Optimization of Operational Parameters in Biofloc Technology

Abstract

Biofloc technology, known as the blue revolution in the field of aquaculture, lowers the concentration of nitrogen, removes harmful substances and converts them into food sources by the addition of carbon through an external source to maintain the C/N ratio in aquaculture water. The purpose of this research was to investigate the effect of different C/N ratios and feed loading rates on the growth of bioflocs and explore the impact of intermittent aeration on the growth performance of Oreochromis niloticus (GIFT) in BFT. This study was performed in two phases. In the first phase, the effect of different C/N ratios and feed loading rates (FLRs) on the growth of bioflocs was studied by measuring TSS, VSS and FV. Moreover, the concentration of ammonia nitrogen (NH4 + -N), nitrite nitrogen (NO2 - -N) and nitrate nitrogen (NO3 - -N) in indoor tanks without fish were measured. The C/N ratio with the maximum concentration of TSS, VSS, and FV and minimum concentration of ammonia nitrogen (NH4 + -N) was identified. Three feed loading

rates 20 g/m2 , 40 g/m2 , 60 g/m2 for each C/N ratio of 12:1, 16:1, and 20:1 was studied using 9 treatments in duplicates, set up in indoor tanks with a volume of 70.4 L. The results demonstrated that the highest concentration of TSS and FV was achieved in C/N 16:1 and the feed loading rate of 60 g/m2

. The variation patterns of the average levels of total ammonia nitrogen showed a decreasing trend and maximum removal in the tank with the maximum concentration of TSS, VSS and FV. Proximate composition results showed an increasing trend in the Crude Protein content with the increase in FLR and C/N. The highest crude protein content (25.06 ± 0.22%) was observed in C/N 16:1 and FLR 40 g/m2

. In the second phase, the impact of different rates of intermittent aeration on water quality and the growth performance of Oreochromis niloticus (GIFT) with a C/N ratio of 16:1 was studied in a 47-day trial. A total of 224 fish (124.79 ± 5.89), fed twice daily with a commercial diet at 2% of their body weight, cultured in 4 treatments, continuous aeration (CA) and intermittent aeration with different duration of aeration and non-aeration cycles (CA, IA 5 min OFF/55 min ON, IA 10 min OFF/ 50min ON), IA 15 min OFF,45 min ON), in 8 outdoor tanks with a volume of 1000 L and a stocking density of 28 fish/tank. The results indicated a difference in the values of DO, EC, TDS, TSS, VSS and FV between treatments, the concentration decreased with the increase in the off-period aeration duration. TAN and phosphates showed a decreasing trend with the increase in off-period duration while nitrites and nitrates were not different among treatments. The highest fish weight gain (107.3 ± 2.90 g), length gain (1.6 ± 0.03 cm), and protein efficiency ratio (PER 3.45 ± 0.09) were measured in CA. The lowest (1.77 ± 0.03) and highest