Desalination of seawater with reverse osmosis (RO) membranes is a key technology for addressing water scarcity issues around the globe, but seawater desalination is energy-intensive and the brine discharge can create coastal environmental problems. The company Flocean AS (Oslo, Norway; www.flocean.green) is among a handful of companies developing technology for deepwater RO desalination, an approach that has a number of cost and operational advantages over conventional seawater RO.
“Terrestrial seawater RO requires high pressures and is susceptible to bio-fouling of the membranes, as well as negative environmental impacts associated with chemical pre-treatment of seawater and discharge of concentrated brine,” explains Alexander Fuglesang, CEO of Flocean. Deepsea RO takes advantage of the high surrounding hydrostatic pressures, which align with the osmotic pressure needed for desalination. This reduces the energy required to push water through the membranes by 30 to 50% compared to land-based RO, Flocean says.
Installation in deep water also allows the high-pressure pump to be placed downstream of the RO membranes, on the permeate side, drawing water over the membranes rather than pushing it through (diagram). This means energy is focused only on the product water, unlike in terrestrial seawater RO plants, where energy is used to pressurize the entire feed stream, the company states.
In addition to the energy savings, the water properties at depths of 400–600 m offer considerable advantages for RO. “Seawater at that depth contains minimal algae, so pre-treatment requirements are reduced, and the temperature, pressure and salinity are much more consistent than surface water, which has operational advantages,” Fuglesang remarks.
Further, because of the energy and operational advantages, deepwater RO can be economically feasible at much lower recovery rates than conventional RO (10–20% water recovery with deepsea, versus 40–50% for conventional). This alleviates many of environmental impacts of the brine discharge, as well as reducing biofouling and scale formation
Flocean has its origins in a Norwegian company with expertise in building and installing deepsea pumping systems for the offshore oil and gas sector. The ideas and concepts for deepwater RO have been around since the late 1990s, but with costs of underwater robotics coming down, and water scarcity issues growing, it makes more sense now, Fuglesang explains.
Flocean recently announced a new round of investment that will further construction of a demonstration plant on the west coast of Norway. The company plans to start up the facility in early 2026. Fuglesang says his company is currently negotiating commercial “water-as-a-service” contracts for clients in the Mediterranean Sea and Red Sea regions.