Capacitive Deionization (CDI) was developed in the 1960s, however, research has intensified recently as CDI shows promise in producing drinkable freshwater from brackish water sources. This exciting new research has led to the development and production by swt of a scalable and portable state-of-the-art CDI that is being used in our project. This modular and scalable CDI has already been employed successfully in aquaponics (the combined practice of hydroponics and aquaculture) to control water quality. We are implementing the CDI into RAS to directly remove off-flavour compounds from the water, reducing the requirement for purging. The CDI is additionally being employed for the removal of ammonia from the water such that the CDI may replace the need for biofiltration to some extent. Thus, the CDI might indirectly remove taste and odour molecules from the water if the biofilter is a source of off-flavour and therefore further lessen the requirement for purging.
RAS water is treated in biofilters to avoid accumulation of toxic nitrogenous wastes that are a biproduct of fish metabolism. A shortcoming of biofilters is the process of cleaning and restarting it, which may be necessary in case of disease outbreak. Restarting the biofilter is expensive as it may take up to 1.5 years before it becomes fully established again.
The CDI however, can be cleaned, restarted and return to full operational capacity within hours. A large-scale CDI may work in series with the biofilter, which could be especially important after a biofilter restart.
An established biofilter houses beneficial bacteria that detoxify nitrogenous wastes. However, Geosmin and MIB producing bacteria may also colonize the biofilter and seed the fish tanks with off-flavour molecules. Thus, the biofilter can not be used during fish depuration where the fish must then be starved to avoid nitrogen toxicity.
The CDI however, can be used without the risk of seeding the fish tanks with off-flavour. A large-scale CDI implemented into RAS may then allow for some degree of feeding while depurating. This could reduce the problem with pre-harvest weight loss and the associated economic concerns.
