Aerators & Their Design in The Aquaculture Farm and Hatcheries.pdf

Not only fish but also all animals, must obtain oxygen from the environment for respiration. Oxygen is far less available to aquatic organisms than it is to air-breathers, and the dissolved oxygen content of water may limit the activities of fish. In most natural waters, the supply of oxygen to water (diffusion from the atmosphere and production from underwater photosynthesis) exceeds the amount used in oxygen-consuming processes, and fish seldom have problems obtaining enough oxygen to meet normal metabolic demands.

In aquaculture ponds, however, the biomass of plants, animals and microbes is much greater than in natural waters, so oxygen is sometimes consumed faster than it is replenished. Depending on how low the dissolved oxygen concentration is and how long it remains low, fish may consume less feed, grow more slowly, convert feed less efficiently, be more susceptible to infectious diseases, or suffocate and die. Aqua culturists avoid these problems by aerating ponds mechanically to supplement normal oxygen supplies.

1. Course Title: Aquaculture Engineering
Course Code: FIMS 4103, Year 4 Term 1

Aerators and Their Design in Aquaculture Farm and
Hatcheries


Submitted to Submitted by
Dr. Shyamal Kumar Paul
Assistant Professor,
Department of Fisheries & Marine
Science, Noakhali Science &
Technology University
Nazmul Haque Syekat
Roll: ASH1802050M
Session: 2017-18
FIMS 13 Batch, NSTU
Noakhali Science & Technology University
Sonapur, Noakhali -3814
Department of Fisheries and Marine Science



An Assignment On
Date of Submission: 02/ 08/2022

2. 1

INDEX OF THE ASSIGNMENT












SL. Name of Topics Page
1 INTRODUCTION 2
2 AERATORS 2-3
3 WHY NEED AERATION? 4
4 BENEFITS OF AERATOR 4-5
5 BASIC PRINCIPLE OF AERATOR 5-6
6 TYPES OF AERATOR & THEIR DESIGN 6-18
7 CRITERIA FOR SELECTION OF IDEAL AERATOR 19
8 CONCLUSION 19
9 REFERENCES 20

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Aerator & Their Design in The Aquaculture
Farm and Hatcheries

INTRODUCTION
Not only fish but also all animals, must obtain oxygen from the environment for respiration.
Oxygen is far less available to aquatic organisms than it is to air-breathers, and the
dissolved oxygen content of water may limit the activities of fish. In most natural waters,
the supply of oxygen to water (diffusion from the atmosphere and production from
underwater photosynthesis) exceeds the amount used in oxygen-consuming processes, and
fish seldom have problems obtaining enough oxygen to meet normal metabolic demands.

In aquaculture ponds, however, the biomass of plants, animals and microbes is much
greater than in natural waters, so oxygen is sometimes consumed faster than it is
replenished. Depending on how low the dissolved oxygen concentration is and how long it
remains low, fish may consume less feed, grow more slowly, convert feed less efficiently,
be more susceptible to infectious diseases, or suffocate and die. Aqua culturists avoid these
problems by aerating ponds mechanically to supplement normal oxygen supplies.

AERATORS
Aerators are various devices used for aeration, or mixing air with another substance, such
as soil or water. These devices are used to add oxygen to the water. Aeration brings water
and air in close contact in order to remove dissolved gases (such as carbon dioxide) and
oxidizes dissolved metals such as iron, hydrogen sulfide, and volatile organic chemicals.
The aim of Aqua farmers is the maximize production and profits and profits by minimizing
risks. Aerators offers the most immediate and prompt solutions for quality quality
management and oxygen deficiency. In aquaculture each species is habituated to different
living conditions during their evolution, the species which live in fast flowing and oxygen
rich stream need high quantities of oxygen, and a small change or decrease of dissolved
oxygen can cause complete loss of the species. Aeration removes the chemicals such as

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Ammonia, Chlorine, Carbon dioxide, Methane, Hydrogen Sulfide, Iron and Manganese
which affects the ponds in Aquaculture.

Fig: Paddlewheel aerators swirl the water in the air, breaking it into as tiny droplets as possible to
ensure a maximum contact area for gas exchange.

The main purpose of aerators is providing oxygen and mixing to disperse oxygen
throughout the pond. When selecting aerators, it is very important element to be considered
is oxygen dispersion. It involves both subsurface circulation and oxygenation, to create a
destratified pond environment. The concept is very much important as it leads to increased
size, increased survival and increased profit. For species like shrimp which lives in the
bottom of the pond, oxygen distribution to the bottom layer of the pond is a must. Mixing
and distribution of oxygen results less wastage of feed, bottom of the ponds clean and risk
free from diseases.
Water aeration is the process of increasing the oxygen saturation of the water. This also
helps to produce active sludge which can be used as fertilizers. Water aerators are various
devices used for aeration, or mixing air with another substance, such as soil or water. These
devices are used to add oxygen to the water.

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WHY NEED AERATION?
In aquaculture ponds, the biomass of plants, animals and microbes is much greater than in
natural waters, so oxygen is sometimes consumed faster than it is replenished. Depending
on how low the dissolved oxygen concentration is and how long it remains low, fish may
consume less feed, grow more slowly, convert feed less efficiently, be more susceptible to
infectious diseases, or suffocate and die. So, for solving this problem by aerating ponds
mechanically to supplement normal oxygen supplies.

✓ Rise in atmospheric temperature causes an increase in the rate of biological
degradation of organic matter and subsequent depletion of oxygen concentration in
water.
✓ Prolonged cloudy conditions cause reduction in the photosynthetic activity by green
plants in ponds results in reduction in oxygen concentration
✓ Increased stocking rate of animals in semi intensive and intensive farming practices
requires greater amount of oxygen for respiration for all aquatic organisms results
in depletion of oxygen concentration in water.
✓ Aeration in ponds helps in mixing and circulation of pond water. Mixing and
circulation is more critical in scientific farming which also helps in feed distribution
and waste disposal.

BENEFITS OF AERATOR
An aeration system – is an easy, natural way to supply man-made and natural ponds with
dissolved oxygen. Dissolved oxygen (DO) is a measure of how much oxygen is dissolved
in the water – the amount of oxygen available to living aquatic organisms. The amount of
dissolved oxygen in a stream or lake directly correlates with the water quality. Aquatic
animals, such as fish and aquatic invertebrates, require DO to breathe and function. In the
case of low or fluctuating DO levels (which can occur alongside algae blooms, plant and
algae die-offs or during the winter months), aquatic life can die in large quantities in an
event known as a ‘Fish Kill’ The aerator has the following benefits:
❖ Reduce organic sediment or muck
❖ Break down nutrients causing harmful plant growth and algae blooms
❖ Support aerobic digestion and oxidation

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❖ Improve fish habitat
❖ Reduce midge and mosquito breeding
❖ Contribute to the visual aesthetic lake or pond
❖ Help increase property values
❖ Mitigate odors
❖ Support community satisfaction with the waterbody
BASIC PRINCIPLE OF AERATOR
With aerator the aim is to create conditions as near equilibrium as possible between the gas
in the air and the gas in the water. Eventually super-saturated gas, especially nitrogen, will
be aerated out and oxygen will be supplied if the concentration is below saturation. The
aim in constructing an aerator is to achieve optimal conditions for exchange of gas between
air and water, so that equilibrium can be reached.
By creating a large contact area between the water and the air a good gas–water exchange
will occur; see equations for gas transfer and the A/V relationship. The layers of air or water
ought to be as thin as possible. To create thin layers, it is important that both the current of
air and the current of water are turbulent so that effective gas transfer can occur at the
water–air interface. The aeration process needs time, and effective aerators will need less
time to achieve the same degree of saturation than ineffective ones. Mass transfer from the
air will occur into a tank of non-saturated water, almost 100% saturation being achieved,
but this will take a very long time.

Fig: Two main methods are utilized for aeration. Either air can be supplied into a flow of water, or
water may be supplied into a flow of air.

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Two main methods are utilized for aeration. Either air can be supplied into a flow of water,
or water may be supplied into a flow of air. An example of the first method is bubbling of
air through a water column; droplets of water passing through a layer of air illustrate the
second method. Since the droplets are small, a large surface area between the water and the
air is created; the smaller the bubbles or droplets, the larger the surface area.
Aerators can be constructed either for supplying oxygen to the water (gassing) or removing
nitrogen or carbon dioxide from the water (degassing). An aerator built for gassing is not
necessarily good for degassing; aerators for both O2 and N2 are usual.

TYPES OF AERATOR & THEIR DESIGN
There are various types of aerator configurations that can be used to increase DO
concentrations in aquaculture ponds. Proper aeration system selection is based on several
factors including the following:
✓ Pond size
✓ Pond depth
✓ Pond shape
✓ Power source availability
✓ Aeration type (i.e., emergency or continuous)
✓ Aerator efficiency
✓ Seasonal changes (e.g., ice cover)
✓ Fish harvest methodologies
Aerator performance is measured as either standard oxygen transfer rate (SOTR) or
standard aeration efficiency (SAE). The SOTR is the amount of oxygen added to the water
in 1 hour under standard conditions, expressed as pounds of O2/hour. The SAE is the
standard oxygen transfer rate divided by the horsepower (hp) of the unit, expressed as
pounds of O2/hp-hour transferred to the water. Some Aerator that uses in aquaculture farm
and ponds are mentioned below:
1. Vertical Pumps Aerators
2. Surface aerators
3. Pump sprayer

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4. Propeller-aspirator-pumps
5. Electric paddlewheel Aerators
6. Diffused Aerators
7. Gravity Aerators
8. Cascades or Falls aerators
9. Natural aerators
10. Turbine Aerators
11. Tractor powered aerator

1.VERTICAL PUMP AERATOR
Design and Construction
Vertical pump aerators, also known as impeller aerators, consist of an electric motor with
either a single or dual impeller attached to the motor shaft. Motors range in size from less
than 0.5 hp to greater than 5 hp, with typical aquaculture units being 2 hp or less. Impeller
design, combined with high shaft speeds of the motor (between 1,730 and 3,450 revolutions
per minute (r/min)) throw pond water up into the air to increase gas transfer and induce
surface disturbance.

Typically, the entire unit is suspended just below the surface of the water by a float. The
float must have two anchor points to keep the unit in place and prevent rotation of the unit
during operation. Anchor ropes or cables can extend to a weighted object on the pond
bottom (such as a concrete block), or to a fixed point on the pond edge. Anchor ropes or
cables that extend to the pond edge facilitate easier removal and installation of the unit if
Fig-: Design of a Float mounted vertical aerator in operation

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needed for maintenance or to remove or reposition the unit at harvest time. Vertical pump
aerators can also be mounted to a dock or other fixed feature, such as a pole embedded in
the pond bottom or a tripod stand. Intake screens or cages are often installed on the units to
prevent the uptake of debris and fish into the impeller housing. Minimum operating depths
range from 21 to 48 inches depending on the size of the unit and the pumping efficiency.
Some vertical pump aerators can be mounted so that the motor and impeller are fully
submerged to reduce surface disturbance and act as a circulator.
Advantages:
1. High pumping capacity suitable for low and high energy.
2. Reduce surface disturbance.
3. Act as a circulator.
Disadvantages:
1. Only the water near the surface of aerator is jetted into the air.
2. Only applied in small and shallow shrimp ponds

2.SURFACE AERATORS
Design and Construction
Surface aerators are commonly use in ponds, but may also be used in large tanks, in
distribution basins and in sea cages under special conditions. A great number of different
designs of surface aerators are available. Normal designs use rotating wheels with a type
of paddle, or horizon-tally placed propellers. They function by throwing the water into the
air and creating thin films or bubbles. This establishes a large exchange surface area
between water and air where gas exchange can take place. Surface aerators are driven by
electricity, solar power or from tractors through a shaft; SAE values are between 1.2 and
2.9 kg O2/(kW h).

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Fig: Various types of surface aerators are available. (A) and (B) show a paddle wheel aerator, whilst (C), (D)
and (E) show a propeller aerator, (F) shows an inka aerator. (D) A propeller aerator being used in a close cage.
Advantages:
1. Need low electricity.
2. Low maintenance cost.
3. Small space.
Disadvantages:
1. Used only surface level of the water.
2. Oxygen does not distribute through whole water body.

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3.PUMP SPRAYER AERATOR
Design and Construction
Pump sprayer aerators consist of high-pressure pumps powered by either a tractor power
take off (PTO) or an electric motor, and function by pumping water under high pressure
through one or more orifices into the air through pipes or manifolds. These units can be
operated in shallow depths, provided the intake for the pump is sufficiently submerged.



PTO-powered pump sprayer aerators are a popular choice for emergency aeration
operations. They can be quickly moved from pond to pond and operated in shallow depths
with little concern for suspension of pond bottom sediments and wastes
Advantage: Low cost
Disadvantage: Complex method

4.PROPELLER-ASPIRATOR PUMPS
Design and Construction
Propeller-aspirator pumps consist of a submerged impeller-diffuser mounted to a rotating
shaft contained within a hollow housing. The rotating shaft is connected to an electric motor
Fig-: Design of a Pump sprayer aerator in operation

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that spins the shaft at speeds of up to 3,450 rpm. The hollow housing allows air to be drawn
down into the water column where it is mixed with the pond water as a result of the vacuum
produced by the turbulence and water velocity created by the spinning impeller. Ambient
air, which is drawn down the tube, enters the water column through the diffuser as fine
bubbles where it is mixed by the impeller. The unit is mounted to a float or system of floats,
which allows adjustment of both the angle of the unit and the depth of the impeller.
Propeller-aspirator pumps can create significant circulation as well as aeration and are
therefore more efficient in deeper ponds. Finally, screening considerations to prevent
small-bodied fish from injury associated with spinning impellers should be considered
where appropriate.



Fig-: Design of an electric propeller-aspirator aerator

Advantages
1. Fine bubbles creates good dissolve oxygen
2. High aeration capacity
Disadvantages
1. Need much energy for creating high water pressure

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5.PADDLE WHEEL AERATOR
Design and Construction
Paddle wheel aerators consist of an arrangement of paddles attached to a rotating drum or
shaft. The pattern, length, and shape of the paddles affect the aeration efficiency of the unit.
Paddle wheel aerator designs range from farm-manufactured units consisting of an
automotive axle and differential with paddles welded to a wheel, to precisely machined and
manufactured paddles attached in a spiral pattern around a drum
Typically, the paddles are 2 to 10 inches wide and are attached to a drum in an alternating
or spiral pattern. Drum speeds range between 70 and 120 rpm, and the spinning paddles are
typically submerged in 3 to 6 inches of pond water.

Fig-: Design of a Paddle aerator in operation
Advantages
1. Simple design
2. Need low electricity
3. Low maintenance cost
4. Greatest amount of oxygen for the least energy consumption
Disadvantages
1. Oxygen does not distribute whole pond
2. Fish are sometimes injured by aerator wheel

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6.DIFFUSED-AIR SYSTEM
Design and Construction
Diffused-air systems use one or more regenerative blowers or rotary vane compressors to
pump ambient air at low pressure and high volume to submerged diffusers. The most
common diffusers are glass-bonded silica stones, however diffusers constructed of porous
plastic, synthetic perforated membranes, and ceramic are also used. Diffusers can be
various-sized rectangular or square stones, round or square disks, or elongated tubes and
pipes.

Fig-: Design of a diffuser with sis individual silica air stone mounted on a bottom plate
The efficiency of diffused-air systems is primarily a function of bubble size and diffuser
depth. Diffusers that produce smaller bubbles, commonly referred to as fine-pore diffusers,
are more efficient than diffusers that produce large or coarse bubbles. Smaller bubbles have
more surface area relative to their volume, which facilitates more efficient oxygen transfer.
In addition, when the bubbles are released at a greater depth, hydrostatic pressure from the
water increases the DO saturation concentration, thereby increasing the saturation deficit
when compared to surface water. Concurrently, deeper release points allow more contact
time for the bubbles to diffuse oxygen into the water column as they rise to the surface.
Placing diffuser stones above the bottom of the pond helps minimize suspension of bottom
sediments.
Diffuser depth also has an impact on water circulation rates within the pond. As the bubbles
rise to the surface and expand, water is entrained. This process creates an air-lift, which

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pumps the bubbles and entrained water to the surface. Deeper water is typically cooler and
denser than the surface water and slowly spreads out and away from the rising column of
bubbles, creating vertical circulation between the pond bottom and the surface. This
circulation cell has a limited horizontal extent and, therefore, diffused aeration systems
usually require several diffusers arranged in a grid pattern to effectively aerate and circulate
the impoundment.

Advantages:
1. Increasing DO from bottom to surface.
2. More efficient in deeper ponds.
Disadvantage:
1. Not used in shallow ponds.
2. High capital cost.
3. Unpopular technology.

7.GRAVITY AERATION
Design and Construction
Gravity aerators are simple to construct and are reliable. These are the most common type
of aerators used in small semi-intensive shrimp farms. In this method water is allowed to
rise above, the pond/tank level and then to fall freely in the pond or tank through
atmosphere, where water comes in contact with oxygen and thus aeration is done. In simple
water falling and splashing into pond and aeration is done.

During the process of water raising or falling, potential energy is converted into kinetic
energy. That serves to break apart the falling water. When water is broken into droplets,
the area over which the diffusion can take place is increased, thereby increasing the
dissolved oxygen of the water.

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Figure: Diagrams of gravity aerators. (a) Simple weir (b) splashboard (c) inclined corrugated sheet
(d) inclined corrugated sheet with holes (e) lattice aerator and (f) cascade aerator.
Advantages:
✓ Low cost.
✓ Easy to management.
✓ Low energy needed.
✓ Aeration occur properly.
✓ Used in waste water treatment.
Disadvantages:
✓ Disease management poor.
✓ Need good infrastructure.

8.CASCADE AERATOR OR WATERFALL AERATOR
Design and Construction
In cascade aerator, water fall down in a thin film over a series of steps or baffles. It can be
rectangular or circular in shape. As the water falls down and turbulence is created, the
exchange of gases takes place.

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Fig-: Design And operation of a cascade aerator or waterfall aerator

Advantages:
1. Used in Water treatment.
2. Low cost.
3. Removal of iron and manganese from groundwater

Disadvantages:
1. Requires more space to operate.
2. Need good infrastructure.

9.NATURAL AERATOR
Design and Construction
They mainly manage dissolve oxygen naturally & maintained in extensive culture ponds.
Operated by –

❖ By swimming in the water.
❖ By hit the water with bamboo.
❖ By entering water through inlet which is situated 10 cm or more above to the water
surface.
❖ By allow duck to swim in the water.
❖ Drive the boat into water.

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Fig: Aeration is done by allowing duck to swim in the water

Advantages:
• No need electricity.
• Useful for extensive aquaculture.
• Low cost.
Disadvantages:
• Aeration does not distribute whole pond.
• Aeration does not occur regularly.
• Production low.


10.TURBINE AERATOR
Design and Construction
An effective method of high oxygen transfer for small tanks to large lagoons which
incorporated easily into existing plants. Axial flow aerators have high efficiency due to
their maximum transfer of kinetic energy to water surface. Turbine aerators are usually up
flow types that rely on violent agitation of the surface and air entrainment for their
efficiency. Common advantages include high oxygen transfer, wide range of installation
from small tanks to massive lagoons, no need of gearbox, low maintenance cost, simple
and flexible Installation and removal, easily incorporated into existing plants, customized
mooring arrangements to suit site conditions and low cost by saving energy and high
performance.

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Fig: Design & Operation of a turbine aerator


Advantages:
1. High oxygen transfer.
2. Low maintenance cost.
3. Simple and flexible Installation and removal.
Disadvantages:
1. Water may become corrosive.
2. Requires energy support.

11.TRACTOR POWERED AERATOR
Used for emergency aeration in larger ponds. Such aerators are driven by the power-take-
off (PTO) of farm tractors: they are large & can qickly raise DO concentration, they are
mobile and can be easily moved
from pond to pond, and they do not
require an electrical service. They
require a large tractor to power
each unit less efficient than electric
aerators. Therefore, the use of
tractor-powered aerators is rapidly
diminishing.

Fig: A tractor powered aerator in operation

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Advantages
1. Easily movable
2. Rapid aeration in certain time in certain place
Disadvantages
1. Not used regularly
2. Need more energy
3. High cost value
CRITERIA FOR SELECTION OF IDEAL AERATOR
Some criteria will be need while buying a good aerator
1. Low noise operation
2. Long working life
3. Low maintenance
4. Impact resistance
5. Lightweight
6. Easy to replace and install
7. Higher oxygen transfer capacity
8. Stainless frames.
9. Mechanical seal against oil leakages
10. Rugged construction
11. Durable
12. Flawlessness

CONCLUSION
With the advancement of Aquaculture, the aquaculture machinery is also getting advanced
with the usage of latest technology in aerators which are very much efficient and easy to
use. Now we have aerators with highly efficient electric motor with low power
consumption which are mostly preferred by all the farmers. Earlier farmers faced the
challenge of getting the spare parts for aerators, now even spare parts are easily available
at manufacture and online.

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REFERENCES
1. Design and construction of aerators: Basic principles, Evaluation criteria. (n.d.).
BrainKart; www.brainkart.com. Retrieved August 1, 2022, from
https://www.brainkart.com/article/Design-and-construction-of-aerators--Basic-
principles,-Evaluation-criteria_15048/
2. The Types and Benefits of Aeration Systems for Ponds | Clarke. (2021, November
3). Clarke; www.clarke.com. https://www.clarke.com/blog/types-benefits-
aeration-systems-ponds/
3. Gravity aeration devices - Aquaculture technology flowing water and static water
fish culture. (n.d.). Ebrary; ebrary.net. Retrieved August 1, 2022, from
https://ebrary.net/52965/engineering/gravity_aeration_devices
4. admin. (2017, July 17). Role of Aerators in Aquaculture – AquaDeals Blog. Role
of Aerators in Aquaculture – AquaDeals Blog; blog.aqua.deals.
http://blog.aqua.deals/role-of-aerators-in-aquaculture/
5. Mechanical Turbine Aerator. (n.d.). » Mechanical Turbine Aerator; napier-
reid.com. Retrieved August 1, 2022, from https://napier-
reid.com/products/mechanical-turbine-aerator/