USE OF PHA COLUMNS TO CONTROL NITRITE PEAKS DURING ACCLIMATION OF MARINE SHRIMP PRODUCTION

AST Filters was awarded a USDA SBIR grant to investigate and modify the stability of inland shrimp production biofloc systems. Two configurations were involved is this research. Configuration 1 reflects current shrimp biofloc design practice, utilizing a simple clarifier for solids control. A PolyGeyser floating bead bioclarifier served as a fixed film operation for Configuration 2. Each configuration was conducted in 75 gallon glass aquarium tanks, with shrimp stocked at a rate of 300 PL/m² to simulate intensive growout of shrimp farming. During the course of this grant, the first replicates of both configurations (Tank B1 and Tank P1) experienced acclimation issues aggravated by analytical error. As a reference, in shrimp systems, it is recommended to maintain ammonia (TAN) below 3 mg/L and nitrite at 5-25 mg/L. In our systems, we experienced spikes in nitrite of 134 mg/L and 133 mg/L in the PolyGeyser and biofloc tanks, respectively. This resulted in both systems losing over three quarters of the shrimp stock. Once these higher nitrite concentrations were discovered, actions were taken to recover the remaining shrimp and stabilize the systems. This resulted in utilizing a column filled with Polyhydroxybutyrate (PHB), a bioplastic, as a quick-fix solution to diminish nitrite accumulation in the systems.

PHB acts as an energy and carbon source. It comes in a pellet form, and can degrade either aerobically or anaerobically. As it degrades it is able to serve as a feed source for the bacterial populations and promote growth.  In our application, flow was restricted in the column to promote anaerobic conditions, in which more efficient nitrogen assimilation can occur. In 7 days, nitrite decreased from peak to 2 mg/L in Tank P1 and for Tank B1, nitrite decreased from peak to 1 mg/L in 10 days. The tanks were then able to be restocked up to the desired density and procede with the study. After roughly two weeks of running online, the external PHA columns were turned off. The tanks have so far shown no sign in nitrite instability.