Geosmin fluctuations and potential hotspots for elevated levels in recirculated aquaculture system (RAS): A case study from pikeperch (Stizostedion lucioperca) production in Denmark

Abstract

Effect of water treatment on concentrations of the off-flavor geosmin was examined in a RAS facility for commercial production of pikeperch (Stizostedion lucioperca). Short-term (minutes) and long-term (days) variations in concentrations of geosmin were measured in grow-out tanks, at inlet and outlet of biofilters and at the denitrification unit. Geosmin in water of the grow-out tanks ranged typically from <10 to about 20 ng/L. Only a minor increase in geosmin (1–3 ng/L) was observed during recirculation of water through the tanks. Water passage through the biofilters did typically not affect the geosmin concentration, while the denitrification unit caused a 3.5–5-fold increase in the geosmin content. Cleaning caused a temporary outburst of geosmin up to 100–200 ng/L (in biofilters) and 210 ng/L (in denitrification unit). The geosmin level stabilized at the initial level after about 30 min passage of system (grow-out tanks) water. The study of the pikeperch RAS shows that management practices with respect to water treatment, especially when using denitrification, should be considered to maintain a low geosmin concentration. For biofilters, increased cleaning of the filter-bed carriers might also help reduce the observed geosmin outburst.