Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Thomas B. Lawson


The performance of combinations of the Norpac$\sp\circler$ tube RBC with a bead filter (System I), a tube settler (System II), and a sand filter (System III) in pilot scale recirculating systems stocked with tilapia were evaluated and compared. Good fit empirical equations were obtained relating TAN and NO$\sp2$-N (both exponential), and DO (linear) with daily amount of feed. Likewise, linear equations relating bead filter or sand filter pressure with feed, and flow with pressure were obtained. Systems I and II maintained favorable water quality up to the maximum feed load studied of 3 kg/day. System III effectively handled only 1.2 kg/day because the sand filter clogged at higher feed rates. At this feeding level, the sand filter removed most of the TAN and NO$\sb2$-N leaving the RBC substrate-limited and ineffectual. Performance of the bead filter-RBC combination was found to be affected by the backwashing process. In the combination, the bead filter removed TAN but not NO$\sb2$-N, and functioned primarily as a solids removal filter, and the RBC handled most of the nitrification. The best backwashing option studied was 30-second propeller agitation with daily backwashing. A hydraulic overflow rate of 119.5 m$\sp3$/m$\sp2$-day was suitable for settling with the Bio Strata media, with a retention time of 7-11 minutes. Mean TSS sludge harvest rate was 249.9 g dry solids/kg feed, significantly higher than that of the bead filter (175 g dry solids/kg feed) as a result of the flushing procedure followed. The settler produced TAN and NO$\sb2$-N so the RBC was predominately responsible for nitrification in System II. There was no significant difference in TAN and NO$\sb2$-N removal by the 2 one-inch and the two-inch diameter tube RBC. The RBC was shown to have a good aeration capacity, which was higher for the two-inch RBC. Modified Monod expressions were derived that closely described the relationship between the areal TAN or NO$\sb2$-N loading with removal rate, and was used to determine the recommended design value of TAN or NO$\sb2$-N removal of 0.357 g/m$\sp2$-day at 36.5 percent efficiency for the tube RBC.