Recirculating Aquaculture Systems | Biofiltration - episode 3
Summary
TLDRDr. 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
🐟 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.
🌡️ 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.
Mindmap
Keywords
💡Recirculating Aquaculture Systems (RAS)
💡Biofiltration
💡Ammonia
💡Total Ammonia Nitrogen (TAN)
💡pH
💡Nitrosomonas
💡Nitrobacter
💡Nitrates
💡Oxidation
💡Surface Area
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
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