Biofilter Inoculation Station (BIS)
An Easy-to-Use Commercial-Scale Chemostat for Nitrification
A Biofilter Inoculation Station (BIS) is a novel automated system that grows nitrifying bacteria on biofilter media.
The nitrification process consists of transforming ammonia into nitrite and into non-toxic nitrate. It is part of the natural nitrogen bio-degradation cycle in soils, lakes, and oceans. Nitrifying bacteria, a slow-growing group of bacteria, require oxygen and extract their growth energy from inorganic nitrogen (NH4, NO2).
Since they do not feed on organic matter, which provides much more energy, they can easily be overgrown by heterotrophic bacteria. The Biofilter Inoculation Station creates the best possible environment for these slow-growing bacteria.
A light biofiltration media, packed into movable mesh bags, is set into a BIS where it is fed with increasing amounts of ammonia. Once coated with an active nitrifying population, the bag is simply removed from the BIS and inserted into the biofilter of a given biofiltration system.
All AquaNit™ biofilter media from AQUABIOTECH INC. is likewise light and movable.
This process prepares a biofilter to its planned ammonia load. The result is a truly performing biofilter delivered on time with tremendous savings in maintenance time before loading.
The need to feed the biofilter, dose ammonia/nitrite/nitrate daily, and adjust pH is completely eliminated.
For years, all our biofilters have been pre-activated at our factory before delivery to save our clients time and add peace of mind. Now the automated process is made available.
A Self-Regulated Process
The BIS was designed from the graduate work completed by Hélène Drouin, AQUABIOTECH INC. co-founder, during her Ph.D. research on nitrifying biofilters at Université Laval, Canada. Now integrated into the Inoculo-Monitron™ and associated hardware, the bio-inoculation process is self-regulated. Water temperature, pH, and water make-up are specifically adjusted to keep nitrifying bacteria under exponential growth conditions. The injection of ammonium growth solution and nutrients automatically increases as the nitrifying population grows. When the daily ammonia consumption target is reached, the BIS enters Maintenance Mode.
The BIS is equipped with an air blower that provides these aerobic bacteria with the oxygen they require.
Applications
- Aquatic and marine laboratories operating with highly recycled water
- Aquaculture RAS systems
- Biofilters for lobster storage systems
- Biofilters for industrial treatment of nitrogenous waste
- Maintenance of nitrifying biofilters during winter or off‑season periods
Laboratory and Industrial Scale Models
Two models of Biofilter Inoculation Stations are currently available: a smaller station for laboratories capable of activating one cubic metre of biofilter media, and a larger BIS for industrial-scale projects.
Biofilter Inoculation Station (BIS) for Laboratories
Adds Bio-Safety to an Aquatic Laboratory
With a BIS, we know exactly how much ammonia is oxidized daily by the biofilter media.
Once it has proven itself ready for the future ammonia load, the biofilter bags can be transferred into the biofilter of a given RAS.
Fish or invertebrates can then be safely added to the system.
This process saves substantial technician time by eliminating continual ammonia dosing, pH adjustment, and bacterial feeding.
Eight Biofilter 100‑L Bags Activated at a Time
A standard BIS for wet laboratories can simultaneously inoculate eight AquaNit™ biofilter bags or thirty-two 1‑L Siporax filter bags.
The unit is supplied with an air blower and requires a 115V / 60Hz electrical connection together with a source of
dechlorinated fresh or seawater.
Three storage reservoirs hold the pH buffer solution, growth medium, and nutrient medium. These solutions are supplied by Aquabiotech and are replenished manually.
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Industrial-Scale Biofilter Inoculation Station (BIS-8m³)
This outstanding BIS offers the same characteristics as the BIS-1m³ but with additions allowing the operator to easily inoculate up to 8 m³ of bacterial substrate.
This model also has the ability to automatically prepare growth and pH control solutions.
Simply fill the hoppers (capacity 22 kg) with chemicals in powder form and the system automatically manufactures the required aqueous solutions.
Subsequently, the Inoculo-Monitron™ injects these aqueous solutions in increasing amounts as required to inoculate the bacterial substrate.
This bio-inoculation unit requires a 115V / 60Hz electrical connection and a source of dechlorinated fresh or seawater.
It is furnished with three solution tanks containing the liquids necessary for the bio-inoculation process:
- pH buffer solution
- Growth medium
- Nutrient medium
The nutrient reservoir is filled manually by the operator.
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Technical Details
The following technical notes summarize key operating principles and performance characteristics of the Biofilter Inoculation Station (BIS) and AquaNit™ biofiltration technology.
pH Control in BIS
The precise follow-up of pH in a BIS is important.
pH measurement occurs in a water sampler that completely shunts electrical interference such as errant electromagnetic waves.
A solenoid valve activates the circulation pump to collect a water sample at regular intervals and the pH level is displayed on the Inoculo-Monitron™.
Dissolved gases in BIS
High-flow, low-pressure air from a blower flows through the BIS in a counter-current fashion for improved gas transfer.
The incubator lid is provided with a chimney that traps humidity before the air is expelled from the BIS. Condensation drains away through a vinyl tube.
The BIS is efficient at both CO₂ degassing and oxygenation.
AquaNit™ Biofilter Characteristics
| Advantage | Suitability to Application |
|---|---|
| Self-cleaning |
|
| Absence of flow limitation within the bioreactor |
The biofilter can accept nearly unlimited flow rates. A high flow rate across the biofilter favors nitrification, keeps the biofilm thin and active, and provides superior oxygen and ammonia transfer through the biofilm. |
| Low operating pressure | Reduces pumping costs. Water only needs to be pumped to the top of the biofilter before trickling down through the media without pressure build-up. |
| No gradual reduction of water flow | Very important for operator peace of mind. Since gradual clogging does not occur, the flow rate across the biofilter remains constant. |
| Very light, economical media with high surface area and electrostatic affinity for bacterial cells |
|
| Excellent oxygenation and degassing |
|
| Negligible water loss | Ideal for highly recycled and closed water systems. |
Biofilm within Biofilter
The AquaNit™ Biofilter is designed to keep the biofilm thin and active for optimal nitrification.
A thin biofilm favors the diffusion of carbon dioxide (CO₂), ammonia, and oxygen through the biological layer surrounding the media.
The flow rate across the bioreactor promotes a self-cleaning action through the constant shearing of excess microbial biomass.
By maintaining a thin and active biofilm, the transfer of oxygen and ammonia from the water to the nitrifying bacteria is maximized, resulting in improved nitrification performance.
Starting and stopping the flow within a biofilter increases local turbulence and can promote the sloughing of excess biofilm that may have accumulated on portions of the media.
This sloughing process is normal and beneficial because it helps maintain a biologically active surface while preventing excessive accumulation of biomass within the reactor.
Biofilter Maintenance
The energy obtained from the oxidation of ammonia and nitrite is considerably lower than that derived from organic compounds. As a result, nitrifying microorganisms grow very slowly.
In pure culture, reproduction time ranges from 8 to 24 hours. In wastewater, reproduction may require 20 to 40 hours. Their populations are rapidly exceeded by heterotrophic bacteria whenever significant organic matter is present.
Some heterotrophic bacteria can double their numbers in as little as 30 minutes. For this reason, Aquabiotech ensures that a sufficient population of nitrifying bacteria is established within its biofilters before delivery.
Our proprietary activation process promotes the development of a dynamic and efficient biofilter capable of immediately handling substantial biological loads. Periodic additions of bacterial cultures are generally unnecessary.
After startup, a biologic filter can operate for many years without backwashing. Depending on operating conditions, performance may even improve as beneficial microbial communities continue to develop.
Recommended Operating Practices
- Do not disturb or wash the bacterial support media.
- Maintain pH above 7.0 at all times.
- Maintain alkalinity above 100 mg/L.
- Minimize the entry of organic matter into the biofilter.
- Maintain moderate water exchange rates to avoid washing nitrifying bacteria from the system.
When all aquatic organisms are removed from a system, inorganic nutrients should continue to be supplied so that the nitrifying bacteria remain active.
Temporarily stopping water flow will generally not affect the bacterial biofilm because the biofilter remains humid. A healthy biofilm can often remain viable for one to two weeks under these conditions.
Following prolonged shutdowns, re-inoculation may be required. If a system has been inactive for several months, allow approximately six weeks for complete re-establishment of the nitrifying bacteria population.
Feeding and Biological Loading
A biofilter behaves like a living organism. Sudden increases in feeding rate can temporarily increase ammonia (TAN) and nitrite concentrations while the bacterial population adjusts to the new loading conditions.
Additional biomass should therefore be introduced gradually and accompanied by a controlled increase in feeding rate.
The colder the water, the longer the biofilter may require to adapt to increased biological demand.
Temperature Effects
The optimal temperature range for nitrifying bacteria is generally between 25°C and 30°C.
In cold-water systems, nitrification rates decrease because the bacteria grow more slowly. Nevertheless, once established, nitrifying populations remain active at significantly lower temperatures.
Biofilters installed on cold-water systems should therefore be monitored carefully whenever feeding rates are increased.
Managing Biofilm Sloughing
Frequent starts and stops of water flow encourage biofilm sloughing. Under heavy biological loading, natural sloughing events may occur every two or three months.
Temporary increases in water turbidity may be observed during these periods. Increasing water replacement rates can reduce stress on aquatic organisms.
To minimize excessive biofilm accumulation, Aquabiotech recommends
briefly interrupting flow through the biofilter once per month to
encourage controlled sloughing.
Long-Term Storage
Biofilters can be stored for several months with little attention provided the media remains protected from freezing and direct sunlight.
Before storage, ensure that the purge has been emptied and that only a thin layer of biofilm remains on the media. The lid should remain closed to preserve humidity within the biofilter.
Properly stored media will typically retain a thin grey gelatinous coating of nitrifying bacteria and can later be reactivated for continued service.
Water Parameters that Favor Nitrification
| Parameter | Recommended Range | Importance |
|---|---|---|
| Suspended Matter / Turbidity |
Less than 2 mg/L suspended matter Less than 5 NTU turbidity |
Suspended solids and turbidity contribute to Biological Oxygen Demand (BOD), which favors heterotrophic bacteria at the expense of nitrifiers and may reduce biofilter performance. |
| Alkalinity | Greater than 100 mg/L | Alkalinity stabilizes pH and facilitates the movement of inorganic carbon through bacterial cell membranes. |
| pH | 7.3 – 8.8 | Higher pH values favor ammonia oxidation. Values below 7.0 can inhibit Nitrosomonas species and reduce nitrification efficiency. |
| Dissolved Oxygen | Greater than 6 mg/L | Nitrifying bacteria require oxygen to survive. High oxygen concentrations improve oxygen transfer through the biofilm and support efficient nitrification. |
| Temperature | 7°C – 30°C | Nitrifiers grow faster at warmer temperatures (25–30°C), but once established they remain active at considerably lower temperatures. |
| Sterilization (UV/Ozone) | Minimize when possible | UV and ozone destroy nitrifying bacteria suspended in the water column. Excess sterilization may reduce bacterial colonization and recovery within the biofilter system. |
Maintaining these water quality parameters within the recommended ranges promotes stable nitrification, improved ammonia removal, and long-term biofilter performance.
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