The salty truth

In the quest for water security, desalination becomes both an answer and a problem

SINGAPORE (Feb 18): Like many land- and water-scarce countries, Singapore is proud of its desalination facilities. There are three plants in the southernmost part of its west coast, supplying 130 million gallons of water a day that can meet up to 30% of Singapore’s current water demand. Two more plants will be built by 2020, and the five plants will secure up to 30% of the city state’s water needs in 2060. Last year, national water agency PUB also announced plans for a new process that can cut the energy consumption of desalination plants by half, leading to cost savings.

The growth of Singapore’s desalination industry is crucial for the country’s water self-sufficiency. For a small and densely populated island, sources of clean water are limited even as demand grows. Currently, water recycling, which was initiated in 2003, can meet up to 40% of Singapore’s water requirements. The bulk of the country’s water supply, or 50% of current demand, comes from Malaysia. Reservoirs help make up the rest.

Singapore buys raw water from its neighbour under a water purchase agreement that expires in 2061. However, the city state’s relations with Malaysia look to be increasingly fractious and the latter has been pushing for the terms of the water agreement to be reviewed — specifically, a significant hike in the price of raw water. Against this background, desalination is a prized “national tap”.

Desalination is a process of obtaining fresh water that researchers say is relatively free of climate risks; the biggest challenge has been the cost of building and operating plants, owing to its high energy requirements.

But a United Nations-backed paper published last month — in the journal Science of the Total Environment — is raising new concerns about desalination’s environmental impact. The paper revealed that the volume of toxic brine produced from desalination plants globally is at least 50% more than previous estimates, totalling 51.7 billion cu m a year. On average, every litre of desalinated water produces 1½ litres of brine.

Previously, desalination was assumed to produce one litre of brine for every litre of fresh water produced. While there has been no conclusive data on the total volume of brine produced globally, the latest study, using a new set of methodology, suggests that the past assumption may have grossly underestimated the severity of the problem.

Brine is the salty by-product of extracting fresh water from the sea and it is typically disposed of into the ocean. This means the salinity of the receiving water may rise over time, reducing oxygen in the water — which is called hypoxia — and posing a threat to marine life, says Manzoor Qadir, one of the authors of the study and assistant director of UN University Institute for Water, Environment and Health. Hypoxia can lead to so-called dead zones in the ocean, which have quadrupled in size since 1950.

According to the study, most of the brine comes from desalination plants in the Middle East and North Africa region, which accounts for 48% of the world’s desalinated water and 70% of global brine production. These plants are typically older and use less efficient methods such as thermal desalination, which produces four times more brine than the modern membrane-based process. On average, the ratio of fresh water to brine is 0.5.

But as more desalination plants are expected to be built across the globe in the next few years from Australia to Singapore and the Middle East, researchers worry about the extent of the environmental cost on the oceans and marine life. There are relatively few studies on the environmental impact of desalination plants, with wildly contrasting views, and results are at best inconclusive. Most studies are also very limited in scope and cannot be extrapolated to other regions. Researchers also say that data on actual brine produced today as well as estimates for the future are largely unavailable.

In Singapore, PUB has said that brine from desalination plants is unlikely to have any impact on a global scale, and long-term monitoring of the SingSpring and Tuaspring desalination plants has shown no change in seawater quality. “When planning for desalination plants, PUB carries out Environmental Impact Assessments [EIAs] and water-quality modelling to understand the impact of brine discharge on the marine environment,” says a PUB spokesperson.

But researchers who spoke to The Edge Singapore say the industry should be taking action to reduce environmental harm before it is too late. “I, for one, would prefer that the industry heeds the warning from the current research and the latest model from the UN and work towards a more sustainable way of discharging. A way forward could be for future plants to have combined land and ocean discharge, or even transport the brine to areas of greater mixing potential with a larger ocean basin,” says Karen Lykkebo Petersen from Stockholm University’s department of ecology, environment and plant sciences.

Briny problem

Before brine is discharged into the ocean, most facilities employ a few methods to reduce its harmful impact. These include diluting the brine with cooling water or using a diffuser to increase the mixing of the brine and seawater at the point of discharge. In Singapore, PUB carries out EIAs to ensure any impact is within “tolerable limits”. It also carries out regular seawater quality monitoring at discharge points and receiving waters.

“[Given] the current low number of desalination plants, with an enlightened brine disposal system, Singapore practices should not have a perceptible impact on its marine ecosystem,” says Asit Biswas, founder of the Third World Centre for Water Management in Mexico and a distinguished visiting professor at the Lee Kuan Yew School of Public Policy in Singapore. “However, as the number of desalination plants increases in the future, the potential impact of brine disposal has to be assessed very carefully. Technically, this is a very difficult process. PUB is very much aware of this issue and is working on it. I do not expect any problem until at least 2035.”

Researchers on the subject are divided on the environmental impact of desalination, particularly in reference to the latest UN-backed report. Some have pointed out that brine can be disposed of safely — as in the case of Singapore. A study by King Abdullah University of Science and Technology in 2014 showed that waters five metres away from the brine discharge point remain unaffected. Another study in 2019 by researchers at the University of California, Santa Cruz found no significant impact on marine life in local waters. The study analysed the environmental impact of the Carlsbad Desalination Plant in California, which started operating in 2015.

But the same study also indicated salinity levels rose more than what was permitted by local authorities, even though the desalination facility took all the necessary steps to dilute the concentration of brine. This may suggest that brine management and its environmental footprint are not fully understood.

Other studies in recent years also show a change in seawater quality around desalination plants. For instance, a study by the University of Western Cape in 2017 found 14 organic compounds in seawater samples and marine organisms near desalination plants. While these substances were already present in the seawater, brine from desalination could return these compounds to the sea in greater concentration.

Differing standards

In the coming years, there will be more desalination facilities, says Qadir, as the technology becomes more affordable. “Irregular rainfall causes long periods of floods and droughts in certain regions. And that means there is a need for [a more consistent] water supply,” he points out.

But as the industry grows, more transparency around brine production is necessary. One of the biggest challenges for the industry is obtaining data from companies operating in the field. Hyflux, which has a 30% equity interest in SingSpring and owns Tuaspring, says it does not disclose the actual volume of brine, as it is commercially sensitive information. Keppel Infrastructure Trust, which has a 70% stake in SingSpring and is building the fourth desalination facility in the country, gave a similar reply.

“Before release, Hyflux has online analysers installed in the outfall pipe of the plants, to measure the discharge flow rate, dissolved oxygen, turbidity, conductivity, free chlorine, temperature and pH of the water,” says a Hyflux spokesperson.

“These parameters are monitored continuously by a SCADA [supervisory control and data acquisition] system to ensure they fall within allowable limits. The SCADA is a computer system used for gathering and analysing real-time data. Samples of water are also sent regularly to external consultants to measure suspended solids and chlorine levels, ensuring all parameters are within regulatory allowance limits. In Singapore, all parameters listed in NEA’s [National Environment Agency] water quality standards of Trade Effluent Discharge to Watercourse are also tested, in accordance with regulatory allowable limits,” the person adds. The limits set by NEA include temperature not above 45ºC, no more than 50mg per litre of suspended solids and less than 1mg of total metals.

One of the strictest limits on desalinated water is that set by the state of California in the US, which stipulates that brine must be cleaned to remove most metals and chemicals. The recommended guideline states that the salinity of receiving water must not rise above 5% in the first 100m of discharge point.

EIAs conducted by operators of desalination facilities should also be made available to researchers and the general public. Without these data points, it may be difficult to assess the potential long-term environmental harm posed by these facilities. There may also be no impetus to take precautionary measures without understanding the longer-term repercussions of the desalination process.

Still, it is not feasible, observers say, to have common universal guidelines, as conditions differ significantly from plant to plant. What is worrying, though, is that there is also no consensus on when the level of environmental impact caused by brine discharge is considered harmful.

A study by hydrogeologists Thomas Missimer and Robert Maliva last year titled Environmental issues in seawater reverse osmosis desalination: Intakes and outfalls, notes: “There is no agreement as to the threshold for impacts to be considered significant or unacceptable… A single desalination plant discharging concentrate to a bay or gulf would not have a material impact on the salinity of the receiving body. However, multiple desalination plants operating over a very long time could cause increases in salinity.”

Stockholm University’s Petersen says: “A main issue is that many of the larger ­desal-facilities in Saudi Arabia [and the region] have been built in time periods when the ocean was viewed as an unchangeable water body. We now know that we most definitely can change the ocean and especially the coastal zones. With projected climate change, I think it is important to try to find new methods to deal with brine. One way could be to have more on-land salt fields to prevent it from going into the ocean and harvest the salt for other purposes.

“There is no definite answer or proof of how bad brine is, because it is very hard to measure it on an ecosystem scale versus just individual organisms. If this [problem is escalated with the increase in water temperatures due to] climate change and general pollution, I think it is a very serious concern that the industry would have to take into account.” Observers say the cost of desalination may rise in the long run if it does not deal with the potential environmental problems early on.

“The technology and engineering power is here already, but is currently more expensive than [doing] business as usual, which seems a common theme in environmental issues,” Petersen notes.

More transparency needed

Desalination is likely to remain a key solution for countries such as Singapore. “Desalination is unique, as it is a ‘secure’ water source that can provide a steady supply of high-quality water. It is best suited to supplying water to urban centres close to the coasts,” says Adina Paytan, one of the authors of the University of California, Santa Cruz study. “Desalination has an impact on the environment, but these are not necessarily greater than those of building dams and diverting water.”

And it may become even more important for Singapore, despite desalination’s being one of the most energy-intensive ways of obtaining water. “If the alternative is buying water from Malaysia, and if Malaysia raises prices eventually, then desalination becomes part of a sustainable solution,” says Raul Lejano, associate professor at New York University in the US.

But it will be important to find ways to mitigate the environmental impact as the country ramps up capacity. Qadir, who co-authored the UN-backed report, says, “We need to find a way to treat brine economically. We also need substantial effort to reduce the volume of brine. Studies in this field have always been limited to small sample sizes or pilot programmes. We need to scale this up.” Brine has been tested on aquaculture and agriculture systems. In one case, it raised fish biomass by 300%. It has also been tested on spirulina cultivation.

Still, today brine management is extremely expensive and technically difficult, says Qadir. Brine management makes up about one-third of companies’ outlay. PUB said two years ago that harvesting salt for use from brine was uneconomical.

But Qadir acknowledges the number of studies and experiments to advance desalination technology, reduce brine and study the environmental impact is growing. In Qatar University, students are testing ways to break down brine into sodium bicarbonate, calcium chloride and ammonia. With concerted efforts to improve technology, along with more data being made available, the unwanted environmental effects of desalination could be better dealt with and the process could provide a truly sustainable fresh water source.

This story appears in The Edge Singapore (Issue 869, week of Feb 18) which is on sale now. Subscribe here