Published on IDRA Global Connections Fall 2021 Issue
By Dr. Ahmad Al Amoudi and Eng. Nikolay Voutchkov, Desalination Technology Research Institute (DTRI) of the Saline Water Conversion Corporation (SWCC), Saudi Arabia
Over the past decade seawater desalination has experienced an accelerated growth driven by advances in membrane technology and material science. Recent technological advancements such as advanced pressure-exchanger based energy recovery systems, higher efficiency reverse osmosis (RO) membrane elements, nanostructured RO membranes, innovative membrane vessel configurations, and high-recovery RO systems, are projected to further decrease the energy and costs for seawater desalination and be a backbone for disruptive decease in the cost of fresh water produced by desalination of saline sources (seawater, brackish water and treated wastewater).
High Recovery SWRO Systems. A recent trend aimed at the reduction of the cost for fresh water production is the use of SWRO system configurations that allow to increase the overall recovery of the desalination plant from a typical range of 40 to 50% to a range of 55 to 60%.
Advanced Membrane Technologies and Materials. A recent trend in the quest for lowering the energy use and fresh water production costs for desalination is the development of nanostructured RO membranes, which provide more efficient water transport as compared to existing conventional thin-film membrane elements. These nanostructured membranes reportedly have much higher specific permeability than conventional RO membranes at practically the same high salt rejection. In addition, nanostructured membranes have comparable or lower fouling rate than conventional thin-film composite RO membranes operating at the same conditions, and they can be designed for enhanced rejection selectivity of specific ions.
Beneficial Use of Concentrate. Over the last several years the desalination industry has developed a number of brine concentration and mineral extraction technologies which enable the manufacture of commercially valuable products from the brine. Extracting minerals from seawater is a more environmentally friendly enterprise than terrestrial mining. As technologies for beneficial reuse of brine evolve, revenues from commercial scale extraction of high-value minerals from the brine, such as magnesium, lithium, and pure sodium chloride, can be used to offset the costs for production of desalinated water, thereby converting desalination from the highest- to the lowest-cost sustainable source of fresh water supply.
Chemical Free Desalination. Chemicals used for brackish and seawater RO membrane cleaning are typically the same as these used in toothpaste, soaps and commercial detergents. Both backwash water and membrane cleaning water are typically treated to remove solids or other contaminants prior to being added to the desalination concentrate for discharge. The state-of-the-art desalination processes employed in contemporary desalination plants use a very limited amount of chemicals. Recent desalination industry shifts toward chemical-free desalination and recovery of valuable minerals and rare metals from concentrate are expected to transform desalination into one of the most environmentally sound and sustainable water supply alternatives of the 21-st century.
Breaking Down the Energy Use Barriers. At present, most desalination plants worldwide are supplied by power generated from fossil fuel. In parallel with the exploration of renewable power alternatives, the world’s leading research centers in the USA, Saudi Arabia and Europe are working on the development of new generation of energy recovery devices, high pressure pumps, and membranes which aim to bring the total energy use of desalination plants to less than 2.5 kWh/m3 and the energy demand of the reverse osmosis desalination system below 1.8 kWh/m3. These advancements will result in the reduction of the total energy use and carbon footprint of desalination plants with over 30%. The new technologies are tailored to fit equally well in both existing desalination plants and future reverse osmosis facilities.
What Does the Future Hold?
The steady reduction of desalinated water production costs coupled with increasing costs of water treatment driven by more stringent regulatory requirements, are expected to accelerate the current trend of increased reliance on the ocean as an attractive and competitive water source by year 2030. These technology advances are expected to ascertain the position of desalination as a viable and cost–competitive processes for potable water production and to reduce the cost of fresh water production from seawater by 25% in by year 2022 and by up to 60% by year 2030 as shown on Table 1.
Table 1 – Forecast of Energy Use and Costs for Seawater Desalination Plants
| Parameter for Best-in Class Desalination Plants | Year 2020 | Year 2025 | Year 2030
|
| Total Electrical Energy Use (kWh/m3) |
3.5 – 4.5 |
2.8 – 3.2 |
2.1 – 2.4 |
| Cost of Water
(US$/m3) |
0.4 – 2.5 |
0.3 – 1.0 |
0.2 – 0.5 |
| Construction Cost
(US$/MLD) |
0.8 – 2.2 |
1.0 – 1.8 |
0.5 – 0.9 |
| Membrane Productivity (m3/membrane) |
28-48 |
55-75 |
95-120 |
