feeding in a continuous or intermittent mode. An advantage of upstream injection is disinfection of the cartridge filters, a common source of biogrowth. When feeding biocide continuously at low levels, ensure that the bisulfite is not being fed in excess. Excess bisulfite will deactivate non-oxidizing biocides.

Bisulfite: Can be fed either upstream or downstream of the cartridge filters. An advantage of downstream injection is that chlorine residual is maintained through the filters and biogrowth within the cartridge filters is prevented.





10. Coagulant Feed and Selection Coagulant use in RO prefiltration systems is frequently necessary to reduce suspended particulates and turbidity of feed water to RO machines. This prevents deposits from forming on the membrane surface and in the feed/concentrate channel. Coagulants are mainly positively charged molecules.

Coagulants can be inorganic-based such as alum, polymerized alum (ACH or PAC), iron-based, organic cationic polymers, or a combination of inorganics and cationic polymers.

An ongoing debate exists about the impact organic cationic polymer use ahead of the prefiltration equipment might have on RO membranes. While cationic polymer coagulants may function well in reducing suspended solids and turbidity, they may also pass through to the RO system and foul the membrane surface with a difficult to clean residue.

There exists extensive evidence to support the use of SELECTED cationic polymer coagulants in RO pretreatment applications. There are a large number of existing customers that have used these polymeric coagulants for years without incident. In addition, published articles in technical journals and published laboratory data support the use of selected cationic polymer coagulants in RO pretreatment applications. GE Water has approved all coagulants in the Solisep MPT product line for compatibility with polyamide membranes.

The Best Practice is to recommend feeding coagulants at minimum levels required to produce water quality acceptable to feed to the RO. Typical feed rates can range from 1 ppm to as high as 15 ppm for the coagulants.

To determine the optimum product choice and optimum feed rate:

1. Conduct jar testing to select best performing product and approximate dose range.

2. Conduct SDI test pre and post multimedia to establish baseline condition before initiating coagulant feed.

3. Conduct online testing to determine optimum product dose by monitoring SDI post MMF at increasing coagulant feed levels, looking for lowest feed rate to produce the lowest SDI without increasing turbidity.

Always select chemical feed pumps sized to feed the targeted dose level in the middle of the pump’s dose range. Feed at a point that provides the most in-line mixing energy/time.



Streaming Current Detectors Some systems use streaming current detectors (SCD’s) to monitor and control coagulant addition. These on-line electro kinetic analyzers essentially measure the net electrical charge of suspended solids after coagulant dosing. They provide a feedback signal to adjust the chemical feed pump in response to the degree to which the charge on the suspended particles has been neutralized.

Warning Statements Controlling coagulant dosage is critical to prevent over/underfeeding. Underfeeding and overfeeding will both result in particulate build-up in membrane elements. Overfeeding can also result in membrane fouling.

It is important to select a coagulant that is chemically compatible with the antiscalant specified in the RO pretreatment program. Cationic polymer coagulants should not be used in conjunction with antiscalants that contain anionic dispersing agents.

Product Selection The selection guide on the following page can be used as a general guideline for coagulant application. Jar testing followed by online validation is always recommended for designing a coagulant program.

Note: Each global region has a limited number of products available. Refer to your country's price book for product availability.



11. Feed Water pH ControlThe pH of the RO feed water might require adjustment to improve coagulant performance, promote metals precipitation, or reduce scaling potential.

When addressing scaling potential, the acid dosage required to meet a given pH target can be estimated using Argo Analyzer software. Continuous pH monitoring is recommended.

Typically, sulfuric acid (Betz MPH9300) or citric acid (Betz MPH5000) is used to reduce pH. These products are competitively priced and NSF certified for use in potable applications.

Hydrochloric acid can also be used if it is desirable to avoid additional sulfate feed in potential sulfate scaling conditions. Always consult with a GE Engineer when considering hydrochloric acid to ensure compatibility with all materials of construction.

Always select chemical feed pumps sized to feed the targeted dose level in the middle of the pump’s dose range.

Betz MPH5000 Citric acid-based formulation50% Active Acid strength: Mild Typical dosage: 10 – 100 ppm (No max use limit for potable)Inhibits Fe and Al scaling Preferred for high sulfate waterAdditional cleaner functionality.Safe; non-toxic, non-corrosive

Betz MPH9300Sulfuric Acid-based formulation93% Active Acid Strength: Strong Cost-effective pH adjustment Typical dosage: 5 – 50 ppm (Max use limit = 50 ppm for potable)Preferred for use in large flow applications (economical)



12. Antiscalant Selection The reject stream from an RO machine is typically 4-5 times more concentrated than the feed stream (as illustrated below). As the ions from the feed water concentrate up, they often exceed saturation limits. Most systems will form scale/deposit without some form of pretreatment. Depending on the make up water, scale is prevented using pH adjustment, softening, antiscalant addition or some combination of these.

Hypersperse antiscalants are used to inhibit scaling and fouling in RO systems. The selection guide on the following page provides an overview of all Hypersperse products and shows which types of scale/deposit they effectively inhibit. Final selection and dosing requirements are determined using Argo Analyzer.



Note: Each global region has a limited number of products available. Refer to your country's price book for product availability



13. Argo Analyzer Software Program

Argo Analyzer is a software tool used to optimize antiscalant treatment programs for RO systems. It is simple to use, requiring the input of operating data and feed water quality (recovery, temperature, pH, elemental analysis).

This software uses the machine recovery to calculate the concentration factor. Based on the feed water analysis, the scaling potential in the system is then predicted. The user can compare the impact that each Hypersperse product has on saturation indices for a given feed water. Software outputs clearly specify the product, dosage, and additional operating guidelines such as pH adjustment (see illustration below). The software also contains many advanced features for skilled users as well as information about cleaner selection and cleaning procedures.



14. Bisulfite Feed and Dechlorination There are several reasons for feeding bisulfite-based products in a membrane application including:

Chlorine and oxidant removal Biocide deactivation Maintaining a reduced state to ensure iron solubility

Chlorine Removal Polyamide-based membranes are subject to damage upon exposure to chlorine or other oxidizing agents. There are several methods used to remove harmful oxidizers such as chlorine and chloramines from RO feed water including chemical reduction, UV radiation, and activated carbon. Sodium bisulfite is a commonly used chemical reducing agent that destroys chlorine via:

Hypochlorous acid removal: HOCl + Na2HSO3 NaCl + H2SO4

Chloramine removal: NH2Cl + Na2HSO3 + H2O NH4Cl + NaHSO4

Approximately 1.5 ppm of active sodium bisulfite is required to remove 1 ppm active chlorine, measured as total Cl2. The available sodium bisulfite-based products and recommended dosages for chlorine removal are provided in the following table.

Deactivation Product Dosage required to deactivate 1 ppm Total Chlorine (Cl2)*

BetzDearborn DCL30 / DCL32 4.5 ppm

BetzDearborn DCL95 1.5 ppm

*Note: Generally sodium bisulfite is overfed at 0.5 to 1.0 ppm (active sodium bisulfite) to provide a margin of safety. For example, 6 ppm of DCL30 might be recommended for a feed stream containing 1 ppm total chlorine. No more than a slight overfeed is recommended, as excess sodium bisulfite can indirectly contribute to biofouling.



Biocide Deactivation Sodium bisulfite-based products are also used to deactivate isothiazoline and DBNPA-based non-oxidizing biocides that are used to sanitize RO machines. Local regulatory authorities often require deactivation of these biocides prior to discharge or disposal. For deactivation, sodium bisulfite-based products can be fed directly to the concentrate discharge or they can be fed to a collection tank (such as the CIP tank after a biocide clean-in-place).

Note that biocides are typically rejected by RO membranes (there will be some passage of actives depending upon several variables). Therefore, their increased concentration must be accounted for in the concentrate stream when designing a bisulfite program (e.g. 3 ppm biocide in the RO feed will translate to approximately 12 ppm in the concentrate stream at 75% recovery).

The following table contains recommended dosages for biocide deactivation.

Dosage required to deactivate 1 ppm Biocide Deactivation Product

Biomate MBC781 Biomate MBC2881

BetzDearborn DCL30 / DCL32 2.3 ppm 2.4 ppm

BetzDearborn DCL95 0.8 ppm 0.9 ppm



15. Microbiological Control

Overview and Detection Microbiological fouling is a very common problem in membrane systems due to the chlorine free environment that is required for polyamide membranes. It can pose a significant threat to membrane equipment operation. It must be treated and/or prevented in order to maintain consistent equipment output and to minimize operational costs associated with maintenance and CIP operations.

Microbiological fouling is generally characterized by a rapid loss in RO performance as bacteria form slime layers that impede flow through the membranes. Feed pressure to the machine will be increased to maintain flow and differential pressure may increase. The presence of biofouling can sometimes be detected onsite via Bioscan™ ATP testing or culture-based methods. Microbiological fouling can also be detected in an off-site foulant analysis at The Woodlands facility. The cartridge filter housings and pressure vessels should be inspected for slime.

There are a wide range of methods used to treat and prevent microbiological fouling in polyamide-based membrane systems including chemical oxidation (e.g. peracetic acid, chlorine dioxide), ozonation, UV radiation, non-oxidizing biocides, biodispersants, and aggressive alkaline cleaning. The use of non-oxidizing biocides is generally the most common approach in industrial applications.

Biomate MBC Product Profile GE offers several Biomate MBC non-oxidizing biocides for use in membrane systems. These products are based on either isothiazoline or 2,2-Dibromo-3-nitrilopropionamide (DBNPA) chemistries.

DBNPA-based biocides function by inhibiting transport across cell membranes. These are fast-acting products that provide a rapid kill. Isothiazoline-based biocides function by disrupting cellular biosynthesis processes. These are slower acting products that provide long-term activity.

All Biomate MBC products are approved for compatibility with standard RO membranes and their decomposition processes yield benign by-products. See product selection guide on the following page.



Important: All biocide products must be used in compliance with federal, state, and local regulations. End users must strictly adhere to the instructions and restrictions on the EPA label. Biomate MBC non-oxidizing biocides must not be used in any application that is potable or where product water could be consumed by or injected into humans or animals. Contact the global Product Stewardship group for all questions and concerns related to biocide usage.



Microscopic image of a Biofouled Membrane at 1000X

Methods of Feeding Biomate MBC Biocides: Intermittent: This method of application is limited to DBNPA-based products due to their fast-acting nature. The product should be injected into the RO feed for 30 to 60 minutes during normal operation of the RO machine, with permeate and concentrate directed to drain or neutralization tank in accordance with site regulations. This is done periodically, from once or twice a week to quarterly. Dosage must not exceed label limits.

Clean-in-Place (CIP): Either DBNPA or isothiazoline-based biocides may be used. This method of application is often desirable for applications where an injection point is not available in the RO feed line, where discharge volume is limited, or where strict control and thorough deactivation of the biocide is required. The biocide solution is contained in the CIP tank and can be readily deactivated prior to discharge. Biocide CIP is most effective after an alkaline CIP cleaning but is sometimes conducted between cleanings, similar to intermittent treatment. Alkaline cleaning helps to disperse and remove biofilm. It is recommended that biocide CIP be conducted as a separate step in the cleaning sequence; contact a technical marketing expert to discuss options for combining with another cleaning step. Dosage must not exceed label limits. Note that a minimum of 4 hours contact time is recommended when using isothiazoline-based biocides in CIP Mode while 30 minutes to 2 hours is sufficient for DBNPA-based products.

Continuous: Either DBNPA or isothiazoline-based biocides may be used for this method of application. Continuous feed is generally limited to small to moderately sized systems due to the elevated cost of treatment. This method is also used for systems with unique microbiological fouling conditions that require a constant biostatic environment. Biocide product should be fed continuously to an injection point prior to the cartridge filters. Typical treatment will require initially higher dosages that can be reduced over time. Dosage must not exceed label limits.



Biocide Deactivation For systems where it is undesirable to discharge biocide-laden concentrate or CIP solution to municipal wastewater systems, BetzDearborn DCL30, DCL32, or DCL95 should be fed on the discharge side of the membrane equipment or directly to the CIP tank according to the guidelines in Section 14 “Bisulfite Feed and Dechlorination” of this handbook.

Potable applications: Non-oxidizing biocides cannot be used in potable water RO systems. These products are not approved for applications where permeate water or products formulated with permeate water can be consumed by or injected into humans or animals. The use of peracetic acid is the most common method for sanitizing membranes in these applications. GE Water does not supply peracetic acid based products for technical and commercial reasons.

Some general notes and guidelines are discussed below. Always follow the application guidelines and safety instructions of the chemical supplier:

Peracetic acid is a strong oxidizer and it can damage membrane elements. The general industry recommended dosage is 400 ppm (mg/L) maximum, of peracetic acid in off-line CIP cleaning mode. The peracetic acid cleaning solution should be circulated/soaked for less than 1 hour of contact time to minimize the potential for membrane damage. Any residual transition metals in or on the membrane will catalyze the oxidation process and result in rapid membrane damage, so it is critical that the membranes are thoroughly cleaned (acid and alkaline) prior to a peracetic acid sanitization. The system should be thoroughly rinsed before returning to normal operation.



16. RO Normalization Data Collection/Interpretation

Data collection and normalization are critical to monitoring RO performance. Data normalization is a process that corrects for changes in temperature, feed TDS, pressures, and other factors that affect RO system operation but may be unrelated to fouling or other membrane degradation processes. Typically, as the RO runs it slowly fouls over time. To compensate for this, the operating pressure is increased. The normalized flow shows what the flow would be if the pressure were not increased and therefore measures the degree of fouling that has occurred. Data normalization is especially important when the feedwater temperature is not constant. A one degree C change in feed temperature causes approximately 3% change in permeate flow. See Appendix 1 “Temperature Correction Factors”

Flow, differential pressure, and salt rejection are the 3 critical factors to monitoring system performance. When these performance indicators are charted, it is easier to detect changes in performance and troubleshoot potential problems before they become critical. An example of a typical data collection sheet and normalization graphs are shown on the following pages. A downloadable spreadsheet is available in Sales Edge.

Data collection should begin immediately following start up. A baseline to determine operational norms is established after a minimum of 24 hours and could take a week of continuous running. This gives the membranes time to flush out preservatives, to seat properly, and to settle into their operating environment.

Best Practice: A cleaning should be conducted when there is:

A reduction in normalized permeate flow of 10 to 15%, And/or an increase in normalized differential pressure of 25%, And/or an increase in normalized salt passage of 25% (see note below).

Notes on these guidelines: most membrane manufacturers set the same or similar guidelines. If these guidelines are exceeded, in some cases it becomes difficult to restore membrane performance. The recommendation for salt passage as a trigger for cleaning is a rough guide and will vary greatly depending on the need for permeate quality. Depending on the type of fouling, the % rejection may or may not be



affected. Typically, the rejection will remain somewhat constant and slowly decrease over time as the membranes age. Usually, when the rejection is graphed, we look for the steady decline from aging, or sudden changes that occur from mechanical leaks such as o-ring failures. Membrane fouling does not always cause an increase in salt passage and will sometimes improve rejection. Membrane scaling can, however, lead to increased salt passage. Permeate quality will not always be restored by cleaning and it may worsen.

Data Collection Sheet (spreadsheet)

GE Infrastructure Water & Process TechnologiesReverse Osmosis Data Collection Sheet

Feedwater Quality: Units

pH RO Feed

Free RO Feed ppm

Total RO Feed ppm

In NTU

Out NTU

RO Feed NTU

In

Out

RO Feed

Machine Readings: Units

Temperature F

Run Time Meter Elapsed Hours Hrs

Feed GPM

Permeate GPMBrine GPM

In PSI

Out PSI

Feed PSI

Interstage 1 PSI

Interstage 2 PSI

Brine PSIPermeate PSI

Feed µmhos

Permeate µmhosBrine µmhos

Pressures Cartridge Filter

RO

Conductivity RO

MMF

Flows RO

Date

Chlorine

Turbidity MMF

SDI



Normalization Spreadsheet Graph Examples

Normalized Flow Vs Time

0

50

100

150

200

250

300

350

Date

Flo

w

Permeate Flow Normalized Permeate Flow

Differential Pressure Vs Time

-

20

40

60

80

100

120

Date

Dif

fere

nti

al

Pre

ssu

re

System DP

Normalized Salt Passage Vs Time

0.0%

0.5%

1.0%

1.5%

2.0%

Date

% S

alt

Passag

e

Salt Passage Normalized Salt Passage



17. RO Troubleshooting Guidelines Troubleshooting actions are based on evaluation of normalized data charts. Identify which of the following parameters has changed from baseline (start up or last clean):

Normalized permeate flow Normalized salt passage Normalized differential pressure

The primary steps to troubleshooting are

1. Analyze data and establish change in performance 2. Identify possible causes. 3. Perform additional test to verify the cause. 4. Implement the corrective action.

To aid in troubleshooting, use the next two charts to locate the problem (steps 1 & 2) and identify possible solutions (steps 3 & 4).

Locating RO Problems Symptoms

Normalized Permeate

Flow

Normalized Salt Passage

Normalized Pressure

Drop

Location Possible Cause

Decreased Normal to increased

Normal to increased First stage

Metal oxide fouling, Colloidal Fouling, Biological Fouling

Decreased Increased Increased Last bank Scaling (CaSO4, BaSO4,SiO2,)

DecreasedDecreased or moderately increased

Normal to increased All banks Organic fouling

Normal to low Increased Decreased All banks Recovery too high

Normal to increased Increased Normal Random

O-ring leaks, end or side seal glue leaks, backpressure damage

Increased Increased Normal First bank,

slightsecond

Chlorine oxidant attack, Abrasion of membrane by crystalline material



Solving RO Problems

Possible Cause Verification Possible Corrective Action

Metal oxide fouling Analysis of metal ions in cleaning solution, current water analysis

Improved pretreatment to remove metals. Cleaning with acid cleaners.

Colloidal fouling

SDI measurement of feed. X-ray diffraction analysis of cleaning solution residue ICP metals?

Optimize pretreatment system for colloidal removal. Clean with high pH, anionic detergent formulation

Biological fouling Slime in pipes and vessels. Septic smell in the vessels or filter housings.

Shock or online treatment of Non-oxidizing Biocide. (Non Drinking water) Clean with alkaline (High pH) anionic surfactant. Chlorine dosage up-stream with subs. Dechlorination. Replace cartridge filters. Check for SBS overfeed.

Scaling (CaSO4,BaSO4, SiO2,)

Analysis of metal ions in cleaning solution. Check LSI of reject. Calculate maximum solubility for CaSO4, BaSO4, SiO2, in reject analysis.

Increase acid addition and scale inhibitor for CaCO3 and CaSO4. Reduce recovery. Clean with an acid formulation for CaCO3, CaSO4 and BaSO4.

Organic fouling Destructive testing, e.g. FTIR analysis.

Optimization of pretreatment system (e.g. coagulation process). Resin/activated carbon treatment. Clean with high pH cleaner.

Recovery too high Check flows and pressures against design guidelines.

Reduce conversion rate. Calibrate sensors. Increase analysis and data collection.

O-ring leaks, end or side seal glue leaks Probe test. Vacuum test. Replace O-rings. Replace

elements. Chlorine oxidant attack

Chlorine analysis of feed. Destructive element test.

Check chlorine feed equipment and Dechlorination equipment.

Abrasion of membrane by crystalline material

Microscopic solids analysis of feed. Destructive element test.

Improved pretreatment. Check all filters for media leakage.



18. RO CIP CleaningAll RO systems require cleaning--some applications require frequent cleaning (e.g. monthly), while others require infrequent cleaning (e.g. yearly). Generally, quarterly is considered a desired target for cleaning frequency. During the operation of an RO, the levels of dissolved solids in the concentrate can increase beyond saturation limits, resulting in precipitation on the membrane surface. In addition, organic materials and suspended solids in the incoming water can accumulate on the membrane surface and within the feed channels.

Membrane fouling can result in decreased permeate flow, increased pressure drop, and in some cases, increased salt passage. When foulants accumulate to a level where RO performance is impacted, a clean-in-place (CIP), off-line cleaning should be conducted. Indications of the need for cleaning include:

A reduction in normalized permeate flow of 10 to 15%, And/or an increase in normalized differential pressure of 25%, And/or an increase in normalized salt passage of 25% (see Section 16).

Cleaning Sequence

A typical cleaning procedure specifies low and high pH cleaning solutions. It is generally more common to clean with acid first, however the cleaning sequence should be dictated by the nature of the foulant. For example, if the system is predominantly fouled with organics, particulate material, or microbiological species, then alkaline cleaning should precede acid cleaning. When appropriate, an additional biocide-cleaning step is also incorporated into the sequence.

Product Selection:

The chemical products used for membrane cleaning should be selected based upon the nature of the suspected foulant, regional availability, and any system specific limitations such as membrane compatibility, regulatory restrictions (e.g. use of EDTA), and handling limitations for powders or liquids.

For most products, 2.0-2.5 lbs of cleaner are recommended per 8-inch by 40-inch element. Estimating the amount of chemical and dilution water to use for cleaning can be difficult. There are online CIP tools available to estimate chemical addition and water volumes in order to ensure an effective cleaner concentration.



The selection guide below can be used to identify specific cleaners, typical product dosages, and make-down pH and conductivity targets.

Note: Each global region has a limited number of products available. Refer to your country's price book for product availability



CIP System Design CIP system design can be either 1) high pressure, full machine or 2) low pressure, bank by bank cleaning. GE has standard platform equipment that incorporates each method. Appendix 2 contains a sample procedure for high pressure, full machine cleaning. Low pressure cleaning will follow similar steps. Specific procedures are included in O&M manuals.

High pressure cleaning (up to 175 psi) employs a booster pump from the CIP tank and the high pressure skid pump to deliver the appropriate flow. The pressure is controlled by a throttling valve on the main pump discharge, and either a concentrate valve or a bypass valve (in the case of orifice plate back pressure control). This method cleans all banks of the skid simultaneously. There will be a lower capital cost for this equipment, and less cleaning chemical and time will be required to clean the system.

Low pressure cleaning (40 to 100 psi) is typically available when the skid is piped to allow bank-by-bank cleaning. If the machine has three banks, the second and third banks are generally cleaned together. The primary pump for this cleaning is an independent CIP pump which bypasses the main pump, delivering cleaning solution directly to the feed manifolds. Bank by bank cleaning prevents the potential redeposit of particulate materials in subsequent banks by maintaining optimum flow velocities in each bank. The low pressure minimizes the generation of permeate which pulls foulant toward the membrane instead of across the membrane and out of the system. Higher flow velocities are achieved using this method and it can be more effective in cases of severe fouling.

Foulant-Specific Cleaning The next several chapters discuss common foulants in general terms. Generic cleaning strategies are discussed without specific reference to any GE Water performance products. Use the cleaner selection guide on the previous page and/or consult a Technical Marketing Expert to develop a site-specific cleaning strategy.



SEM Image of CaCO3 Scale on a membrane surface

19. Calcium Carbonate Scale Calcium carbonate precipitation occurs quickly and before the precipitation of other scaling species. Fortunately, there are several methods of preventing this scale in an RO and, if it occurs, it is generally easily cleaned. The commonly used criterion to determine calcium carbonate scale potential is the Langelier Saturation Index (LSI). Argo Analyzer is an excellent software tool that uses LSI calculations to predict calcium carbonate scaling and model the effects of pH, temperature, unit recovery, and antiscalant use.

Calcium carbonate scaling occurs primarily in the last bank of multi-banked systems. Scale formation is characterized by significant losses in flux and salt rejection and an increase in differential pressure. Scale formation generally proceeds rapidly after an initial induction period that may last from several days to several weeks.

Cleaning strategy

Calcium carbonate scale can be readily dissolved in a low pH solution. A pH below ~4 is typically required to dissolve and prevent re-deposition. For severe cases, an overnight soak may be warranted. Cleaning solutions should be periodically circulated to introduce “fresh” cleaning solution to the scaled membrane surface. The pH of the cleaning solution should be checked frequently since the acid solution will be partially neutralized as scale is removed. Add additional acid as need to maintain the target pH.

When calcium carbonate scale is identified as the primary foulant, the cleaning sequence should specify acid cleaning first, followed by alkaline cleaning.

Chelating agents such as citric acid or EDTA may improve cleaning performance by removing the metal ions from complex foulant matrices and subsequently allow for other cleaning mechanisms to take place.



SEM Image of BaSO4 Scale on a membrane surface

20. Sulfate-Based Scale Sulfate-based scales are among the most challenging foulants for RO systems because they are difficult to clean. Sulfates are present in raw water sources and levels in RO feed water are often elevated by the use of pretreatment chemicals such as sulfuric acid for pH control or aluminum and iron sulfates for coagulation.

The solubility of sulfates in water is limited and dependent upon the concentrations of divalent ions such as barium, strontium, calcium, and magnesium. Sulfate-based scale is most often precipitated as calcium or barium sulfate. Barium sulfate is the least soluble sulfate salt and is particularly difficult to clean. When barium is present in water at levels greater than 0.05 ppm, there is potential for rapid precipitation that can subsequently catalyze scaling of other sulfate salts (i.e. calcium or strontium). The adjacent SEM image shows barium sulfate scale on a membrane.

Cleaning strategy Calcium sulfate may be removed by using an alkaline solution containing EDTA and elevated levels of bicarbonate. The mode of action for this method is believed to involve displacement of the sulfate with carbonate to form calcium carbonate and liberate sulfate ion into solution. The EDTA is present to chelate the calcium ions and keep them in solution. Extended soak times and elevated temperatures improve foulant removal. The alkaline cleaning step should be followed by an acid cleaning step to remove any insoluble calcium carbonate or calcium hydroxide that remains.

Barium and strontium sulfate scales are very difficult to remove. It is critical that pretreatment steps be taken to prevent these types of sulfate scales.



21. Iron and Manganese Fouling Iron and manganese exist either in a reduced state, which is generally considered soluble, or an oxidized state, which has negligible solubility. The solubility curve below shows the significant difference in solubility of iron in the reduced and oxidized states.

In most water sources, iron is more prevalent than manganese. Most well water sources tend to have elevated levels of iron that must be addressed with pretreatment equipment and chemicals. Other sources of high iron levels include carbon steel pretreatment equipment and piping or overfeed of ferric-based coagulants.

Ferrous iron is rapidly oxidized to colloidal ferric hydroxide in the presence of oxygen, permanganate, or chlorine. Low levels (>0.05 ppm) of iron or manganese in the oxidized state can foul an RO system if not treated by a suitable antiscalant. Precipitation of these metals tends to cause fouling in the first bank of multi-banked systems. Symptoms of metal precipitation are loss of flow and salt rejection and sometimes increased differential pressure.

Since iron is so readily oxidized to an insoluble state, most systems specify upstream oxidation and filtration for removal prior to the RO. This can be accomplished with multi media filters or greensand filters, which are specifically designed for this purpose. Note that an alternative method of preventing iron fouling is to maintain a reduced environment via excess reducing agent (e.g. bisulfite). This approach has had some success, but it has not been extensively employed.



Image of an iron-fouled membrane

Cleaning strategy Effective cleaning is strongly correlated with pH. The pH of the cleaning solution should be less than 2.5 for ferric iron solubility (refer to previous solubility curve). It is critical that the membrane manufacturer’s limit for minimum cleaning pH (typically ~2) is not exceeded. Chelating agents such as citric acid or EDTA will improve cleaning performance.

When iron or manganese is identified as the primary foulant, the cleaning sequence should specify acid cleaning first, followed by alkaline cleaning.

For severely fouled systems, strong reducing agents such as sodium bisulfite or hydrosufite (sodium dithionite) can be used to reduce the iron to a ferrous state. Sodium dithionite works very effectively in this application, but handling caution is required as it is a hazardous material with significant reactivity concerns.



22. Aluminum Fouling The presence of aluminum in feed water can derive from a variety of sources. In surface waters, aluminum may exist as naturally occurring silt or it may react with silica to form aluminum silicates. Municipally treated waters often contain aluminum carryover from aluminum-based coagulants.

There are three basic strategies to address incoming aluminum: (1) antiscalant addition, (2) injection of a chelating agent such as citric acid, and (3) pH adjustment. As shown in the solubility curve below, minimum solubility of aluminum occurs at pH ~6.7. Adjusting to pH 6.7 ahead of media filters reduces soluble aluminum levels and enables removal via filtration, thus reducing membrane fouling potential.

In an RO application, aluminum fouling can occur via several mechanisms, therefore it is recommended that the aluminum level in the feed water be maintained below 0.1 ppm. Precipitation of aluminum tends to cause the greatest degree of fouling in the first bank of multi-banked systems. Symptoms of aluminum precipitation are loss of flow and salt rejection and sometimes increased differential pressure. The increased differential can occur in the front of the system, due to blockage of the feed/concentrate channel, or in the back of the system due to increased flows caused by the fouling. In the latter case, differential pressure will be reduced when the foulant is removed from the front of the system.



Cleaning Strategy High or low pH cleaning solutions can be effective at removing aluminum-based foulants based upon the solubility of aluminum (see solubility curve above). Aluminum oxide and aluminum hydroxide are typically cleaned using an acidic cleaning solution. Aluminum that is complexed in a colloidal form is best cleaned with alkaline cleaning followed by acid cleaning. Chelating agents such as citric acid or EDTA will improve cleaning performance. High pH cleaners containing neutralizing amines are often most effective for removing colloidal aluminum.



23. Silica Scaling and Fouling Silica has two forms in natural waters: soluble and colloidal. Both are of concern for RO system operation. Solubility is quickly exceeded in the reject stream of an RO system when the feed water contains high levels of silica. Soluble or dissolved silica is usually represented as monomeric Si(OH)4, though its exact form in unknown. Colloidal silica is comprised of polymerized Si(OH)4 which forms Si-O-Si links. Colloidal silica has very little charge at low pH and a negative charge in neutral pH or higher.

There are three forms of deposition that can occur in an RO system:

Soluble silica supersaturation: 1. Soluble silica can deposit as an impervious glass-like film on the

membrane surface. This occurs as scale beginning in the back of the system.

2. The soluble silica can polymerize to form colloidal particles.

Colloidal particle deposition: 3. Colloidal particles not removed by pretreatment can deposit on

the membrane surface. This is typically a problem in the front of the system, but can also occur in the last bank if the RO is run at high recovery and not enough cross-flow is achieved. It is more likely to occur if there is biological fouling.



Cleaning Strategy When membranes are scaled by silica, the scale is almost impossible to remove. Some high pH cleaners applied with extended soak times (12-24 hours) generally improve, but do not restore, the performance. More effective cleaning solutions are limited to dilute ammonium bifluoride or hydrofluoric acid. These chemicals are, however, extremely hazardous, and are not recommended for use.

Deposits of colloidal silica can be removed by high pH cleaners, as long as soluble silica did not also deposit. Maximum pH and temperature will improve chances for success in cleaning. Alkaline cleaning should be followed by acid cleaning to remove any inorganic scale.



Colloidal Fouling on a membrane surface- Open View

24. Colloidal Fouling A colloid is a fine, suspended solid that resists settling. Colloidal fouling occurs in all pressure driven membrane separation systems, regardless of the feed water source. In natural waters, colloidal foulants include clays, silica, hydrous metal hydroxides, and organic debris. For process streams, colloidal foulants may include the product to be separated or concentrated by the membrane process (e.g., paint pigments, proteins, bacterial and yeast cells, high molecular weight alcohols). Colloidal substances generally have surfaces that are slightly charged and may be attracted to the membrane.

In multi-banked membrane systems, colloidal fouling is often most severe in the first bank. Symptoms of colloidal fouling are reduced permeate flow and increased differential pressure. In RO processes, salt rejection may remain the same or decrease slightly as fouling progresses. If colloidal fouling is allowed to proceed unabated, all banks will eventually be affected.

For RO applications, the SDI test is widely used to predict the colloidal fouling tendency of feed waters. This test is not always a good predictor of fouling since it does not truly simulate the cross-flow hydraulics of spiral wound RO and NF elements.

Cleaning Strategy When metal hydroxides are present with other colloidal foulants, such as clays, sequential cleaning is recommended, starting with acid. When metals are absent, clay (aluminum silicate) fouling generally can be cleaned with the alkaline solution alone.

When systems are fouled by colloids, high velocities and high temperatures are essential for effective cleaning, especially if there are high differential pressures. Sometimes, alternating between soaking and recirculating the cleaning solutions can help dislodge particles caught in the feed spacer of RO elements. Overnight soaking of fouled elements in an alkaline cleaning solution may also be necessary.



Biofilm fouling on a membrane feed channel

25. Microbiological Fouling Microbiological fouling is a very common problem in membrane systems due to the chlorine-free environment that is required for polyamide membranes. It can cause a significant performance issue for membrane equipment and must be prevented to minimize operational costs associated with maintenance and CIP operations.

Microbiological fouling is generally characterized by a rapid loss in RO performance as bacteria form slime layers that impede flow through the membranes. Feed pressure to the machine will be increased to maintain flow and differential pressure may increase.

The presence of biofouling can sometimes be detected onsite via Bioscan™ ATP testing or culture-based methods. Membrane elements can also be opened and examined under microscope at the Woodlands facility to detect microbiological fouling. The cartridge filter housings and pressure vessels should be inspected for slime.

Biofouling affects membrane system performance in several ways including:

As bacteria colonize and multiply on membrane surfaces, they may exude slime (e.g., polysaccharides), which is a potent membrane foulant.Bacteria and slime accumulations also affect boundary layer conditions above the membrane surface, thereby increasing the potential for colloidal fouling and scale formation.Bacteria may colonize on the permeate side of elements and periodically slough slime and bacteria into the permeate stream. Because permeate is used for rinsing and process applications, many industries, including the electronics and biomedical, cannot tolerate even moderate numbers of bacteria in the permeate stream



Cleaning Strategy A system that is fouled with biofilm and microbiological species should always be cleaned first with an alkaline cleaning solution. This is critical because exposure to strongly acidic conditions can cause biological foulants to crosslink, resulting in a “hardened” foulant layer that is very difficult to clean.

The pH of the alkaline cleaning solution is strongly correlated to the ability to remove biofilm. Studies have shown that a pH=12 cleaning solution will be approximately 10 times more effective at removing biofilm than a pH=10.5 cleaning solution.

In systems that have experienced or are prone to biofouling, a biocide or sanitizing program should be considered. Refer to Section 15 “Microbiological Control” for detailed recommendations and strategies for controlling and preventing microbiological fouling.



Hydrocarbon fouling on the feed end of a membrane

SEM image of a membrane fouled by incompatible chemicals

26. Organic and Chemical Fouling Organic and chemical fouling can result from a very broad class of chemical species including natural organics (e.g. humic and fulvic acids), polymers, hydrocarbons (oils & grease), surfactants (cationic and most nonionic), quaternary amines, and many others. Fouling results in a loss of flux, which can be difficult to restore with cleaning.

Chemical fouling typically occurs when soluble or emulsified, reactive organics contained in feedwaters adsorb to membrane surfaces. In some cases the bonding to the membrane surface can be irreversible. The following properties of organic molecules tend to result in organic fouling via the adsorption mechanism:

High molecular weight (e.g. certain classes of polymers) Cationic charge (e.g. quaternary ammonium salts) Low water solubility or hydrophobic character (e.g. hydrocarbons and certain classes of surfactants)

Another form of organic fouling can result from precipitation reactions. Many feedwater constituents, including naturally occurring species, chemical additives, and heavy metals, may be incompatible. Examples of incompatible chemicals are anionic polyacrylate antiscalants with cationic polymer coagulants.

It is not always possible to predict whether specific organic chemicals will adsorb to membrane surfaces. For example, it is known that quaternary ammonium chloride surfactants bind irreversibly to PA type membranes, however some quaternary amine coagulants do not. Compatibility of all pretreatment chemicals should be verified.



Cleaning Strategy Alkaline cleaners containing surfactants are best suited for most organic foulants. Maximum pH and elevated surfactant levels will generally improve cleaning performance by penetrating, breaking up, and/or emulsifying organic foulants. Cleaning with high pH cleaners first is critical since exposure to strongly acidic conditions can cause some organic foulants to crosslink, resulting in a “hardened” foulant layer that is very difficult to clean. Chemical contact time is important and extended soak time is highly recommended.

Polymer fouling often presents a unique challenge for RO systems. In many cases, aggressive alkaline cleaning is not sufficient to remove the foulant and restore performance. In these situations a “brine squeeze” may be considered. A ~5% NaCl solution adjusted to pH 11 is circulated through the system in CIP mode at low pressure (<60 psi). Brine solutions can be very effective at removing chemical foulants. It is critical that a full-machine, high pressure cleaning is not attempted using a brine solution.



27. Membrane Autopsy Results and Interpretation An elemental autopsy is recommended when all non-destructive testing procedures and troubleshooting steps have been conducted and they have failed to uncover the cause of the reduced RO system performance. If there is an issue with the performance of the membrane and suspected warranty claim, the issue should be handled through the manufacturer of the membrane. For GE membranes, this is processed through the Minnetonka, MN office. An RGA (Returned Goods Authorization) is required.

Membrane issues that would be examined through the autopsy process include membrane oxidation and backpressure damage. In most cases of troubleshooting, a deposit/foulant analysis is sufficient. For situations where there is severe scaling or fouling, a high cleaning frequency, or difficulty cleaning and the deposit needs to be characterized, then a deposit/foulant analysis, not a membrane autopsy, should be performed.

The results of an autopsy are evaluated to identify the potential cause of reduced membrane performance and to develop remedies and treatments for the conditions leading to the cause. It is crucial to the process to have normalized operating data, as an autopsy is only one part of the troubleshooting process. A qualified specialist should interpret the autopsy.

The steps in a membrane autopsy are shown on the following page.



Steps in a membrane autopsy:



28. RO Storage Practices and Procedures When an RO machine is shut down, careful consideration must be paid to storage procedures in order to minimize the potential for microbiological growth in the system. Stagnant, untreated conditions create a thriving environment for microbiological organisms. Over time, a biofilm will form and it can be very difficult to remove.

Short term shut down of an RO system (24-48 hours) generally does not require special membrane storage procedures. The RO should be cycled (run in operational mode) for at least 15 minutes every 24-48 hours to reduce the potential for bio-growth and stagnation within the system. Some systems use a permeate flush during shutdown. This type of cycling will allow the system to remain “operationally” ready, and it will allow for a slightly longer time between flush cycles.

For prolonged storage (i.e. several days to several months), the following procedures are recommended. These procedures will help protect and preserve the elements from bacterial growth. The elements can be left in their housings or unloaded and stored separately.

Typically, one of the following lay-up solutions is used depending upon application, regulatory limitations, preference, and chemical availability:

1. 0.5 to 1.0% sodium bisulfite or 3.0% BetzDearborn DCL30 2. Isothiazoline-based non-oxidizing biocide such as Biomate

MBC781 according to EPA use-limitations. 3. 1.0 to 2.0% citric acid or 4% Betz MPH5000; 2% Kleen MCT442;

10% Kleen MCT882.

Note: DBNPA-based biocides such as Biomate MBC2881 have been successfully used for membrane lay-up, however some membrane manufacturers do not recommend using this chemistry due to the potential by-products formed by a long-term hydrolysis mechanism.

The following procedure is recommended for RO storage in sodium bisulfite or biocide solution.

1. Clean the membrane elements via standard clean-in-place procedures, and thoroughly rinse the RO system.

2. Prepare the appropriate strength sodium bisulfite or biocide solution in the CIP tank by diluting with permeate water.

3. Circulate the solution through the RO system for 15 to 20 minutes.



4. When the RO system is filled with this solution, close the valves to retain the solution in the RO.

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

6. When the RO system is ready to be returned to service, flush the system to drain until the permeate water meets quality specifications, then return the machine to service.

Important Note: Over time, sodium bisulfite will become oxidized and form sulfuric acid, lowering the pH. The pH of the lay-up solution should be monitored monthly and fresh solution added if the pH drops to pH=3 or lower, in order to safeguard the membranes.

An alternate procedure that requires less maintenance specifies the use of citric acid or a low pH cleaning solution to “Pickle” the system. The following procedure is recommended:

1. Clean the membrane elements via standard clean-in-place procedures, and thoroughly rinse the RO system.

2. Prepare the appropriate strength citric acid solution in the CIP tank by diluting with permeate water.

3. Circulate the solution through the RO system for 15 to 20 minutes.

4. Shut the RO system down. 5. Valve off CIP tank and drain tank. 6. Leave the acid solution in the RO machine.

The elements can remain in the housings for over a year without any change in element performance, provided the storage temperature is below the maximum element operating temperature.



29. Membrane Element Installation Membrane Elements produce permeate in their “membrane envelope” which contains two sheets of membrane glued together on the outer edges with a permeate carrier between them. The open end of the membrane envelope is arranged to deliver permeate to the perforated permeate tube. Membrane envelopes are separated by a feed water carrier that carries the concentrated feed through the element and on to the next element or the housing exit (see image below).

The element structure is usually contained in a hard casing (fiberglass wrap). Anti-telescoping devices (ATD) are present on both ends of the element and a brine seal is located on the feed end to prevent by-pass between the element and the wall of the housing. In some applications, for example in the beverage and food industries, full-fit membranes are used to eliminate the difficult-to-clean stagnant areas between the membrane casing and housing. Full-fit membranes do not have a hard outer casing. They are wrapped in netting material and have no brine seals.

Element Housing is the tube in which the elements reside.

Interconnectors are hollow plastic tubes with O-rings on each end. They are designed to fit into the countersunk permeate tube and to provide a sealed connection between elements. Solid interconnectors are used when spacer tubes are installed (see appendix 3).

Brine Seal is the gasket on one end of the element that forms a barrier to concentrate flow around a membrane element so that the concentrate is



forced to flow through the element feed spacer instead of bypassing the element.

Membrane Element Loading Instructions 1. Load an element into the upstream or feed end of the pressure

vessel. The brine seal should face the upstream end of the vessel to prevent feed bypass when the unit is in operation. Leave 6" of the element exposed beyond the end of the pressure vessel to facilitate loading succeeding elements.

2. Record the serial number and location of the element. 3. Apply glycerine to the O-rings of an interconnector. With a twisting

motion, insert the interconnector into the central tube on the upstream end of the previously loaded element. Rotate the interconnector to insure that the O-rings have been seated.

4. Line up a second element with the interconnector of the first element. With a gentle pushing and twisting motion, insert the interconnector into the downstream end of the second element.

5. Push both elements forward until about 6" of the second element extends beyond the feed end of the pressure vessel.

6. Record the serial number and location of the second element. 7. Repeat the loading process for the remaining elements. 8. When all elements have been loaded into a pressure vessel, insert

glycerine lubricated product end adaptors into the first and last elements in the vessel.

9. Connect the downstream pressure vessel end cap to the product end adapter and secure the end cap.

10. The following figure illustrates the correct placement of interconnectors and elements within a pressure vessel.

Typical Installation



30. Pressure Vessel ProbingThe timely and proper interpretation of operational plant data is key to maintaining RO system performance and minimizing unscheduled maintenance.

Many factors can affect permeate quality including changes in feed water quality or temperature, changes in recovery rate or flow, physical or chemical degradation of membranes, and leaking seals and o-rings. When a significant change in salt passage (or salt rejection) performance is observed, a further study should be conducted to differentiate between: 1) membrane degradation affecting permeate quality across all banks, or 2) a localized problem that may require isolation of only one or several vessels.

The permeate conductivity of all pressure vessels should be measured regularly at each individual sample port to detect general poor salt rejection from any given portion of the RO system. Below is an illustration of a typical 2-bank system permeate conductivity profile:

Same-bank vessels should have a similar permeate conductivity. The average permeate conductivity will increase toward the back of the system. So, the second bank should have a higher average conductivity than the first bank. In 3-bank systems, the last bank will have the highest average permeate conductivity.

If one of the vessels shows a higher conductivity than the rest of vessels in the same bank (shown in red in the image above), this vessel should be probed. This will help confirm possible O-ring leakage or membrane damage. By comparing probing results to expected conductivity values the root cause(s) of poor permeate quality can be identified.



General Probing Instructions The 1-inch permeate plug should be removed from the end of the pressure vessel and replaced with a permeate port sample valve that will accommodate ¼-inch tubing. A suitable length of ¼-inch tubing should be introduced through the sample valve and into the permeate collecting tube. The tubing should be pre-measured to ensure it reaches the far end of the vessel and spans the entire vessel length. While the machine is running in normal operation, conductivity should be measured and recorded at regular intervals throughout the pressure vessel by extracting the ¼-inch tubing incrementally between each measurement. Measurements should be taken at the ends of the vessel, at the center of each element, and at each interconnector. The ¼-inch tubing can be pre-marked for each interval or a tape measure can be used to accurately measure the length of tubing that is pulled out of the sample valve between each measurement.

The above graph shows vessel probe profile data for a vessel containing an interconnector with an O-ring failure (red line) versus the expected profile (black line). Suspect elements should be unloaded for an O-ring inspection. If membrane degradation is confirmed, affected element(s) should be replaced.



Appendix 1. Temperature Correction Factors (TCF) Temperature Correction Factors for thin film composite membranes:

Note: This table is only to be used for PA (TFC) membrane elements.

A Temperature Correction Factor (TCF) is used to predict what a membrane element will produce at a temperature different from the temperature specified by manufacturer’s flow rating. This TCF table relates flow at given temperature (T) to flow at 77°F (25°C). The table assumes 200 psig (13.7 bar) effective pressure.

Corrected Flow at given T = Flow rating at 77F TCF at given T

Example: An Osmo PRO 100 produces 100 gpm of product at 60°F (15.5°C). To determine what the machine will produce at 55°F, the equation above is applied (correcting flow up from 60F rating, and then down for 55F actual temperature).

The machine will produce: 100 gpm x 1.3958 (TCF @ 60°F) = 89 gpm 1.4280 (TCF @55°C)



Appendix 2. Sample Cleaning Procedure The following is a sample procedure for high pressure, full machine cleaning for a PRO-Series RO system. Low pressure cleaning will follow similar steps. Specific procedures are included in O&M manuals.

1. Install new pre-filters. GE recommends replacing the pre-filters prior to and after cleaning.

2. Fill the CIP tank. 2.1 With the RO machine running, open the CIP permeate service

valve. The CIP permeate valve is on the RO machine next to the service permeate valve.

2.2 Open CIP tank drain valve. 2.3 Close the permeate service valve. Permeate water will flow into

the CIP tank. 2.4 Let the water run through the CIP tank and the CIP drain valve

for 2 – 3 minutes. This ensures the tank is thoroughly rinsed. 2.5 Close the CIP tank drain valve. The CIP tank will begin filling with

RO permeate. 2.6 When the CIP tank has filled to at least 3/4 full, turn the

OFF/AUTO/HAND/FILL switch on the RO machine to the OFF position.

3. Divert the permeate and concentrate streams for recirculation. 3.1 RO machine is OFF. 3.2 Close the service inlet valve. 3.3 Open the service CIP inlet valve. 3.4 Open the CIP concentrate valve. The CIP concentrate valve is

next to the service concentrate valve 3.5 Close the service concentrate valve. These steps divert the

permeate and concentrate streams to the CIP tank for recirculation and isolate the RO and CIP from the rest of the water treatment system.

4. Recirculate the cleaning water. 4.1 Turn the CIP HAND/OFF/AUTO switch to the AUTO position. 4.2 Turn the main OFF/AUTO/HAND/FILL switch to the HAND

position.4.3 Recirculate the water. 4.4 Add chemical cleaners to CIP tank per cleaner instructions.

Recirculate the cleaning solution for approximately 30 – 90



minutes. When cleaning with the high pH (alkaline) cleaner, recirculate until the solution temperature reaches 100°F (38°C). CAUTION: DO NOT EXCEED 110°F (38°C). The membrane elements can only handle temperatures in excess of 85°F (29°C) for short periods of time. If heat rise occurs too quickly, larger volumes of cleaning solution or the use of a heat exchanger will slow the temperature rise. (Soaking with recirculation can be an alternative.)

4.5 Turn the main OFF/AUTO/HAND/FILL switch to the OFF position. 4.6 Let the machine soak for 10 – 30 minutes.

5. Purge the dirty solution from machine. 5.1 Turn the OFF/AUTO/HAND/FILL switch to the HAND position

and begin recirculating the solution. Recirculate the solution for 5 – 10 minutes.

5.2 Open the service concentrate valve (to drain) and close the CIP concentrate valve. Allow the permeate to return to the CIP tank. This action will purge the concentrated dirty cleaning solution from the system.

5.3 Watch the CIP tank level. When the level reaches 1/4 full, turn the main OFF/AUTO/HAND/FILL switch to the OFF position

6. Flush the cleaning solution from machine. 6.1 Close the CIP inlet valve. 6.2 Open the service inlet valve. 6.3 Open the CIP drain valve. This diverts the permeate and

concentrate streams to drain.

7. Operate the machine as described in Step 6 for 1 hour and/or until the system pH and conductivity readings return to near normal operating levels.

NOTE: After the high pH cleaning the conductivity of the permeate may actually increase temporarily due to the effects of higher pH and the nature of the surfactants. The rinse period for conductivity of the permeate to return to normal periods can be lengthy and unacceptable. To speed this process, repeat the cleaning procedure with the low pH cleaner at ½ concentration for a few minutes. Then rinse to quality.

8. Turn the main OFF/AUTO/HAND/FILL switch to the OFF position.



9. Install new pre-filters (Section 4.5.1).

10. Return machine to normal operation. 10.1 Open the service permeate valve. 10.2 Open the service concentrate valve. 10.3 Close the CIP permeate valve. 10.4 Close the CIP concentrate valve.

The machine is now ready for operation.



Appendix 3. Spacer Tube Installation Spacer tubes are used when it is desirable to reduce the output of a machine by reducing the number of elements in it. Spacer tube placement depends on concentrate flow and utilizes open and blank interconnectors as well as anti-telescoping devices to prevent vibration of the spacer tube in the housing during machine operation. The spacer tubes are installed at the upstream end of the pressure vessel. Detailed installation instructions are available from GE Engineering.

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M1000EN Feb-08

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