Halamid® designed for use with biofilters

Recirculation systems equipped with biofilters are of growing importance for the aquaculture industry, either for environmental reasons, or to limit the risk of pathogen introduction into the farm. Such closed circuits are equipped with among others, biofilters to keep water clean.

With fish, ammonia and urea are the main nitrogenous excretion products. As these substances can be toxic to fish in higher concentrations, they should be removed. Biofilters contain bacteria (primarily Nitrosomonas and Nitrospira) that convert ammonia into nitrates. This is the critical step. Subsequently nitrates are removed by denitrifying bacteria. This process is analogous to what happens in nature, but due to the higher stocking densities in an aquaculture farm and consequently the higher production of nitrogenous substances, the same effect can only be achieved by a high concentration of these useful bacteria, such as in a biofilter.

Halamid® is used for water treatment during the production cycle and therefore in the presence of aquatic animals and with an operating biofilter.

The question that easily comes up is: “will Halamid® affect the useful bacteria in the biofilter?”.

Several studies have concluded that Halamid® – at recommended dosage – is compatible with the useful bacteria in biofilters and causes no detrimental effect to their functioning. Notably Boardman et al (2009) * showed in a series of controlled tests that a bio filter’s activity (measured by the rate of nitrate formation) at 20ppm Halamid® in the recirculated water, does not affect the nitrification process.

The study above can be considered a worst-case set-up. After all, in most farms, as is our recommendation,  treatment with Halamid® is done in one tank at a time, so that the effluent from this tank is quickly diluted with the effluent from other, non-treated tanks causing a strong reduction of the active substance concentration in the water, before it reaches the biofilter.

Finally, a point of attention. A bio filter offers conditions that favour the proliferation of useful bacteria. However, it does the same for pathogenic bacteria that may harbour in the biofilter as well. In case a farm operating a recirculation system experiences continued presence of elevated levels of pathogenic bacteria, then the biofilter may need treatment with a disinfectant. This will destroy all bacteria in the biofilter and thus should be a last resort.  Halamid® can also be used for this, albeit at higher, typical disinfectant concentrations, with excellent results.