How to troubleshoot if the reverse osmosis membrane fails?

1．Do 3 things first: Eliminate "false faults"

Calibrate first

• pressure gauges, flow meters, and conductivity meters often "lie": for example, the flow meter is stuck, which will misjudge the decrease in water production; If the pressure gauge is inaccurate, it may be mistaken for abnormal pressure.
• Simple calibration method: use a spare pressure gauge to compare the inlet water / concentrated water pressure; Calibrate the conductivity meter with a standard solution (e.g. 100μS/cm) to ensure reliable data.

Look through the historical data to find the "abnormal starting point"

• Take out the running records of the past 1-3 months (if you don't record it, you must remember it next time!). ), compare the key data before and after the failure:
• Water production has dropped? Is there a simultaneous increase in pressure?
• Poor water quality? Has the residual chlorine and turbidity of the influent water suddenly exceeded the standard?
• Data comparison can help you narrow down the scope, for example, "less water production + pressure rise" is most likely pollution, and "poor water yield + high residual chlorine" may be the membrane oxidized.

Measure the quality of influent water to eliminate "source problems"

• The water inlet is the "ration" of the membrane, and poor water quality directly leads to failure, focusing on 3 items:
• Turbidity: >1NTU = Pretreatment failure (e.g. filter backwash);
• Residual chlorine: >0.1mg/L = the membrane should be oxidized (activated carbon should be replaced);
• Hardness / silicon content: too high is easy to scale, and follow-up investigation should be focused on.
• Tips: Use the "smearing method" to measure microorganisms, and sudden bursts of bacteria will also cause the membrane to "strike".

2．3 major fault scenarios, step by step investigation (with solution ideas)

Scenario 1: Significant decrease in water yield (be wary of a drop of more than 10%).Let's look at the "non-membrane problem" first: Is the parameter out of line?

• The inlet water temperature is low?

For every 1°C drop in temperature, water production is reduced by 2-3%! For example, if the groundwater is cold in winter, quickly turn on the heating device, adjust it back to 20-25°C (the optimal temperature of the membrane), and observe whether the water volume has recovered.

• Not stressed enough?

If the inlet water pressure is less than 1.0MPa (look at the membrane model, some are 1.5MPa), check the high-pressure pump: Is the current normal? Is the import valve fully open? If the pressure difference of the pretreatment filter exceeds 0.1MPa, it should be backwashed, and the pressure will not rise if it is blocked.

• Too high a recycling rate?

The recovery rate exceeds the design value by more than 10%, the concentration of concentrated water is too high, and the membrane "cannot pass through water". Adjust the thick water discharge valve to reduce the recovery rate, and then look at the water volume.

• Check again "the membrane itself": is it blocked or broken?
• Step 1: Check "Inrush - Concentrated Water Pressure Difference"
  The normal pressure difference < 0.2MPa, if it rises by more than 0.1MPa, it must be blocked:Rapid rise in differential pressure (1-2 weeks) + sudden drop in water volume: particle pollution (open the precision filter to see if the filter element is stained with sediment);
  Slow increase in differential pressure (1-3 months) + water gradient: colloidal/organic contamination (remove 1 end membrane to see if there is a sticky layer or yellowish-brown deposition on the surface).
• Step 2: Confirm the type of contamination
  Suspected scaling (excessive hardness of water intake): measure the hardness of concentrated water, or try with pickling (citric acid 1-3%), if it can be washed through, it is scaling;
  Suspected biological contamination: scrape the sediments on the surface of the membrane, see if there are microorganisms under the microscope, and sterilize them first and then wash them alkali.
• Step 3: See if there is physical damage to the film.After eliminating contamination and parameter problems, remove the film shell and check:
  Sealing ring: aging and deformation will lead to concentrated water channeling, indirectly affecting the water volume, try changing to a new sealing ring;
  Diaphragm: There are wrinkles and tears (such as high-pressure pump pressurization too quickly), and the membrane components can only be replaced, there is no other way.

Scenario 2: Poor quality of produced water (high conductivity / TDS)

• Is the membrane element seal broken?

The "central tube sealing ring" at both ends of the membrane is aging and misaligned, and the concentrated water will run from the central tube into the production water. When the film is removed, the rubber ring is cracked and deformed, and it is replaced with a new one.

• Is the end cap of the membrane shell leaking?

Apply soapy water to the seam of the end cap, if there are bubbles, it will leak! Replace the O-ring, tighten the bolt evenly, do not twist it crookedly.

✨ Tips: Single membrane investigation method
If multiple membranes are connected in series, each membrane is connected to the test device separately, and the conductivity is measured through the standard water inlet.

• Check "membrane performance" again: Is it declining?
• Slowly deteriorating (1-3 months): Most likely pollution

Organic contamination (e.g., humic acid) will cover the surface of the membrane, reducing the retention rate, and wash with alkali wash (sodium hydroxide 0.5-1%) + surfactant;
Biofilm will destroy the membrane structure, first sterilize (sodium hypochlorite 50-100mg/L soaking), and then alkali wash.

• Sudden deterioration (1-2 days): Beware of "membrane oxidation"

If the residual chlorine in the influent water is measured > 0.1mg/L, the "skeleton" of the membrane (aromatic polyamide) will be interrupted, and the retention rate will be permanently reduced! In this case, you can only change the film, and next time you must keep an eye on the residual chlorine. Finally, check "pretreatment": Is it not blocking pollutants?

• Pretreatment is the "first line of defense" that fails when contaminants are directly applied to the film:
• Multi-media filter: pressure difference exceeds 0.15MPa without backwashing, sediment enters the film;
• Activated carbon filter: used for more than half a year, residual chlorine penetration, oxide film;
• Precision filter: The filter element is not changed for more than 3-6 months, and the particles block the membrane.
• Solution: Backwash the backwash, replace the replacement, repair the pretreatment and then look at the water quality.

Scenario 3: Abnormal operating pressure (sudden rise / sudden drop)

• Is the concentrate pipe blocked?

Check the concentrated water discharge valve: try to switch it manually, is it stuck? The thick water flow meter is removed to clean up the impurities inside, and if it is blocked, the concentrated water will not be able to drain out and the pressure will soar.

• Is the membrane runner blocked?

Particle pollution will block the flow channel of the inlet end of the film, if there is a accumulation of particulate matter at the inlet end, rinse with high-pressure water below 0.3MPa, do not use too high pressure, it will wash away the film.

• Water inlet side leak?

Check the water inlet pipe, high-pressure pump flange: is there any leakage? If the bolt is loosened and tightened, the gasket will be replaced if it is broken, and the water leakage will cause the actual pressure to be insufficient.

• Is the high-pressure pump broken?

Listen to the sound of the pump: if there is an abnormal noise, the impeller is worn; Look at the current: low current may be due to pump intake. Disassemble the pump for maintenance, and replace the pump if it doesn't work.

• The membrane is broken?

The diaphragm is torn in a large area, and the incoming water flows directly into the production water, and the pressure cannot be built, which will also lead to poor water quality. If there is a hole, change the film.

• What to do after investigation: verify + record to avoid repeating the next offense
• Verify the effect:

if the parameters are adjusted, run continuously for 24 hours to see if the water volume, water quality, and pressure have returned to normal;

If the film is washed, the recovery rate of water yield after washing should be ≥ 80%, and the water quality must meet the standard to be considered successful;

If the film is changed, rinse at low pressure for 30 minutes (below 0.2MPa) after replacement, and then operate normally.

• Safety Reminder:

Downtime investigation must first relieve pressure! Turn off the high-pressure pump and open the water production discharge valve to avoid high pressure of the membrane shell and injury during disassembly; Remove the film and handle it gently, don't break the membrane.

• Keep a good log:

Write down the investigation process, causes, and solutions, and compare them directly with similar faults next time, saving time and effort.