Mitigating off-flavour compounds geosmin and 2-methylisoborneol

Currently, intensive RAS production involves the risk of off-flavor accumulation requiring purging of fish in clean flow through systems for up to 14 days with feed withdrawn. While this effectively removes the off-flavor, the harvest ready fish also suffer significant weight loss during this period with associated value loss. Capacitive deionization (CDI) technology has been developed for water deionization and has now reached an efficiency where it is routinely used in a variety of water treatment scenarios including sterilization and drinking water production from brackish water. This is achieved with very low power consumption. Here we test the feasibility of using the CDI for ammonia removal to allow for continued feeding during purging to avoid weight loss. We also evaluate the removal of off-flavor molecules to improve the purging process. We have demonstrated by running the CDI at different ammonia loads that it can control ammonia levels simulating fish densities commonly found in commercial RAS. Similarly, we have used the CDI to simulate purging regimes with maintenance feeding levels using rainbow trout (Oncorhynchus mykiss). These data will be presented. As the technology is completely scalable it can be implemented into specialized high-flow RAS units intended for off-flavor removal. In this system maintenance feeding can continue to avoid weight loss while the up-scaled CDI eliminates ammonia build up. The CDI concentrates ammonia in a small volume of water that may subsequently be used as plant fertilizer. Since bacteria typically carry surface charge, they will likewise be removed from the CDI treated water. Results from our small-scale RAS system offer a promising proof of concept for improving purging in commercial RAS.