Читать книгу Fundamentals of Aquatic Veterinary Medicine - Группа авторов - Страница 27

The conversion of ammonia to nitrite and nitrate is critically important in aquasystems where new water exchange is minimal. These systems must be treated with care to ensure that adequate levels of beneficial bacteria are maintained to perform this conversion. In cases of high recirculating water reuse systems that recirculate water in the 90% range, a dedicated biofilter is used before the water reenters the main system. In the biofilter, the conversion is accomplished through the use of specialized media designed to maximize bacterial performance.

Features of a biofilter that impact its capacity to convert ammonia through to nitrate in any aquasystem are the type of media used and the surface area per unit volume for bacterial growth, as well as the water flow pattern, degree of oxygen exchange and adequacy of sediment removal. Most biofilters use plastic composite material, although older systems may employ lava rock. Sand can also be used in upflow‐designed tanks, called fluidized bed bioreactors, after the water has been cleared of settleable solids. Many types of biological filters that use varying technologies are already in use in recirculating aquaculture. This field is rapidly growing and expanding. With increasing popularity and utility of recirculating systems, the capabilities of these units continue to improve and it is important that a system is designed to allow for upgrades and improvements. While biofiltration conserves water and increases production capacities, these filters require substantial floor space and add a high cost to initial system installation. In selecting this type of system, the long‐term benefits such as water usage savings, increases in production capacity, and decreased effluent discharge should be weighed against the initial cost. The details of biofilters are complex. Additional information can be found in specialized texts such as Recirculating Aquaculture by Timmons et al. (2018). Further study is recommended prior to working with these types of complex systems.