Posted: January 13, 2014, 1:35 p.m. EDT
By Patrick Donston
Biological filtration is a model of research and development that brings technical aspects of microbial principles and balanced ecosystems to captive animal care. It incorporates true biological processes for the development of natural environmental contexts. Dr. Valerio Zupo’s "Empirical Approach to Marine Aquarium Filtration” (Tropical Fish Hobbyist, August 2011) detailed a design that we attempted to replicate more than two years ago.
Dr. Zupo emphasized the importance of surface area within biological media in both aerobic and anaerobic modules. Her research confirmed through electron microscopy, a globular aerobic autotroph cultured efficiently within porous media, such as ceramic cylinders. A spaghetti-shaped anaerobe was discovered to be dominant on harder plastic surfaces, such as bio balls. She recommended a porous ceramic media in the aerobic module and the use of plastic bio balls in the anaerobic module (see diagram in Part 1). We did use bio balls in our anaerobic module, while keeping our present nitrifying media from our old system, which consisted of 60 percent bio balls and 40 percent porous beads.
In order for this system to work efficiently, Zupo emphasized proper biological flow. According to her, "The rate of water flow must be proportional to the total volume of filter media” (Zupo, 2011). Zupo explained that velocity of flow is key; too fast may wash bacteria from media and too slow may not provide proper oxygen to culture efficient growth. She calculated laminar flow by liters/cm²/hour (or gallons/in²/hour). Take the gph of the water flow entering divided by the cross-section of the surface area. I deciphered proper flow rate should be around 6 - 12/in²/hour in our own application of the system.
We did not notice any change of nitrification as parameters continued to remain stable at zero ammonia and zero nitrite. Denitrification results occurred approximately four to six months later; nitrate levels dropped and remained consistent at 20 - 50 ppm. Around the two-month mark, we noticed a significant difference in water clarity. Our redox potential (ORP) started at 210 when the filtration was installed and slowly climbed to 300 over the first year. We did not alter our gravel-vacuum and water-change regimens when we transitioned to the new system. I believe our denitrification efficiency could be improved if we change the media contained in our aerobic chamber to one that is more porous and exhibits a higher surface area as Zupo suggests. We are in the process of evaluating oxygen levels entering and exiting chamber one. We believe that lowering chamber one to the same height as chamber two will improve our oxygen depletion rate exiting the aerobic module. This would increase our anaerobic module’s efficiency of denitrification.
Overall, we have been pleased with the results so far. We are still reviewing Zupo’s "Empirical Approach to Marine Aquarium Filtration” article in hopes of balancing our seawater biologically in an effort to simulate the natural environment of our fish.
Remember, the more aerobic microbe growth that occurs in module one, the lower the oxygen in the water entering the de-nitrification chamber.
Zupo, Valerio PhD. Aquarium Science: An Empirical Approach to Marine Aquarium Filtration.
Tropical Fish Hobbyist. August 2011.
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