Chapter: Aquaculture Engineering : Ammonia Removal
Management of biological filters
Management of biological filters
A biofilter will always need a
certain start-up time before it becomes functional (Fig. 9.6) because it takes
some times to establish the culture of nitrifying bacteria on the filter medium
(the biofilm). Of course there must be nitrificants in the water and the
environment must be suitable, for instance with
If a biofilter is put into
service before the bacterial culture has been established, there will be no or
low efficiency. Normally, the start-up time for the filter is between 20 and 40
days, depending upon, among other factors, temperature and pH.28,35
The start-up time can be reduced by inoculation or placing old bacterial
cultures in the filter. It is normal to only clean a part of the biofilter each
time so that there will always be some biofilm left on a parts of the filter.
Old filter surfaces will always have some film left, so the start-up time for a
pre-viously used filter surface will be reduced compared to completely new
ones.
In the start-up period, some
nitrite may be sup-plied to the fish with the water that has passed through the
biofilter because this is the end product of the first process that takes place
in the filter. This is therefore a critical period, because small
concen-trations of nitrite can be toxic to the fish and care must therefore be
taken at this stage. The best course of action is to have as few fish as
possible in the start-up period or to inoculate the filter with bacteria.
Related Topics