Desalination

In seawater desalination plants, brine is the salty byproduct returned to the ocean. It is nearly twice as salty as seawater because about 40-45% of the freshwater is removed.

Brine may contain very small amounts of food-grade chemicals like anti-scalants and cleaning agents, used in the desalination process. They are used to keep the membranes working efficiently. Only chemicals approved by the Department of Health for use in drinking water are used. 

We begin the environmental impact assessment (EIA) and approval process after we complete The potential environmental impacts of desalination proposals are defined, assessed, managed, and monitored under the Environmental Protection Authority’s (EPA’s) Environmental Quality Management Framework (EQMF) for the State’s marine waters. The EQMF is set out in the EPA’s (2016) Technical Guidance: Protecting the Quality of Western Australia’s Marine Environment.   

Our planning, investigations and concept design. The process includes referring the proposal to the EPA under Part IV of the Environmental Protection Act 1986. EIA is a step-by-step way to assess how a proposal might impact the environment. A key step in EIA is finding effective controls and management measures. These help reduce possible negative environmental impacts. The referral must show we're using the best measures. It must also show we have genuinely evaluated the location and design options for the proposal. This, along with the proposed environmental management measures, will ensure the EPA’s environmental objectives are met. The public is encouraged to join the EPA process via its consultation hub.

Bitterns are salts and minerals left after seawater evaporates. Bitterns are sometimes used in table or industrial salts. They are much saltier than seawater and can be toxic to some marine life. We do not produce or discharge bitterns into the environment.

We considered several options before we built our desalination plants. Building more dams isn't feasible due to reduced rainfall across Perth, the South West and Great Southern regions. A study found a pipeline from the north would be too expensive and negatively impact the environment. The CSIRO advised cloud seeding was unlikely to be effective in much of Australia. 

Brine is returned to the ocean through a brine pipeline with a diffuser at the end. Diffusers help rapidly mix and dilute the brine with seawater so that salinity reduces to match the surrounding seawater, generally within tens of metres. Mixing and dilution minimises the impact on marine life and ecosystems.

Brine continues to mix with seawater after it leaves the diffuser. It will not form pools of hypersaline water or collect in depressions or basins.

Machinery and equipment will produce temporary noise during drilling and installation of the marine infrastructure. Once the construction methods are established, we will conduct a noise impact assessment. Noise-generating activities will be short-term, will avoid the whale migration period and will managed according to the relevant guidelines. During operation, the sound of the brine being released will be similar to the natural sounds of waves and moving water.

No, the diffusers are designed specifically for the chosen location and waves are not always required for the diffuser to work effectively. However, periods of wave energy would improve the dispersion. We consider the slope of the seabed (bathymetry) and complete modelling that uses local wave, current and tide data to tell us the best place to put the diffuser. 

Whenever we can, we try to avoid sensitive marine habitats, such as seagrass. We prefer to install brine diffusers in areas with bare sand. 

The effect on stationary marine life, like seagrass, will be limited to the area where the highly diluted plume touches the seabed. We use brine dispersion modelling and habitat mapping to predict where this will happen. This helps us find areas that reduce impacts and avoid sensitive spots, like seagrass. It also helps us design the brine diffusers specifically for the location where they will be installed, so that we ensure the brine is being effectively dispersed into the surrounding ocean.

Mobile marine life that prefers lower salinity will move away from the brine. However, many species that tolerate high salinity will thrive near the diffuser. Mussels, starfish, seahorses and fish often gather around these structures and grow on them, creating unique ecosystems.

Our diffusers at the Southern and Perth Seawater Desalination Plants show that they create habitats for marine life. Fish, mussels, starfish, seahorses and crayfish all thrive on and near the diffusers.

Our marine monitoring has demonstrated continued compliance with environmental regulations at our existing seawater desalination plants.

We completed a study in Albany to investigate the option of brine recycling, known as zero liquid discharge - for managing brine rather than returning it back to ocean.

The infrastructure required, such as evaporation ponds or advanced treatment technologies, would be extremely costly and energy intensive. For example, evaporation ponds would need hundreds of hectares of land and cost hundreds of millions of dollars, likely requiring clearing or repurposing of agricultural land. Alternative methods like evaporators and crystallisers also have high energy demands and operating costs.

The salt produced is not suitable for food-grade use, and there no known industrial demand in Albany for low-grade salt, meaning it would need to be sent to landfill.

For all these reasons, brine recycling is not a practical, environmentally sound or cost-effective solution. Based on our experience operating desalination plants, we are confident that ocean discharge can be managed in a way that is safe for the environment and acceptable to the community.

Seawater desalination is four times more energy intensive than groundwater collection and over 40 times more energy intensive than water sourced from dams.