What Is the Most Common Way to Discharge Concentrated Brine from Large-Scale Seawater Desalination Plants?| Insights by AQUALITEK

Introduction

Large-scale seawater desalination plants typically convert only 40–50% of incoming seawater into fresh water, while the remaining 50–60% becomes high-salinity concentrated brine.

Managing this large volume of saline concentrate is one of the most critical environmental and engineering challenges in seawater desalination projects.

Globally, the most common and technically mature method for brine disposal is deep-sea outfall discharge using engineered diffuser systems.

1. The Most Common Method: Submarine Outfall Discharge

1.1 What Is Submarine Outfall Discharge?

Submarine outfall discharge involves:

•Transporting concentrated brine via pipelines

•Releasing it into deep offshore waters

•Using diffuser systems to rapidly dilute the brine

This method allows:

•Fast mixing with surrounding seawater

•Significant reduction of salinity concentration

•Minimal ecological disturbance when properly designed

1.2 Why It Is the Global Standard

Over 90% of large-scale SWRO plants worldwide use submarine outfall systems because:

•Ocean has enormous dilution capacity

•Reliable hydrodynamic dispersion

•Proven long-term environmental safety

•Lower cost compared to zero-liquid-discharge solutions

•High regulatory acceptance

Major desalination projects in:

•Middle East

•Australia

•Spain

•China

•North Africa

all rely on submarine outfalls as the primary brine discharge solution.

2. Key Engineering Design Principles

2.1 Deep-Water Discharge Location

Outfall diffusers are typically installed:

•Several hundred meters to several kilometers offshore

•At depths of 10–40 meters or more

This ensures:

•Strong natural mixing

•Rapid dilution

•Reduced shoreline environmental impact

2.2 Multi-Port Diffuser Systems

Instead of a single outlet, modern systems use:

•Multiple small-diameter nozzles

•Jet dispersion

•High-velocity mixing

This allows:

•Rapid dilution (often >100:1 within seconds)

•Prevention of localized hypersalinity zones

2.3 Hydrodynamic and Environmental Modeling

Before construction, engineers perform:

•CFD hydrodynamic simulations

•Environmental impact assessments (EIA)

•Long-term salinity dispersion modeling

Ensuring:

•No chronic salinity accumulation

•Marine ecosystem protection

•Compliance with environmental regulations

3. Environmental Safety and Compliance

3.1 Dilution Requirements

Most regulatory frameworks require:

•Salinity increase at mixing zone boundary ≤ 1–2 PSU

•No long-term accumulation

Submarine outfall systems typically achieve:

•Initial dilution > 50–100 times

•Final salinity levels close to natural seawater

3.2 Ecological Protection Measures

Additional measures often include:

•Blending brine with cooling water discharge

•Diffuser orientation optimization

•Continuous salinity monitoring

•Marine biological impact assessments

4. Why Alternative Brine Disposal Methods Are Rare in Large Plants

4.1 Evaporation Ponds

•Require huge land areas

•Extremely high cost

•Unsuitable for coastal mega-projects

4.2 Zero Liquid Discharge (ZLD)

•Extremely energy-intensive

•Very high capital and operational cost

•Mainly used in inland brackish desalination

4.3 Deep-Well Injection

•Geologically restricted

•High risk of groundwater contamination

•Rare in coastal desalination projects

Therefore, submarine outfall remains the only economically viable and environmentally accepted solution for large SWRO plants.

5. Typical Brine Discharge System Configuration

1.Brine collection manifold

2.Onshore discharge pumping station

3.Submarine pipeline

4.Offshore diffuser array

5.Environmental monitoring system

6. Case Examples

•Sorek Desalination Plant (Israel) – 624,000 m³/day → deep-sea diffuser system

•Ras Al Khair Plant (Saudi Arabia) – >1,000,000 m³/day → offshore multi-port discharge

•Sydney Desalination Plant (Australia) – multi-nozzle diffuser at 20 m depth

All use engineered submarine outfall discharge systems.

Conclusion

The most common and globally accepted method for disposing of concentrated brine from large-scale seawater desalination plants is submarine outfall discharge using engineered diffuser systems.

This method:

•Ensures rapid dilution

•Minimizes environmental impact

•Meets regulatory standards

•Provides economic feasibility at large scale

As desalination capacity continues to expand worldwide, advanced diffuser technology and environmental modeling will play an increasingly critical role in sustainable brine management.