Key Differences Between Cleaning Agent Formulations for Seawater RO Membranes and Brackish Water RO Membranes| Insights by AQUALITEK

Introduction

Chemical cleaning is an unavoidable part of reverse osmosis (RO) membrane operation.
However, cleaning agent formulations used for seawater RO (SWRO) membranes differ significantly from those used for brackish water RO (BWRO) membranes.

These differences are driven by:

•Feed water chemistry

•Operating pressure and salinity

•Dominant fouling mechanisms

•Membrane material tolerance and aging behavior

Understanding these distinctions is essential for effective cleaning, membrane protection, and long-term operating cost control.

1. Fundamental Difference: Fouling Characteristics

The most important reason for different cleaning formulations lies in fouling composition.

Seawater RO (SWRO) Membranes

Dominant fouling types:

•Biological fouling (biofilms, EPS)

•Colloidal and particulate fouling

•Organic fouling (marine organics)

•Calcium sulfate and mixed salt scaling

Brackish Water RO (BWRO) Membranes

Dominant fouling types:

•Calcium carbonate scaling

•Iron and manganese fouling

•Silica scaling

•Organic fouling (terrestrial sources)

SWRO fouling is more complex and mixed, requiring broader-spectrum and more robust cleaning formulations.

2. Difference in Alkaline Cleaning Agent Formulations

2.1 SWRO Alkaline Cleaners

SWRO alkaline cleaners are typically:

•Stronger in formulation

•Designed to attack biofilms and marine organics

Common components include:

•High-performance surfactants

•Dispersants

•Biofilm penetration agents

•Enzyme-enhanced additives (in some cases)

Typical pH range:

•pH 11.0–12.0

Key objectives:

•Break down extracellular polymeric substances (EPS)

•Remove organic slime layers

•Disperse colloidal deposits

2.2 BWRO Alkaline Cleaners

BWRO alkaline cleaners are generally:

•Milder in formulation

•Focused on organic and iron-related fouling

Common components include:

•Standard surfactants

•Mild dispersants

Typical pH range:

•pH 10.5–11.5

BWRO membranes rarely experience the dense biofilms common in SWRO systems, allowing gentler chemistry.

3. Difference in Acid Cleaning Agent Formulations

3.1 SWRO Acid Cleaners

SWRO acid cleaners must address:

•Calcium sulfate (gypsum)

•Mixed sulfate scaling

•Iron deposits embedded in biofilms

Common acids used:

•Citric acid

•Phosphoric acid

•Specialized organic acid blends

Typical pH range:

•pH 1.5–2.5

Key design considerations:

•Controlled dissolution of sulfate scale

•Corrosion inhibition for high-alloy materials

•Compatibility with high-pressure membrane elements

3.2 BWRO Acid Cleaners

BWRO acid cleaning focuses primarily on:

•Calcium carbonate

•Iron hydroxide

•Mild inorganic scaling

Common acids used:

•Citric acid

•Hydrochloric acid (more common than in SWRO)

Typical pH range:

•pH 2.0–3.0

BWRO systems tolerate stronger mineral acids due to lower chloride concentrations.

4. Difference in Oxidant and Biocide Considerations

SWRO Cleaning Formulations

•Strong restrictions on oxidants

•Oxidative cleaning agents are generally avoided

•Biofouling is addressed chemically via surfactants and enzymes rather than oxidants

Reason:

•SWRO membranes operate in extremely high chloride environments

•Oxidants dramatically accelerate membrane degradation

BWRO Cleaning Formulations

•More flexibility in oxidant use

•Short-term exposure to certain oxidants may be allowed under controlled conditions

•Iron fouling sometimes benefits from oxidative cleaning

5. Difference in Cleaning Frequency and Strategy

SWRO Cleaning Strategy

•Less frequent but more intensive cleanings

•Longer soak times

•Multi-step alkaline → acid cleaning sequences

•Higher solution circulation volumes

BWRO Cleaning Strategy

•More frequent but milder cleanings

•Shorter contact times

•Often single-step cleaning is sufficient

6. Summary Table: SWRO vs BWRO Cleaning Agent Differences

Conclusion

The cleaning agent formulations used for seawater RO membranes differ fundamentally from those for brackish water membranes due to more severe biofouling, higher salinity, and complex mixed fouling conditions.

Using BWRO-style cleaning chemicals in SWRO systems often results in:

•Incomplete fouling removal

•Accelerated membrane aging

•Increased cleaning frequency

Optimized SWRO cleaning formulations must be stronger, broader in action, and more carefully controlled to balance cleaning efficiency and membrane protection.