1. How Often Should a Reverse Osmosis System Be Cleaned?
The RO system shall be cleaned when the normalized flux drops by 10–15%, the salt rejection rate decreases by 10–15%, or the operating pressure and inter-stage differential pressure rise by 10–15%.
The cleaning frequency is directly related to the degree of feed water pretreatment. If SDI₁₅ < 3, cleaning may be required 4 times a year; if SDI₁₅ is around 5, the frequency may double. However, the actual cleaning cycle depends on on-site conditions of each project.
2. What Is SDI?
Silt Density Index (SDI, also known as fouling index) is currently the most effective standard to assess colloidal fouling potential in RO/NF feed water, and a critical parameter to be confirmed prior to RO system design.
SDI testing must be conducted regularly during RO/NF operation (2–3 times daily for surface water sources), complying with ASTM D4189-82 test standards.
The SDI₁₅ limit for membrane feed water shall not exceed 5. Effective pretreatment technologies to reduce SDI include multimedia filters, ultrafiltration, microfiltration, etc. Dosing polyelectrolytes before filtration can sometimes enhance the performance of physical filtration and lower SDI values.
3. Should Reverse Osmosis or Ion Exchange Be Selected for General Feed Water?
Both ion exchange resin and reverse osmosis are technically feasible under many feed water conditions; process selection is determined by economic comparison. Generally speaking, reverse osmosis is more cost-effective for high-salinity water, while ion exchange is more economical for low-salinity water.
With the widespread application of reverse osmosis technology, combined processes such as RO + ion exchange, multi-stage RO, and RO coupled with other advanced desalination technologies have become widely recognized solutions with superior technical and economic performance. Consult a professional water treatment engineering firm for in-depth details.
4. What Is the Typical Service Life of Reverse Osmosis Membrane Elements?
Membrane service life is determined by chemical stability, physical integrity, cleanability, feed water source, pretreatment standard, cleaning frequency, and daily operation & maintenance management. Economic analysis indicates a typical service life of over 5 years.
5. What Is the Difference Between Reverse Osmosis and Nanofiltration?
Nanofiltration is a membrane liquid separation technology falling between reverse osmosis and ultrafiltration. RO removes the smallest solutes with molecular sizes below 0.0001 μm, while NF intercepts solutes with molecular sizes around 0.001 μm.
Essentially a low-pressure reverse osmosis technology, nanofiltration is applied in scenarios where ultra-high product water purity is not required, and suits groundwater and surface water treatment.
NF is suitable for water systems that do not demand the high salt rejection of RO, yet boasts excellent hardness removal capacity, hence nicknamed "softening membranes". NF systems operate at lower pressure and consume less energy than equivalent RO systems.
6. What Separation Performance Do Membrane Technologies Deliver?
Reverse osmosis is the most precise liquid filtration technology available. RO membranes retain dissolved inorganic salts and organics with molecular weights above 100, while allowing water molecules to permeate freely. Typical salt rejection rates for soluble salts range from 95% to 99%. Operating pressure varies from 7 bar (100 psi) for brackish water to 69 bar (1,000 psi) for seawater.
Nanofiltration removes impurities larger than 1 nm (10 angstroms) and organics with molecular weights of 200–400. Its total dissolved solids (TDS) rejection ranges from 20% to 98%. Rejection of monovalent salt ions (e.g., NaCl, CaCl₂) is 20–80%, while divalent salt ions (e.g., MgSO₄) achieve high rejection rates of 90–98%.
Ultrafiltration separates macromolecules larger than 100–1,000 angstroms (0.01–0.1 μm). All dissolved salts and small molecules pass through UF membranes, which retain colloids, proteins, microorganisms and high-molecular-weight organics. Most UF membranes have a molecular weight cutoff (MWCO) of 1,000–100,000.
Microfiltration removes particles ranging from 0.1 μm to 1 μm. Suspended solids and large colloids are intercepted, while macromolecules and dissolved salts freely permeate MF membranes. MF is used to eliminate bacteria, microflocs and total suspended solids (TSS), with typical trans-membrane pressure of 1–3 bar.
7. Who Supplies Membrane Cleaners or Provides Cleaning Services?
Specialized membrane cleaners and professional cleaning services are available from water treatment companies. End users may also purchase cleaning agents independently following recommendations from membrane manufacturers or equipment suppliers.
8. What Is the Maximum Allowable Silica Concentration in RO Feed Water?
The threshold silica concentration depends on temperature, pH and antiscalant dosage. Without antiscalant dosing, the maximum allowable silica concentration in concentrate is 100 ppm. Certain antiscalants permit silica levels up to 240 ppm in concentrate; consult your antiscalant supplier for accurate limits.
9. What Impact Does Chromium Have on RO Membranes?
Heavy metals such as chromium catalyze the oxidation reaction of chlorine, leading to irreversible performance degradation of membrane sheets. Hexavalent chromium (Cr⁶⁺) is less stable than trivalent chromium (Cr³⁺) in water, and higher-valence metal ions exert stronger destructive effects. Therefore, chromium concentration shall be reduced in pretreatment, or Cr⁶⁺ shall be reduced to Cr³⁺ at minimum.
10. What Pretreatment Is Generally Required for RO Systems?
A standard pretreatment train consists of the following units: coarse filtration (~80 μm) to remove large particles, oxidant dosing (e.g., sodium hypochlorite), precise filtration via multimedia filters or clarifiers, sodium bisulfite dosing to neutralize residual chlorine and other oxidants, and finally a cartridge filter installed upstream of the high-pressure pump.
As its name suggests, the cartridge filter acts as a final safeguard to prevent damage to high-pressure pump impellers and membrane elements from accidental large particle ingress. Water sources with high suspended solids require enhanced pretreatment to meet feed water specifications. For hard water sources, softening, acid dosing or antiscalant addition is recommended. For feed water rich in microorganisms and organics, activated carbon filtration or fouling-resistant membrane elements shall be adopted.
11. Can Reverse Osmosis Remove Microorganisms Such as Viruses and Bacteria?
RO membranes feature an extremely dense structure, delivering high log reduction values (LRV ≥ 3 log, removal efficiency >99.9%) for viruses, bacteriophages and bacteria. However, microbial regrowth may still occur on the permeate side in many cases, determined by system assembly, monitoring and maintenance protocols. In short, a system’s microbial removal performance relies primarily on proper design, operation and management rather than membrane material itself.
12. How Does Temperature Affect Permeate Flow Rate?
Permeate production rises with increasing temperature and falls as temperature drops. When operating at elevated temperatures, adjust operating pressure downward to maintain stable permeate flow, and vice versa. Refer to relevant technical documents for the Temperature Correction Factor (TCF) used to calibrate flux for temperature variations.
13. What Is Particle and Colloidal Fouling, and How to Measure It?
Particle and colloidal fouling severely reduces permeate flow and sometimes lowers salt rejection in RO/NF systems.
An early indicator of colloidal fouling is rising system differential pressure. Sources of particles and colloids in feed water vary by location, including bacteria, silt, colloidal silica, iron corrosion products, etc. Improperly flocculated coagulants such as polyaluminum chloride, ferric chloride or cationic polyelectrolytes that escape clarification or media filtration will also cause membrane fouling.
Additionally, cationic polyelectrolytes react with anionic antiscalants to form precipitates that foul membrane elements. SDI₁₅ testing evaluates fouling tendency and pretreatment effectiveness; see dedicated sections for detailed testing procedures.
14. What Is the Maximum Permissible Shutdown Duration Without System Flushing?
Systems dosed with antiscalant: 4 hours at water temperature 20–38 °C; 8 hours below 20 °C
Systems without antiscalant dosing: approximately 24 hours
15. Can RO Pure Water Systems Be Frequently Started and Stopped?
Membrane systems are designed for continuous operation, yet regular startup and shutdown cycles are unavoidable in practical application.
Upon shutdown, low-pressure flushing with system permeate or qualified pretreated feed water is mandatory to displace concentrated brine containing antiscalant inside membrane elements. Prevent full water drainage and air ingress into the system; drying of membrane elements will cause irreversible flux loss.
For shutdown periods shorter than 24 hours, no microbial inhibition measures are required. For longer downtime, preserve membranes with preservation solution or implement periodic flushing cycles.
16. How to Confirm the Installation Direction of Brine Seals on Membrane Elements?
Brine seals shall be mounted on the feed end of each membrane element, with the lip opening facing the feed flow direction. When feed water enters the pressure vessel, the seal lip expands to fully block bypass flow between membrane elements and the inner wall of the pressure vessel.
17. How to Remove Silica from Water?
Silica exists in two forms in water: reactive silica (monomeric silica) and colloidal silica (polymeric silica). Colloidal silica carries no ionic charge but has a relatively large particle size, removable via fine physical separation such as RO or coagulation clarification. Ion exchange resins and continuous electrodeionization (CEDI), which separate contaminants based on ionic charge, show limited removal efficiency for colloidal silica.
Reactive silica has a much smaller particle size and cannot be eliminated by conventional physical treatments including coagulation, filtration and dissolved air flotation. Effective reactive silica removal technologies include reverse osmosis, ion exchange and CEDI.
18. How Does pH Affect Salt Rejection, Permeate Flow and Membrane Service Life?
Composite RO membranes operate stably across a pH range of 2–11, with minimal direct pH-induced damage to the membrane material itself, a key distinction from other membrane types. However, the ionic state of many dissolved contaminants is highly pH-dependent. Weak acids like citric acid exist primarily as neutral molecules at low pH and dissociate into charged ions at high pH. Higher ionic charge leads to higher salt rejection by the membrane, while neutral or weakly charged species exhibit low rejection rates. Therefore, pH exerts a significant impact on the removal efficiency of specific contaminants.
19. Correlation Between Feed Water TDS and Conductivity
Conductivity readings must be converted to TDS values for RO design software input. For most water sources, the conductivity-to-TDS conversion ratio ranges from 1.2 to 1.7. For ROSA design software, a ratio of 1.4 is adopted for seawater and 1.3 for brackish water to achieve accurate approximation.
20. How to Determine If Membranes Are Fouled?
Common symptoms of membrane fouling include:
Reduced permeate flow under standardized operating pressure
Higher operating pressure required to maintain design permeate output
Increased differential pressure between feed and concentrate streams
Increased weight of removed membrane elements
Obvious fluctuation (rise or fall) in salt rejection rate
When the element is extracted from the pressure vessel and stood vertically, water poured onto the feed end fails to pass through the element and overflows from the end cap (indicating complete blockage of feed channels)
21. How to Prevent Microbial Growth in New Membrane Original Packaging?
Turbid preservation solution indicates microbial proliferation. Membranes preserved with sodium bisulfite solution shall be inspected every three months.
If turbidity occurs, remove elements from sealed packaging and soak in fresh food-grade 1 wt% cobalt-free sodium bisulfite preservation solution for 1 hour, drain thoroughly and re-seal.
22. Feed Water Requirements for RO Membrane Elements and IX Ion Exchange Resins
In theory, feed water supplied to RO and IX systems shall be free of the following impurities:
Suspended solids
Colloids
Calcium sulfate scaling precursors
Algae
Bacteria
Oxidants such as residual chlorine
Oil and grease (below instrument detection limit)
Organics and iron-organic complexes
Metal oxides including iron, copper and aluminum corrosion byproducts
Feed water quality drastically impacts the service life and performance of RO elements and ion exchange resins.
23. What Contaminants Can RO Membranes Remove?
RO membranes deliver excellent removal of ions and organics with higher rejection rates than nanofiltration. Typical salt removal efficiency reaches 99%, and organic rejection exceeds 99%.
24. How to Select the Correct Cleaning Method for Membrane Systems?
Targeted cleaning chemicals and procedures are critical to maximize cleaning efficacy; improper cleaning will degrade system performance. Generally, acidic cleaning solutions treat inorganic scale fouling, while alkaline cleaners address organic and biological fouling.
25. Why Is the pH of RO Permeate Lower Than Feed Water pH?
In a closed aqueous system, the equilibrium ratio of CO₂, HCO₃⁻ and CO₃²⁻ shifts with pH: CO₂ dominates at low pH, bicarbonate at neutral pH, and carbonate at high pH.
RO membranes retain dissolved ions but cannot block dissolved gases. Permeate retains nearly the same CO₂ concentration as feed water, while bicarbonate and carbonate ions are reduced by 1–2 orders of magnitude. This breaks the original carbonate equilibrium, triggering the following reversible reaction to form new equilibrium:
CO
2
+H
2
O⇌HCO
3
−
+H
+
If feed water contains dissolved CO₂, permeate pH will always decrease by 1–2 pH units, with larger pH drops in high-alkalinity feed rich in bicarbonate. Minimal pH variation occurs in feed water with low carbonate species concentration.
Dosing sodium hydroxide via metering pumps raises permeate pH to alkaline levels. Optimal RO desalination efficiency is achieved at pH 7.5–8.0.
26. How to Reduce Energy Consumption of Membrane Systems?
Low-energy membrane elements can be installed, though their salt rejection performance is slightly lower than standard membranes.
27. Why Do Sealing O-rings in RO Equipment Swell?
Three types of sealing gaskets are installed in pressure vessels to isolate flow sections. Lubricate O-ring surfaces with clean water or glycerin during installation to reduce assembly resistance.
Avoid petroleum-based lubricants such as petroleum jelly, which cause permeate tube cracking and severe O-ring swelling. Swollen gaskets do not directly impair system operation but lead to difficult disassembly and re-installation after shutdown.
28. Do All Membrane Elements Along the RO Train Produce Equal Permeate Flow?
A pressure drop exists between the feed and concentrate end of each element, and concentrate salinity rises progressively along the system, increasing osmotic pressure sequentially for each downstream element.
Ignoring permeate backpressure and osmotic pressure effects, permeate flow of each element is proportional to the net driving pressure (operating pressure minus osmotic pressure), resulting in gradually declining permeate production along the RO train.
29. Does pH Affect RO Membrane Rejection and Service Life?
Most RO membranes are composite polyamide membranes stable within the pH operating range of 2–11; pH within this window causes negligible permanent membrane damage.
pH impacts salt rejection indirectly by altering the ionic charge and dissociation state of dissolved contaminants. Neutral or weakly charged species exhibit low rejection rates, severely lowering overall contaminant removal efficiency.
RO membranes cannot remove dissolved CO₂. Raising feed water pH converts CO₂ into carbonate ions that can be intercepted by the membrane, improving desalination performance, yet scaling risks must be closely monitored under high pH conditions.
30. Standard Startup Procedures for New RO Equipment
Purge air trapped in piping with low pressure and low flow before full operation, maintaining pressure at 0.2–0.4 MPa during flushing. Discharge all concentrate and permeate to drain during air purging.
Rapid pressure rise during startup indicates trapped air inside elements, generating radial hydraulic impact that may rupture membrane outer wrapping and cause irreparable damage. All RO systems shall be configured with automatic low-pressure pre-flush upon startup.
31. How to Replace Cartridge Filter Elements in RO Equipment?
Cartridge filter elements shall be replaced when differential pressure across the filter housing exceeds 0.03 MPa due to fouling.
Replacement steps:
Shut down the entire RO system
Release internal pressure by activating the pressure relief valve until the pressure gauge reads zero
Unscrew filter housing with a dedicated wrench
Extract fouled element and install a new cartridge
Tighten filter housing securely with the wrench
32. Cleaning and Disinfection Protocols for RO Systems
Chemical cleaning shall be performed by professional technicians or certified supplier personnel. Chemical cleaning is required when any of the following thresholds are reached:
Permeate flow drops by 5–10% compared with initial or post-cleaning baseline data
Salt rejection declines by 2.5–5% relative to baseline
Inter-stage differential pressure rises to 1–2 times the initial value
Long-term system shutdown requiring membrane preservation solution
Note: Permeate flow and salt rejection are temperature-sensitive; performance comparison must be conducted under identical feed water temperature conditions.
33. Is RO Equipment Effective for Fluoride Removal?
Excessive fluoride in drinking water poses severe health hazards, and reverse osmosis is widely adopted for groundwater defluoridation. Fluoride ions in groundwater originate from mineral rock dissolution alongside numerous other dissolved ions. Desalination performance declines for high-salinity fluoride-laden groundwater. Nevertheless, RO defluoridation offers simple operation and stable treatment efficiency compared with alternative technologies.
34. Basic Water Quality Specifications for Purified Water Equipment Effluent
Purified water systems serve pharmaceutical, biotech and medical manufacturing. Pharmacopoeia standards (Chinese Pharmacopoeia, European Pharmacopoeia) mandate raw feed water must at minimum comply with domestic drinking water standards; pre-treatment is required for substandard source water.
Total heterotrophic bacteria shall not exceed 100 CFU/mL with zero detectable E. coli. Internal equipment fouling frequently occurs during purified water production. Regular system cleaning and disinfection are mandatory, and terminal sterilization units shall be installed on purified water distribution pipelines.
35. Key Characteristics of Purified Water Equipment Effluent
Purified water produced by dedicated systems meets national sanitary standards and customized enterprise production requirements, featuring two core design characteristics:
Widespread integration of inline disinfection and sterilization modules
Recirculating distribution pipelines replacing dead-end delivery piping
Both designs mitigate microbial proliferation and endotoxin accumulation. Pipeline flow velocity requires strict control: low flow rates or pipeline blockages accelerate bacterial growth and degrade water quality.
36. Key Points for Softener Installation Location Selection
Guidelines for siting ion exchange softening equipment:
Install as close to drainage outlets as possible
Reserve sufficient space for auxiliary water treatment equipment
Allocate dedicated storage space for industrial salt replenishment
Maintain a minimum 3-meter separation from boilers to prevent hot water backflow and equipment damage
Avoid installation in environments with temperatures below 1 °C or above 49 °C
37. Operation Precautions for Water Softeners
Water softeners remove calcium and magnesium ions to reduce water hardness; follow these operational guidelines for long-term stable performance:
Keep the inlet valve fully open during normal operation; only close during maintenance. Shut the outlet valve when water production is unnecessary.
Manually initiate regeneration if incomplete regeneration leads to unqualified softened water effluent.
Fill the brine tank with saturated salt solution for membrane preservation during long shutdowns.
For system restart: prepare standard saturated brine, open the inlet valve, power on the controller, complete automatic reset, run one manual regeneration cycle, then open the outlet valve.
Clean the brine tank annually if low-grade impure industrial salt is used to guarantee smooth brine suction.
38. Installation Standards for Ultrapure Water Equipment
Installation specifications for ultrapure water production systems:
Select flat, clean installation sites with convenient access to power and feed water supply
Avoid proximity to open flames and heat sources to prevent efficiency loss from thermal exposure
Do not install equipment outdoors in northern regions to prevent internal freezing and damage to instrumentation and filter elements
Ensure unobstructed drainage space for smooth wastewater discharge
Calibrate feed pump operating pressure within 1.0–1.2 MPa, running pumps under rated head conditions only
39. Low Pressure Boost Pump / High Pressure Pump Priming Failure
Troubleshooting:
380V three-phase pumps: Check for reverse rotation. Swap any two power supply wires if reversed. If rotation is normal, open the pump vent valve to bleed trapped air or fully prime the pump casing with water.
220V single-phase pumps: Reverse rotation cannot occur. Bleed air via the vent valve or refill pump casing with water to restore suction.
40. High Pressure Pump Startup Failure
Troubleshooting:
Verify relay contact actuation and tight wiring terminals
Check low-water protection indicator light: Illumination signals insufficient raw water supply. The low-water interlock cuts pump power to prevent dry-run damage. Replenish feed water until the interlock pressure threshold is reached and the indicator extinguishes before restarting.
41. Abnormal Noise from High Pressure Pump
Troubleshooting: Noise often occurs during partial pump dry-running and typically subsides within 1–3 minutes. If abnormal sound persists beyond 3 minutes, open the pump vent valve to bleed air or fully prime the pump casing.
42. Pipeline Bursting
Root cause: Poor raw water quality with excessive suspended solids, expired melt-blown cartridges or heavily fouled RO membranes elevate system pressure and rupture piping.
Remedial actions: Inspect and replace fouled melt-blown filters, perform chemical cleaning of RO membranes. For persistently high-fouling raw water, install upstream ion exchange softeners or dose antiscalant to reduce contaminants, extend membrane service life and stabilize effluent quality.
43. Gradually Declining Permeate Flow Rate
Root cause: Common in groundwater-fed systems (rare for municipal tap water feed). Excessive suspended solids foul RO membrane channels and reduce production capacity.
Solutions: Implement regular backwashing of pretreatment filters, timely replacement of melt-blown cartridges, and periodic membrane cleaning. Switch to municipal tap water if available; install ion exchange softening and antiscalant dosing systems for untreated groundwater sources to eliminate recurring fouling.
44. Fine White/Black Suspended Particles in Purified Water
Root cause: Pipeline biofouling and microbial proliferation.
Treatment: Dissolve sodium hydroxide and circulate through the cartridge filter. Close the concentrate regulating valve, fully open the permeate valve, start the high-pressure pump, and recirculate permeate back to the cartridge filter for 30 minutes. Activate inline pipeline sterilizers for systems equipped with UV or ozone disinfection modules.
45. Membrane Damage Caused by Water Hammer from Trapped Air Under High Pressure
Two primary scenarios:
Rapid pressurization without full air purging after complete system drainage. Purge residual air at 2–4 bar before gradual pressure ramp-up.
Air suction via loose leaking joints between pretreatment and high-pressure pumps (especially downstream of microfilters) during insufficient feed supply or microfilter blockage. Clean or replace clogged microfilters and repair all pipeline leaks.
General rule: Ramp up operating pressure only when flowmeters show zero bubbles. Depressurize gradually and inspect for air ingress if bubbles appear during operation.
46. Membrane Damage from Incorrect RO Shutdown Procedures
Two improper shutdown practices cause irreversible fouling:
Sudden rapid depressurization without adequate flushing. Concentrate brine retains high mineral concentrations prone to scaling if trapped inside elements.
Flushing with chemically dosed pretreated water, which accelerates membrane fouling during idle periods.
Standard shutdown protocol: Stop all chemical dosing, gradually reduce pressure to approximately 3 bar, flush with clean pretreated feed water for 10 minutes until concentrate TDS matches raw feed TDS.
47. Microbial Fouling from Inadequate RO Disinfection and Preservation
A widespread issue for polyamide composite membranes, which exhibit poor tolerance to free chlorine. Insufficient disinfection protocols and neglected maintenance lead to severe biological fouling and microbial out-of-specification permeate in many pure water systems.
Common contributing factors:
New membrane elements shipped without factory preservation solution
Failure to sanitize full piping and pretreatment trains post-installation
Lack of disinfection/preservation for intermittently operated systems
Absent periodic sanitization of pretreatment and RO units
Degraded or under-dosed membrane preservation fluid
48. Insufficient Residual Chlorine Monitoring for RO Systems
Residual chlorine breakthrough irreversibly oxidizes polyamide membranes due to:
Malfunctioning sodium bisulfite dosing pumps
Degraded reducing agent solution
Fully exhausted activated carbon filters
49. Permanent Membrane Performance Degradation from Delayed or Improper Cleaning
Beyond natural aging, fouling-induced performance loss severely impairs system output. Common fouling types for EDI ultrapure water equipment include inorganic scaling, organic/colloidal fouling and biological contamination, each presenting distinct operational symptoms varying by fouling duration.
Case example of calcium carbonate scaling:
1-week mild fouling: Rapid salt rejection decline, slow differential pressure rise, minimal flux loss; full performance recovery achievable via citric acid cleaning.
1-year severe fouling: Salt passage rises from 2 mg/L to 37 mg/L (raw water TDS 140–160 mg/L), permeate flow drops from 230 L/h to 50 L/h. Post-citric acid cleaning: salt passage recovers to 7 mg/L, flux restores to 210 L/h.
Mixed fouling types complicate symptom diagnosis. Comprehensive evaluation combining raw water quality, design parameters, SDI data, operational logs, performance trends and microbial testing is required to identify fouling categories:
Colloidal fouling: Rapid cartridge filter fouling with fast rising differential pressure; sustained SDI₁₅ > 2.5
Biological fouling: Elevated bacterial counts in both permeate and concentrate, indicating absent routine disinfection and preservation
Calcium scaling: Predicted via Langelier Saturation Index (LSI) calculations based on feed water chemistry and recovery rate. For carbonate water at 75% recovery: LSI < 1 with antiscalant dosing; LSI < 0 without antiscalant prevents carbonate scaling
On-site component profiling: Insert 1/4-inch PVC tubing into pressure vessels to test performance variations along membrane stages
Performance trend analysis to classify fouling types
Acid cleaning trial (citric acid, dilute nitric acid): Evaluate cleaning efficacy and analyze spent cleaning fluid to confirm inorganic scaling
Chemical analysis of raw feed, fresh cleaning solution and spent cleaning effluent for definitive fouling identification
After confirming fouling type, apply targeted cleaning agents followed by system disinfection. If fouling type remains unidentified, adopt universal cleaning sequence: alkaline organic cleaning → 0.1% hydrochloric acid pickling (pH = 3) → full system disinfection.
50. Membrane Performance Loss from Improper Storage and Preservation
New RO membrane elements are sealed in airtight packaging saturated with a solution of 1 wt% sodium bisulfite and 18% glycerol. Unopened elements retain full performance for approximately 1 year. Once packaging is breached, deploy membranes promptly to avoid sodium bisulfite oxidation and element degradation; delay element unpacking until commissioning.
Two proven long-term preservation methods post-system commissioning:
Run the system continuously for 15–24 hours, then fill the entire loop with 2 wt% formaldehyde preservation solution (suitable for extended idle periods, higher operational cost)
Operate the system for 2–6 hours, then preserve with 1 wt% sodium bisulfite solution. Fully vent all pipeline air, eliminate leakage and close all inlet/outlet isolation valves (ideal for short downtime cycles, lower cost)
Both protocols deliver reliable long-term membrane protection.
