Solid Removal Schemes and the Rotating Biological Contactor in Recirculating Fish Culture Systems.
Date of Award
Doctor of Philosophy (PhD)
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.
Delos reyes, Aurelio Alfonso Jr, "Solid Removal Schemes and the Rotating Biological Contactor in Recirculating Fish Culture Systems." (1995). LSU Historical Dissertations and Theses. 5948.