46 MARCH 2022 • WORLD AQUACULTURE • WWW.WA S .ORG no bubble formation and no biomass were observed in the control treatment, while the 3:1 treatment had the greatest accumulation of bubbles, taking the form of foam and very little solids biomass accumulation. Tanks of the 1:1 and 5:1 treatments had nonfoaming microbubbles and greater solids biomass accumulation at the surface, with the 1:1 treatment having the greatest accumulation. The results indicate that denitrification is possible without added substrate and may be a practical strategy to reduce water use for producers utilizing hybrid biofloc-RAS. Ethanol was a suitable carbon source, and the best performing C:N in this study was 3:1, as both nitrite and nitrate concentrations were very low and alkalinity was high at the end of the trial. Additional commercial-scale studies are needed, such as investigating the performance of denitrification relying on naturally occurring particulate matter only. Implementation for Producers The use of denitrifying bioreactors presents an additional expense and operational complication, which can be especially challenging for small-scale shrimp producers. Many of these reactors are costly and “home-made” reactors require either manual carbon additions or the use of expensive and potentially unreliable dosing systems, necessitating the expense of labor and supplemental equipment. The method of denitrification in this study allows for easy calculations and additions without the need of managing the flow rates of water and organic carbon into the reactor. This study suggests that single daily additions of carbon are adequate; however, drawbacks include the time required for complete denitrification and this is a batch-style approach where animals are not cultured in the water simultaneously. The microorganisms in these systems appear to undergo a similar acclimation process to that of nitrification, which leaves the system unusable for animal production until nitrite concentrations decrease to acceptable levels. However, this study demonstrates the removal of approximately one-year worth of nitrate accumulation, so the technique could be implemented rather infrequently in a commercial operation. Overall, this study illustrates a simple method of denitrification requiring little input. Notes Mark E. Johannemann, Leo J. Fleckenstein, and Andrew J. Ray Kentucky State University School of Aquaculture and Aquatic Sciences Corresponding Author: andrew.ray@kysu.edu References Furtado, P.S., B.R. Campos, F.P. Serra, M. Klosterhoff, L.A. Romano and W. Wasielesky. 2015. Effects of nitrate toxicity in the Pacific white shrimp, Litopenaeus vannamei, reared with biofloc technology (BFT). Aquaculture International 23(1):315327. Timmons, M.B., T. Guerdat and B.J. Vinci. 2018. Recirculating Aquaculture. Ithaca Publishing Company, Ithaca, New York USA Torno, J., C. Naas, J.P. Schroeder and C. Schulz. 2018. Impact of hydraulic retention time, backflushing intervals, and C/N ratio on the SID-reactor denitrification performance in marine RAS. Aquaculture 496:112-122. van Rijn, J., Y. Tal and H.J. Schreier. 2006. Denitrification in recirculating systems: Theory and applications. Aquacultural Engineering 34:364-376. Yoon, S., C. Cruz-García, R. Sanford, K.M. Ritalahti and F.E. Löffler. 2015. Denitrification versus respiratory ammonification: Environmental controls of two competing dissimilatory NO3 -/ NO2 - reduction pathways in Shewanella loihica strain PV-4. The ISME Journal 9(5):1093-1104. FIGURE 3. There was a consistent decrease in Total Inorganic Nitrogen (TIN) after week 1 in tanks that received carbon additions, indicating active denitrification. FIGURE 4. There was a rapid decrease in nitrate concentration after week one and a slower decrease thereafter, suggesting first-order kinetics of denitrification. FIGURE 5. Nitrite concentration peaked at 180 mg/L during week 2.
RkJQdWJsaXNoZXIy MjExNDY=