Nitrate Accumulation and Removal
through Sulfur Denitrification in
Georgia Aquarium’s Ocean Voyager
Georgia Aquarium’s Ocean Voyager is a 6.3 million gallon recirculating saltwater exhibit housing whale sharks and manta rays, among many other species. The system has been in continuous operation for over ten years, during which there has been a significant nitrate accumulation. Although sulfur denitrification was part of the original exhibit design, the reactors had a variety of challenges which ultimately prevented them from being effective. Water changes were also ineffective due to cost and logistical restrictions. In early 2015, the original OV denitrification system was completely dismantled and rebuilt using a new design influenced by years of trials and experimentation. Key elements include careful reactor size determination, vertical vessels with recirculating flow, and aragonite in the sulfur chambers. During two years of operation, the OV sulfur denitrification system has dropped nitrate levels from approximately 180mg/L NO3-N to under 60mg/L.
Microbes, Biofilms, Fish and The Environment …
It’s not Just About the Biofilter!
M. Andrew Stamper,
The Seas with Nemo and Friends,
Walt Disney World Resort
In every milliliter of surface seawater, there are 0.5 to 1 million bacteria and 10 million viruses. They are also found on every surface and comprise very complex ecosystems called biofilms. For those who think in terms of bacteria associated with biofiltration as “good” and pathogens as “bad,” the relationships are much more complex. Unfortunately, culturing bacteria which only identifies < 1% of the bacteria in water has greatly limited our understanding of microbes in the environment. Current technologies such as qPCR are quickly developing and are demonstrating a vastly diverse microbial ecosystem. A managed system tested by the author demonstrated over 890 genera and over 2,500 species of bacteria which only accounted for 69% of the bacterial DNA; the rest unidentified. Microbes occur in two realms: planktonic and sessile. The planktonic state is fairly straightforward, whereas the sessile biofilm ecology is extremely complex. Biofilms include organisms beyond bacteria and comprise fungi, algae, protozoans, and metazoans. An intricate ecologic process occurs as various environmental parameters change. These organisms secrete an assortment of chemicals known as extracellular polymeric substances (EPSs), which add to the total organic carbon (TOC) within the water column and are critical to the health of the organisms and water environment. Many factors influence the number and types of microbes in the environment. There have been several papers published on the effects of chemicals on the biofilter and this is the most important consideration when adding therapeutic agents to water. It is important to know that most, if not all, of these drug interactions are dose dependent and affect the biofilter’s efficiency to varying degrees; they should not be considered as having an all-or-nothing relationship. On the flipside, drugs can also be digested/converted by microbes as a food source. When controlling an environment like the aquarium industry’s current standards, millions of bacterial species are starved into inactivity. These bacteria, although they may not be obvious, could still exploit any limiting nutrient sources, whether it is ammonia, nitrite, phosphorus or carbon. This also applies to other nutrients that might enter the water. Nutrients can be any molecule which includes the needed elements, including complex molecules such as therapeutics. When ingested internally, therapeutic agents are absorbed into the body which is, for the most part, a sterile environment. This is not the case when the same chemical is placed into a body of water. It is important to recognize the impact of microbes on chemicals, especially those with carbon chains and associated elements that may be nutrient sources. With the diversity of microbes in a water column, it is possible that one species will have an enzyme to break the chemical chains of the therapeutic and use it as a food resource. Therefore, it is important to invest in procedures for monitoring chemical concentration when treating animals. It is also important to recognize that there are different microbial communities in various institutions and even between tanks which will result in a variety of experiences by husbandry/water quality staff and clinicians.