UNDERSTANDING THE NITROGEN CYCLE
Symbiosis,
The foundation on which everything is built.
Aquaponics would not be possible without the symbiotic relationship of every component involved.
The fish create waste, the waste creates ammonia, the ammonia is food for 2 types of beneficial bacteria, the bacteria waste is food for the plants, plants consume nitrates and phosphates, then return clean water to the fish. Sounds simple enough right?
The process begins with what is known as the nitrogen cycle. Most Auaponics instruction classes or courses describe it like this.
When our fish eat and breathe they produce waste in the form of ammonia.
The ammonia then stimulates the growth of colonies of bacteria called Nitrosomonas. These bacteria feed on the ammonia and produce Nitrite as a waste byproduct.
Both Ammonia and Nitrite can be poisonous to the fish, however another form of bacterial called Nitrobacter will come along and colonize the system to consume the nitrites. These bacteria produce a waste byproduct of Nitrate.
And this is where our plants come in. plants consume the nitrates along with a host of other nutrients. This has the effect of removing ammonia, nitrite, and nitrates from our water. The water is then returned to the fish tank to a happy group of fish.
Ammonia is not only produced from the fish directly, but also is produced from decaying organic matter. There will always be some decaying matter in your system, whether its from fish waste, dead bacteria, dead algae, or un-eaten fish food.
Ammonia is the first thing that we must regulate to keep our fish healthy.
In aquariums or aquaculture systems mechanical filtration mechanism are employed including resins and ammonia absorbing materials in order to eliminate ammonia, nitrite, and nitrate.
However, in aquaponics, we want SOME ammonia waste to feed our other symbiotic organisms. We just have to make sure in the beginning that ammonia doesn’t get out of control and hurt our fish. So when we start up a new system we have to test for and watch ammonia levels to keep them from getting too high. This can be done in a number of ways, which we will discuss in detail later.
We want our system to mimic nature as much as possible, therefore we will encourage natural process to take place instead of eliminating them.
Ammonia is the first thing you need to get your system started.
This cycle occurs in soil based systems as well, the bacteria colonies grow naturally in a wide host of mediums, including soil. This is the driving force behind composting. Bacteria cultures break down the organic matter into basic mineral compounds that can readily be absorbed by the plants.
For more details on the science you can visit these sites and learn more about the nitrogen cycle. Again our focus is aquaponics and I don’t want to digress into pages of detail, as before I would encourage you to learn more about the subject, but an extremely detailed knowledge is not absolutely required for our purposes.
https://eo.ucar.edu/kids/green/cycles7.htm
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/NitrogenCycle.html
http://en.wikipedia.org/wiki/Nitrogen_cycle
When the bacteria culture has established itself In an aquaponics system it is said to have “cycled”. Our goal is to get the new system cycled as quickly and effectively as possible. This can be done in a number of ways, We will discuss the best ways I have found in the chapter on cycling.
Now that you have gotten your feet wet lets get into a little more detail.
I want to describe a basic scenario and how the nitrogen cycle works in the system. We will get into more detail as we go but for now I want to get the basics across to you and explain how each functions in the cycle.
I have seen dozens of systems being promoted that look like this..
The idea behind this arrangement is that fish waste water is pumped to the growbed and the growbed media acts as a filter for the water, catching solid waste and cultivating our beneficial bacterial. The plants grow and absorb the nutrients left behind and walla.. clean filtered water drains back to the fish tank from a gravity fed bell siphon. Simple right? Well, lets look a little closer.
Right now lets just look at strictly the nitrogen cycle side of things.
In order for the bacteria to thrive they need a place to grow. The beneficial bacteria like to take up residence on a surface area where water, oxygen, and ammonia are in abundant supply. So naturally the thinking is that the grow bed is the perfect place for these beneficial bacterial.
Fish waste water is pumped directly to the grow bed media. Solid fish poo gets sucked up into the pump and dumped into the media grow bed. When waste water is put into these beds lots of ammonia is present. The grow bed media provides lots and lots of surface area for the bacteria to colonize and grow. And just like that, you have an ecosystem. Looks like an easy simple setup right?
The Problem is, Solids take much longer to beak down than liquid borne ammonias and nitrates, so you wind up with solids settling in the bottom of your grow bed. While some organisms like worms thrive on these solids, plants can’t deal with them. Plants only absorb nutrients in a liquefied or gaseous state. And unlike leaves, plant roots absorb oxygen, not carbon dioxide. Solids collecting around our roots choke off the oxygen and limit the nutrient flow to the root system of the plant. This is where another aspect of the nitrogen cycle comes into play.
The beneficial bacteria that we want, depend on oxygen to thrive and survive. But in any waste system with organic matter breaking down there will also be present a certain amount of bacterial that do not depend on oxygen. These bacterial are known as anaerobic bacteria.
These bacteria live in soil and aquatic sediment and rob the oxygen zone away from the aerobic (oxygen loving) bacteria. These bacteria thrive and multiply rapidly in areas where solid organic waste is present.
What this does is establishes zones in your grow bed.
The first zone is the dry zone, or area that is not touched by the water of the system, the second is called the biological zone, and the third is called the sludge zone by many groups who teach aquaponics.
This is way the zones are commonly portrayed.
Problem is the sludge zone isn’t just sludge, its full of solid fish waste and cultivates yet another biological zone. This third biological zone is where many problems arise with new systems. The third zone or “sludge zone” is where the anaerobic bacteria live.
This zone rapidly grows until it takes over the other oxygen loving zone and chokes out the roots of the plants. At some point, depending on your fish density, your grow bed will become a septic tank field line, where nothing but nasty bacteria grow.
This anaerobic bacteria is rarely given much more than a foot note in most educational books and courses on aquaponics. The fact is this arrangement will likely lead you down a bad road. One day everything is lush and green the next, every thing is wilted, brown, covered in mold, bugs, and the fish water is green with an awful sewage stink.
I had this very same exact scenario happen to me because I did not know how to deal with the solid fish waste. In fact I didn’t know I needed to. I was going under the impression given to me in the courses, that the fish waste would readily break down in the grow bed and provide the nutrients the plants needed.
After all, we have all seen how the grass grows lush and green over the septic tank field lines right?
Only thing is that the oxygen rich soil on top of those field lines are wicking up the nutrients being broken down by the anaerobic bacteria. If you were to plant directly into the gravel right next to the “sludge” in the field lines your plant would wither and die pretty quickly. This situation also encourages growth of numerous molds, and nasty insect colonies that are difficult if not impossible to eradicate.
In multiple “courses” I purchased this was never mentioned. They talked about the nitrogen cycle and how everything works together, and one even mentioned the anaerobic bacteria, but failed to mention that it would take over your system, or that something could be done to prevent it.
So now when I see someone promoting this arrangement I just shutter. Because chances are when you build this setup your doomed to have it crash on you, left unchecked it WILL go septic.
Any talk about the nitrogen cycle WITHOUT a good discussion about the anaerobic component will leave you woefully ill equipped to build a system that will last, without constant maintaince. Unless you just like the idea of sticking your hands down into and flushing out hundreds of gallons of raw sewage 2 times per year, then you should consider a different strategy.
Why anyone would leave this information out is beyond me. Maybe the thinking is it would reduce sales, or maybe they simply want to maintain some mystique about being an aquaponics GURU, I can’t say. The only thing I know is that if you want to learn aquaponics, You should be aware of this pit fall early on. The way to avoid it is fairly simple, but not if you don’t know it exists.
Unfortunately most just simply skip over this information and jump straight into “the build”. Many times the “build” omits the critical step to avoid this situation.
Now that we know there is a nasty side of the nitrogen cycle, we will want to minimize the anaerobic zone in our grow beds. We cant get rid of it completely, nor would we need or want to, we simply need to keep most of the “sludge” where it belongs, and that’s not in the bottom of our grow bed. There will always be some “sludge” accumulation in our grow beds. However we can manage it in such a way as to keep it to a bare minimum.
With our new found knowledge lets look at the nitrogen cycle again, except this time lets add in the anaerobic component.
There are many minerals and nutrients locked up in our fish waste. The nitrogen cycle breaks down and releases those minerals, and nutrients that other organisms use as food.
There are a number of ways this occurs.
Continued in part 2