fbpx

Desalination

Desalination is the process of removing salts dissolved in water. This is most commonly used to treat ocean water, but the same process can also be applied to brackish (salty) groundwater.

The most simple form of desalination, thermal distillation, has been around for millennia; this involves heating saltwater and collecting the water vapour, with the salt remaining in the pan. Heating the water requires significant amounts of energy too inefficient to use for drinking water supply. However, kids may enjoy making a DIY solar still as described in this video.

Modern techniques for desalination are more efficient. The most common is reverse osmosis [RO], where saltwater is forced through a semi-permeable membrane to remove ions (the chemical particles that make up dissolved salt). This leaves a salt-rich brine solution on one side of the membrane, and pure water on the other.

The brine is a waste byproduct of desalination. This is typically disposed through an “ocean outfall”, a pipeline into the ocean. Good engineering design can eliminate or minimise the impacts of brine disposal in a well-flushed ocean site. The Gold Coast desalination plant (see video below) has a pipeline that takes brine 1.5km offshore. In this best-base scenario, an artificial reef has formed around the outfall infrastructure. However, some marine environments are not well-flushed, such as the top of Spencer Gulf in South Australia, where there were concerns that brine discharge could harm a fragile ecosystem. Each site must be assessed for its ecology, and the infrastructure must be engineered to prevent disturbance. The Gold Coast desalination plant shows that this is achievable.

Though more efficient than thermal distillation, Reverse Osmosis (RO) still requires large amounts of energy to purify water. Renewable energy sources are one solution, and researchers are also looking at making the process itself more efficient. (Such as this team at RMIT).

As a smart water option, desalination has the benefit of being modular. This means you can build a small facility to start, and add capacity as needed, giving the system flexibility and adaptability to meet future demands. The addition of a desalination plant to a system increases drought resilience because these plants produce water without rain.

Deslination FAQ

In 2020 Rous County Council commissioned a proof-of-concept investigation into desalination[1] which found the capacity to supply Byron Bay’s entire bulk water needs[2]. Internationally, desalination technology is proven[3] as an on-demand solution to changing water consumption[4] and rainfall patterns.

What about all the waste brine (salt)?

Desalination produces a bi-product call brine, which has been an environmental issue in the past. These days, experts believe we can dispose of brine safely[5]. Specially designed dispersal jets referred to as ‘duckbill’ nozzles are used to provide adequate dilution[6]. Designers of desalination plants often suggests a merger of desalination brine waste with existing sewage ocean outflow[7]. Some research has actually found an increase in marine life as a result of discharged brine from a desalination plant in NSW[8].

Isn’t desalination very expensive?

The costs of desalination are decreasing with improving technologies[9]. The Australian Water Association cites the cost of desalinated water to users at $1-$4/kilolitre[10]. Rous currently sell water at $1.66/kilolitre (wholesale)[11] and $2.43/kilolitre (retail)[12]. The cost of desalination plants and desalinated fresh water is not prohibitive and is in fact will within reason.

Aren’t there a lot of plastic filters used?

Another contentious issue is the perceived waste generated by virtue of standard ‘blown cartridge’ filters[13] which have created a pollution issue[14] alongside concerns of microplastics generally[15]. However, the most up-to-date desalination plants are utilising titanium membranes[16], ‘cross-flow’ filters[17], and other advances to achieve advanced ‘clean-in-place’[18] methods for vastly increasing the life of reverse osmosis filters[19] and potentially creating reusable filters, eliminating the filter waste problem altogether[20].

Doesn’t it require lots of energy and generate large CO2 emmisions?

Dams require 1kWh/Kl to prepare water for consumption, but a modern desalination plant consumes as little as 2.5kWh/Kl[21]. Moreover, common desalination plants throughout the world[22] increasingly utilise 100% renewable energy[23] especially solar power[24]. Based on Rous’ projected desalination energy consumption rate (4kWh/Kl)[25] and current solar panel efficiencies, 5 hectares of solar-farm (2% the space of a Dunoon Dam footprint) would produce the required energy for 10MLD (Mega-Litres per Day) fresh water production – which is 73% of Rous’ entire Future Water Strategy’s projected bulk water requirements. While research is ongoing[26] some desalination plants are currently operating with stored renewable energy[27] and there’s no reason why we cannot do that in Byron Bay also.

A desalination plant in Byron Bay would create effective independence of Byron Bay from the Rous bulk supply network – effectively freeing up current bulk water sources for the remaining Rous network.


Notes

24 “Solar desalination offers a sustainable solution to growing global water demand due to the geographical coincidence between high solar availability and severe water scarcity”: https://wdrc.kaust.edu.sa/Pages/Pub-2020-SSS.aspx