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19-08-2021, 08:30 AM
Characteristics of a Good Carrier Media
Characteristics of a Good Carrier Media
Tom owns a production factory. Every day, the factory produces 10 kg of a certain product. Based on his experience, Tom
knows that, on average, one trained worker with correct tools could manage to pack and ship out 1 kg of the product daily.
Being a predictive man, Tom considers the probability that one worker might get sick. To be on the safe side, he has
11trained workers instead of 10. This helps him prevent an overcapacity situation in the warehouse in the event that one of
them is sick or the factory has to increase its production capacity. With his 11 trained workers and correct tools, Tom’s
factory operates smoothly every day without trouble.
Now, let’s compare this with the biological wastewater treatment process. The product is the organic load to be removed
by means of wastewater treatment; the trained workers and tools are equivalent to the carrier media and biomass in the
wastewater treatment process, respectively. Similar to the workers who cannot pack and ship out the products without tools,
the carrier MBBR media cannot remove the organic load from the
wastewater without biomass.
If one day Tom’s factory starts producing another product that requires a different packing method, he doesn’t dismiss
his 11 workers and hire a new group. Rather, he allows his workers time to become familiar with their new working tools. The
same applies to biological wastewater treatment: The biomass that grows on the carrier
MBBR bio carrier media will gradually adapt itself to remove
a different type of organic load or concentration.
In order for Tom to ensure his factory can run smoothly, he needs both skilled workers and a good set of tools for them
to use. The lack of either will slow down the packing speed. For biological wastewater treatment with MBBR, the biomass as
well as the carrier media that acts as the housing for the bacteria are very important.
A good MBBR carrier media provides more than just a protected habitat for the bacteria to grow; it also ensures that all
bacteria that grow on it are sufficiently supplied with nutrients for their metabolism. During the biological treatment
process, the bacteria consume dissolved organic substances. Without sufficient nutrients, the growth of the bacteria is
hindered, or worse, the bacteria die off. These phenomena will reduce the removal efficiency and lead to an unqualified
wastewater discharge. Hence, a proper selection of the carrier media is essential. This decision will affect both the organic
removal performance and the cost required to run the plant.
A good MBBR carrier has the following characteristics:
? A large protected surface area to maximize the amount of biomass;
? A porous surface to strengthen the biomass’s adhesion;
? An optimal substrate diffusion depth to ensure the metabolism;
? Wear-resistance for durability.
In terms of treatment, a good MBBR carrier aquaculture
filter media ensures that all biomass is active to remove the organic substances from the water. From the user’s
perspective, a good MBBR carrier media eases the operation and provides a variety of savings, such as in construction and
operation.
In a wastewater treatment application, the required amount of MBBR carrier media depends on the organic load that needs
to be removed by means of the bacteria’s metabolism, the rate of which is influenced by water temperature and the type of
substrate.
Although MBBR carrier media might just be a little piece of plastic (or some other material), its role in
wastewater treatment is vital to keep the biomass
active in order to deliver the best possible organic removal performance. WW
Moving Bed Biofilm Reactors (MBBR) are used increasingly in closed systems for farming of fish. Scaling, i.e. design of
units of increasing size, is an important issue in general bio-reactor design since mixing behaviour will differ between
small and large scale. Research is mostly performed on small-scale biofilters and the question is to what extent
this can be upscaled to a commercial level. Therefore, the objective of this research was to establish the effect of mixing
and scale on MBBR performance. The research was done in two major parts; firstly effects of scale-sensitive factors were
studied in small reactors. Secondly, performance of these small reactors was then compared to increasingly large reactor
sizes, using the same inlet water quality and biofilm.
Firstly, a 200 L MBBR (medium scale) was operated continuously using a synthetic feed solution. Biofilm carriers
from this reactor was used for short-term experiments in 0.8 L reactors (small scale) and compared with the performance
of the 200 L medium scale reactor. Reactor geometry and superficial air velocity (m h?1) were identical in these
experiments. Subsequently, the small reactors were incubated with biofilm carriers from three commercial farms and
performance compared with these large scale reactors. In a number of additional experiments the effect of mixing and Total
Ammonia Nitrogen (TAN) was tested at small and medium scale.
The results showed that MBBR scale has a significant effect on TAN removal rate. In general, the larger the scale the
better the performance. TAN removal (rTAN) at small scale (0.8 L) is about 80% compared to that at medium scale
(200 L). The difference between small scale and large scale (>20 m3) is even higher. These findings warrant further
studies on whether a plateau is reached in rTAN at a certain scale; a study which will have considerable importance
for optimal design and dimensioning of commercial scale RAS. It was further found that superficial air velocity is not a good
scaling factor for MBBRs. Upscaling while maintaining geometry implies increasing air injection depth and therefore increased
energy input will be required at a comparable superficial air velocity, which is not incorporated in the superficial air
velocity term (m h?1). Superficial air velocity and
plastic media filling% were found to have a strong effect on mixing time at small scale. An air velocity below a
threshold of 5 m h?1 decreased TAN removal at both small and medium scale. Intense mixing at small scale
increased TAN removal at low TAN concentration. However, at a high TAN concentration, the small scale MBBR always performed
at not more than 80% of the capacity of the medium scale system, irrespective of the mixing conditions. Hence, the capacity
of full scale systems will be under-estimated when based solely on small scale experiments.
Suspended particles in recirculating aquaculture systems (RAS) provide surface area that can be colonized by
bacteria. More particles accumulate as the intensity of recirculation increases thus potentially increasing the bacterial
carrying capacity of the systems. Applying a recent, rapid, culture-independent fluorometric detection method (Bactiquant?)
for measuring bacterial activity, the current study explored the relationship between total particle surface area (TSA,
derived from the size distribution of particles >5 μm) and bacterial activity in freshwater RAS operated at increasing
intensity of recirculation (feed loading from 0.043 to 3.13 kg feed m?3 make-up water). Four independent
sets of water samples from different systems were analyzed and compared including samples from: (i) two
individual constructed wetlands treating the effluent system water from two commercial,
freshwater rainbow trout (Oncorhynchus mykiss) farms of different recirculation intensity; (ii) an
8.5 m3 pilot scale RAS; and (iii) twelve identical, 1.7 m3 pilot scale RAS assigned one of four micro-
screen treatments (no micro-screen, 100, 60, or 20 μm mesh size micro-screens) in triplicate. There was a strong,
positive, linear correlation (p < 0.05) between TSA and bacterial activity in all systems with low to moderate
recirculation intensity (i.e. feed loading ≤1 kg feed m?3 make-up water). However, the relationship
apparently ceased to exist in the systems with highest recirculation intensity (feed loading 3.13 kg feed m?
3 make-up water; corresponding to 0.32 m3 make-up water kg?1 feed). This was likely due to the
accumulation of dissolved nutrients sustaining free-living bacterial populations, and/or accumulation of suspended colloids
and fine particles less than 5 μm in diameter, which were not characterized in the study but may provide significant
surface area. Hence, the study substantiates that particles in RAS provide surface area supporting bacterial activity, and
that particles play a key role in controlling the bacterial carrying capacity at least in less intensive RAS. Applying fast,
culture-independent techniques for determining bacterial activity might provide a means for future monitoring and assessment
of microbial water quality in aquaculture farming systems.
Microbial water quality in recirculating aquaculture systems (RAS) is important for successful RAS operation
but difficult to assess and control. There is a need to identify factors affecting changes in the bacterial dynamics – in
terms of abundance and activity – to get the information needed to manage microbial stability in RAS. This study aimed to
quantify bacterial activity in the water phase in six identical, pilot scale freshwater RAS stocked with rainbow
trout (Oncorhynchus mykiss) during a three months period from start-up. Bacterial activity and dynamics were
investigated by the use of a patented method, BactiQuant?. The method relies on the hydrolysis of a fluorescent enzyme-
substrate and is a rapid technique for quantifying bacterial enzyme activity in a water sample. The results
showed a forty-fold increase in bacterial activity within the first 24 days from start-up. Average BactiQuant?
values (BQV) were below 1000 at Day 0 and stabilized around 40,000 BQV after four weeks from start. The study revealed
considerable variation in initial BQV levels between identically operated and designed RAS; over time these differences
diminished. Total ammonia nitrogen, nitrite and nitrate levels were very similar in all six RAS and were neither related to
nor affected by BQV. Chemical oxygen demand (COD) and biological oxygen demand (BOD5) were highly reproducible
parameters between RAS with a stable equilibrium dynamic over time. This study showed that bacterial activity was not a
straightforward predictable parameter in the water phase as e.g. nitrate-N would be in identical RAS, and showed
unexpected sudden changes/fluctuations within specific RAS. However, a bacterial activity stabilization phase was observed as
systems matured and reached equilibrium, suggesting a successive transition from fragile to robust microbial
community compositions.
Characteristics of a Good Carrier Media
Tom owns a production factory. Every day, the factory produces 10 kg of a certain product. Based on his experience, Tom
knows that, on average, one trained worker with correct tools could manage to pack and ship out 1 kg of the product daily.
Being a predictive man, Tom considers the probability that one worker might get sick. To be on the safe side, he has
11trained workers instead of 10. This helps him prevent an overcapacity situation in the warehouse in the event that one of
them is sick or the factory has to increase its production capacity. With his 11 trained workers and correct tools, Tom’s
factory operates smoothly every day without trouble.
Now, let’s compare this with the biological wastewater treatment process. The product is the organic load to be removed
by means of wastewater treatment; the trained workers and tools are equivalent to the carrier media and biomass in the
wastewater treatment process, respectively. Similar to the workers who cannot pack and ship out the products without tools,
the carrier MBBR media cannot remove the organic load from the
wastewater without biomass.
If one day Tom’s factory starts producing another product that requires a different packing method, he doesn’t dismiss
his 11 workers and hire a new group. Rather, he allows his workers time to become familiar with their new working tools. The
same applies to biological wastewater treatment: The biomass that grows on the carrier
MBBR bio carrier media will gradually adapt itself to remove
a different type of organic load or concentration.
In order for Tom to ensure his factory can run smoothly, he needs both skilled workers and a good set of tools for them
to use. The lack of either will slow down the packing speed. For biological wastewater treatment with MBBR, the biomass as
well as the carrier media that acts as the housing for the bacteria are very important.
A good MBBR carrier media provides more than just a protected habitat for the bacteria to grow; it also ensures that all
bacteria that grow on it are sufficiently supplied with nutrients for their metabolism. During the biological treatment
process, the bacteria consume dissolved organic substances. Without sufficient nutrients, the growth of the bacteria is
hindered, or worse, the bacteria die off. These phenomena will reduce the removal efficiency and lead to an unqualified
wastewater discharge. Hence, a proper selection of the carrier media is essential. This decision will affect both the organic
removal performance and the cost required to run the plant.
A good MBBR carrier has the following characteristics:
? A large protected surface area to maximize the amount of biomass;
? A porous surface to strengthen the biomass’s adhesion;
? An optimal substrate diffusion depth to ensure the metabolism;
? Wear-resistance for durability.
In terms of treatment, a good MBBR carrier aquaculture
filter media ensures that all biomass is active to remove the organic substances from the water. From the user’s
perspective, a good MBBR carrier media eases the operation and provides a variety of savings, such as in construction and
operation.
In a wastewater treatment application, the required amount of MBBR carrier media depends on the organic load that needs
to be removed by means of the bacteria’s metabolism, the rate of which is influenced by water temperature and the type of
substrate.
Although MBBR carrier media might just be a little piece of plastic (or some other material), its role in
wastewater treatment is vital to keep the biomass
active in order to deliver the best possible organic removal performance. WW
Moving Bed Biofilm Reactors (MBBR) are used increasingly in closed systems for farming of fish. Scaling, i.e. design of
units of increasing size, is an important issue in general bio-reactor design since mixing behaviour will differ between
small and large scale. Research is mostly performed on small-scale biofilters and the question is to what extent
this can be upscaled to a commercial level. Therefore, the objective of this research was to establish the effect of mixing
and scale on MBBR performance. The research was done in two major parts; firstly effects of scale-sensitive factors were
studied in small reactors. Secondly, performance of these small reactors was then compared to increasingly large reactor
sizes, using the same inlet water quality and biofilm.
Firstly, a 200 L MBBR (medium scale) was operated continuously using a synthetic feed solution. Biofilm carriers
from this reactor was used for short-term experiments in 0.8 L reactors (small scale) and compared with the performance
of the 200 L medium scale reactor. Reactor geometry and superficial air velocity (m h?1) were identical in these
experiments. Subsequently, the small reactors were incubated with biofilm carriers from three commercial farms and
performance compared with these large scale reactors. In a number of additional experiments the effect of mixing and Total
Ammonia Nitrogen (TAN) was tested at small and medium scale.
The results showed that MBBR scale has a significant effect on TAN removal rate. In general, the larger the scale the
better the performance. TAN removal (rTAN) at small scale (0.8 L) is about 80% compared to that at medium scale
(200 L). The difference between small scale and large scale (>20 m3) is even higher. These findings warrant further
studies on whether a plateau is reached in rTAN at a certain scale; a study which will have considerable importance
for optimal design and dimensioning of commercial scale RAS. It was further found that superficial air velocity is not a good
scaling factor for MBBRs. Upscaling while maintaining geometry implies increasing air injection depth and therefore increased
energy input will be required at a comparable superficial air velocity, which is not incorporated in the superficial air
velocity term (m h?1). Superficial air velocity and
plastic media filling% were found to have a strong effect on mixing time at small scale. An air velocity below a
threshold of 5 m h?1 decreased TAN removal at both small and medium scale. Intense mixing at small scale
increased TAN removal at low TAN concentration. However, at a high TAN concentration, the small scale MBBR always performed
at not more than 80% of the capacity of the medium scale system, irrespective of the mixing conditions. Hence, the capacity
of full scale systems will be under-estimated when based solely on small scale experiments.
Suspended particles in recirculating aquaculture systems (RAS) provide surface area that can be colonized by
bacteria. More particles accumulate as the intensity of recirculation increases thus potentially increasing the bacterial
carrying capacity of the systems. Applying a recent, rapid, culture-independent fluorometric detection method (Bactiquant?)
for measuring bacterial activity, the current study explored the relationship between total particle surface area (TSA,
derived from the size distribution of particles >5 μm) and bacterial activity in freshwater RAS operated at increasing
intensity of recirculation (feed loading from 0.043 to 3.13 kg feed m?3 make-up water). Four independent
sets of water samples from different systems were analyzed and compared including samples from: (i) two
individual constructed wetlands treating the effluent system water from two commercial,
freshwater rainbow trout (Oncorhynchus mykiss) farms of different recirculation intensity; (ii) an
8.5 m3 pilot scale RAS; and (iii) twelve identical, 1.7 m3 pilot scale RAS assigned one of four micro-
screen treatments (no micro-screen, 100, 60, or 20 μm mesh size micro-screens) in triplicate. There was a strong,
positive, linear correlation (p < 0.05) between TSA and bacterial activity in all systems with low to moderate
recirculation intensity (i.e. feed loading ≤1 kg feed m?3 make-up water). However, the relationship
apparently ceased to exist in the systems with highest recirculation intensity (feed loading 3.13 kg feed m?
3 make-up water; corresponding to 0.32 m3 make-up water kg?1 feed). This was likely due to the
accumulation of dissolved nutrients sustaining free-living bacterial populations, and/or accumulation of suspended colloids
and fine particles less than 5 μm in diameter, which were not characterized in the study but may provide significant
surface area. Hence, the study substantiates that particles in RAS provide surface area supporting bacterial activity, and
that particles play a key role in controlling the bacterial carrying capacity at least in less intensive RAS. Applying fast,
culture-independent techniques for determining bacterial activity might provide a means for future monitoring and assessment
of microbial water quality in aquaculture farming systems.
Microbial water quality in recirculating aquaculture systems (RAS) is important for successful RAS operation
but difficult to assess and control. There is a need to identify factors affecting changes in the bacterial dynamics – in
terms of abundance and activity – to get the information needed to manage microbial stability in RAS. This study aimed to
quantify bacterial activity in the water phase in six identical, pilot scale freshwater RAS stocked with rainbow
trout (Oncorhynchus mykiss) during a three months period from start-up. Bacterial activity and dynamics were
investigated by the use of a patented method, BactiQuant?. The method relies on the hydrolysis of a fluorescent enzyme-
substrate and is a rapid technique for quantifying bacterial enzyme activity in a water sample. The results
showed a forty-fold increase in bacterial activity within the first 24 days from start-up. Average BactiQuant?
values (BQV) were below 1000 at Day 0 and stabilized around 40,000 BQV after four weeks from start. The study revealed
considerable variation in initial BQV levels between identically operated and designed RAS; over time these differences
diminished. Total ammonia nitrogen, nitrite and nitrate levels were very similar in all six RAS and were neither related to
nor affected by BQV. Chemical oxygen demand (COD) and biological oxygen demand (BOD5) were highly reproducible
parameters between RAS with a stable equilibrium dynamic over time. This study showed that bacterial activity was not a
straightforward predictable parameter in the water phase as e.g. nitrate-N would be in identical RAS, and showed
unexpected sudden changes/fluctuations within specific RAS. However, a bacterial activity stabilization phase was observed as
systems matured and reached equilibrium, suggesting a successive transition from fragile to robust microbial
community compositions.