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RO & NF chemical cleaning
This document provides an overview of cleaning reverse osmosis and nanofiltration membrane elements. It discusses common types of fouling and scaling like carbonate, sulfate, organic and biological, and recommends appropriate cleaning methods. Cleaning solutions may include acids, bases, chelating agents and detergents. The document outlines the cleaning process, safety procedures, and recommends feed flow rates during cleaning based on element size and pressure. The goal of cleaning is to remove buildup and restore membrane performance by reducing pressure and increasing permeate flow.
In this document
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Introduction to the RO training course and subject matter covering RO and NF membrane elements.
An overview of cleaning techniques, types of foulants, and safety measures necessary during cleaning.
Discussion on when to clean membranes, the effectiveness of cleaning, and the importance of design.
Indicators for cleaning membranes and different chemical methods according to type of fouling.
Methods to analyze and characterize foulants in membranes, ensuring effective cleaning.
Critical pH ranges and temperature limits during cleaning with recommended cleaning agents.
Details on carbonate scaling causes, symptoms, and specific cleaning solutions for removal.
Sulfate scaling causes and symptoms, along with cleaning protocols and challenges.
Organic fouling issues, causes, symptoms, and efficient cleaning solutions.
Iron fouling issues from feedwater, symptoms, and effective cleaning strategies.
Identifying and addressing silt fouling and recommended cleaning methods.
Carbon fouling causes, effects, symptoms, and difficulties associated with cleaning.
Discussion on damage from chemical attack and permeate back pressure leading to replacement.
Step-by-step process for cleaning RO/NF systems and recommended flow rates.
Description of the cleaning system setup, safety protocols, and handling of chemicals.
Open session for questions and closing remarks of the presentation.
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RO & NF chemical cleaning
- 1.
- 2. Cleaning RO andNF Membrane Elements
- 3. Overview Introductory Remarks When toClean Cleaning Method Selection Defining a Foulant and Scalant pH and Temperature Limits FT30 Resistance to Cleaning Agents Cleaning Carbonate Scaling Cleaning Sulfate Scaling
- 4. Overview (cont.) Cleaning OrganicFouling Cleaning Biological Fouling Cleaning Iron Fouling Cleaning Silt Fouling Cleaning Carbon Fouling Chemical Attack Permeate Back Pressure The Cleaning Process Safety
- 5. Cleaning Introductory Remarks Cleaningis a means of removing mineral scale, organic matter, biological growth, colloidal particles, or insoluble constituents which build up on the surface of the membrane Frequent cleaning should not be required for a properly designed and operated RO/NF system Membranes may become fouled or scaled due to improper operation or change in feedwater quality
- 6. Cleaning Introductory Remarks (cont.) Membranes’elements can be cleaned effectively because: chemical stability broad pH tolerance high temperature limits Elements with oxidized membrane or mechanical damage must be replaced
- 7. When to Clean Normalizedflow declines by 10% Pressure drop increases by 15% Normalized salt passage increases by 5%* *Dependent on individual system design
- 8. Cleaning Regimen basedon System Performance and Water Chemistry A wrong choice can aggravate a scaling/fouling problem Acids for scaling Alkaline for biological fouling Alkaline with detergent for organic fouling Frequently both alkaline and acid cleanings are required
- 9. Characterizing Foulant or Scalant Analyzethe normalized plant performance Analyze feed water quality Check performance after previous cleanings Analyze cartridge/SDI filter residue
- 10. Characterizing Foulant or Scalant Inspectlead element and feed scroll end for suspended solids fouling Inspect scroll of tail element for scaling Clean and analyze cleaning solutions (control samples required) Destructive autopsy
- 11. pH Range andTemperature Limits During Cleaning Max Temp Max Temp Max Temp 50°C 35°C 30°C pH Range pH Range pH Range SW30/SW30HR 3 - 10 2 - 11 2 - 11.5 BW30/TW30 2 - 10 1 - 11 1 - 11.5 NF45 3 - 10 2 - 11 2 - 11 NF70 3 - 10 2 - 11 1 - 11.5 NF90 3 - 10 2 - 11 1 - 11.5
- 12. FT30 Cleaning Agents Agent% Concentration Resistance Hydrochloric Acid* 0.2 Excellent Na-EDTA* 1.0 Excellent Sodium Hydroxide* 0.1 Excellent Nitric Acid 5.0 Excellent Acetic Acid 5.0 Excellent Boric Acid 5.0 Excellent Phosphoric Acid 0.5 Excellent Sodium Salt of Dodecylsulfate (DSS or Lauryl Sulfate) 0.05 Excellent Sodium Hydrosulfite 1.0 Excellent Trisodium Phosphate (TSP) 2.0 Excellent Sodium Triphosphate (STP) 2.0 Excellent *Most common agents used
- 13. Causes: HighHardness High pH High alkalinity High recovery rates Symptoms: Heavy element Low permeate flow Poor salt rejection High pressure drop Carbonate Scaling
- 14. Carbonate Scaling (cont.) Cleaning 0.2%(Wt) hydrochloric acid, HCI 0.5% (Wt) phosphoric acid, H3PO4 0.2% (Wt) sulfamic acid, NH2SO3H
- 15. Sulfate Scaling Causes Exceeding solubilitylimits Loss of antiscalant High recovery rates (Means increase saturation level than solubility product) Symptoms Heavy element Low permeate flow Poor salt rejection High pressure drop
- 16. Sulfate Scaling (cont.) Cleaning Verydifficult to clean 2.0(Wt)% Na-EDTA and 0.1(Wt)% NaOH at pH12, 30°C maximum Overnight soak/recirculation may be necessary-- reaction slow
- 17. Biological/Organic Fouling Causes Impropermembrane preservation Biological/Organic material in feedwater Improper carbon bed maintenance Symptoms Odor Moldy or discolored scroll end Low permeate flow High salt rejection High pressure drop
- 18. Biological/Organic Fouling (cont.) Cleaning (bestsolution) 0.5% - 1.0%(Wt) Na-EDTA and 0.1%(Wt) NaOH At pH 12 and < 30°C (86°F) Cleaning (alternate solutions) 0.1% (Wt) NaOH and .05% Na-DSS at pH 12 and < 30°C (86°F) 1.0% (Wt) STP and 1.0% (Wt) Na-EDTA or 1.0% (Wt) TSP and 1.0% (Wt) Na-EDTA
- 19. Iron Fouling Causes Rusty wellcasings or piping Air with greater than 0.1 ppm Fe in feedwater Symptoms Rust coloring on scroll end or ATD* Rusty colored concentrate upon start-up Low permeate flow Poor salt rejection *Anti-telescoping device
- 20. Iron Fouling (cont.) CleaningSolutions 1.0% (Wt) sodium hydrosulfite (best) Na2S2O4 2.0% Citric acid (Alternative) 0.5% (Wt) phosphoric acid H3PO4 0.2% (Wt) hydrochloric acid HCL
- 21. Silt Fouling Causes Turbid surfacewaters High suspended solids Inadequate pretreatment Symptoms Dirty feed scroll end Low permeate flow/poor salt rejection High permeate flow/very poor salt rejection Heavy element
- 22. Silt Fouling (cont.) Cleaning Difficultto clean Caustic and Na-EDTA Proprietary Detergents
- 23. Carbon Fouling Causes Incorrect backwashand rinse rates resulting in inadequate flushing of carbon bed Soft carbon Symptoms Black deposits on scroll end Low permeate flow (early stage) Poor salt rejection
- 24. Carbon Fouling (cont.) Cleaning Verydifficult to clean Proprietary Detergents
- 25. Chemical Attack Causes Incomplete dechlorination(oxidation) Exposure to strong oxidants (i.e., permanganate) Prolonged exposure to pH extremes Symptoms Very high permeate flow Very poor salt rejection Damage irreversible, elements must be replaced
- 26. Permeate Backpressure Damage Causes Mechanical failurein system Inappropriate design Operation error Symptoms High permeate flow and very poor rejection Evidence Wrinkles in membrane near back glue line Damage irreversible, elements must be replaced
- 27. Cleaning Process Steps Mixcleaning solution Low flow pumping (low psi) Recycle Soak High flow pumping (low psi) Flush out Use permeate for solutions and flush
- 28. Recommend Feed Flow RatePer Pressure Vessel Element Diameter Feed Pressure* Feed Flow Rate inches (psig) gpm 2.5 20-60 3-5 4 20-60 8-10 6 20-60 16- 20 8 20-60 30- 40*Dependent on number of elements in pressure vessel
- 29. Cleaning System ® Permeate from StorageTank Cleaning Tank Cartridge Filter RO Unit Permeate to Storage Tank (Normal Operation) Permeate to Cleaning Tank (Cleaning Operation) Concentrate to Cleaning Tank (Cleaning Operation) Concentrate to Drain (Normal Operation)
- 30. Safety Review MSDS documents Useprotective equipment: goggles, gloves and clothing Vent tanks and/or cleaning area Assure chemical compatibility with system hardware Dispose of spent solutions and chemicals accordance with local regulations Properly mix chemicals (i.e., acid into water, etc.)
- 31.
- 32. Thank you foryour attention