Enwa works closely with universities and industry partners to develop advanced aquaculture water treatment solutions for recirculating aquaculture systems (RAS). One of the most critical challenges in land-based aquaculture is the risk of hydrogen sulfide (H₂S) formation — a well-known cause of fish mortality in RAS facilities using brackish or seawater.
Hydrogen sulfide formation is strongly linked to the presence of sulfate (SO₄²⁻), which naturally occurs in seawater and is often introduced during the smoltification process, when fish are transitioned from freshwater to seawater.
Sulfate Removal to Reduce H₂S Risk in RAS
Within the Norwegian Research Council (NFR) project Aquasulfate, the partners are investigating how sulfate removal from intake water can significantly reduce the risk of hydrogen sulfide formation in RAS facilities.
The project evaluates the use of nanomembrane filtration as a method for sulfate removal in aquaculture water treatment systems — enabling safer and more stable operation of land-based RAS facilities.
Enwa Water Technology is the project leader of this three-year R&D initiative, carried out in collaboration with:
University of Bergen (UiB)
NIVA
DTU – Technical University of Denmark
University of Stirling (UK)
Enwa has designed and delivered the water treatment system used for sulfate removal, supporting the use of seawater as make-up water in RAS while improving operational safety.
Pilot Aquaculture Water Treatment Plant at Hardingsmolt
As part of the development work, Enwa has partnered with Hardingsmolt to build a pilot-scale aquaculture water treatment plant for sulfate removal. The pilot facility is connected to Hardingsmolt’s RAS smolt production plant in Tørvikbygd, Hardanger.
The objective is to treat seawater before it enters the RAS system, reducing sulfate concentrations and minimizing the risk of hydrogen sulfide formation. This enables more predictable water chemistry and improved fish welfare.
At the core of the system is a nano-filtration unit that removes sulfate and reduces other dissolved components. Extensive testing is performed to optimize:
Water quality and water chemistry
System performance in RAS operation
Fish health, growth conditions, and welfare
UiB and NIVA are key contributors to the scientific evaluation of these parameters.
Cross-Industry Technology for Sustainable Aquaculture
The sulfate removal technology used in this aquaculture water treatment system is based on proven solutions from the oil and gas industry. By adapting cross-industry technologies, Enwa delivers robust and scalable solutions tailored for modern RAS facilities.
“For Enwa, it is highly exciting to apply our experience from other industries to develop new solutions for aquaculture,”
says Bjørn Dørum, Director at Enwa Water Technology.
“The results from the pilot project will help us deliver even more efficient and reliable RAS water treatment solutions in the future.”
Bjørn adds.
Supporting Fish Welfare and Sustainable RAS Operations
The project is supported by Innovation Norway through its Environmental Technology Development Program, highlighting its importance for sustainable aquaculture development.
Through research collaboration, pilot testing, and advanced aquaculture water treatment technologies, Enwa Water Technology contributes to:
Improved fish welfare in RAS
Reduced risk of hydrogen sulfide incidents
Safer and more sustainable land-based aquaculture
