Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering

First Advisor

Ronald F. Malone


A fluidized bed/upflow sand filter configuration, was developed and designed for utilization in recirculating aquaculture system, specifically the soft-shell crab and soft-shell crawfish industries. These filters were selected and designed because of their ability to withstand clogging and still maintain high levels of water quality for aquaculture production. The effectiveness of sand grain size was used to evaluate fluidized bed filter performance with filter loadings ranging from 16 to 1285 pounds of crawfish per cubic foot of filter sand. A coarse sand grain size was recommended as a filter media because of it's ability to shear excessive biofilm growth from the sand, thus prohibiting clogging from occurring within the filter bed. The fluidized bed/upflow sand filter combination was evaluated in terms of nitrification and oxygen consumption when used with a recirculating crab shedding system. The filter combination's carrying capacity (700 crabs per cubic foot of sand media) exceeded that observed with the submerged rock filter by more than 20 times and was largely explained by the filter's solids removal ability which significantly reduced the filter's oxygen loading rate (OLR). Nitrification rates with the filter combination were extremely high as total ammonia and nitrite levels remained below 1.0 mg-N/L. Verification of a volumetric loading criteria (150 pounds per cubic foot) for this filter combination was further established with performance data obtained from a commercial soft-shell crawfish facility. Water quality monitoring results indicated that the filters maintained total ammonia and nitrite levels below 1.0 mg-N/L under typical operating conditions. Shock loading, pH control, and over-feeding, rather than filter capacity, dominated water quality fluctuations, thereby indicating that the loading criteria was sufficient for commercial operation.