Nitrification Efficiencies of Three Different Biofilter Media in Small Scale Recirculating Systems for Red Sea Bream Pagrus major Culture

Abstract

Ammonia is one of the most toxic compounds in the aquaculture system, especially in closed recirculating system. Biofilter is needed to remove the ammonia in the system. Biofilter efficiencies itself is depends on many factors, such as temperature, fish density, media type, flow rate, ammonia loading rate, etc. Red sea bream (Pagrus major) is one of the most important fish in Korea and Japan. However, winter temperature is one of the limiting factors rearing red sea bream in Korea because this species neds warm water for maximum growth. Therefore, recirculating aquaculture system (RAS) is one of the considerations for culturing red sea bream. To make a successful culture of this fish in RAS, a serious of experiments were conducted. The first study was investigation of ammonia excretion rate of red sea bream under different temperature regimes and densities. The second study was to figure out the nitrification performance of three biofilter media, i.e. sand, polystyrene micro bead and Kaldnes bead using synthetic waste water in the closed recirculating system. Different ammonia loading rates were applied to investigate the efficiency of volumetric removal by those biofilter media. In the final study, the biofilter efficiencies with three different media were evaluated for their performance with culture of red sea bream. Red sea bream (Pagrus major) with the mean body weight of 29 g were selected and distributed into aquaria with triplicated design. Endogenous and exogenous ammonia excretion rate of this species were investigated under the combination of four different temperatures regimes (10, 15, 20 and 25 ℃) and two different densities (5.5 and 11 kg m^(-3)). The ammonia excretion of red sea bream was significantly increased with increasing temperature and fish with higher density also excreted significantly higher ammonia than that in lower density. In fasting condition, the endogenous ammonia excretions of red sea bream with lower density under 10, 15, 20 and 25 ℃ were 88.76, 101.06, 125.02 and 143.26 mg kg^(-1) d^(-1) while those in higher density were 105.24, 119.18, 141.49 and 168.82 mg kg^(-1) d^(-1), respectively. The relationship between endogenous ammonia excretion rate (Y) and temperature (T) in low density was Y = 18.746 T + 67.66 (R² = 0.9865) and that in high density was Y = 21.306 T + 80.416 (R² = 0.9804). In feeding condition, the exogenous ammonia excretions of red sea bream under 10, 15, 20 and 25 ℃ with lower density were 343.48, 403.72, 535.74 and 601.74 mg kg^(-1) d^(-1) while those in higher density were 391.92, 479.74, 611.86 and 683.40 mg kg^(-1) d^(-1), respectively. The relationship between exogenous ammonia excretion (Y) and temperature (T) in low density was Y = 90.68T+244.47 (R² = 0.9772) and that in high density was Y = 100.66T + 290.09 (R² = 0.988). The ammonia excretion rate per ingested N value was increased with increasing temperatures and densities. Amount of ingested nitrogen in low density under 10, 15, 20 and 25 ℃ were 27.9, 32.8 44.2 and 50.1%, respectively while those in high density were 31.6, 39.1, 50.1 and 56.9%, respectively. Total ammonia nitrogen (TAN) removal efficiencies of sand, polystyrene micro bead and Kaldnes bead media were evaluated under different ammonia loading rates (25, 50, 75 g m^(-3) d^(-1)). Each volume of filter media was 7 L and the amount of flow rate was 24 L min^(-1). The specific surface areas of the sand, polystyrene microbead and Kaldnes bead were 7,836, 3,287, and 500 m² m^(-3), respectively. Sand filter was operated as fluidizing method and the other two media were trickling method. Volumetric removal rate of TAN in the sand filter is the highest followed by polystyrene microbead filter and the Kaldnes bead filter. The TAN removal rates in sand, polystyrene microbead and Kaldnes bead under the loading rate of 25 g, were 241.66, 193.13 and 157.77 g m^(-3) d^(-1), respectively and under the ammonia loading rate of 50 g, the ammonia removal efficiencies were 460.54, 439.80 and 427.16 g m^(-3) d^(-1), respectively. When the ammonia loading rate was 75 g, the ammonia removal efficiencies of the filters were 680.67, 536.84 and 497.66 g m^(-3) d^(-1), respectively. Volumetric removal rate of TAN increased with the increasing ammonia loading rate within the tested ranges. These results are due to the differences of specific surface area among the filter media. The TAN removal efficiencies of biofilters, sand, polystyrene microbead and Kaldnes bead were compared with actual rearing of red sea bream recirculating systems. The system consists of one circular tank (80 x 80 x 60 cm), one biofilter cylinder (diameter 19 cm, length 100 cm) and one pump. Total water volume used in each system was 200 L and all study was duplicated. Water temperature was maintained 23±1°C. Seven liters of three biofilter media were installed in each filter cylinder and each system was stocked 25 red sea bream with mean body weight of 29 g. Growth performance of the fish were measured and specific growth rate (SGR) and feed conversion ratio (FCR) were calculated. Concentration of TAN in the system with Kaldnes bead filter remained higher (0.73 mg L^(-1)) than sand filter (0.44 mg L^(-1)) and polystyrene microbead filter (0.50 mg L^(-1)) during the experiment. The volumetric ammonia removal rate of sand filter showed the best performance followed by microbead media filter and Kaldnes bead and actual removal rates of them were 193.83, 183.94 and 142.64 g m^(-3) d^(-1), respectively. The concentrations of NO₂-N in the system with sand filter (0.318 mg L^(-1)) and microbead filter (0.337 mg L^(-1)) were significantly lower than that in Kaldnes bead filter (0.535 mg L^(-1)). In the NO₂-N removal efficiencies per pass, those of sand filter (11.25%) and microbead filters (10.18%) were significantly higher than Kaldnes bead (5.37%). The average body weight of fish in sand, polystyrene microbead and Kaldnes bead filter during experiment periods were increased from 29 g to 47, 45 and 41 g, respectively. The SGR value of fish in sand, polystyrene microbead and Kaldnes bead filter were 0.73, 0.68 and 0.51% d^(-1), respectively. The SGR of fish in sand filter was not significantly different from that in microbead filter but both of them were significantly higher than that in Kaldnes bead filter. The FCR of fish in sand, polystyrene microbead and Kaldnes bead filter were 1.87, 1.94 and 2.35, respectively while those of the FCE were 53.64, 51.67 and 42.64 %, respectively. There were no significant differences between fish in sand and those in microbead filter in FCR and FCE values. On other hand, FCR and FCE values of fish in Kaldnes bead was significantly different from that in sand and Kaldnes bead.