Evaluation of modified biofloc system with filtration unit in controlling suspended solids and inorganic nitrogen concentrations in a recirculating aquaculture system

Abstract

BACKGROUND Biofloc technology systems (BFT) often encounter difficulties in controlling suspended solid levels in tanks. The oxygen consumption rates and ammonia removal rates of bioflocs as the BFT system shifts from assimilation towards nitrification have rarely been reported. Thus, the performance of the BFT system with a filtration unit was evaluated. RESULTS Preliminary work found that the optimal screen pore size and recirculating flow rate were 100 μm and 3000 L day−1, respectively. The BFT system with the filtration unit could maintain suspended solids in the fish tank below 50 mg‐SS L−1 while retaining significantly higher suspended solids in the biofloc reactor (509 ± 44.6 mg‐SS L−1). The daily starch addition at a C:N mass ratio of 10:1 in phase I (day 1–38) induced the biofloc formation that kept TAN and nitrite levels below 1.0 mg‐N L−1. The fraction of inorganic nitrogen compounds increased from 2.5% in phase I to 27.6% in phase III (day 56–70). TAN removal rates increased from 3.0 mg‐N g‐SS−1 day−1 during phase I to 10.34 ± 0.392 mg‐N g‐SS−1 day−1 after complete nitrification occurred. Relatively constant oxygen consumption rates of the bioflocs (149.1 ± 9.53 mg‐ O2 g‐SS−1 day−1) were observed for the entire experiment. CONCLUSION The BFT system with a filtration unit was effective in controlling suspended solid and inorganic nitrogen concentrations. Nitrogen treatment pathway of BFT system was assimilation during startup period but gradually shifted to nitrification. Oxygen consumption rates of the bioflocs are relatively constant regardless of the pathways responsible for nitrogen treatment. © 2021 Society of Chemical Industry (SCI).