Submitted to: International Aquaculture Meeting
Publication Type: Proceedings
Publication Acceptance Date: 12/30/1999
Publication Date: 3/30/2000
Citation: Pfeiffer, T.J., Beecher, L.E., Malone, R.F. 2000. Evaluation of alternative media for enhancing nitrification rates in propeller-washed microbead filters. International Aquaculture Conference Proceedings.p.562. Interpretive Summary: Propeller-washed floating bead filters, PFBF, use a non-moving bed of floating plastic media to remove ammonia and solids from the culture water in a recirculating aquaculture system. To obtain optimal ammonia removal along with superior clarification the biofilm which develops on the plastic media must be properly managed. This study was conducted to evaluate and establish a biofilm management regime for three different types of media to enhance ammonia and solids removal rates in propeller-washed floating bead filters.Six experimental scale recirculating systems were constructed for use in this study. Each system consisting of a 25 liter circular tank, and a single 4 liter PFBF. Water was recirculated through the PFBF at a flow rate of 0.6 Lpm. Each recirculating system was stocked with approximately 10-15 tilapia for a total weight of 400g. The daily feed rate was 10.2 g of feed per tank. The experimental-scale PFBFs (10.2 cm in diameter and 46 cm in height) were filled with 1.3 L of media. Three different types of floating plastic media (Kaldness media, modified beads, and thick-walled tubes) were evaluated for ammonia and solids removal at three different backwashing frequencies (once every 12, 24, and 48 h). The modified beads (indented circular plastic beads) provided the best solids and ammonia removal. For each type of media and under each of the three backflush regimes, the ammonia removal rate was greatest six hours after backflushing the filters. The outcome of the study indicated that frequent backflushing (every 6-12 hrs) of short duration (4-5 seconds) provided the best ammonia removal and minimized flow reduction while enhancing solids removal.
Technical Abstract: Propeller-washed floating bead filters, PFBF, consist of a static filtration bed of floating plastic media that are intermittently washed by motor driven, embedded propellers. To achieve optimal nitrification performance along with superior clarification careful biofilm management of the media used in the filters must be implemented. This study was conducted to evaluate and establish a biofilm management regime for different types of media to enhance nitrification rates in propeller-washed floating bead filters. Six experimental recirculating systems were assembled with each consisting of a 0.025 m3 circular tank, and a single 0.004 m3 experimental-scale PFBF. A 0.5 kW pump recirculated the fish tank water through the PFBF at an initial flow rate of 0.6 L-min-1. Each recirculating system was stocked with 400 g of tilapia (35.3 g average weight) and the daily feed loading rate was 0.06 kg feed per liter of media or 10.2 g of feed per tank. The experimental-scale PFBFs (10.2 cm in diameter and 46 cm in height) have a volume of 3.6 L and were filled with 1.3 L of media. Three different types of media (Kaldness media, modified beads, and thick-walled tubes) with a total surface area ranging from 40 to 60 m2 were evaluated. Backwashing frequencies of onceevery 12, 24, and 48 h were evaluated. Influent and effluent sampling for each filter bed was conducted for total ammonia nitrogen (TAN), nitrite-nitrogen (NO2-N), and dissolved oxygen. Sampling was conducted at 6 to 12 hour intervals during steady state operation to determine the total daily volumetric nitrification rate (VNR, g TAN converted-liter of beads-d-1) for each filter media. Over the course of the study the PFBF nitrification performance for all backflush intervals and each media was greatest at the six hour interval and decreased over time.