Course:EOSC270/2022/Group 7- Seawater Desalination

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What is specific about Seawater Desalination?

Fig1.1: Standard desalination plant in Perth, Australia
Fig1.2: Flow chart of common seawater desalination plants
  • What is seawater desalination?

Seawater desalination is an artificial process used to remove salt and other impurities in seawater, so as to increase the total amount of fresh water without being affected by time, space and climate, and ensure the stable supply of drinking water for coastal residents and make-up water for industrial boilers[1]. With the increasing maturity of technology and the increasing demand for water sources in recent years, seawater desalination is gradually evolving into a new and developing artificial technology. Seawater desalination itself is divided into many types, including osmotic desalination, distillation desalination, membrane desalination and so on. It is widely used in developed areas in North America or Europe, or in the Middle East and Africa, where water resources are extremely scarce[2].



  • Worldwide usage of desalination

Generally, the shortage of fresh water has become one of the most serious environmental problems threatening life all over the world. Therefore, desalination technology is gradually being used by countries like the US, Arabian countries, Japan and Italy[3]. The Arabian nations around Persian Gulf are financially benefited from petroleum export, so they can maintain the operation of  expensive outdated desalination systems, and four of them produce 55 percent of global desalinated brine[4]. Even western countries use more modern technology-reverse osmosis, US coastal regions still  contribute 12 percent of the world's desalinated water with 10 desalination facilities in California[5].


  • What are some problems associated with seawater desalination?

Over the years, seawater desalination has been a controversial topic. Although this is a mature technology and has been used for a long time to provide drinking water to many parts of the world, it is often criticized for its high energy consumption. In addition, different ways of seawater desalination will bring many other negative effects[1]. These impacts include but are not limited to:

1. Organisms are entrained or entrapped into the desalination system together by seawater intake system, which may be killed, injured and weakened, leading to biological pollution, reducing abundance and diversity and changing the relative contribution to natural communities[1].

2. High concentration brine (the main discharge of seawater desalination) may make the water quality stratified, and then affect the whole water cycle. This will lead to the decrease of oxygen solubility (oxygen content) in the water. Since the density of high concentration brine itself is much higher than that of the upper water area, salt ions will continue to penetrate into the deeper sea area, follow up by being attached near resource points such as seabed sunken wood and whale carcasses, causing unpredictable harm to the whole marine ecosystem.

3. Seawater desalination will raise the water temperature after the desalination system, partly because of high temperature distillation, and partly because of the accelerated movement of the ion reverse osmosis membrane (two major desalination methods). Meanwhile, the warming phenomenon has a very high propagation speed in the ocean[6]. Obviously, this will directly disrupt the metabolism of some animals, or make them have to change their habitat in order to find suitable temperature, thus endangering the normal marine ecosystem and food chain.

4. Chemicals and corrosive materials which come from the desalination system used in nuclear power plants and fossil fuel plants. The consequences of this hazard are particularly obvious, since excessive harmful substances will make the ocean lose its original self purification ability, and it is potentially fatal to marine organisms.. First of all, the accumulation of chemical toxins will directly affect the water quality, and the consequence is to cause the death of marine organisms, which will further pollute the ocean. Secondly, these emissions will affect the light on the sea surface (coastal darkening phenomenon), which will affect the reproduction rate of algae or herbivorous plankton, and then affect the birds and mammals that feed on them[7].

5. Greenhouse Gas(GHG) Emission. Some old desalination technology requires intensive energy from burning fossil fuel. GHG pollutants such as CO2 and sulfuric oxide can be released when producing steam and contribute to global warming[8].

  • How pervasive is the problem?

As there are not many countries and regions that reserve scientific, technological and economic strength to support large-scale seawater desalination for a long time, the impact space of this problem is actually limited. In order to ensure the sustainable development of the environment, people must weigh the impact of seawater desalination on the environment and the expansion of the use of fresh water resources. Although the research on the consequences of seawater desalination has continued, until recently, there was little information on the rules and regulations of seawater desalination. Most governments have not put forward more complete instructions and restrictions on the planning system of seawater desalination. In general, this is still the last resort to obtain fresh water resources.

How does Seawater Desalination impact marine ecosystems

  • How and why does it impact the identified ecosystems ?

First of all, it exacerbates climate change due to substantial greenhouse gas emissions from burning fossil fuels especially in thermal desalination facilities. In addition, the screening rack installed in water intake system directly causes harm to marine life and biodiversity. The most obvious ocean pollution comes from the discharged concentrated brine water when they are not treated properly.

  • Are their unique characteristics of this habitat that make it vulnerable ?
Fig 2.1: Discharge brine wastewater

There is no specific biological habitat that vulnerable as far as the researches are concerned. But essentially, a large portion of almost obsoleted facilities are widely used in water deficient countries such as the Middle East. Both water intakes and outfalls in the old desalination system bring significant adverse affect to the marine ecosystems.

  • What organisms does it impact ?

The salt concentration of the treated desalinated brine water is 1 to 2 times that of normal seawater. It can impose a huge negative effect on almost every marine species such as fish, jellyfish, seagrass, phytoplankton, coral reefs and so on.

  • How and why does it impact these organisms ?

The specific harmful impacts of desalination are discussed in detail in this section:

  1. The excessive salt corrupts the osmotic balance of marine species with their environment, causes dehydration of cells, decrease of the turgor pressure, and brings death to species[8]. In addition, the brine usually contains chemical residues like sodium sulfite (Na2SO3) and heavy metals like copper that are used in the desalination process for anti-corrosion or anti-foaming purposes. Not only themselves can contaminate the environment, some of the substances are oxygen scavengers that reduce the oxygen solubility in the water[9].
  2. The temperature of the brine produced by thermal-based plants is usually 10~15°C higher than ambient water[10], it not only has a higher concentration of toxic chemicals, but also disturbs the vital biological properties like protein content which reduces the reproductive function of marine invertebrates[11].
  3. The method of  brine disposal must be carefully chosen to respect the sensitive hydrological, biological features and unique physicochemical  characteristics of the ecosystem. Unfortunately, none of the existing methods has pure advantage, and the most widely used method can directly pollute marine  environments due to insufficient dilution[12]. In some hydrological conditions, the high-salinity stream may flow 5 km away from the disposal point.
  4. Many desalination plants use surface water intake systems to collect large amounts of feed water from open sea with a low cost. When the system pumps water, lots of marine organisms such as fish, phytoplankton may be flushed inside and get impinged (juvenile and adult stages) or entrained (early life stages) at the screen mesh installed in the water channel[9][13]. With a high mortality rate, this can cause loss of biodiversity in the surrounding area.

What is the extent of the problem of Seawater Desalination?

  • What are some specific risks resulted in desalination brine disposal ?
Fig 3.1: Different methods of brine disposal and specific stages causing environmental contamination.

The supplies for freshwater are insufficient for both animals and humans at the current stage. The development of seawater desalination aims to mitigate the problems of freshwater shortage and promote sustainable water management. However, the implementation of desalination technologies has posed severe health issues and increased the risk of habitat loss to marine organisms, and these irreversible impacts are mainly triggered by improper management of desalination brine (Figure 3.1). Desalination brine contains a high concentration of salt, toxic chemicals, and heavy metals that can contaminate the marine ecosystem[14]. Chemical residues remaining after the desalination brine process often include sodium chloride, sodium hypochlorite, iron (III) chloride, aluminum chloride, sulfuric acid, hydrochloric acid, and sodium bisulfite[15]. These chemicals are primarily used for growth inhibition of algae, corrosion prevention, scale inhibitor, and pH adjustment, yet the marine animals that come into contact with these toxic chemicals suffer from various diseases and eventually die as a result[15]. Water stratification resulted in desalination brine disposal will lead to the decrease of oxygen solubility (oxygen content) in the water, and the salt will be attached near resource points such as seabed sunken wood and whale carcasses, causing unpredictable harm to the whole marine ecosystem[6].

  • What is the current status of desalination technology compared to the past ?
Fig 3.4: Change in energy consumption of RO technology every 10 year since 1970
Fig 3.2: Growth of desalination plants and capacity from 1960 to 2020
Fig 3.3: Desalination technologies used at plants worldwide in 2019



The first industrial desalination plant was built in 1961 in the U.S. In the following 60 years, the number of desalination plants and capacities has risen steadily to satisfy the increasing need for freshwater to stand off the frequent droughts (Figure 3.2). Seventy-four percent of facilities nowadays use reverse osmosis (RO) technology to replace thermal-based ones (Figure 3.3). RO technology has been advanced in recent years, and it consumes only one-eighth of the energy in 1970 with less harmful brine exhausted (Figure 3.4)[8].

  • What are some predictable long-term effects of desalination on the marine ecosystem ?

If the increased salinity resulting in brine desalination exceeds the salt tolerance of marine organisms, ocean plants and phytoplankton will stop growing and photosynthesis, leading to massive fish kills and even marine extinction[9].

How can we mitigate or eliminate the impact of Seawater Desalination?

  • What are the local solutions, if any ?

There are two main methods of desalination. One is thermal desalination which is the natural evaporation of water and the formation of a concentrated salt solution is used in this process of extracting minerals from saltwater and seawater desalination brine. When the saturation point is reached, the dissolved salts in the solution will crystallize[3]. It was the preferred technique in Middle Eastern countries since the widely available fossil fuel supply and inferior quality of water in the local water supply. But now, Membrane technology has improved swiftly, and they currently outperform thermal treatments of new equipment. The most significant advantages of membrane processes for the protection of the marine ecosystem are low energy consumption and no chemicals added. Furthermore, the modular steps make it easier to manipulate[15] For the membrane technology, the diffusion of water is through a membrane, but salts are virtually totally remained, which comprises reverse osmosis (RO) and electrodialysis (ED)[15]. Among them, RO membrane is currently the most widely used since reverse osmosis (RO) membrane desalination is high efficiency and low energy consumption[16]. However, excessive membrane usage might result in membrane contamination. The No-secreting probiotic biofilm alliance can acts as a powerful antibiotic biofilm agent infiltration membrane system, thereby reducing membrane contamination. Therefore, people thought of using probiotics to apply filtration membranes to filtration systems. Since probiotic microorganisms are ecologically friendly, non-hazardous, effective, and inexpensive to produce[17].

  • What are the global solutions, if any ?
desalination plant.
Fig 4.1: Typical configuration of collocated desalination plant.

In addition, in California the integrated seawater desalination system of the region was made up of desalination plants[18](Figure 4.1) for brackish water interior, brine interceptor or collector for the area, and central seawater desalination plant by the sea are the three types of desalination facilities[18]. The job of the brine collector for the area is to transport the concentrate from the interior desalters to the seawater desalination plant for the area, where it is utilized as additional supplying water for the desalination process[18]. The benefits of the management are that brine from interior desalters that use brackish ground water sources is normally free of pathogens, making it a secure and appropriate supply of water for seawater desalination. Consequently, instead of being discharging to the deep ocean, brackish water concentrate might be utilized to produce potable water[18].

References

  1. ↑ 1.0 1.1 1.2 Kress, N (2019). Marine impacts of seawater desalination: Science, management, and policy. Elsevier All Access Books. ISBN 978-0-12-811953-2.
  2. ↑ Angelakis, A. N., Valipour, M., Choo, K.-H., Ahmed, A. T., Baba, A., Kumar, R., Toor, G. S., & Wang,, Z (2021). "Desalination". From Ancient to Present and Future. Water,. 13(16): 2222.CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  3. ↑ 3.0 3.1 Zhang, X., Zhao, W., Zhang, Y., & Jegatheesan,, V (2021). "A review of resource recovery from seawater desalination brine". Reviews in Environmental Science and Bio/Technology. 20: 333–361.CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  4. ↑ Simon, Matt (2019, January 14). "Desalination Is Booming. But What About All That Toxic Brine?". WIRED. Check date values in: |date= (help)
  5. ↑ Robbins, Jim (June 2019). "As Water Scarcity Increases, Desalination Plants Are on the Rise". Yale Environment 360. Retrieved February 9, 2022.
  6. ↑ 6.0 6.1 HOKKAIDO, UNIVERSITY (May 2020). "There is no escaping from climate change, even in the deep sea". EurekAlert!. Retrieved February 9, 2022.
  7. ↑ Johnson, D (2021, February 10). "The Environmental Threat You've never heard of". Hakai Magazine. Retrieved February 9, 2022. Check date values in: |date= (help)
  8. ↑ 8.0 8.1 8.2 Panagopoulos, Argyris; Haralambous, Katherine-Joanne (December 2020). "Environmental impacts of desalination and brine treatment - Challenges and mitigation measures". Marine Pollution Bulletin. 161 – via Elsevier Science Direct.
  9. ↑ 9.0 9.1 9.2 Ihsanullah, I; Atieh, M; Sajid, M; Nazal, M (2021, August 1). "Desalination and environment: A critical analysis of impacts, mitigation strategies, and greener desalination technologies". Science of The Total Environment. 780 – via Elsevier Science Direct. Check date values in: |date= (help)
  10. ↑ Ahmad, N; Baddour, R (2014, January). "A review of sources, effects, disposal methods, and regulations of brine into marine environments". Ocean & Coastal Management. 87: 1–17 – via Elsevier Science Direct. Check date values in: |date= (help)
  11. ↑ Johnstone, J; Nash, S; Hernandez, E; Rahman, M (2019, August). "Effects of elevated temperature on gonadal functions, cellular apoptosis, and oxidative stress in Atlantic sea urchin Arbacia punculata". Marine Environmental Research. 149: 40–49 – via Elsevier Science Direct. Check date values in: |date= (help)
  12. ↑ Panagopoulos, A; Haralambous, J; Loizidou, M (2019, November 25). "Desalination brine disposal methods and treatment technologies - A review". Science of The Total Environment. 693 – via Elsevier Science Direct. Check date values in: |date= (help)
  13. ↑ Hogan, T (2015, April 08). Intakes and Outfalls for Seawater Reverse-Osmosis Desalination Facilities. Springer, Cham. pp. 57–78. ISBN 978-3-319-38429-0. Check date values in: |year= (help)
  14. ↑ Lee, Sangho; Choi, Juneseok; Park, Yong-Gyun; Shon, Hokyong; Ahn, Chang Hoon; Kim, Seung-Hyun (March 2019). "Hybrid desalination processes for beneficial use of reverse osmosis brine: Current status and future prospects". Desalination. 454: pp. 104-111 – via Elsevier Science Direct.CS1 maint: extra text (link)
  15. ↑ 15.0 15.1 15.2 15.3 Asadollahi, M., Bastani, D., & Musavi,, S. A (2017). "Enhancement of surface properties and performance of reverse osmosis membranes after surface modification". A review. Desalination. 420: 330–383.CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link) Cite error: Invalid <ref> tag; name ":1" defined multiple times with different content
  16. ↑ Wang, J., Wang, Q., Gao,, X (2020). "Surface modification of mesoporous silica nanoparticle with 4-triethoxysilylaniline to enhance seawater desalination properties of thin-film nanocomposite reverse osmosis membranes". Front. Environ. Sci. Eng. 14: 6.CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  17. ↑ Maitreya, A., Pal, S., Qureshi, A., Reyed, R. M., & Purohit,, H.J. (2021;2022). "Nitric oxide–secreting probiotics as sustainable bio-cleaners for reverse osmosis membrane systems". Environmental Science and Pollution Research International. 29(4): 4911–4929. Check date values in: |date= (help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  18. ↑ 18.0 18.1 18.2 18.3 Voutchkov,, N (2018). "Energy use for membrane seawater desalination – current status and trends". Desalination. 431: 2–14.CS1 maint: extra punctuation (link)





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