Here we go again with, yet another effective tool for minimizing nitrate levels in a marine aquarium setting. The sulfur reactor, otherwise known as Autotrophic sulfur denitration has gained great popularity in Europe and deals with eliminating nitrates through the use of a sulfur based medium and autotrophic bacteria. This system works along the same line as the vodka scenario dealt with in a past article of mine.
Sulfur acts as a food source, similar to the ethanol found in vodka, a carbon source, and supplies the energy needed by the autotrophic bacteria. Under aerobic conditions the bacteria uses oxygen to carry out the process whereas under anoxic conditions, bacteria oxidize various forms of sulfur to sulfates which reduces the nitrate level in a marine or freshwater aquarium. This is unique and and effective means of eliminating or at least reducing the amount of nitrate in both fresh and saltwater aquariums. By incorporating bacteria, which isn’t soluble in water, to colonize in the substrate without any other energy source, the sulfur is able to be consumed slowly over the course of time to consistently reduce nitrates.
Professor Guy Martin is credited with the development and use of elemental sulfur and autotrophic bacteria to eliminate nitrates from drinking water. By 1991 a past student of Guy Martin was credited with taking this method one step further and incorporated this procedure to saltwater, Not knowing the consequences of toxic effects carried out in the aquarium, to his surprise no recordable negative implications were evident. As mentioned above the sulfur denitrator, unlike those employed with heterotrophic denitrification, is able to work without an external source of carbon(IE. methanol or ethanol) being added to carry out this process making this a much easier approach to negating nitrates in aquarium water.
The only drawback to the employment of a sulfur reactor to an aquarium functionality is the fact that an emergence of low pH will develop probably as a result of excess hydrogen ions being released by this reaction. The fact that hydrogen ions combine with bicarbonate in aquarium water forming carbon dioxide may be another contributing factor in reduced pH of the water. To combat these effects a second chamber could be employed filled with calcareous gravel. This enables the effluent from the sulfur reactor to pass through the gravel to dissolve which will bring about an elevated pH. Incorporating a Kalkwasser solution into the mix will also promote a higher pH level to combat the reduced pH brought on by the sulfur reactor, since the pH level of kalkwasser is around 12. Increasing the amount of dissolved oxygen to tank water will also help to raise the pH. Simply by increasing the surface agitation by a powerhead at the waters surface will increase the gas exchange of carbon dioxide to oxygen to help with the stability of pH and the effectiveness and beneficial importance of running a sulfur reactor.
The establishment of a sulfur reactor is fairly easy to achieve. A chamber filled with sulfur beads, which can be purchased through the wine making industry. The water runs through this chamber in a reverse flow which is beneficial for two reasons. The first being that it reduces the likelihood of the chamber clogging due to the degrading of the beads over time. Also this set up helps to rid the chamber of nitrogen gas into the atmosphere. Because of this second scenario, it is pertinent that the unit not be airtight to afford the release of the nitrogen gas. the unit should be roughly five times taller than its diameter. The reasons for this are autotrophic bacteria will not break down nitrates until the oxygen within the chamber is almost depleted so contact time, flow rate and reactor height are very important. A columnar fluidized filter works exceptionally well and is easy to come by. Fluidized sand bed filters and even a phosphate reactor will work well since they work from the bottom up and are excessively taller than they are wide. This is where a second chamber should be employed to combat the lower pH evident as an end product of this process. This chamber, again, will be comprised of a calcareous gravel to raise pH and retain sulfate. Incorporating a ball or gate valve will allow you to monitor and adjust the flow rate inside the chambers for the best efficiency and effectiveness of the filter. The volume of the sulfur beads should be about 1% of the total volume of water in the aquarium. If extremely high levels of nitrate exist(>50mg/L a 2% amount of sulfur beads can be employed but this usually requires a larger reactor or multiple reactors being used. Performing a water change will also help to bring down the amount of nitrates in the aquarium to help aid the sulfur reactor.
If flow rate is to fast the nitrates will pass right through the filter back into your aquarium. If the flow rate is too slow, the water exiting the filter will smell like hydrogen sulfide(rotten egg smell). If the water flow is right on, nitrate reading will soon read zero!!!! Periodically purging the unit by increasing the water flow through the unit will ensure that the unit doesn’t get clogged over time. You will notice this by the hydrogen sulfide smell in your living room, which will not be very appealing. This will flush the effluent from inside the chambers to ensure that it is running at its full potential. Simply running the increased water flow through the filter and into a bucket will help to remove sediment that is reducing the flow and efficiency of the unit.
So, once again you have another means in which to help to maintain a beautiful and successful salt or freshwater aquarium, by reducing nitrates that can spur unwanted algae blooms that can mess up an aquarium in no time. Not to mention that these elevated nutrient levels contradict those wanting to maintain a reef aquarium surrounded by hermatypic small polyped stony corals.