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.

Outlines

00:00

🐟 Understanding Biofiltration in Aquaculture Systems

Dr. Sara Barento introduces the concept of biofiltration in recirculating aquaculture systems (RAS), focusing on the oxidation of ammonia. She explains that fish excrete ammonia, which exists in two forms: molecular and cationic, with the former being more toxic and increasing with higher pH levels. The goal is to maintain ammonia levels below 0.02 milligrams per liter to prevent toxicity. The biofilter, or endofilter, is a crucial component where bacteria perform the nitrogen cycle. Chemoautotrophic bacteria, such as Nitrosomonas, oxidize ammonia to nitrite, while Nitrobacter converts nitrite to less toxic nitrate. The efficiency of these bacteria is optimal at a pH of at least 7. High nitrate levels should be managed through water exchanges. The total ammonia nitrogen (TAN) is the sum of both ammonia forms, and its percentage in molecular form depends on temperature and pH. The tutorial emphasizes the importance of maintaining low ammonia levels and the right pH for the biofilter bacteria to function effectively.

05:02

🌡️ pH and Ammonia Toxicity in Aquaculture

This section delves into the relationship between pH and the toxicity of ammonia, highlighting the importance of maintaining a pH of at least 7 for the biofilter bacteria to oxidize ammonia effectively. The tutorial explains that at lower pH levels, the more toxic molecular form of ammonia is minimized, reducing the risk of toxicity. However, the pH must be balanced to ensure the biofilter's functionality. A graph is used to illustrate the maximum concentration of total ammonia nitrogen (TAN) that can be tolerated at different pH levels, emphasizing the need for vigilance as pH increases to keep ammonia levels low. The tutorial also discusses the initial stages of starting a biofilter, where ammonia levels rise as fish begin to excrete, and the subsequent oxidation process by bacteria. Different types of biofilter media, such as plastic discs and fixed pad biofilters, are mentioned, along with the necessity of oxygen for the bacteria to perform their oxidation tasks. The video concludes with a reminder of the importance of biofiltration in RAS and an invitation to explore more videos on the topic.

Keywords

💡Recirculating Aquaculture Systems (RAS)

Recirculating Aquaculture Systems (RAS) are a type of closed-loop aquaculture, where water is continuously recycled and treated within the system. This is a key concept in the video, as it sets the context for the discussion on biofiltration. The video explains that RAS components include a biofilter, which is crucial for maintaining water quality by managing the nitrogen cycle.

💡Biofiltration

Biofiltration is a critical process in RAS where harmful substances like ammonia are converted into less toxic forms by beneficial bacteria. The video tutorial focuses on this process, explaining how it is essential for the health of fish in the system. The biofilter provides a surface for bacteria to grow and oxidize ammonia.

💡Ammonia

Ammonia is a toxic byproduct of fish waste that is excreted into the water. The video discusses the importance of managing ammonia levels to prevent toxicity to fish. It exists in two forms: molecular (NH3) and ionic (NH4+), with the former being more toxic and its concentration influenced by pH.

💡Total Ammonia Nitrogen (TAN)

Total Ammonia Nitrogen (TAN) is a measure of the combined concentration of ammonia and ammonium in the water. The video emphasizes that maintaining TAN levels below 0.02 milligrams per liter is crucial for fish health. TAN is a significant parameter in RAS as it indicates the amount of nitrogenous waste that needs to be processed.

💡pH

pH is a measure of the acidity or alkalinity of water and plays a critical role in the biofiltration process. The video explains that as pH increases, the proportion of toxic molecular ammonia increases, which is why pH management is essential. A pH of at least 7 is necessary for the optimal functioning of the bacteria involved in the nitrogen cycle.

💡Nitrosomonas

Nitrosomonas is a genus of bacteria that plays a key role in the nitrogen cycle by oxidizing ammonia to nitrite. The video describes how these bacteria are essential in RAS biofilters, where they use ammonia and oxygen to produce nitrite, which is a step towards converting ammonia into less toxic forms.

💡Nitrobacter

Nitrobacter is another genus of bacteria crucial in the nitrogen cycle, which oxidizes nitrite to nitrate. The video explains that after Nitrosomonas converts ammonia to nitrite, Nitrobacter further processes it into nitrate, which is less toxic and can be more easily managed in the RAS.

💡Nitrates

Nitrates are the end product of the oxidation process of ammonia by Nitrosomonas and Nitrobacter. The video mentions that while nitrates are less toxic than ammonia, they still need to be kept below 2.5 milligrams per liter. High nitrate levels can be managed by water exchanges in RAS.

💡Oxidation

Oxidation, in the context of the video, refers to the chemical process where ammonia is converted to nitrite and then to nitrate by bacteria. This process is essential for detoxifying ammonia in RAS and maintaining a healthy environment for fish. The video highlights the importance of oxygen in this process, as bacteria require it to oxidize ammonia.

💡Surface Area

The surface area provided in a biofilter is crucial for the colonization of bacteria that perform the oxidation of ammonia. The video discusses different types of surfaces, such as plastic discs with grooves, which increase the surface area for bacteria to grow. A larger surface area allows for more bacteria to be present, enhancing the biofiltration process.

Highlights

Biofiltration is a key component of recirculating aquaculture systems.

Fish excrete ammonia in molecular and ammonium forms, totaling as Total Ammonia Nitrogen (TAN).

Ammonia toxicity in fish depends on pH, with higher pH increasing molecular ammonia.

Ideal TAN levels should be below 0.02 milligrams per liter for fish safety.

Biofilters support bacteria that perform the natural nitrogen cycle.

Chemoautotrophic bacteria like Nitrosomonas oxidize ammonia to nitrate.

Nitrobacter bacteria further convert nitrates into less toxic nitrates.

Optimal pH for biofilter bacteria operation is a minimum of 7.

Nitrates should be kept below 2.5 milligrams per liter for fish health.

Total ammonia nitrogen (TAN) includes both molecular ammonia and ammonium, with proportions affected by temperature and pH.

The biofilter startup involves an initial ammonia spike followed by a gradual decrease.

Different types of surfaces can be used to enhance bacteria settlement in biofilters.

Air supply is crucial for bacteria to oxidize ammonia.

Fixed pad biofilters are an alternative type of biofilter for recirculating systems.

Maintaining proper pH and TAN levels is essential for a balanced aquaculture system.

The tutorial provides insights into managing recirculating aquaculture systems for optimal fish health.

Transcripts

welcome to the recirculating aquaculture

systems tutorials i'm dr sara barento

and this tutorial is going to be about

biofiltration

in the previous tutorials we've been

discussing the different components of

recirculating aquaculture systems

today we're going to be focusing on the

biofilter and oxidation of ammonia

so the first thing you need to

understand is that the fish

excretes to the water a mixture of

ammonia in the molecular form and

ammonium in the cation form the

combination of these two is the total

ammonia as nitrogen

what's also called tan

so ammonia

the molecular form constitutes the main

part of this question but

this depends on the ph actually as the

ph increases

this ammonia molecular form increases

and the ammonium in cation form

decreases

what you really want to achieve is uh

you need to have

clear in mind that levels as low as 0.02

milligrams per liter can become toxic to

fish this will depend on the species

but as a rule of thumb you want to keep

these values below this amount

so what is the biofilter in the

endobiofilter is just a surface

where you're going to have bacteria that

will be doing the natural nitrogen cycle

so where ammonia is being oxidized by

this group of

chem autotrophic bacteria basically

chemical eaters

and as you know fish will be feeding

they will be excreting fecal matter and

then it and feed will also be

accumulating in the system

and most of what they're going to

excrete is going to be ammonia in this

molecular form

then you will need to have in your

system as the surface that will

facilitate the growth of this strain of

bacteria nitrosomonas

so that they can actually use the

ammonia and add a molecule of oxygen

oxidized ammonia and create this nitrate

molecule

and then you're going to have another

strain of bacteria the nitrobacter

which again what they do is they're

going to add oxygen to nitrates and

convert them into nitrates which are way

less toxic

for the biofilter in this bacteria to

operate at their best the ph should be a

minimum of seven

if the nitrates increase uh to above a

certain level which we'll see in a

minute what you need to do is just

remove it by you know doing water

exchanges

so uh ammonia as i mentioned it's toxic

it needs to be kept really low so as low

as 0.0.1 milligrams per liter

and then the nitrates as you can clearly

see is less toxic but still needs to be

kept low below 2.5 milligrams per liter

and then nitrates way less toxic you

know they can you can you can be a bit

more relaxed because they can be lower

than 200 milligrams per liter

one thing that is very important is that

remember the total ammonia is nitrogen

is a combination of the sum of ammonia

in the molecular form and ammonium the

cation

and the percentage of the molecular form

present is dependent on both temperature

and ph and increases with both

temperature and ph so if you look at

here if you have a ph below seven

actually you have almost no toxic

components to this 10.

you have a minimal amount zero

but we also mentioned that for the bio

filter to operate it needs to be at a

minimum ph seven so you have two counter

forces happening and and you can also

clearly see here as the ph

increases the less toxic

component of ammonia it actually

um decreases because the more toxic

molecular format is increasing with the

ph

so

this graph tells you what is the maximum

concentration of the total ammonia as

nitrogen so that you can make sure

that your level of ammonia the molecular

form in h3 is below this 0.02 milligrams

per liter

and as you can see as the ph increases

you really need to pay attention because

the 10 needs to be way low

so and the opposite is a lower ph

if you go to this left-hand side

it actually minimizes the risk of

exceeding the toxic ammonia you can have

now if you have a lower ph you can

actually afford to have a higher total

ammonia as nitrogen because then you

have a more a greater proportion of the

cation which is not toxic

but again remember that you need to have

a ph minimum of seven so that your

bacteria can actually oxidize the

molecular form of ammonia

what we see in this graph is when you

just start a biofilter

so when you just add your fish to the

system and let me just remind you about

the cycle so you have ammonia that's

going to be oxidized to nitrates by

nitrosomonas and then these

nitrates are going to be oxidized by

nitrobacter to get nitrates so here you

have ammonia in the beginning

at the beginning of the start of your

biofilter of course you have your fish

starting to excrete so this is the very

beginning of your system and the money

is going to build up okay as soon as you

have the money going to build up you're

going to have the opportunity you're

going to give the opportunity for the

nitrous sumerians to start working on

that ammonia adding oxygen and starting

producing nitrate to node two here

and then when you have this this uh

molecule you can actually then have

because you can see it grows the the

nitrobacter are now acting upon this

nitrate and producing nitrates and

actually now you can have the system

it's a bit more balanced here this is

exactly what you want you want to

decrease the amount of ammonia and it

has really gone really low you can have

a bit of nitrates as a consequence but

and then you have nitrates at a greater

amount

so uh this is uh and this is the time

it's not the time it takes for this

bacteria to start uh

to start activating and being in the

system and doing

their process of adding oxygen to the

ammonia

so you can have the surface is

fundamental for your

bacteria and you can have different type

of surfaces to

improve the

settlement of this bacteria you can have

this type of what i call viable there

are plastic

discs let's say 3d discs that they have

many grooves to increase the surface to

area volume of course then you need to

have some source of air so

remember these bacteria they're going to

add oxygen they need oxygen to be able

to oxidize ammonia

you can also have a different type of

biofilter which is you know a fixed pad

biofilter

where you this is this is moving usually

this is not moving you again you have a

water inlet and then you have water

going through and of course you need to

have the air

also the oxygen is is fundamental to

this equation

so this is the the video on

biofiltration i hope it was useful um

if you are interested in rust systems

there are two other videos and there

will be more uh that will focus on the

remaining components of rice systems