SINGAPORE (Feb 18): Desalination — the process of turning vast amounts of water from oceans and rivers into fresh water — has been held up as the hope of water-starved nations such as Singapore.
Desalination is Singapore’s prized fourth “national tap”. According to PUB, the city state is set to have five desalination plants by 2020, and desalinated water would meet up to 30% of the population’s daily water needs by 2060.
But last month, a United Nations-backed study revealed that desalination actually poses a danger to the environment as a result of the higher-than-expected amounts of toxic by-product — containing high concentrations of salt and chemicals — released into the sea. According to estimates, nearly 52 billion cu m of this toxic brine is discharged every year.
The brine raises the salinity of the seawater and affects the marine ecosystem. Additionally, according to the authors of the report, the by-product is polluted by the chemicals used in the desalination process, including chlorine.
The national water agency as well as the companies running the three currently operational desalination plants in Singapore — Hyflux and Keppel Infrastructure Trust — have declined to provide The Edge Singapore with details on just how much brine is produced from their operations. Hyflux only says that brine flow increases correspondingly with the increase in desalination volume.
According to Hyflux’s 2017 Sustainability Report, high-concentration brine and backwash wastewater from desalination operations are discharged into the sea. Before that is carried out, “online analysers installed in the outfall pipe measure discharge flow rate, dissolved oxygen, turbidity, conductivity, free chlorine, temperature and pH”.
The operators maintain that all discharge from the desalination process is constantly monitored to ensure that waste products are within “regulatory allowance limits”. On Singapore’s National Environment Agency website, the “allowable limits” stipulate that effluent discharged must not contain radioactive material; any pesticide or other similar chemicals; any solid waste matter; petroleum or other flammable solvent; or any other hazardous or “objectionable” substances. The limits also specify a maximum temperature of 45ºC, as well as how much salts, metals and minerals are allowed, such as a total of 1mg of chlorine or 1mg of metal per litre of discharge.
On its part, PUB says long-term monitoring of the SingSpring and Tuaspring desalination plants has shown no change in seawater quality. One water management expert expressed confidence that Singapore’s “enlightened brine disposal system” should not affect the marine ecosystem too much.
To be sure, there are no common standards globally for brine discharge, mainly because conditions at the facilities, in various regions, differ. That presents a challenge — as well as an opportunity. The best practice currently seems to ensuring that the by-product is treated, diluted and cooled, then released slowly.
The roughly 16,000 desalination plants around the world are concentrated in the Middle East, North Africa, Australia, Japan, coastal cities in China, as well as some cities in the US. Most of these plants are seawater desalination facilities, but many, particularly in the US and Europe, use brackish water and river water as feedstock. Seawater desalination produces more brine per cu m of fresh water than facilities that use river water.
One expert tells The Edge Singapore that it would be much better for the industry to take heed of the UN-backed study and start taking precautions before it is too late. Indeed, the arguments that the impact is not quite perceptible yet, or that it will become a problem only 10 or 15 years later, cannot be excuses for inaction. As more desalination plants become operational, it would be only a matter of time before the massive amounts of concentrated brine released into the oceans cause a real and possibly irreversible problem.
Desalination is already a very expensive process, owing to the huge amount of energy required. It is an option typically available to wealthier countries — in other words, countries with the resources to invest in R&D to ensure fresh water is not produced at the expense of the broader ecosystem.