Submitted to: Book of Abstracts World Aquaculture Society
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2001
Publication Date: 1/27/2002
Citation: PFEIFFER, T.J. AIR SCOURING EFFECTS AND CONTROL ON A FLOATING BEAD BIOFILTER FOR A SMALL-SCALE RECIRCULATING AQUACULTURE SYSTEM. BOOK OF ABSTRACTS WORLD AQUACULTURE SOCIETY. 2002. p.22.
Technical Abstract: In recirculating aquaculture systems (RAS), water containing total ammonia nitrogen (TAN) is toxic in the unionized form (NH3-N) to the fish being cultured in the system. The amount of TAN in the water is related not only to the species of fish being cultured but also by the quantity of feed provided to the fish and the protein content of the feed. In recirculating aquaculture systems, water is recycled through biological filters, which contain nitrifying bacteria that convert TAN into relatively non-toxic nitrate-nitrogen (NO3-N). The success of biological filtration depends on careful control and maintenance of the nitrifying bacterial biomass on the filter media, especially during the filter backwashing cycle. For biological filters, an effective backwashing strategy involves removing excess biomass while not totally removing the attached biomass essential for the next filter cycle. Air scouring the filter media for bacterial biomass control represents a useful option to consider in developing backwashing strategies for a floating bead biofilter (FBB). A floating bead biofilter was modified to allow for several air-scrubbings per day with the equivalent volumetric loss of a single backflush. With several computer controlled air-scrub/solids purging per day (4 per day) the feed loading rate capabilities of the FBB was doubled (0.45 kg/day) without a significant reduction in water flow. The peak volumetric nitrification rate (VNR) measured approximately six hours after feeding were in the range between 400 and 700 gram ammonia removal per m3 of media per day. A three-minute settling time after each air scrub was based upon suspended solids settling observations of the backflush material using Imhoff cones. Visual observation of the settable matter also indicated greater than four air scrubs/purging per day at the feed rate of 0.45 kg/day did not provide greater solids removal nor did water quality analysis indicate a significant increase in filter VNR. Air scrubbing and purging of the settled solids is one method of enhancing the FBB nitrification and solids removal capabilities.