A Comparative Analysis of Three Biofilter Types Treating Wastewater Produced in Recirculating Aquaculture Systems

Nine recirculating systems at the Virginia Tech Aquaculture Center were placed on line and stocked with yellow perch, Perca flavescens, fingerlings. Fish were stocked at a density of approximately 455 fish m³. Biofilter types were the only factor differing among system designs and were an upflow pulsed bed bead filter, packed tower trickling filter and a rotating biological contactor (RBC). After stocking, systems were allowed to acclimate using ammonia excreted by the yellow perch. Following acclimation, a comparative analysis on biofilter performance began. To evaluate filter performance, water quality parameters tested were temperature (°C), pH, dissolved oxygen (DO), total ammonia-nitrogen (TAN), nitrite-nitrogen (NO₂⁻-N), nitrate-nitrogen (NO₃⁻-N), alkalinity (as CaCO₃), water hardness (as CaCO₃), carbonaceous biochemical oxygen demand (cBOD₃), dissolved organic carbon (DOC), and total suspended solids (TSS). Basic water quality analysis encompassed samples drawn at 8 AM. TAN mass removal analysis encompassed water quality samples drawn at 8 AM and over 24 hours. Higher TAN mass removal rates were achieved in trickling and RBC filters than in bead filters for 8 AM (0.037, 0.14, and 0.004 g/m²/d, respectively) and diurnal sample periods. Analysis of areas under mass removal curves depicted RBC filters as surface area limited. Trickling filters proved most effective at carbon dioxide stripping and pH maintenance and also effectively removed TSS from the culture water. The study did not show filter type as having a significant effect on median organic water quality parameter values.