Transformative technology can make water shortage a thing of the past
Seawater reverse osmosis (SWRO) desalination has surged in the past decade. Climate-change-associated drought and increasing water demand have contributed to water scarcity around the world, making desalination more attractive as a solution. Rising energy costs have nudged thermal desalination, SWRO’s inefficient competition, closer to obsolescence. At the same time, advances have improved SWRO efficiency. Today, reverse osmosis is the globally dominant desalination process. Let’s explore this transformative technology.
Seawater Reverse Osmosis Cost Efficiency
SWRO has been considered too expensive in many scenarios, particularly because of the high energy requirement but also the cost of membrane upkeep and replacement. The question of whether this desalination technology is too costly, however, must be met with another question: “Compared to what?”
SWRO is certainly more costly than pumping from traditional surface or groundwater sources in most cases, but in some instances, traditional water resources have been depleted or have become contaminated. Access to the water that remains is often highly competitive and expensive, which radically changes the calculus for SWRO’s economic viability.
Given a virtually endless supply of seawater, the choice often boils down to two options. One is to compete for the remaining fresh water in the region, which can lead to conflict and litigation between public and private concerns. The other choice is to adopt reverse osmosis, balancing its costs against the true costs of surface or groundwater withdrawal in today’s water-scarce environment.
In our water-stressed world, an honest cost-benefit analysis will often tip the scales in favor of SWRO as a sustainable solution. Sometimes, businesses or industries build in excess capacity to share with public utilities, flipping the script from an adversarial story to one of mutual reliance and support.
Understanding How SWRO Desalination Works
SWRO works by forcing pressurized seawater through membranes with tiny pores (0.001-0.0001 microns) that reject salt and other impurities. The desalinated water, also referred to as permeate, is then fresh and ready for use, but an SWRO plant has various other stages to support the reverse osmosis process and mitigate impacts.
SWRO Intake: First, seawater enters the plant through an open sea intake (catchment) or beach well. The prescreening process is done with a simple mesh and mechanical rake. A screen, or sometimes a granular media filter, removes large and insoluble solids, including plants, fish, barnacle larvae, seashells, and microorganisms. Low suction velocities can minimize interaction of marine organisms with the screen via entrainment (larger organisms being pinned against the screen) and impingement, (smaller organisms passing through the screen and into the equipment). Seven Seas has developed innovations in seawater intakes to exclude turtles and other sea life.
SWRO Pretreatment: Screened feed water proceeds to pretreatment, which is vital to the membrane’s lifespan. Conventional processes include flocculation and chemical dosing with antiscalants to prevent membrane biofouling, but membrane-based pretreatment with microfiltration, ultrafiltration, and nanofiltration is also effective.
SWRO Pumping and Pressurization: The water is pressurized with pumps that power high- and low-pressure systems. The pressurized reverse osmosis vessels contain multiple membrane elements where salt is finally removed. They manage flow rates, overcoming the natural osmotic pressure to push the feed water through the pores of the semipermeable RO membrane.
SWRO Energy Recovery Devices: Energy recovery devices (ERDs) then recover and reuse energy from the excess water pressure in the brine stream that would otherwise be wasted after brine is rejected from the membrane stage and is discharged.
Brine Discharge and Environmental Protection: Brine discharge should be thoughtfully planned because it is hypersaline and contains chemicals that can cause unacceptable environmental impacts, especially to seafloor ecosystems. Environmental impact studies inform the placement of brine outfalls away from more sensitive ecosystems, and diffusers dilute and spread out the brine discharge to make it less impactful. Independent brine monitoring programs at Seven Seas plants allow operators to control discharges to minimize impact.
SWRO Post-treatment: In the permeate destined for human use, post-treatment phases such as remineralization, disinfection, and pH adjustment may be applied. For example, because reverse osmosis demineralizes water, permeate to be used for drinking water might be remineralized.
Innovations in Seawater Reverse Osmosis
SWRO technology has seen significant advancements that enhance both efficiency and cost-effectiveness. Key developments include:
Energy Recovery Devices: Highly efficient ERDs are a relatively new advance that captures and reuses energy in the form of excess pressure from brine streams, drastically reducing energy consumption and slashing the overall cost of SWRO.
Advanced RO Membranes: Improvements in membrane technology are continuous. Today’s thin film composite membranes have reduced cost and energy use.
These technological advancements not only bolster the efficiency and economic viability of seawater reverse osmosis but also set the stage for addressing the environmental impacts associated with desalination processes. As we continue to refine these technologies, it’s crucial to consider how they can be further optimized to minimize their ecological footprint.
Environmental Considerations of SWRO
Seven Seas takes care to minimize the environmental impacts of SWRO. Intakes are designed to minimize entrainment and impingement of sea life. Brine discharge systems are informed by environmental impact studies in the planning stage and are thoughtfully designed to adequately dilute the brine at the outfall to neutralize its impacts. Many aquatic ecosystem impacts can be prevented by siting plants away from more sensitive ecosystems.
The Seven Seas Water Group project in Point Fortin, Trinidad serves as a key example of balancing technological efficiency with environmental stewardship in the face of severe drought and water scarcity. In partnership with the Water and Sewerage Authority of Trinidad and Tobago, Seven Seas fast-tracked the construction of a desalination plant that now delivers 7.2 MGD (27,252 m³/d) of fresh water. This project, completed in just 14 months despite significant challenges such as a sensitive marine ecosystem and the unexpected discovery of an oil well, dramatically improved water availability, providing a continuous supply to residents previously limited to weekly access.
In addition to addressing water scarcity, Seven Seas implemented a comprehensive environmental management program to monitor and mitigate the impact of reverse osmosis brine on the marine environment. Collaborating with independent firms, the project consistently ensures high-quality effluent and protection of marine life. Highlighted by a Harvard study for its exceptional freshwater quality and positive community impact, this initiative not only showcases Seven Seas’ commitment to environmental protection but also sets a benchmark for integrating SWRO technologies with ecological responsibility in future desalination efforts.
SWRO in All Sectors
SWRO has applications in the municipal, commercial, industrial, and even agricultural sectors, providing a lifeline for communities and economies facing the risk of drought and water scarcity.
While the energy cost of SWRO is higher than pumping from traditional sources, inadequate water supply or even no water at all carries considerably higher costs. SWRO is not just about producing fresh water; it is about reshaping our approach to water sustainability for generations to come. Seven Sea Water Group’s history with desalination started half a century ago, and we have grown into a global SWRO provider. Let’s continue to explore together the transformative impact of SWRO on the future of water resources.
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