Biofiltration reactivation kinetics of a Cyclobio fluidized sand filter in a warmwater recirculating aquaculture system

Authors: Pfeiffer, Tim; Ott, Brian

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2022
Publication Date: 4/5/2023
Citation: Pfeiffer, T.J., Ott, B.D. 2023. Biofiltration reactivation kinetics of a Cyclobio fluidized sand filter in a warmwater recirculating aquaculture system. North American Journal of Aquaculture. 85(2):166-173. https://doi.org/10.1002/naaq.10282.
DOI: https://doi.org/10.1002/naaq.10282

Interpretive Summary: Recirculating aquaculture systems are widely used in university research facilities, state and federal fish hatcheries, and small-scale systems in schools throughout the country. A RAS can also support traditional pond culture through broodstock and fingerling production. The technology of recirculating aquaculture is well developed and a key to good water quality for the fish environment is system biofiltration. Biofilters house the bacteria that dissolves the nitrogenous waste products excreted by the fish. A biological filter holds media such as plastic beads or sand that has a huge surface area that nitrifying bacteria cells can colonize. This nitrifying bacteria within the filter must be well developed before stocking the fish especially for large units that have not been in operation. The Cyclobio sand filter is a relatively new filter design and allows for large units to be constructed thereby reducing capital costs and providing good water quality for a large density of fish. Authors measured the nitrification rate of the hatchery's commercial-scale Cyclobio sand filter during start-up by adding ammonium chloride to the filter on a daily basis. After 4 weeks of substrate addition the filter's ammonia removal rate was great enough to support 800 kg of fish feed 40 kg of a daily ration. After reducing substrate dosing to a weekly basis the filter conversion rate dropped 60% but was sufficient to keep the filter stabilized during nonseasonal use.

Technical Abstract: The ability of a commercial-scale Cyclobio fluidized sand filter was evaluated for ammonia and nitrite removal by dosing with ammonia chloride, NH4Cl, as part of the water treatment unit for the U.S. Department of Agriculture Agricultural Research Service Warmwater Aquaculture Research Unit's (WARU) catfish hatchery in Stoneville, Mississippi, USA. Treatment system water was recirculated through the Cyclobio filter for several months without any feed inputs; thus, our objective was to investigate how quickly a full-scale Cyclobio fluidized sand filter could be reactivated with NH4Cl substrate dosing in preparation for the upcoming spawning season. A second objective of the study was to examine the decline of the filter's nitrification ability when the supplementary NH4Cl substrate dosings were removed or limited. The effects of daily and weekly substrate additions were evaluated over a 14-week winter period, with the system water temperature ranging between 20° and 23°C. Total ammonia nitrogen (TAN) concentration decreased within hours of initial dosing. After approximately a 2-h lag period, the nitrite–nitrogen concentration peaked and then decreased. The rate of TAN nitrification followed a simple first-order reaction kinetics and increased over time during the 4'weeks of daily NH4Cl substrate dosing. The return to a weekly substrate dosage resulted in a decrease in the kinetic reaction rate, but adequate to maintain the filter during periods of system inactivity. The once-daily substrate dosage was consumed within hours of the initial dosing and was sufficient for current system loading.