How Does the Chemical Cleaning of Seawater Desalination Membranes Differ from That of Brackish Water Membranes?| Insights by AQUALITEK

Introduction

Chemical cleaning (CIP) is a critical maintenance activity for all reverse osmosis (RO) systems. However, seawater desalination RO (SWRO) membranes operate under fundamentally different conditions than brackish water RO (BWRO) membranes.

As a result, cleaning chemistry, procedures, frequency, and risk control requirements differ substantially. Applying BWRO cleaning practices directly to SWRO systems can lead to ineffective cleaning, accelerated membrane damage, or irreversible performance loss.

This article explains how and why SWRO membrane chemical cleaning differs from BWRO cleaning, and outlines best practices for each.

1. Fundamental Differences Between SWRO and BWRO Operating Environments

Before comparing cleaning methods, it is essential to understand the operating differences:

Key difference:
SWRO membranes experience less classical scaling due to lower recovery (40–50%), so acid cleaning is often secondary, while BWRO systems rely heavily on acid cleaning.

4. Cleaning Temperature Control Differences

Temperature has a strong impact on cleaning efficiency and membrane safety.

•SWRO membranes:

Cleaning temperature strictly limited (often ≤30–35°C)

Higher temperatures accelerate chemical attack under high salinity

•BWRO membranes:

Wider allowable temperature range

More flexibility to enhance cleaning kinetics

SWRO cleaning prioritizes membrane protection over cleaning speed.

5. Differences in Cleaning Frequency and Triggers

SWRO Cleaning Strategy

•Less frequent, but more carefully planned

•Triggered by:

Biofouling indicators

Differential pressure increase

Normalized flow decline

•Over-cleaning risks membrane damage

BWRO Cleaning Strategy

•More frequent cleaning cycles

•Triggered by:

Scaling indices

Rapid pressure drop increase

Recovery-related fouling

Key takeaway:
SWRO cleaning is preventive and conservative, while BWRO cleaning is often corrective and frequent.

6. Rinsing and Neutralization Requirements

SWRO Systems

•Longer flushing time required

•Complete chemical removal is critical

•Residual chemicals can:

Damage downstream materials

Kill beneficial bio-control dosing balance

Affect permeate quality significantly

BWRO Systems

•Shorter rinse cycles generally sufficient

•Less risk of residual chemical concentration effects

7. Materials and Corrosion Considerations

SWRO cleaning systems must consider:

•High chloride concentration

•Stress corrosion cracking risks

•Compatibility with duplex/super duplex steels

As a result:

•Chemical compatibility checks are mandatory

•Cleaning solution conductivity and chloride levels must be monitored

BWRO systems face lower corrosion risks during CIP.

8. Operational Risk: Why SWRO Cleaning Is Less Forgiving

Mistakes during SWRO membrane cleaning may result in:

•Irreversible membrane oxidation

•Rapid loss of salt rejection

•Increased boron passage

•Shortened membrane life

BWRO membranes are generally more tolerant of minor cleaning errors.

Conclusion

Chemical cleaning of seawater desalination membranes is not simply a higher-salinity version of brackish water membrane cleaning. It requires:

•Different chemical priorities

•Stricter temperature and pH control

•Longer and more thorough rinsing

•Greater focus on biofouling rather than scaling

Applying BWRO cleaning logic to SWRO systems is a common but costly mistake. Tailored cleaning strategies are essential for long-term SWRO performance and membrane longevity.