An eight-month study at Dalhousie University found significantly lower geosmin concentrations, reduced oxygen use and a more stable response to a system disruption in an Atlantic salmon RAS using Moleaer nanobubble technology.
For recirculating aquaculture systems, maintaining stable water quality becomes increasingly important as operators look to increase production without adding more energy, oxygen or treatment complexity.
New research from Dalhousie University offers a closer look at how oxygen nanobubbles may contribute.
During a recent European Aquaculture Society (EAS) webinar, Theresa Afi, a researcher at Dalhousie University’s Centre for Water Resources Studies, presented findings from an eight-month study comparing two Atlantic salmon RAS systems: one using Moleaer nanobubble technology and one using conventional oxygen diffusers.
The researchers initially set out to investigate whether oxygen nanobubbles could reduce geosmin, the earthy-tasting compound that can accumulate in RAS water and affect the taste of fish.
The results showed a clear difference.
The RAS using nanobubbles had an average 82% reduction in geosmin concentrations compared with the control.
Geosmin concentrations in the control ranged from approximately 3 to 15 nanograms per liter during the study. In the nanobubble RAS, concentrations were mostly below the detection limit; when geosmin was detected, concentrations ranged from approximately 3 to 5 nanograms per liter.
That matters because people can detect geosmin at extremely low concentrations. In commercial production, managing it can require fish to be purged in clean water before harvest, adding time, water and production cost.
The study was designed to understand not only whether geosmin could be reduced, but also what might be happening within the RAS to produce that result.
One of the most interesting findings emerged following a formalin treatment during the study.
Formalin is used in aquaculture to address infectious agents, but as a disinfectant it can also disrupt the microbial community within a RAS.
Following treatment, researchers observed a significant spike in nitrite in the control system. The nanobubble RAS maintained comparatively stable nitrite levels.
The finding led the research team to look more closely at whether nanobubbles could be influencing microbial communities and biological degradation within the system.
The early microbial data showed slight differences between the two systems, including differences among bacterial groups associated in previous research with geosmin production and degradation.
Afi was careful not to draw a causal conclusion from those results. More targeted research is needed to determine exactly how nanobubbles may affect geosmin-producing and geosmin-degrading species.
But the results provide a promising direction for further study.
The research also looked at oxygen consumption.
During a 44-day sampling period, the nanobubble RAS used approximately 40% less oxygen than the control system using conventional oxygen diffusers.
The researchers have not yet quantified exactly where those oxygen savings occur within the system or calculated oxygen transfer efficiency. The finding refers specifically to the amount of oxygen supplied from the gas source to maintain the systems.
The webinar also compared the Dalhousie findings with results from commercial RAS facilities using Moleaer nanobubble technology.
At a post-smolt RAS facility in Chile, total suspended solids declined from approximately 17 mg/L to less than 5 mg/L. Sulfide concentrations fell from approximately 20 mg/L to less than 10 mg/L, while operators also observed reduced foam and improved water clarity.
At a freshwater Atlantic salmon RAS facility in Norway, operators recorded a 30% reduction in turbidity after 50 days, a 67% reduction in ozone demand and an increase of more than 60% in biofilter nitrification rates.
The commercial results don't prove the mechanisms being investigated at Dalhousie, but they provide useful context. Across both the research and commercial settings, the data points to nanobubbles having an impact beyond oxygenation alone.
The full EAS webinar brings together Afi’s research findings with commercial RAS data presented by Jan-Eric Haagensen, General Manager of Moleaer AS and Senior Director for Scandinavia.
Watch the full discussion to learn more about the Dalhousie study, the commercial RAS results and the questions researchers are now exploring around geosmin, microbial activity, water quality and biofilter performance.
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