Biological filters are typically used in
aquaculture to control ammonia and nitrite.
Three categories of factors affect biological filters: the biological
community, the water physico-chemistry and the physical design.
Biological
Community — Control of ammonia and nitrite in biological filters is accomplished
by nitrifying bacteria.
Nitrifying
bacteria are very sensitive to environmental conditions; this is particularly
true for Nitrobacter. Many factors can inhibit these bacteria. The active area
of the biological filter should be in the dark; light is inhibitory. Excess organic
material inhibits nitrifiers. A balanced population of heterotrophic bacteria
is essential to control levels of soluble organic pollutants. Water
Physico-Chemistry — Ammonia and nitrite are only sources of nitrogen for the
bacteria. Other nutrients including carbon, phosphorus and trace elements are
also essential. Carbon must be inorganic and is measured as carbonate alkalinity.
Sodium bicarbonate (baking soda) is commonly used to add carbonate alkalinity.
Water with more than 100 mg carbonate alkalinity/L is normally adequate; lack
of carbonate alkalinity will stop nitrification. The
alkalinity provides pH buffering. The optimal pH for nitrification is near 8.0.
Values outside of 6.0 — 8.5 can be expected to reduce nitrification efficiency.
Nitrosomonas produces acid during its growth; the pH must be monitored and adjusted.
Nitrifying bacteria
absolutely require adequate oxygen. Water exiting a biological filter should always
contain at least 4 ppm oxygen. The optimal temperature for nitrification is about
30°C; the rate can be expected to be cut in half for every decrease of 10°C. Thus
a filter working at 30°C may remove the same amount of ammonia as one twice as
large but operating at 20°C. Physical
Design — The role of all biological filters (trickle filters, RBCs or fluidized
beds etc.) is to provide a home for the microorganisms. More surface area allows
for the development of larger bacterial populations. Surface area, however, must
be balanced against open area within the filter. Biological filtration results
in the growth of bacterial biomass; filters with inadequate surface area block
rapidly.
A well designed biofilter should be virtually self-cleaning. The nature of the
physical substrate can also affect start-up time. Slippery surfaces are more difficult
for the bacteria to colonize than rough ones.
Water
flow patterns are very important. An adequate flow is essential to assure that
the pollution or food reaches the bacteria, which are immobile. They use the nutrients
around them, sufficient water movement is essential for good growth and performance.
All water should be physically filtered or clarified to remove solids before the
biological filter; these solids should be removed from the system as quickly as
possible. Inadequate water flow combined with solids accumulation can be the cause
of major headaches. Anoxic zones will develop where there can be a synthesis of
ammonia and nitrite even in the biofilter. Nitrite is produced not only as a by-product
of ammonia removal but also from the partial denitrification of nitrate.
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The Bacta-Pur System
The
Bacta-Pur System for biological filters consists of: - Bacta-Pur
N3000 — a balanced community of nitrifiers and selected heterotrophs;
- Bacta-Pur Pre-starter 1
— nitrite plus growth enhancers for Nitrobacter,
- Bacta-Pur
Pre-starter 2 — ammonia and essential nutrients.
- Bactivator
— automatic system to activate Bacta-pur products
Starting
Filters — It is desirable to establish a biological filter prior to introducing
the animals. Nitrobacter growth is inhibited by high levels of ammonia. Excessively
high levels of nitrite can develop before the ammonia drops sufficiently to permit
Nitrobacter to grow. Start-up time is reduced by first developing the populations
of Nitrobacter. Use Bacta-Pur N3000 and Bacta-Pur
Pre-starter 1 to provide the nutrients and the desired bacterial community.
Once the population of Nitrobacter
has been established, Bacta-Pur Pre-starter 2 is added to feed the Nitrosomonas.
Bacta-Pur Pre-starter 2 is also used to maintain biological filters when biomass
is low or before sudden increases in stock.
Symptoms
- biofilter
difficult or slow to start
- high
ammonia and/or nitrite
- fluctuating
loads
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Treatment Benefits - start
biofilters rapidly
- bring
ammonia and nitrite to safe levels
- stabilize
filter performance
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Filters with Fluctuating Loads — The ideal way to handle fluctuating loads
is to use multiple or modular biological filters where a portion of the physical
substrate, on which the bacteria grow, can be isolated from the rest of the system.
The isolated section can be fed artificially by adding Bacta-Pur Pre-starter 2.
Ammonia is monitored and more Bacta-Pur Pre-sterter 2 is added as needed. When
the new load of biomass arrives the isolated section of the filter can be drained
of liquid to remove residual ammonia and/or nitrite and then returned into operation.
All water sterilization
equipment should be turned off during start-up of a biological filter.
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Dose Rates Starting
a Biological Filter with Animals Present — Add 100 mL Bacta-Pur N-3000 / 1000
L of tank water. Continue additions of half this dose daily until filter activity
has stabilized. Starting
a Biological Filter without Animals Present — Step 1: add 100 mL Bacta-Pu
N-3000 / 1000 L of tank water (continue additions of half this dose daily until
filter activity has stabilized) and 1 kg Bacta-Pur Pre-sterter 1 / 4000 L tank
water. Step 2: monitor nitrite, and when it is less than 1 ppm add 1 kg Bacta-Pur
Pre-sterter 2 / 4000 L tank water. Step 3: monitor ammonia and nitrite, and add
animals when safe levels are reached. Step 4: switch to ‘Maintaining a Biological
Filter’. Maintaining
a Biological Filter — Add weekly 100 mL Bacta-Pur N-3000 / 1000 L of tank
water. Small cold water systems, such as for lobster tanks, should have weekly
additions of 100 mL Bacta-Pur N-3000 / 200 L of tank water. Maintaining
a Biological Filter with Fluctuating Loads — Add to each 100 L water containing
isolated sections of biofilter 100 g Pre-starter 2 and 100 mL Bacta-Pur N-3000.
Monitor ammonia, and add more Bacta-Pur Pre-staerter 2 as necessary.
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To
help you evaluate your needs contact
us.
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