This page has been developed to give you a lot of valuable general information about nitrates, the nitrogen cycle, and the denitrification process.  

If you specifically want to learn more about and look at aquarium nitrate reactors go to the Denitrators / Nitrate Reactors web page.

The Nitrogen Cycle

Lets start with some basic facts. Every living thing is composed of only a few primary elements. Other elements are only present in minute trace amounts. The most common organic elements are oxygen, carbon, hydrogen and nitrogen. Together, these atoms form 96.3% of the Human body by weight. There are a handful of other elements that are commonly found in living animals such as sulfur, phosphorus, calcium, sodium, magnesium, and potassium. These elements compose the building blocks for our organic molecules, like proteins, sugars, fats, and genetic material. These elements also consist of ions needed for common organic processes, like nerve cells communicating with each other or moving muscles.

Bacteria eventually break all of the complex proteins and molecules in a living organism down back to its basic elements. This is part of the cycle of life. Most of this is done by aerobic (with oxygen) bacteria. The most abundant end products of aerobic bacteria are carbon dioxide, water, nitrates and nitrites, sulfates, and phosphates. This corresponds to the top 6 elements in the body: oxygen, carbon, hydrogen, nitrogen, sulfur, and phosphorus respectively. The top three elements are not a problem at all as they are simply converted to carbon dioxide, oxygen gas and water. Sulfur and phosphorus are not much of a problem either as they are present in much, much lower quantities as nitrogen. Also, sulfates and phosphates present much less of a problem and are less toxic than nitrates (unless perhaps you use a sulfur reactor and artificially pump vast amounts of sulfates into the tank.) Only nitrogen in the form of the seemingly ever present nitrates present a real problem.

800px-Nitrogen_Cycle_svgIn a natural and balanced ecosystem, plants will use up most of the nitrates and available and then animals eat the plants and the cycle begins again.  The nitrates that the plants do not absorb are reduced to nitrogen gas by a process called denitrification.  This is commonly called the Nitrogen Cycle and is represented in the image to the left.  You can see the denitrification process is just one part of the nitrate cycle.


Denitrification reduces nitrates and nitrites to nitrogen gas, which returns to the air.  In a sense it is the reverse of the nitrification process in that several different species of bacteria are used in a multi-step process.

NitrificationWith the nitrification process one type of bacteria converts ammonia to nitrites and then another bacteria converts the nitrites to nitrates.  The reduction of nitrates via the denitrification process can only occur in very low oxygen conditions.  This is why it naturally occurs only underground or at the bottom of sediments in lakes and oceans.  They use nitrates as an alternative to oxygen in their cellular respiration (a process that helps the bacteria use energy.)  There are likely numerous different species of bacteria that will accomplish this in fresh, salt, and brackish water with possibly slightly different actions.  Basically one bacteria will convert the nitrates back into nitrites and then other bacteria will further break that down into nitrogen gas.  All of these bacteria and processes participate in closing the nitrogen cycle.

oceandeadzoneThis denitrification process is completely natural and occurs underground and in many areas at the bottoms of the worlds lakes and oceans.  Unfortunately, humans create far more nitrates than nature can normally absorb.  By far, the primary source of water pollution is nitrates.  There are dead zones thousands of square miles wide in waterways and oceans around the world where no fish can live due to nitrate pollution.  The inability of the natural denitrification processed to handle the nitrates we produce is a major concern throughout the world.

denitrification plant
denitrification plant

Fortunately, denitrification is becoming more commonly used to remove nitrogen from sewage, municipal, industrial, and agricultural wastewater to counteract the pollution.  Various types of denitrification reactors (aka denitrators) and methods are now used and are effective in removing nitrate from agricultural run off and even manure.  On a large scale some of the gas produced can even be burned for energy!  The process can also be used to break down many various dangerous industrial chemical compounds.  Carbon energy nutrient compounds are often added to the reactors just like with the Aquaripure denitrification reactor (aka Nitrate Removal Denitrator Filter.)

An aquarium is in many ways similar to a polluted body of water.  An aquarium is a man made system and it usually does not have enough plants, if any, to use up the available nitrates and high nitrates will inevitably climb and lead to algae problems. Most aquariums also have a higher concentration of fish than is found in nature which compounds the problems.

dead-fishNitrates that build up due to a lack of denitrification are less toxic than ammonia or nitrites, but they are still toxic to humans, animals and fish. The EPA maximum allowable nitrates in tap water is under 10 ppm. In humans it causes a condition called blue baby syndrome which is a very serious condition that develops in infants exposed to nitrates. It causes a similar condition in livestock and fish. The condition is caused because organisms tend to convert some of the nitrates back into nitrite which is extremely toxic. Nitrates are also a strong diuretic and effects the smooth muscles which is why they are used as medication for people with heart problems. They have many serious side effects in large doses. For example check out The EPA Consumer Factsheet on Nitrates. Fish will definitely feel adverse effects and become more stressed above 40 ppm which is very easy to reach in your average fish tank.

Denitrification with an Aquaripure Nitrate Filter

Small Aquaripure for tanks 15-50 gallons
Small Aquaripure for tanks 15-50 gallons

Fortunately, with the Aquaripure Nitrate Removal Filter Denitrator, there is now a natural, cost effective way to remove the nitrates from your tank using the anaerobic (without oxygen) denitrification process which breaks down the nitrates into nitrogen gas. Nitrates are much more of a problem than phosphates due to their greater toxicity and much greater abundance. Remember, it is the fourth most common element in the body.

The most common end products from the full denitrification process are mostly carbon dioxide and nitrogen, with trace amounts of methane and hydrogen sulfide. These are all gases and will be present in the effluent in small amounts. The nitrogen, methane, and hydrogen sulfide are not very soluble in water, much less so than oxygen and carbon dioxide.   This is actually very similar to water commonly found in underground wells where the water is aerated before use.  When the effluent is aerated through your normal tank circulation, all of the nitrogen, methane and hydrogen sulfide will be rapidly released into the atmosphere and replaced with oxygen.

All aquariums have enough water flow to aerate the water as the fish constantly use up oxygen in the water. If there were not adequate water flow the fish would suffocate. When the denitrator is used, the oxygen and carbon dioxide in the tank will balance each other out and the methane, nitrogen, and hydrogen sulfide will escape into the atmosphere. They will not build up or remain in the aquarium. The nitrates (NO3) are simply converted to gases during the denitrification process and then are released into the atmosphere.