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  • Writer's pictureAlexander Fuglesang

The Dual Role of Desalination Plants; Tackling Microplastics, not only Water Scarcity.

Updated: Oct 2, 2023

Our oceans grapple with an inescapable threat: microplastics. Defined as smaller than 5mm, these particles comes from degraded plastic waste, and have infiltrated marine ecosystems globally. They are found in our deepest ocean trenches as well as in the fish we eat. Alarmingly, some estimate around 8 million tons of plastic find its way into oceans annually.

While some of the microplastics such as the polypropylene and polyethylene (bottle caps and plastic bags) are lighter than water and hence tend to float near the surface, a large part of the microplastics such as nylons, PVCs, polystyrene and PETs (fishing nets, traps, bottles) are broken into pieces denser than water and migrate to the deeper ocean levels.

Detecting and Collecting Microplastics with Seawater Reverse Osmosis (SWRO) plants

A major focus should be on preventing plastic from ending up in the ocean in the first place. However, the challenge is already massive which means detection and collection need to take place at a rapid pace to tackle the issue. Reverse osmosis (RO) desalination plants, typically known for addressing water scarcity, can help with both.

They typically incorporate advanced sensors to monitor water quality and ensure optimal operations. Expanding on this capability, pioneering technologies are being developed to equip these plants with sensors that can detect microplastics in real-time. Such sensors can quantify the concentration of these particles in water, giving us unprecedented insights into pollution hotspots and the efficacy of intervention measures.

Besides detection, the desalination process can contribute to mitigation. Before water reaches the reverse osmosis membranes, it undergoes filtration, typically capturing 5-10 micron-sized particles. If filters aren't backflushed, they can trap a significant amount of microplastics. This method ensures these particles are not only detected but also physically removed from the marine ecosystem.

Shifting Gears with Subsea Desalination

Traditional SWRO plants are power-hungry, chemical- and land-intensive and often discharge high-salinity brine into surface waters. FSubsea is currently offering affordable and eco-friendly subsea (RO) desalination plants. Here one takes advantage of the naturally clean and pressurized water at minimum 400 meter water depth to desalinate water with up to 50% energy reduction and without toxic brine discharge.

One single installation could pre-filter seawater volumes of around 300 million litres per day or more than 40,000 olympic-size swimming pools per year. Based on a recent study which aggregate study-data from 18 locations around the globe, this translates to an expected 500 million to 1.1 trillion plastic particles that will be trapped in the filters. Depending on the project specifics, the particles could be retrieved or automatically backflushed into a separate collection unit.

While these volumes are considerable, they only represent a small drop of the total ocean. Another impactful functionality is that, the subsea desalination “Pods” can work as real-time marine science stations. They can capture video feed of marine life, detect the important physical, biological and chemical properties of surrounding seawater, and they can also be made to detect deeper ocean microplastics in real-time.

Deep ocean-conditioned sensors for the latter is becoming increasingly available as part of the explosion in marine drones, robotics and sensor systems. This will be of incredible value to the ocean- and environmental science community. Moreover, positioning the desalination near urban coastal areas – microplastic hotspots – can magnify the impact.

Maximum Environmental Impact

By both mitigating water scarcity as well as detecting and directly collecting microplastics, desalination plants can serve a dual purpose. Further maximizing the environmental impact with low-energy, chemical-free subsea RO plants, we are moving closer to restoring the health of our oceans.

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