Fine solids removal by foam fractionation in a low-salinity recirculating aquaculture system for red drum juveniles, Sciaenops ocellatus

Authors: Pfeiffer, Tim; BAPTISTE, RICHARD - Florida Atlantic University; WILLS, PAUL - Florida Atlantic University

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2024
Publication Date: 6/25/2024
Citation: Pfeiffer, T.J., Baptiste, R.M., Wills, P.S. 2024. Fine solids removal by foam fractionation in a low-salinity recirculating aquaculture system for red drum juveniles, Sciaenops ocellatus. North American Journal of Aquaculture. https://doi.org/10.1002/naaq.10345.
DOI: https://doi.org/10.1002/naaq.10345

Interpretive Summary: Foam fractionation is considered an effective way of removing fine solids and excessive nutrients from aquaculture systems, specifically marine land-based recirculating aquaculture systems. Accumulation of fine solids is considered problematic because the organic matter provides space and energy for bacterial growth in these systems that can lead to increased dissolved oxygen demand, clogging of the biofilter media, and reduced biofilter nitrification capacity. Foam fractionators can also be used with or without using ozone in the bubble induction process. Ozone is a strong oxidizer and has been shown to improve foam fractionator efficiency and improve water quality. Different methods of operating a foam fractionator were evaluated for removing fine solids from a low salinity recirculating aquaculture system for juvenile red drum fingerling production. Salinity of the culture water was roughly 30% of seawater(11-13 ppt). Methods for bubble induction included Venturi injection of ozone and liquid oxygen, and pump aspiration. Two different water head heights were used in the unit with head heights 0.3m apart. All methods of operation led to a reduction in the fine particle concentration. The most solids removed and greatest volume of foammate produced was by employing ozone to the Venturi injector for bubble induction and flowing water through at the high head height with a hydraulic retention of approximately 2.5 minutes.

Technical Abstract: Foam fractionation is an effective way of removing fine solids and excessive nutrients from aquaculture systems, specifically saltwater systems. Organic matter accumulation provides more space for bacterial growth in these systems that can lead to increased dissolved oxygen demand, clogging of the biofilter media, and reduced biofilter nitrification capacity. To test the ability of foam fractionation for fine solids removal in a low salinity system (30% seawater strength) a combination of bubble induction and operating conditions were evaluated. Generating microbubbles through impeller shearing of air from a submersible pump three times more solids were removed with the water flow at a head height in the riser cone of the foamate collection chamber versus below the riser cone (a head difference of approximately 0.3 m). The foamate was wetter and volume 36% greater. Venturi injection of ozone improved solids removal for the lower head height almost 4 fold but the amount of solids removed at the higher head height was still 1.6x greater. Foamate volume also increased five-fold while only increasing two-fold at the lower head height. Using LOX with the Ozone in the venturi injector did not further increase solids removal or foamate volume. Flow ranged from 217 to 314 Lpm providing a hydraulic retention time between 4.0 to 2.7 minutes for bubble and particle contact time. Amount of solids removed per volume of water treated increased with the longer contact time. Over the foam fractionator experimental trial period, the system TSS decreased from 6.3 mg/L to 4.9 mg/L and the percent of particles less than 50 microns in the influent water decreased 20% . Overall, using ozone in the Venturi injector at a water level and flow to produce a wet foamate with a long retention time for particle and bubble contact in the reactor chamber provided the best results for fine solids removal.