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Sequencing reveals different nitrifying bacteria in freshwater and seawater RAS biofilters Irene Roalkvam and Mark Powell, Marineholmen RASLab AS, Sven Le Moine Bauer, University of Bergen
A recirculating aquaculture system (RAS) has many steps for water purification, including a biofilter where living bacteria convert toxic ammonia to nitrate. In this two-step process, Nitrosomonas species are often involved in the oxidation of ammonia to nitrite, while Nitrospira species are often involved in the oxidation of nitrite to nitrate. However, these bacteria develop slowly and can be sensitive to changes in water quality, making the activation of new biofilters time consuming and challenging. Relatively few nitrifying genera are well-described from cultivation experiments in the lab, but the new generation of sequencing technology available today can reveal the large diversity of nitrifying Bacteria and Archaea in biofilters and provide knowledge on how different farming operations, including feeds, stimulate the development of different communities.
Materials and methods At Marineholmen RASLab, 12 RAS units (Alpha Aqua, Denmark) with a 1,000 L tank each are used for facilitating research and innovation within aquaculture. Due to frequent operational changes between new projects, biofilter activation after disinfection occurs several times per year. RASLab has two storage tanks of 5 m3 each for biofilter chip maintenance so that fresh and active biofilter material can be added to RAS units in new projects, thus shortening the activation
Figure 1. Quantification of nitrogen species in water. The concentrations of ammonia, nitrite and nitrate were measured in water from the seawater storage tank (a) and the freshwater storage tank (b). After an initial increase, the ammonia and nitrite concentrations decreased over time as the bacterial nitrification process was established, while nitrate concentration increased. Not the different scales in the graphs.
Hatchery Feed & Management Vol 9 Issue 1 2021
