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HAVBRUK2-Stort program for havbruksforskning

Sulphate removal by membrane filtration technology to reduce the risk of fish death due to H2S in recirculating aquaclture systems (RAS)

Alternative title: Sulfatfjerning med membranfiltrering-teknologi fra oljenæringen for å redusere risiko for fiskedød på grunn av H2S i RAS-anlegg

Awarded: NOK 7.9 mill.

Project Number:

296545

Project Period:

2019 - 2022

Organisation:

Land-based fish farming is one of the opportunities for ensuring sustainable growth in the aquaculture industry, but this also has its challenges. When farming post-smolt or osalmon to harvest size in land-based facilities, it is often desirable to add seawater. An important risk in land-based recycling facilities (RAS) with seawater addition is the formation of toxic hydrogen sulphide (H2S). Seawater contains a lot of sulphate, and hydrogen sulphide can be formed by bacterial decomposition of sulphate without oxygen present (anaerobic conditions). This has in recent years led to a number of cases of acute fish death. New technology can be absolutely crucial to ensure good water quality and a stable and profitable production of salmonids on land. One possible strategy for solving the H2S problem is to remove sulphate from the production water. The project, which is owned by the company Enwa, tests and further develops a membrane filter technology that reduces the sulphate level in the production water to a minimum. The filtration technology was originally developed for use in the oil industry. In the project, the company works with researchers at the Norwegian Institute for Water Research (NIVA), the University of Bergen and the Technical University of Denmark and Stirling University. We have investigated the bacterial and chemical mechanisms that cause sulphate in seawater to be converted to hydrogen sulphide. These experiments have documented that biofilter media with biofilm have a great potential for H2S production when the biofilter becomes anoxic due to insufficient oxygenation. In 2021, fish trials have been carried out at RASlab in Bergen. The results are still being processed, but so far shows 10 times lower concentration of sulphate in nanofiltered brackish water as well as a 50%reduction of the H2S levels in the fish tanks. There was no difference in growth and condition-factor between the experimental groups, and the need for water chemical adjustments after membrane filtration appears to be limited. Nanofiltration technology can be of high importance both for the industry that avoids fish death, and for the company that offers the technology. The membrane filtration plant is in operation in the recycling plant of Hardingsmolt AS in Norheimsund.

Det har de siste årene forekommet en rekke svært alvorlige hendelser med akutt fiskedød grunnet hydrogensulfid (H2S) i landbaserte resirkuleringsanlegg (RAS) der det tilsettes sjøvann. H2S dannelse er knyttet til bakteriell, anaerob nedbrytning av sulfat (SO42-) til hydrogensulfid (H2S). Uten SO42- kan det ikke dannes H2S. Dette prosjektets vil teste og videreutvikle en ny og innovativ membranfilter teknologi utviklet for bruk i oljenæringen og som reduserer sulfatnivået i produksjonsvannet til et minimum (nanofiltrering av spedevann fra sjø til RAS), og som dermed minimaliserer risikoen for akutt fiskedød forårsaket av H2S. Prosjektet vil således benytte offshore teknologi til å løse grunnleggende kjemiske og biologiske utfordringer innen landbasert oppdrett av laks («cross-over» aktivitet). I tillegg vil den bakterielle og kjemiske mekanismene av H2S dannelse under lav sulfatmengde undersøkes. Dette vil være med å kvalitetssikre teknologien ved at sulfatmengden tilgjengelig etter filtrering er lav nok til at H2S ikke dannes under RAS driftsforhold.

Activity:

HAVBRUK2-Stort program for havbruksforskning