Evaluation of Settling Chamber Hydraulic Retention Time in a Sunshine Bass Biofloc Production System

Abstract

High total suspended solids (TSS) concentrations that result from the high feeding rates used in biofloc technology production systems can negatively impact fish performance. Excess TSS are removed from biofloc production tanks by side‐stream settling chambers. The effects on solids removal, water quality dynamics, and performance of sunshine bass (female White Bass Morone chrysops × male Striped Bass M. saxatilis) from three settling chamber hydraulic retention times (HRTs; 18, 43, and 87 min; designated HRT18, HRT43, and HRT87, respectively) were evaluated in this 126‐d study in biofloc tanks. Corresponding settling chamber flow rates were 7.2, 3.0, and 1.5 L/min, respectively, and corresponding tank turnover times were 8.3, 20.0, and 40.0 h. Upon activation of settling chambers, the TSS concentration decreased faster in the HRT87 treatment than in the other two treatments. The dry matter mass of solids discharged each time the settling chambers were drained and the total dry matter mass of solids discharged both increased linearly with HRT. Compared to the HRT43 and HRT87 treatments, nitrate‐nitrogen in the HRT18 treatment accumulated about 17% more slowly and 25% less sodium bicarbonate was needed, which suggests that nitrification was impacted negatively by the elevated settling chamber flow rate. Denitrification was not detected in settling chambers given the absence of significant differences between influent and effluent dissolved inorganic nitrogen concentrations in all treatments. Sunshine bass performed well in all treatments, with overall production averaging 4.4 kg/m3 at 81.9% survival. Although sunshine bass were grown successfully to market size in biofloc culture, future research should address higher stocking rates and settling chamber operational parameters to maintain higher TSS concentrations and promote denitrification. Thus, the results of this study suggest that a minimum settling chamber HRT of 43 min is appropriate for biofloc culture of hybrid striped bass.