Environmental Impacts of High-Salinity Brine Discharge from Seawater Desalination Plants and How to Mitigate Them| Insights by AQUALITEK

Introduction

Seawater desalination plays a critical role in addressing global water scarcity, but it also generates a by-product that must be carefully managed: high-salinity brine.

This brine stream typically contains:

•Salinity 1.5–2 times higher than seawater

•Residual treatment chemicals

•Elevated temperature (in some cases)

•Trace metals or cleaning residues

If discharged improperly, concentrated brine can pose significant environmental risks, particularly to sensitive marine ecosystems.

This article examines:

1.The main environmental concerns associated with brine discharge

2.The engineering and operational measures used to mitigate these impacts

1. Elevated Salinity and Osmotic Stress on Marine Life

1.1 Impact on Marine Organisms

High-salinity brine increases the local salinity of receiving waters, which can:

•Disrupt osmotic balance in fish and invertebrates

•Cause dehydration stress

•Reduce reproduction and larval survival rates

Sessile organisms such as:

•Corals

•Seagrass

•Benthic invertebrates

are particularly vulnerable due to their limited mobility.

2. Density Effects and Seabed Accumulation

2.1 Brine Is Denser Than Seawater

Brine typically sinks after discharge, leading to:

•Accumulation near the seabed

•Long residence time

•Localized “salinity pools”

This can cause:

•Reduced oxygen exchange

•Altered benthic habitats

•Loss of biodiversity in bottom-dwelling communities

3. Residual Chemicals and Toxicity Concerns

3.1 Chemical Additives in Brine

Brine may contain residual:

•Antiscalants

•Biocides (or neutralized byproducts)

•Coagulants or flocculants

•Cleaning chemicals (during CIP events)

Even at low concentrations, these substances can:

•Affect plankton and microorganisms

•Accumulate in sediments

•Interfere with marine food chains

4. Thermal Pollution (Site-Specific)

In some desalination configurations:

•Intake water may be warmer

•Brine discharge temperature may exceed ambient seawater

Elevated temperature can:

•Reduce dissolved oxygen

•Stress temperature-sensitive species

•Intensify the impact of salinity changes

5. Cumulative and Long-Term Ecological Effects

While short-term impacts may be localized, long-term or cumulative discharge can:

•Shift species composition

•Reduce ecosystem resilience

•Alter nutrient cycling

•Increase vulnerability to climate change stressors

Environmental risks increase significantly when:

•Discharge occurs in enclosed or low-circulation areas

•Multiple plants discharge into the same coastal zone

How Environmental Impacts of Brine Discharge Can Be Mitigated

6. Dilution Through Engineered Outfall Design

6.1 Multiport Diffusers (Best Practice)

Modern desalination plants use:

•Submerged multiport diffusers

•High-velocity jet mixing

•Rapid initial dilution (often >20:1 within meters)

This reduces:

•Salinity peaks

•Exposure time for marine organisms

7. Strategic Site Selection

7.1 Favor High-Energy Marine Environments

Preferred discharge locations include:

•Open coastlines

•Areas with strong currents

•High natural mixing zones

Avoid:

•Enclosed bays

•Lagoons

•Coral reefs

•Seagrass meadows

8. Blending Brine with Other Water Streams

Brine can be blended with:

•Power plant cooling water

•Treated wastewater effluent

•Other low-salinity discharges

This reduces:

•Overall salinity

•Density difference

•Environmental footprint

9. Chemical Optimization and Control

9.1 Minimizing Chemical Load

Best practices include:

•Using environmentally friendly antiscalants

•Avoiding continuous biocide dosing

•Neutralizing cleaning chemicals before discharge

•Strict chemical mass balance control

10. Energy Recovery and Reduced Brine Volume

Advanced energy recovery devices (ERDs):

•Reduce overall seawater intake

•Lower brine flow rate

•Decrease discharge volume

Lower discharge volume = lower environmental impact.

11. Environmental Monitoring and Adaptive Management

11.1 Continuous and Periodic Monitoring

Key monitoring parameters:

•Salinity profiles

•Temperature

•Dissolved oxygen

•Benthic biodiversity

•Chemical residuals

Data-driven monitoring allows:

•Early detection of impacts

•Adjustment of discharge strategy

•Regulatory compliance

12. Zero Liquid Discharge (ZLD) – Special Cases

In environmentally sensitive areas, ZLD solutions may be considered:

•Evaporation ponds

•Crystallizers

•Salt recovery systems

Although costly, ZLD can:

•Eliminate marine discharge

•Enable resource recovery

•Meet strict regulatory requirements

Conclusion

High-salinity brine discharge is one of the most important environmental challenges associated with seawater desalination.

However, with:

•Proper outfall design

•Strategic site selection

•Chemical control

•Advanced energy recovery

•Continuous environmental monitoring

its ecological impact can be effectively minimized.

Sustainable desalination is not just about producing fresh water—it is about protecting the marine environment that makes desalination possible.