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HAVBRUK2-Stort program for havbruksforskning

Nanofiltered intake water to RAS for improved health and welfare of Atlantic salmon postsmolt.

Alternative title: Nanofiltrert inntaksvann til RAS for bedret helse og velferd hos postsmolt

Awarded: NOK 2.9 mill.

In MEMBWELL the focus has been on fish health and welfare when FiiZK (former AkvaFresh) has investigated the use of nanofiltration for partial desalination of sea water for inlet water in RAS for post smolt production. By partially desalinating sea water a different ionic composition is achieved compared to dilution of sea water with fresh water. The purpose of the project was to examine the effect of nanofiltrating the inlet water for RAS on salmon physiology, welfare, and growth and on the water quality in the RAS, which was analysed by Nofima and the Institute of Chemistry at NTNU, respectively. A special focus was on sulphate, as the sulphate reducing capacity of membrane filtration can reduce the risk for formation of H2S, a gas known for its ability to cause mass mortalities in fish tanks. A membrane plant designed by FiiZK was used to reduce the salitity of the inlet water for a RAS from 32 ppt to 12 ppt. As a control a RAS with a salinity of 12 ppt was run by mixing of sea water and fresh water. The fish was 140 g at the start of the trial, and the trial period with brackish water was 10 weeks, after which the systems were both switched to flow through operation with sea water for 4 weeks. Histology and gene expression analyses were performed on gills, intestines, and skin at the start of the trial, after transfer to sea water, and at the end of the trial. Blood samples were taken to measure cortisol and blood plasma ions. Welfare and growth were monitored throughout the whole trial. Post smolt in RAS had better growth compared to traditional RAS. The weight of the fish was 400 and 355 g at the end of the RAS phase, respectively. The same tendency was upheld after transfer to sea water, and at the end of the trial the fish from the RAS with nanofiltrated water was significantly bigger (556 g) than the fish from the control RAS (491 g). No differences between the systems were detected for operative welfare indicators, nor was any morphological differences in the skin of the salmon for the two production systems. In the gills there were some effects of nanofiltrated water, the most important being an increase in the area of the gill lamellae covered in mucus producing cells. Another effect of the nanofiltrated water was an increased number of chlorine cells on the secondary lamellae of the gills. Meanwhile there was no difference in blood plasma ions in for the salmon in the two groups. The effect of nanofiltrated water on the gene expression in skin and gills was small, and only 2 genes in skin and 28 genes in gills showed differences in expression. Increased expression of p450 1a1 (cyp1a1) in the RAS without nanofiltration can indicate that the membrane removed foreign substances from the water, as this is known to induce expression of the gene. The goal for the analyses by NTNU was to study the efficiency of sulphate removal by the nanofiltration membranes, as well as to document the effects of nanofiltration on water quality with regards to pH, salinity (conductivity) and changes in ionic composition. NTNU has done numerous analyses in the project. Amongst these are evaluation of pH, sulphate and sulphur concentration at different points in the systems, levels of specific main and trace elements, and organic matter loads. Analyses of water samples from the two systems indicate that the nanofitration system is an effective method for removing sulphate and sulphuric compounds. In the trial up to a 93 % removal of total sulphur was shown. By comparing nanofiltered water with mixed water, the nanofiltrated water had 91% less sulphur and 86 % less sulphate. The results thus indicate a significant reduction of sulphur, which is a key parameter to prevent formation of H2S. Studies of pH as a central water quality parameter showed no significant difference compared to the control system. Other key parameters that were analysed was magnesium, silicon, potassium, calcium, and bromide. By comparing nanofiltrated water with the control system there was a slight increase in bromide, and a reduction in magnesium, silicone, and calcium. It was also observed a reduction in several trace elements. No significant differences were observed with regards to organic matter, but both systems showed an increase over time, indicating a possible build up of organic matter as the fish grew bigger. This observation was not related to nanofiltration. In short, MEMBWELL has demonstrated that a nanofiltration plant could produce a water quality with reduced sulphate content and the desired salinity, and that this water quality mainly had a positive effect on fish growth and welfare.

Den tydeligste virkningen av prosjektet er en heving av kompetansen om applikasjonen av ny teknologi i landbasert oppdrett, både for deltagere i prosjektet og bransjen for øvrig. Prosjektet har vært grunnlag for en masteroppgave fra NTNU. Nofima har bygget videre på sin allerede betydelige kunnskap om biologi i landbaserte oppdrettsanlegg, nå i et tidligere ukjent oppsett. Nofima og NTNU vil dra nytte av kunnskapen i videre prosjekter, og dermed gi en effekt med videre utvikling av kunnskap både i forskningsmiljøer og næringslivet de samarbeider med. FiiZK Aqua har opparbeidet viktig kunnskap om design og skreddersøm av nanofiltreringsanlegg for denne applikasjonen. En forventet effekt av prosjektet er at fiskevelferd i landbasert oppdrett forbedres som følge av applikasjon av teknologien. En forventet virkning vil også være at FiiZK Akva får leveranseprosjekter på denne teknologien, og dermed kan utvide sin portefølje.

Innovasjonen er å benytte membranteknologi til å kontrollere vannkvaliteten i inntaksvann til RAS (resirkulerende akvakultursystemer) for produksjon av postsmolt av atlanterhavslaks (Salmo Salar). Spesielt rettes fokus mot reduksjon av sulfat for redusert risiko for utvikling av H2S. Oppdrettsbransjen har det siste året hatt store tap som følge av massedødelighet i RAS med brakkvann, hvor H2S antas å være årsaken. Hovedfokus i prosjektgjennomføringen er å dokumentere effekten av nanofiltrert vann på vannkvaliteten i RAS og på helse og velferd til postsmolt.

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Funding scheme:

HAVBRUK2-Stort program for havbruksforskning