Effects of scaled-down dissolved air flotation system on suspended solids removal from Penaeus vannamei culture under biofloc conditions

Suspended solids removal is a fundamental procedure for improving water quality in super-intensive rearing of Pacific white shrimp Penaeus vannamei under biofloc conditions. The aim of this research was to evaluate a dissolved air flotation (DAF) model for removing total suspended solids in a biofloc system for P. vannamei with zero water exchange. The experiment was carried out using a pilot model, with which different combinations of saturation pressures (4.0, 4.5 and 5.0 bar) and recirculation rates (10%, 15% and 20%) were evaluated, totaling nine treatments. The removal rates were calculated for the variables total organic carbon dissolved, biochemical oxygen demand, phosphate, nitrate, nitrite, total suspended solids, and turbidity. The use of DAF for the removal of suspended solids was feasible reaching 60% removal. In addition, great potential was found in other variables removal, such as turbidity and biochemical oxygen demand, with an average removal of 80% and 50%, respectively. Moreover, alkalinity, pH, temperature and salinity remained unchanged, remaining under ideal conditions for P. vannamei under biofloc conditions. Flotation velocity ranged from 2.99 to 11.74 cm min-1 and air/solids ratio ranged from 0.005 to 0.016 mg air mg solids-1. Considering all water quality parameters analyzed, dissolved air flotation presented better performance with saturation pressure above 4.5 bar and recirculation rate above 15%.