Bacteria in aquaponics
Unwanted bacteria
Sulphate reducing bacteria Nitrifying and mineralizing bacteria are useful to aquaponic systems, but some other types of bacteria are harmful. One of these harmful groups of bacteria is the sulphate- reducing group. These bacteria are found in anaerobic conditions (no oxygen), where they obtain energy through a redox reaction using sulphur. The problem is that this process produces hydrogen sulphide (H2S), which is extremely toxic to fish. These bacteria are common, found in lakes, saltmarshes and estuaries around the world, and are part of the natural sulphur cycle.
· Food and Agriculture Organization of the United NationsSystem cycling and starting a biofilter colony
System cycling is a term that describes the initial process of building a bacterial colony when first starting any RAS, including an aquaponic unit. Under normal circumstances, this takes 3-5 weeks; cycling is a slow process that requires patience. Overall, the process involves constantly introducing an ammonia source into the aquaponic unit, feeding the new bacterial colony, and creating a biofilter. The progress is measured by monitoring the nitrogen levels. Generally, cycling takes place once an aquaponic system is built, but it is possible to give the biofilter a head start when creating a new aquaponic system.
· Food and Agriculture Organization of the United NationsNitrifying bacteria and the biofilter
Chapter 2 discussed the vital role of nitrifying bacteria in regard to the overall aquaponic process. The nitrifying bacteria convert the fish waste, which enters the system mainly as ammonia, into nitrate, which is fertilizer for the plants (Figure 5.1). This is a two- step process, and two separate groups of nitrifying bacteria are involved. The first step is converting ammonia to nitrite, which is done by the ammonia-oxidizing bacteria (AOB).
· Food and Agriculture Organization of the United NationsHeterotrophic bacteria and mineralization
There is another important bacteria group, as well as other micro-organisms, involved in aquaponics. This bacteria group is generally called the heterotrophic group. These bacteria utilize organic carbon as its food source, and are mainly involved in the decomposition of solid fish and plant waste. Most fish only retain 30-40 percent of the food they eat, meaning that 60-70 percent of what they eat is released as waste. Of this waste, 50-70 percent is dissolved waste released as ammonia.
· Food and Agriculture Organization of the United Nations