The biochemical tank (biofilter) is the core treatment unit in Recirculating Aquaculture Systems (RAS), primarily purifying water through microbial metabolism. Its design, performance, and operational management are crucial to the overall stability of the system.
The core function of the biofilter tank is the biological transformation of toxic compounds via nitrification and denitrification processes. Nitrifying bacteria oxidize highly toxic ammonia nitrogen into nitrite, and subsequently into far less toxic nitrate. Under anoxic conditions, denitrifying bacteria then reduce nitrate into harmless nitrogen gas N₂, successfully achieving complete nitrogen removal.
Biofilter tanks are typically packed with high-surface-area biological media to promote microbial adhesion and biofilm formation. Treatment efficiency is influenced by flow distribution, dissolved oxygen (DO) levels, and temperature, with continuous aeration and mixing utilized to maintain an optimal aerobic environment.
In modern RAS, biofiltration technology is frequently combined with ozone treatment and UV disinfection to achieve comprehensive, multi-stage water purification.
