Biofilter Inoculation Station (BIS)

• High-flow, low-pressure air from a blower flows through the BIS in a counter-current fashion for better gas transfer.
• The incubator lid is provided with a chimney trapping humidity from the air before it is expelled from the BIS. Condensation drains out by via a vinyl tube.
• The BIS is efficient at both CO₂ degassing and oxygenation. The high air-to-water ratio and large contact area within the chemostat maintain the CO₂ level below 15 mg/L and the water well oxygenated.

The AquaNit™ Biofilter is designed to keep the biofilm thin and active for optimal nitrification.  A thin biofilm favors the diffusion of CO₂, ammonia, and oxygen.  The flow rate across the bioreactor maintains a self-cleaning action via constant shearing of excess microbial biomass.  Starting and stopping the flow in a biofilter increases local agitation and favours the sloughing off of excess biofilm that may have accumulated on some parts of the biofilter.  Sloughing off is normal and useful.

The energy output from the oxidation of ammonia and nitrites is considerably less than that from organic compounds. As a result, the microorganisms have a very slow growth rate. Reproduction time in pure culture is 8-24 hours. In effluent water, it is 20 to 40 hours. Their numbers are rapidly exceeded by those of heterotrophic bacteria in the presence of organic matter. Some of the heterotrophic bacteria are known to double their numbers in as little time as half an hour. It is for this reason that we make sure that a sufficient population has been implanted in the Aquabiotech system biofilters before delivery.  The proprietary method used for biofilter activation ensures a dynamic and efficient biofilter operation, even when it is connected to well-loaded fish tanks.  Periodic additions of sustaining bacteria are not required.

After start-up, biologic filters can operate for several years without backwash. Depending, of course, on the use to which they are put, they may even improve with age as other microorganisms become implanted.  We recommend the following elementary precautions in order to guarantee optimal performance.

• Do not disturb or wash the bacterial support.
• Maintain water pH above 7.0 at all times and alkalinity above 100 mg/L.
• Prevent the entry of organic matter in the biofilter in order to limit the growth of heterotrophs.
• The rate of exchange water (water make-up) must be less than the speed of reproduction of nitrifying in water (12 to 24 h).

As nitrifying bacteria do not survive a long time without organic pollution, it is important to provide inorganic nutrients when you remove all fishes.  In this way, the biofilter remains active between two experiments.

Temporarily stopping the flow of water will not affect the bacterial biofilm, as the sump is full of water. Indeed, the humidity will keep the active biofilm for one to two weeks. A longer period requires re-inoculation of the biofilter when you restart the unit recirculation. Following an interruption of several months, allow at least 6 weeks for re-inoculating the biofilter.

The practice of good management is particularly important in the operation of a closed system.  A biofilter is similar to a living organism; an increase in feed rate may give rise to a temporary increase in TAN and nitrite, and it may take a few days for the bacteria to adapt to this new regime. It is, therefore, most important to keep a tight control on the rate of feed to the aquatic organisms. If supplementary biomass is introduced, it must be followed by increasing the feed rate gradually.  The colder the water, the longer it will take for the biofilter to adapt to an increase in feed rate.

The optimal temperature for nitrifiers in a temperate climate is known to lie generally between 25 and 30°C.  An immediate consequence of using cold-water recirculating systems is the reduced growth rate of nitrifiers and their lower oxidation rate. Regardless of temperature, the growth rate of nitrifiers living in a relatively “clean” environment remains significantly higher than nitrifiers in activated sludge. Point of interest to note: the available data also indicate that the bacterial biomass is less sensitive to variations in temperature than the cells in suspension.

On the other hand, it is known that half saturation constants (K_s) of nitrifiers decrease considerably with decreasing temperature.  For example, the half-saturation constant (Ks) of Nitrobacter sp. goes from 2.67 at 25ºC to 0.30 at 10ºC.  It is thus clear that low levels of ammonia and nitrite can be achieved more readily in cold water than in warm water systems.

Management practices are influenced by this phenomenon of reduced activity of nitrifiers in cold water.  Our biofilter has been sized for a maximum 0.8-kg dry food per day at 15ºC or more.  If the water is colder, it can be assumed that the feeding rate will be less than 0.5 kg to account for the reduced appetite of fish.  If fish appetite is not reduced by cold water, you should watch the biofilter closely, for it is reasonable to assume that the nitrifying capacity of the biofilter will have decreased.

Frequent water flows stop and start in the biofilter causing biofilm sloughing. It is therefore important to minimize this fact. Under conditions of a continuous and heavy charge of biologic material, this kind of sloughing off can naturally occur every two or three months. It may result in a temporary increase in the turbidity of the water for a day or two.  It is recommended to increase the proportion of water make-up to minimize the discomfort for aquatic organisms. A preventive treatment with chloramine is also suggested. To minimise this temporary turbidity, it is suggested to trigger this sloughing off by interrupting the flow through the biofilter for few seconds once a month.  This action will prevent biofilm build up.

A biofilter may be stored for several months without problem. The nitrifying bacteria are able to survive for a considerable time with very little attention. We recommend to simply keep the lid shut in order to conserve the humidity of the media. The bacteria must be protected from direct sunlight and freezing. Before storing the biofilter, make sure the purge has been emptied and that only a thin layer of biofilm covers the media. In general practice the support would already be very clean and coated with a thin, grey, gelatinous deposit.