In recirculating aquaculture systems (RAS), biological filters (or biofilters) are needed to treat ammonia, the primary waste product of fish. The biofilter provides a habitat for beneficial bacteria that convert the ammonia to less toxic forms, nitrite and nitrate.
PAES W.A.T.E.R. is a 12,400 square-foot state of the art Recirculating Aquaculture Systems (RAS) demonstration facility located in Apopka, Florida. At PAES W.A.T.E.R., we are currently in the process of seeding a biological filter. Here's our step-by-step explanation of this process.
After harvesting the last cohort of fish, the PAES W.A.T.E.R. team disinfected the system and began reseeding the biofilter for the next cohort of fish. When seeding a biofilter, we first add ammonium chloride and sodium nitrite to the system to provide the food for the bacteria to grow. Next, they add concentrated bacteria to “seed” the filter, which helps cycle the biofilter faster rather than waiting for bacteria to slowly colonize. Water quality daily is monitored daily for total alkalinity, total ammonia nitrogen (TAN), nitrite, and nitrate. We add ammonium chloride daily to increase TAN to 3ppm.
As the bacteria population grows, the dosage of ammonium chloride is increased to keep the bacteria reproducing. Sodium bicarbonate is used to increase the alkalinity in the system to maintain 250 mg/L throughout the cycling process. This is necessary because the process of converting ammonia to nitrite and nitrate consumes alkalinity. Over time TAN will decrease and nitrite will increase. This is the first step of the nitrification process. Over the next few weeks, the nitrite will begin to decrease and nitrate will increase. Once the biofilter is able to convert the target amount of ammonium chloride efficiently, the system will be ready for fish.
At PAES W.A.T.E.R. team uses Pentair's Sweetwater® SWX Bio-Media as the biomedia for their RAS system. These biofilm carrier elements are created using virgin high-density polyethylene, and have a surface area of 274 ft2/ft3. The proven geometric design provides an abundant amount of surface area for bacteria to colonize.