Bacteria in Aquaponics: Basic Relations and Functions

Bacteria play a vital role in the process of aquaponics, a type of sustainable agriculture system that combines raising fish and growing plants.

Bacteria are essential for breaking down the waste produced by fish, converting it into nutrients that can be used to fertilize plants.

Aquaponic systems rely on an equilibrium between beneficial bacteria and other microorganisms to create a healthy, balanced environment for both fish and plants.

Bacteria in aquaponics system
Image: Bacteria in aquaponics system

Bacteria in Aquaponics

Bacteria are single-celled microorganisms that play an important role in the aquaponics system.

The makeup and well-being of the system’s microbiota determine the growth rates, welfare, and quality production of the plant in aquaponics systems.

They play a crucial role in aquaponics, which is a system that combines aquaculture (raising aquatic animals such as fish) with hydroponics (growing plants in water).

In this system, fish waste provides nutrients for the plants, while the plants filter the water for the fish.

Bacteria are responsible for breaking down the fish waste into forms that the plants can use.

Fish excrete ammonia, which is toxic to both fish and plants in high concentrations.

However, beneficial bacteria called nitrifying bacteria convert the ammonia into nitrite and then into nitrate, which is a form of nitrogen that plants can absorb and use for growth.

In addition to the nitrifying bacteria, there are also other types of beneficial bacteria that help to break down organic matter in the system, such as dead plant material and uneaten fish food.

Microbial communities are crucial to the denitrification and mineralization techniques as well as the system’s overall production, which includes the well-being of fish and the condition of plants.

Factors Affecting Bacterial Activity in Aquaponics Systems

There are several factors that can affect bacterial activity in aquaponics systems. The following are some of the factors that can affect bacterial activity in aquaponics systems:

Water Temperature

Bacterial activity is influenced by water temperature, with warmer water generally leading to faster bacterial growth and activity. However, extreme temperatures can also negatively impact bacterial activity.

Water temperature is a critical factor in aquaponics systems as it affects the growth and health of fish, plants, and microorganisms, and influences the dissolved oxygen content.

Raising the water temperature can increase cellular metabolism and TAN concentration, but nitrification is most effective at temperatures between 25-30 °C, with AOB populations expanding more quickly than NOB.

Sudden temperature changes from 20 to 10 °C can reduce nitrification rates by an average of 58%, and temperature variation can impact bacterial behavior in nitrogen removal systems.

pH Level

In aquaponics systems, pH is a crucial factor in controlling microbial activity, and it must be maintained within a range that is best for fish, plants, and bacteria.

Bacteria have specific pH requirements for optimal growth and activity. In aquaponics systems, a pH range of 6.8 to 7.2 is generally recommended for nitrifying bacteria, which convert fish waste into forms that plants can use.

Nitrifying bacteria prefer pH values above 7.5, with pH values below 6.0 and over 9.0 inhibiting NH4+ oxidation.

Low pH levels (pH 5.2 to 6.0) adversely affect nitrifying bacteria, reduce nitrification, increase N2O emission, and stress fish.

The most prevalent nitrifying bacteria in aquaponics, Nitrosomonas and Nitrobacter, have pH tolerance ranges of 7.2-7.8 and 7.2-8.2, respectively.

A balance between nitrification and nutrient availability is achieved by keeping pH within the range of 6.5-7.0 in aquaponics systems, although it is impossible to obtain an ideal pH for fish, bacteria, and plants in these systems.

Dissolved Oxygen Levels

Bacteria require oxygen to carry out their metabolic processes. Low dissolved oxygen levels can lead to reduced bacterial activity and even death of the bacteria.

In aquaponics systems, maintaining a sufficient level of dissolved oxygen (DO) is crucial for efficient nitrification and the health and growth of fish and plants.

Aeration is often used to regulate DO levels, and maintaining DO concentrations over 5 mg/L is essential for the activity of several bacteria.

In systems with high fish populations, it is particularly important to maintain DO levels of 5 mg/L to counteract the metabolic activity of fish and aerobic microorganisms, which can deplete DO content.

Low DO levels can negatively impact root respiration, reduce water and nutrient intake, and increase the risk of plant root infections.

Ammonia Levels

Ammonia is the primary source of nitrogen for nitrifying bacteria. However, high levels of ammonia can be toxic to both fish and bacteria, leading to reduced bacterial activity.

Organic Matter Accumulation

Organic matter such as uneaten fish food and dead plant material can accumulate in the system and reduce bacterial activity by consuming oxygen and creating an environment for harmful bacteria to grow.

Chemicals and Contaminants

Certain chemicals and contaminants can be harmful to beneficial bacteria, leading to reduced bacterial activity and even death of the bacteria.

Overall, maintaining optimal conditions for bacterial growth and activity is essential for a healthy and productive aquaponics system.

This involves monitoring and adjusting water temperature, pH, dissolved oxygen levels, and ammonia levels, as well as minimizing the accumulation of organic matter and avoiding exposure to harmful chemicals and contaminants.

Role of Nitrifying Bacteria in Aquaponics

Nitrifying bacteria play a critical role in aquaponics systems by converting toxic ammonia (NH3) produced by fish waste into nitrite (NO2-) and then into nitrate (NO3-), which can be taken up by plants as a source of nutrients.

The two main types of nitrifying bacteria involved in this process are Nitrosomonas and Nitrobacter. Nitrosomonas bacteria convert ammonia into nitrite, and Nitrobacter bacteria then convert nitrite into nitrate.

The activity of nitrifying bacteria is influenced by several factors, including water temperature, pH, dissolved oxygen levels, and the presence of inhibitory substances such as chlorine or pesticides.

Therefore, it is crucial to maintain optimal conditions for nitrifying bacteria in aquaponics systems to ensure efficient nitrification and maintain water quality.

Proper management of nitrifying bacteria is essential to promote healthy plant growth, prevent the accumulation of harmful substances, and maintain a balanced ecosystem in aquaponics systems.

Nitrogen Cycle: Steps of Nitrification

The nitrification process is a biological process that occurs in aquaponics systems, converting toxic ammonia (NH3) produced by fish waste into nitrate (NO3-), which can be taken up by plants as a nutrient source.

The process occurs in two main steps:

Step 1: Ammonia Oxidation

The first step of nitrification involves the conversion of ammonia into nitrite by bacteria called Nitrosomonas. This reaction is carried out in two stages:

1.1. NH3 is oxidized to hydroxylamine (NH2OH) by an enzyme called ammonia monooxygenase (AMO).

1.2. Hydroxylamine (NH2OH) is further oxidized to nitrite (NO2-) by another enzyme called hydroxylamine oxidoreductase (HAO).

The overall reaction can be represented as:

NH3 + 1.5 O2 → NO2- + H2O + 2H+

Step 2: Nitrite Oxidation

The second step of nitrification involves the conversion of nitrite into nitrate by bacteria called Nitrobacter. This reaction is carried out in one step:

2.1. Nitrite (NO2-) is oxidized to nitrate (NO3-) by an enzyme called nitrite oxidoreductase (NXR):

NO2- + 0.5 O2 → NO3-

The nitrification process is a critical biological process in aquaponics systems that helps to maintain water quality and provide essential nutrients for plant growth.

Proper management of nitrifying bacteria is crucial to ensure efficient nitrification and maintain a balanced ecosystem in aquaponics systems.


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