Virtual Defense: Steven Rodgers (Ph.D. Candidate)

Title: Bahamian oolitic aragonite sand impact on water quality and mitigation of phosphate and phosphorus removal and recovery in recirculation aquaculture systems

Speaker: Steven Rodgers (Ph.D. Candidate)

Abstract: 

Recirculating aquaculture systems (RAS) require management of water conditions to ensure animal health and limit nutrient discharges.  Oolitic aragonite sand (OAS) forms from whiting events off the coast of the Bahamian Islands is a sustainable, renewable and effective in controlling water quality.  Cyanobacteria mediate the precipitation of aragonite by capturing CO2, internally forming CO32-, which reacts with Ca2+ in seawater forming CaCO3 precipitations. 

Studies in freshwater, brackish and marine waters maintained stable pH and alkalinities.  Initially, OAS removed phosphate rapidly, slowing afterwards. The OAS removed phosphate at rates of 716, 705 and 215 mg PO4/ kg OAS for freshwater, brackish and marine water, respectively. A system with daily P additions showed a removal capacity of 77.8 mg P /kg OAS.  Treatment of phosphorus exposed OAS with 1.0% and 2.0% citric acid solutions show phosphate removals ranging from 17.3% to 93.5%. The citric acid increases the OAS surface area 1.66 times to 4.628 m2/g OAS, confirmed by SEM. Microbiome analysis show similar bacterial phyla exist on the naïve OAS and the OAS used in different salinities.

Under anaerobic conditions, the control of system conditions were favorable for denitrification and anammox processes to occur. In freshwater, a loss of 215.8 gram of nitrogen (a loss of 90.5%) of the added nitrogen to the system occurred. In marine conditions, a loss of 253.04 g nitrogen, representing an 87.6% loss, occurred.  Microbiome analysis identified phyla known to function as denitrifiers, though lacking known phyla for anammox bacteria. Losses of nitrogen in both salinities is likely due to denitrification, as oppose to anammox. 

OAS in RAS holding Eastern and Pacific oysters, showed dissimilar responses.  The water quality remained in acceptable ranges for oyster growth.  The survival in Eastern oysters (≥80%) contrasted with the Pacific oysters (≤56%).  Weight increases occurred only with the Eastern oysters.  Both species shows increases in shell length, width and height, but unchanged or decreases in weight.  Reduced somatic growth and limited shell development occurred, perhaps due stresses from nitrogen spikes in the systems. OAS shows no positive advantage with oyster growth. 

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