PERFORMANCE EVALUATION OF CLOSED AQUACULTURE SYSTEM IN CONTROLLING SOLIDS AND INORGANIC NITROGEN COMPOUNDS DURING INTENSIVE TILAPIA CULTIVATION

Abstract

This experiment aimed to evaluate the performance of compact aquaculture system modified from the original design by Sesuk et al. (2009) by integrating suspended solids removal unit. In the first part, the presence of active nitrifying biofilters and solid removal were important aspect for controlling inorganic nitrogen and solids concentrations. The compact aquaculture system given the length of BiocordTM biofilters at 5.6 m and operation of solid separating unit was able to accommodate the total aquaculture weight as high as 5 kg/m3, which corresponded to the nitrogen loading rate of 8.4 mg N/L/day. In the second experiment, suitable management strategies namely method of solid separation and frequency of biofilter cleaning were determined in order to improve the aquaculture system capacity. By maintaining the aquaculture weight at 7 kg/m3, it was found that filtration by Japanese mats filtered media was more effective in solid-liquid separation than using the gravitational sedimentation in solid separating unit. Moreover, cleaning the filtration unit and BiocordTM by scratching and rinsing with clean water every 4 days was able to maintain good water quality within acceptable range for practical aquaculture cultivation. In the final experiment, the compact aquaculture system with filtration unit was operated using the strategies determined previously to grow tilapia without water exchange for 60 days. Under the described operating condition, ammonium and nitrite concentrations were significantly less than 1.0 mg N/L while suspended solid concentrations varied between 20 and 35 mg SS/L. Survival and growth rates of tilapia were measured at 97% and 3.45 g/day, respectively. Finally, solid removal appeared as critical factor for successful aquacultures in the compact aquaculture system even under extensive or semi-intensive aquaculture cultivation, and finally nitrogen mass balance performed after the conclusion of the tilapia cultivation indicated that nitrification-denitrification were main treatment pathways while solid removal only prolonged the activity of nitrifying biofilters.