What is the difference between nitrification and mineralization?

A client recently asked us to explain the difference between nitrification and mineralization, two very important processes in aquaponics.  Nitrification is essential for fish health, because it converts ammonia to nitrite and then nitrite to nitrate.  Both ammonia and nitrite are toxic to fish at low levels, so there is a great deal of discussion about nitrification related to keeping fish healthy.  Nitrification also generates the nitrogen our plants need to grow.  Mineralization is critical in aquaponics because it is the process in which all of the other minerals are generated from the fish waste.

Nitrification and mineralization are two separate processes. Nitrification is the oxidation (conversion) of ammonia to nitrite to nitrate.  It is only done by nitrifying bacteria (nitrosomonas and nitrobacter) in aerobic conditions.  Nitrification happens throughout the system, on all surface areas and in the water column.  In our Clear Flow Aquaponic Systems®, we provide very specific habitat for the nitrifying bacteria to live and thrive.  Nitrification decreases alkalinity and pH because the process naturally produces nitric acid.  The nitrogen for plant growth comes from nitrification.

There is a converse process happening called de-nitrification, which reduces overall nitrogen levels. De-nitrification happens in anaerobic conditions. In our systems, we allow de-nitrification to happen in the mineralization tanks. As pockets of material build up, de-nitrification begins to occur, resulting in an increase of alkalinity and an off gas of nitrogen gas. The amount of de-nitrification you allow to occur will directly affect the amount of nitrogen you have in relation to all other elements.  When growing vegetative plants, you want a higher ratio of nitrogen, so you can clean the netting more frequently.  When growing fruiting plants, you want a lower ratio of nitrogen so you clean the netting less frequently.

We use de-nitrification to our advantage, as needed, to maintain the ratio of nitrogen to other elements in the range that is most appropriate for the types of crops we are growing.

Mineralization is the breakdown of organic matter into individual elements (macro nutrients like potassium, calcium, sulfate, phosphorous, magnesium and micro nutrients like iron, copper, molybdenum, zinc, etc). Mineralization is done by heterotrophic bacteria in anaerobic conditions.  In our Clear Flow Aquaponic Systems®, the netting in the mineralization tank serves as a means of collection of the fine suspended solids.   We do not aerate this tank to encourage heterotrophic bacteria to thrive and break down the solids into all of the elements the plants need. The dwell time in that tank gives the heterotrophs time to break down the solids.  What is released are the actual elements (minerals) that the plants need.

Both nitrifying and heterotrophic bacteria exist everywhere and do these same processes whether in the water or soil.