Posted: December 9, 2013, 12:35 p.m. EDT
By Patrick Donston
A few years ago, I read a fascinating article written by Valerio Zupo, Ph.D., regarding the development of a marine aquarium filter. Her main objectives were to design something that could handle "harsh” circumstances, efficiency in pollution degradation and withstand overpopulated environments. What interested me most were her key points:
• Oxygen saturation in relation to aerobic chemoautotrophs
• Biological flow, velocity calculation and "sloughing” problems
• Surface area and pore structure of media
• Aerobic bacteria reduction to bypass waste in order to fuel anaerobic growth in a two-chamber system
Although the article analyzes individual aquariums, her data used to substantiate her concerns motivated me to try this system on a larger scale. My marine system manager read the article; we set off to simulate Dr. Zupo’s filtration in our marine fish system.
Schematic Waterflow. Patrick Donston
I estimate our system to be approximately 5,000 gallons, stocked heavily with marine teleosts. Our old filtration supported enough aerobic chemoautotrophic bacteria that we never tested a traceable amount of ammonia or nitrite. In addition, we were always able to maintain a stable or consistent pH (generally 8.0-8.4). However effective the old system was, our nitrate readings slightly fluctuated between 80 and 120 ppm. Water changes and gravel vacuums simply did not cut it; our main objective with the new filtration system was to reduce organic pollutants and nitrate levels.
Dr. Zupo incorporates a two-chamber system in which the first chamber is devoted to oxidizing ammonia to nitrite and finally to nitrate. She calls this first chamber the "aerobic module,”; oxygen must be at saturation as water enters the top and vertically flows to the bottom through the biomedia. The second chamber (anaerobic module) fills from the bottom and continues to flow upward toward the exit at the top.
Water entering the second chamber should be depleted of oxygen if there are efficient aerobic microbes in the first. The anaerobic module (second chamber) consists of nutrient enriched, slow water flow that is ideal for nitrate and organic phosphate reduction through living microbes. Water exiting the anaerobic chamber must pass through a final chemical media stage prior to being pumped back into the system (see diagram).
Dr. Zupo emphasizes that proper media usage and calculation of water flow is key to the performance of the filtration system. The importance of having the two modules connected or running in series is paramount to the success of the filter. Only after the oxygen is efficiently depleted from the water in the first chamber can the leftover organic biowaste accentuate bacterial growth in the second. The pore structure of media will be advantageous to specific strains of bacteria; thus media in both chambers should be different.
In my next blog, I will review Dr. Zupo’s filter design and how we interpreted its use, design and results.
Zupo, Valerio Ph.D. Aquarium Science: An Empirical Approach to Marine Aquarium Filtration. Tropical Fish Hobbyist. August, 2011.
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