Use of floating bead filters to recondition recirculating waters in warmwater aquaculture production systems

Abstract

Floating bead filters (FBFs) are expandable granular filters that display a bioclarification behavior similar to sand filters. They function as a physical filtration device (or clarifier) by removing solids, while simultaneously encouraging the growth of bacteria that remove dissolved wastes from the water through biofiltration processes. Presently, there are two classes of FBFs that exist. Hydraulic and air washed units fall into the ‘gently washed’ category, which display reduced biofilm abrasion during backwashing and must be washed at a high frequency. Conversely, propeller-washed and paddle-washed filters inflict damage to a relatively heavy biofilm during backwashing, and are considered ‘aggressively washed’. FBFs capture solids through four identifiable mechanisms: straining, settling, interception, and adsorption. In the biofiltration mode, bead filters are classified as fixed film reactors, where each bead becomes coated with a thin film of bacteria that extracts nutrients from the recirculating water as it passes through the bed. In this paper the authors first establish application categories and parameters for recirculating system use, then give criterion for the sizing of recirculating system components in tabular form. Sizing variables for FBFs are normalized to the feed application rates, and the primary method for the sizing is based on a volumetric organic loading rate. Evaluation parameter equations are also given for comparison of bioclarifier performance. These equations include volumetric TAN conversion rate (VTR), the volumetric nitrite conversion rate (VNR), and the volumetric oxygen consumption rate of the bioclarifier (OCF).