Smarter desalination for a changing climate

A seven-year research project undertaken by Water Corporation and Curtin University in Perth has shown exciting possibilities for improved efficiency and productivity of desalinated water production at the state’s desalination plants.

Titled ‘Bromide Criteria in Seawater Desalination Plants’, the research looked at whether it was possible to increase bromide concentration in water produced at the Perth (PSDP) and Southern (SSDP) seawater desalination plants without impacting customer experience of the water when it arrived at their taps.

The existing limit on the bromide concentration in desalinated water from both plants is 0.1 mg/L. This figure was based on research undertaken in collaboration with Curtin University (Heitz et al., 2004) at the time PSDP was being scoped.

“At that time, Water Corporation experienced customer complaints in the northern suburbs related to ‘plastic taste’ in water boiled in plastic kettles,” said Sergio Domingos, Water Corporation Research and Development Team Senior Technical Adviser.

“The chemistry of the plastic taste formation was not fully understood at the time, but it was established that the plastic taste was caused by a suite of bromophenols.

“In drinking water, bromophenols form through reactions of bromine, which is produced from the oxidation of bromide by chlorine, with phenol, from plastic appliances.”

Due to the importance of seawater desalination to future water security in Western Australia, Water Corporation was cautious that no plastic tastes could be associated with desalinated seawater, leading to the setting of the conservative bromide limit in the desalinated water.

To get bromide levels to 0.1mg/L, partial two-pass reverse osmosis (RO) configurations are used at both the PSDP and SSDP.

Higher targets

Higher bromide targets reduce the volume of water required to go through the second reverse osmosis pass, resulting in energy and water production benefits.

“Treating the water in this way improves the efficiency and long term sustainability of seawater desalination. For a 45 GL/yr plant, operation at 0.2 mg/L bromide could result in an additional 1.34 GL/yr of water, approximately +3% of its capacity, at an overall reduced operating cost,” Domingos said.

These are exciting possibilities, but they can only be realised if customers and regulators are happy with the final product. In positive results from the study, researchers found increasing the bromide concentration in desalinated water from 0.1 to 0.2 mg/L resulted in no water quality impact in terms of disinfection byproduct (DBP) compliance with the current Australian Drinking Water Guideline values, potential corrosion in the distribution system and the number of customer complaints.

“This is particularly significant as the implementation and planning for future seawater desalination plants progress in WA and the proportion of desalinated water increases in Perth’s Integrated Water Supply Scheme through the new Alkimos Seawater Desalination Plant and regional areas, as there is a new plant planned in the Pilbara at Onslow,” Domingos said.

Understanding risks

As with any adjustment to treatment, it is important that any health and aesthetic risks associated with bromide from desalination plants is well understood.

“This project has delivered the underpinning science to have a clear understanding of these risks by demonstrating no water quality impact in terms of DBP and metals compliance and aesthetic issues when the bromide target is increased to 0.2 mg/L at PSDP or SSDP,” Domingos said.

Domingos added that the research results could change how Water Corporation designs and runs its plants into the future.

“Subject to further planning, Water Corporation is considering a full-scale operational trial of a higher bromide target for SSDP and this will be undertaken with additional water quality monitoring,” he said.

“The success of this project has also provided the opportunity for new research to determine the best practical bromide limit for future desalination plants in the Pilbara region, where warmer waters are prevalent and the DBP risk profile is different. In relation to plant design, incorporation of features to facilitate operation at a range of bromide concentrations may be considered.”

Domingos said that similar principles could be applied to other treatment criteria for similar benefit.

“These are looked at on a case-by-case basis given the geographic spread and diversity of water sources in WA,” he said.

“In the case of bromide in seawater desalination, there is a limit on how high you can push, as the concentration of other parameters of interest such as boron, chloride and total dissolved solids will also increase as more water is bypassed around the second pass RO.”

The bromide research is just one of up to 100 projects each year that Water Corporation runs through its well-established Research and Development Program where it works collaboratively with universities, research institutions, like CSIRO and WaterRA, and other utilities.

“In inland WA, desalination of brackish groundwater may have an important role to play in community water supply,” Domingos said.

“In this space, we are investigating emerging technologies such as integrated forward osmosis reverse osmosis (FO-RO), looking at the potential to combine electrodialysis reversal (EDR) with sonication to minimise membrane fouling and utilising recycled seawater RO membranes in solar powered desalination for brackish water treatment.”

Lead by example

With annual rainfall in many places around Australia declining compared to long-term averages, and becoming more unpredictable, natural replenishment of surface water and groundwater sources has slowed.

In Perth, which has been experiencing this since the 1970s, the impact of climate change combined with population growth has resulted in the city becoming increasingly reliant on desalinated seawater to meet demand, an experience shared by many places around Australia today.

The importance of desalinated seawater to drinking water supplies is only going to increase in the coming years and decades, making research collaborations like this one invaluable.

The energy and water production benefits found through the research offers an example for many water corporations around Australia to follow.

This article was originally published in the 2024 edition of Current magazine.