Abstract
Foam fractionation is often considered an ineffective way of removing organic matter from freshwater due to the low surface tension of the water. There is, however, a lack of studies testing foam fractionation efficiency in replicated freshwater recirculating aquaculture systems (RAS). Foam fractionation can be applied with or without ozone. Ozone is a strong oxidiser previously shown to improve water quality and protein skimmer efficiency. To test the efficiency of foam fractionation and ozonation (20 g O3 kg-1 feed) separately and in combination in freshwater RAS, a two-by-two factorial trial was conducted with each main factor at two levels (applied or not applied). Each treatment combination was carried out in triplicates using 12 replicated pilot scale RAS stocked with juvenile rainbow trout (Oncorhynchus mykiss) and operated at a feed loading of 1.66 kg feed m-3 make-up water. The trial lasted 8 weeks and samples were obtained once a week. Ozone applied by itself significantly reduced the number of particles (83%), bacterial activity (48%) and particulate BOD5 (5-days biochemical oxygen demand; 54%), and increased ultra violet transmittance (UVT; 43%) compared to the untreated control group. Foam fractionation by itself lead to significant reductions in particle numbers and volume (58% and 62%, respectively), turbidity (62%), bacterial activity (54%) and total BOD5 (51%). A combination of both treatments resulted in a significant additional improvement of important water quality variables, including a 75% reduction in total BOD5, 79% reduction in turbidity, 89% reduction in particle numbers and 90% reduction in bacterial activity compared to the control. The removal efficiencies were within the same range as those observed in previous studies conducted with foam fractionators in saltwater systems (with or without ozone), corroborating that foam fractionation may become a useful tool for controlling organic matter build-up and bacterial loads in freshwater RAS.
Highlights
Introduction rnThe build-up of organic matter in recirculating aquaculture systems (RAS), deriving from fish excretions and feed u spill (Schumann and Brinker, 2020), is among the largest challenges in the industry (Martins et al, 2010)
3. Results One fish died during the trial, and no significant differences were found in biomass growth rates or feed conversion rates
There were no differences in ammonium and nitrate levels by the end of the trial, while nitrite was significantly lower in systems fitted with foam fractionators (Tab. 1)
Summary
The build-up of organic matter in recirculating aquaculture systems (RAS), deriving from fish excretions and feed u spill (Schumann and Brinker, 2020), is among the largest challenges in the industry (Martins et al, 2010). As a result of prolonged retention times in RAS, together with the use of technologies which target mainly larger particles, fine solids and dissolved organic matter accumulate in the system (Chen et al, 1993a; de Jesus Gregersen et al, 2019; Fernandes et al, 2014; Patterson et al, 1999) Accumulation of fine solids is considered problematic due to their small size and large surface area to volume ratio providing food and space for bacteria growth (Becke et al, 2020; de Jesus Gregersen et al, 2019; Pedersen et al, 2017). Organic matter build-up in stagnant areas is thought to explain recent cases of H2S driven mortality events (Dalsgaard, 2019; Letelier-Gordo et al, 2020)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
