Control of inorganic nitrogen and suspended solids concentrations in a land-based recirculating aquaculture system

Abstract

This study intended to evaluate the performance of land-based aquaculture system integrating solids separating units, nitrifying biofilters, and tubular denitrifying reactor during the closed-water tilapia cultivation for 98 days. Operation of both solids separating units was able to maintain suspended solids (SS) concentrations in the rearing tank below 35 mg SS/L. Simultaneous operation of nitrifying biofilters, ORP-controlled denitrifying reactor, and two solids separating units was capable of maintaining total ammonia nitrogen (TAN) and nitrite concentrations substantially below 1.0 mg N/L and nitrate concentrations less than 12.0 mg N/L despite nitrogen loading rate and tilapia weight density were as high as 21.6 mg N/L/day and 17.2 kg/m3, respectively. Without solids separating units, TAN and nitrite concentrations drastically increased above the acceptable limits of 1.0 mg N/L. Finally, the result of nitrogen balance analysis indicated that nitrification and denitrification were the primary treatment pathways in this recirculating system capable of removing 49.8% of total nitrogen input, whereas solids separating units removed 9.5% of total nitrogen input yet their presence was essential for sustaining the activity of nitrifying biofilters for an extended period.