Best Immediate Actions to Take When a Sudden Increase in Influent Hardness Is Detected| Insights by AQUALITEK

Why a Sudden Hardness Increase Is Dangerous

Influent hardness—mainly calcium (Ca²⁺) and magnesium (Mg²⁺)—is one of the primary causes of inorganic scaling in RO systems.

A sudden hardness increase can:

•Rapidly exceed membrane solubility limits

•Cause calcium carbonate or sulfate scaling

•Block membrane pores

•Increase differential pressure

•Permanently reduce membrane flux

Immediate action is critical.

1. Immediately Reduce System Recovery or Stop the RO System

Best Option: Emergency Shutdown

If hardness increases sharply beyond design limits:

•Stop the high-pressure pump

•Switch to low-pressure flushing if possible

Alternative (If Shutdown Is Not Possible)

•Immediately reduce recovery rate

•Increase concentrate flow

•Lower salt concentration inside the membrane

⚠️ Continuing normal operation risks irreversible scaling within hours.

2. Verify Pretreatment Performance Immediately

Check Softener or Antiscalant System

•Is the water softener exhausted or bypassed?

•Has resin regeneration failed?

•Is antiscalant dosing interrupted?

•Is chemical tank empty or dosing pump malfunctioning?

Pretreatment failure is the most common cause of hardness spikes.

3. Perform a Low-Pressure Flush to Remove Concentrated Ions

Before restarting or stabilizing:

•Flush membranes with low-TDS water

•Remove high-hardness concentrate

•Prevent ion precipitation during idle time

This step significantly reduces scaling risk.

4. Confirm Hardness Measurement Accuracy

Double-Check the Data

•Retest hardness manually (EDTA titration or lab test)

•Compare with online analyzer readings

•Check for sensor calibration drift

Do not rely on a single data point.

5. Inspect Differential Pressure (ΔP) Across RO Stages

Early warning signs of scaling include:

•Rising ΔP

•Reduced permeate flow at constant pressure

•Increasing required operating pressure

If ΔP has already increased:

•Do not restart at high recovery

•Consider early cleaning intervention

6. Restore Pretreatment Before Resuming Normal Operation

Only resume standard operation when:

•Softener performance is verified

•Antiscalant dosing is stable

•Hardness is back within design limits

If hardness remains elevated, operate temporarily at:

•Lower recovery

•Higher concentrate flow

•Reduced flux

What NOT to Do

❌ Do not ignore the spike
❌ Do not increase pressure to maintain flow
❌ Do not continue operation assuming “it will stabilize”
❌ Do not delay intervention until scaling is visible

Scaling damage is often irreversible.

Follow-Up Actions After Stabilization

•Review historical hardness trends

•Investigate upstream water source changes

•Improve alarm thresholds

•Add redundancy or interlocks for softener/antiscalant systems

•Update emergency response SOPs

Conclusion

A sudden increase in influent hardness is an RO emergency. The best immediate response is to reduce recovery or shut down the system, verify pretreatment performance, flush the membranes, and confirm hardness readings before resuming operation.

Fast, decisive action can mean the difference between normal operation and permanent membrane damage.