Biofiltration is the process of utilising bacteria to convert fish wastes into plant food. Biofilters are used to maintain a healthy water quality in your system allowing for the same water to be recycled over and over. There are many different types of bio filters and they rely on certain environmental conditions to flourish. This blog post explores the fundamentals behind maintaining a healthy bio filter and then goes on to highlight some of the options for gardening aquaponically on a very small scale (standard fish tank up to 300l). It must be remembered that biofiltration works best alongside some form of mechanical filtration.
Biological Surface Area
Your bacteria need a place to live and therefore the greater the biological surface the more nutrients your system can process. Therefore in order to have a compact small scale aquaponics system your biological filtration needs to be very efficient. Choosing a media that maximizes the surface area to volume ratio gives you the best chance of achieving this result.
The rate at which a colony of nitrifying bacteria can oxidize ammonia is dependent on the amount of oxygen that is available to your bacteria. Oxygen can be introduced to your system via numerous techniques (see dissolved oxygen in aquaponics) however some biofilter designs will incorporate an aeration component.
Temperature also has an influence over the de-nitrification process. The bacteria that do the work in a biofilter are only active over about 18°C. Therefore a steady/warmer water temperature is going to yield much better results in your system. If your water temperature climbs too high this too can have a negative impact on your bacteria. At higher temperatures there is less dissolved oxygen in your water and therefore less oxidation of ammonia occuring. Other factors like pH and a water flow/contact time will also play a role in biofiltration.
The standard approach to biofiltration in aquaponics is to rely on your growbed to process the nutrients. A media filled bed to a depth of 300mm will provide ample solids and bio-filtration (see grow bed depth). In order to run a successful nft or deep water culture system however additional biofiltration may be requried. This is also the case if you want to drastically reduce the size and subsequent cost of your media bed system.
I think that we are going to see some huge advances in how biofiltration is tackled in small scale aquaponics systems. There has already been so much work go into this for small scale aquariums and many of the principles are the same. It won’t be long before more of these techniques are adopted in balcony systems, enabling greater design flexibility and opening aquaponics up to a greater number of people. My next blog post is going to cover some aquarium filter designs that offer up a huge opportunity in this area.