Evaluation of Capacitive Deionization (CDI) on Nitrogen compounds and other water quality parameters in Recirculatory Aquaculture Systems (RASs) raising Atlantic salmon under two different organic loads

Abstract

Recirculatory Aquaculture System (RAS) is an intensive fish farming technique that recirculates water used in the system after it is purified through the mechanical and biofilter. Maintaining water quality in RAS is essential including the removal of nitrogenous wastes through nitrification and denitrification.

Capacitive deionization (CDI) is a technology based on the electrochemical method that removes ions from water. Two different organic loads were created in three replicate microRAS systems by using 20 micrometer (µm) and 100 µm drum filter meshes respectively. Capacitive deionization (CDI) was tested for the removal of nitrogen compounds present in RAS water in the morning and the evening. The continuous effects of the CDI usage over eight hours on the RAS system were also tested.

A significant reduction in the level of alkalinity and conductivity was seen in the water treated by the CDI unit. Two instances of a significant reduction in nitrate (NO3-N) levels were also seen during the experiment. An increased level of nitrite (NO2-N) was detected after water was treated by the CDI unit. This might have occurred due to the voltage being used that might have caused the nitrification of ammonium ions or denitrification of nitrate to nitrite. Biofouling might have also occurred which could have caused the denitrification of nitrate to nitrite. Water treated through the CDI unit reduced ammonium (NH4-N) but was not statistically significant.

CDI has a high potential for ion removal from RAS systems, but fine-tuning of the CDI system is required for use in the RAS system.

Key words: Recirculatory aquaculture system , Capacitive deionization (CDI), Reduction , Nitrite increase, Fine tuning