Recirculating Aquaculture Systems | Biofiltration - episode 3

Summary

Dr. Sara Barento's tutorial on recirculating aquaculture systems focuses on biofiltration, a critical process for maintaining water quality. She explains the importance of managing total ammonia nitrogen (TAN), which includes both molecular ammonia and ammonium ions. The tutorial emphasizes the need to keep ammonia levels below 0.02 mg/L to prevent toxicity, and how pH affects the ratio of ammonia forms. Dr. Barento discusses the role of bacteria like Nitrosomonas and Nitrobacter in the nitrogen cycle, converting ammonia to nitrates, which are less harmful. She also highlights the importance of pH for bacterial activity and the use of different biofilter media to support bacterial growth and oxygen supply.

Takeaways

• 🐟 Fish excrete a mixture of ammonia (molecular form) and ammonium (cation form), which is collectively referred to as Total Ammonia Nitrogen (TAN).
• 🔍 The molecular form of ammonia is the main concern, as it can become toxic to fish at levels as low as 0.02 milligrams per liter, depending on the species.
• 🌡️ The pH level significantly affects the toxicity of ammonia; as pH increases, the molecular form of ammonia becomes more prevalent, thus more toxic.
• 🛠️ Biofilters are essential in recirculating aquaculture systems, providing a surface for bacteria to oxidize ammonia through the natural nitrogen cycle.
• 🌱 Chemoautotrophic bacteria, like Nitrosomonas, play a crucial role in converting ammonia into nitrate by adding oxygen to the ammonia molecule.
• 🔄 Another strain of bacteria, Nitrobacter, further oxidizes nitrates into nitrogen gas, which is less toxic and can be safely released into the environment.
• 📉 To maintain a healthy system, ammonia levels should be kept below 0.1 milligrams per liter, while nitrates should be below 2.5 milligrams per liter.
• 💧 Water exchanges are necessary to remove excess nitrates if they exceed safe levels, ensuring the biofilter operates efficiently.
• 📊 The percentage of the molecular form of ammonia in the water increases with both temperature and pH, impacting the biofilter's effectiveness.
• 🏗️ Different types of surfaces, such as plastic discs or fixed pad biofilters, can be used to enhance the settlement and activity of beneficial bacteria.

Q & A

What is the main topic of the tutorial presented by Dr. Sara Barento?

The main topic of the tutorial is biofiltration in recirculating aquaculture systems.

What are the two forms of ammonia excreted by fish into the water?

Fish excrete ammonia in two forms: molecular form and cation form, which are also known as ammonium.

What is the total ammonia nitrogen (TAN) and why is it important?

Total ammonia nitrogen (TAN) is the combination of ammonia in the molecular form and ammonium in the cation form. It is important because it indicates the overall ammonia levels in the water, which can be toxic to fish if not managed properly.

How does pH affect the toxicity of ammonia in the water?

As the pH increases, the molecular form of ammonia increases, which is more toxic, while the less toxic ammonium form decreases.

What is the ideal pH range for the biofilter to operate effectively?

The ideal pH range for the biofilter to operate effectively is a minimum of 7.

What are the toxic levels of ammonia and nitrates that should be maintained in the water?

Ammonia levels should be kept below 0.02 milligrams per liter, and nitrates should be kept below 2.5 milligrams per liter to avoid toxicity.

What is the role of the bacteria Nitrosomonas in the biofilter?

Nitrosomonas is a chemoautotrophic bacteria that oxidizes ammonia by adding a molecule of oxygen, converting it into nitrite.

What is the role of the bacteria Nitrobacter in the biofilter?

Nitrobacter is a bacteria that further oxidizes nitrite by adding oxygen, converting it into nitrate, which is less toxic.

Why is it important to maintain low levels of nitrates in the system?

Although nitrates are less toxic compared to ammonia and nitrite, they still need to be kept below 200 milligrams per liter to ensure the health of the fish.

How does the biofilter start the process of oxidizing ammonia?

The biofilter starts by providing a surface for bacteria like Nitrosomonas to grow and oxidize ammonia to nitrite, which is then further oxidized to nitrate by Nitrobacter.

What types of surfaces can be used to improve the settlement of bacteria in a biofilter?

Different types of surfaces can be used, such as plastic discs with grooves to increase surface area, or fixed pad biofilters, to facilitate the growth of bacteria necessary for the nitrogen cycle.