Best Practices: What to Do When RO Feed Water Quality Suddenly Deteriorates| Insights by AQUALITEK

What Should Be Done If the Incoming Water Quality Suddenly Deteriorates?

Industrial reverse osmosis (RO) systems rely heavily on stable feed water quality. When source water suddenly worsens—due to rainfall, upstream process changes, equipment failure, or seasonal variation—the RO system can suffer rapid fouling, scaling, or performance decline.

To avoid membrane damage, it’s critical to take immediate and correct action.

1. Identify the Type of Water Quality Deterioration

Not all water quality issues are the same. First, determine what has changed.

Common types of deterioration:

•Increased turbidity (mud, suspended solids, rainwater intrusion)

•Higher SDI (poor pretreatment performance)

•Increased hardness (risk of scaling)

•Higher organic load (bacteria, COD, TOC)

•Presence of chlorine (risk of membrane oxidation)

•Temperature fluctuations (affects flux and pressure requirements)

Why this matters

Correct diagnosis determines the correct response strategy.

2. Reduce RO Operating Recovery Immediately

When feed water worsens, maintaining high recovery increases fouling and scaling risk.

Recommended action

•Lower recovery by 10–30%, depending on severity

•This increases concentrate flow and reduces concentration polarization

Benefits

•Protects membrane surface

•Reduces fouling rate

•Prevents sudden differential pressure spikes

3. Increase Flushing Frequency or Perform Continuous Flush

Sudden turbidity or SDI increases can cause rapid clogging.

Countermeasures

•Perform frequent forward flushes

•Switch to continuous flushing if SDI rises above 5

•Avoid full-pressure operation during severe deterioration

Purpose

Flushing helps keep fouling from adhering to membrane surfaces.

4. Check and Strengthen Pretreatment System

A feed water change often indicates pretreatment overload.

Inspect the following:

•Sand filter / multimedia filter turbidity performance

•Activated carbon filter exhaustion

•Cartridge filter (PP/1–5 micron) clogging

•Coagulant dosage (if applicable)

•Softener hardness breakthrough

•UF (if included) operating status

Immediate improvements

•Replace clogged PP filters

•Increase backwash frequency

•Boost coagulant dosage (for surface water applications)

5. Monitor Key Parameters More Frequently

During unstable water conditions, monitoring should be increased.

Critical parameters to track:

•Feed water SDI

•RO inlet pressure

•Differential pressure across membrane stages

•Permeate conductivity

•Temperature

•Turbidity

If any parameter rises sharply, stop the system and investigate.

6. Stop the System if Water Quality Becomes Unacceptable

If feed water exceeds RO design limits, continued operation will damage the membranes.

Example conditions requiring shutdown:

•SDI > 5 for more than several hours

•Turbidity > 1–2 NTU after pretreatment

•Chlorine detected at RO inlet

•Heavy organic contamination

•Low pH / corrosive water

During shutdown

•Keep membranes wet

•Perform periodic flushing

•Do not let the system dry

7. Conduct Immediate Cleaning If Membrane Fouling Occurs

If performance has already begun deteriorating:

Signs cleaning is required:

•Differential pressure rises 15–20%

•Permeate flow drops >10%

•Salt passage rises

•Visual signs of fouling in pretreatment units

Recommended actions

Perform targeted chemical cleaning based on fouling type:

•Acid cleaning: scaling

•Alkaline cleaning: organics

•Biocide cleaning: biological fouling

Early cleaning prevents irreversible membrane damage.

8. Investigate the Root Cause and Restore Stability

Common root causes include:

•Rainfall or seasonal source water changes

•Mechanical failure in pretreatment

•Change in factory wastewater characteristics

•Chemical dosing interruption

•Insufficient backwashing

After correction, gradually restore RO system to full operation.

Conclusion

A sudden deterioration in RO feed water quality is one of the most dangerous operating conditions. By reducing recovery, increasing flushing, strengthening pretreatment, monitoring intensively, and stopping the system when necessary, you can prevent severe fouling and ensure membrane protection.

Swift action is the key to maintaining system stability and extending membrane lifespan.