& Pumping Rates
much oxygen is your aerator really going to deliver and what is the
systems make claims about the oxygen transfer rate and how many pounds
or kilograms of oxygen are added per hour or per kilowatt. This can
be a very effective way to compare the efficiency of an aeration system
based on the biological oxygen demand of the system.
A small pond with
trout or bass will have a different BOD (biological oxygen demand)
compared to a wastewater treatment system. In some cases a bottom
mounted diffuser aeration system can be the most efficient choice
but in other applications a large surface paddlewheel aerator might
be required to meet requirements.
Standard Oxygen Transfer Rates
Most commercial-grade aerators and diffuser systems have been laboratory
tested to determine their SOTR (Standard Oxygen Transfer Rate) but
the resulting SOTR ratings are based on fairly narrow criteria usually
when test water has zero dissolved oxygen and at a defined temperature.
In real world applications the advertised SOTR can almost never be
expected because the actual rate of oxygen transfer is temperature
and existing D.O. (Dissolved Oxygen) concentrations. Any aerator or
diffuser will only provide its measured (advertised maximum) oxygen
transfer rate when the dissolved oxygen levels in the water are at
zero or close to zero.
This chart will help estimate the actual oxygen transfer an aerator
will give when there is already oxygen in the water.
If the water temperature is 59°F (15°C) and the dissolved oxygen level
is 3 Parts Per Million (PPM) or 3 mg/l, an aerator system or diffuser
that is rated at 3 pounds of oxygen per hour will really only provide
64% of the advertised SOTR or around 1.92 pounds of oxygen per hour
(3 lbs x 64 percent = 1.92 lbs).
If the pond temperature is 77°F (25°C) and the dissolved oxygen level
is 5 Parts Per Million (PPM) or 5 mg/l, an aerator system or diffuser
that is rated at 3 pounds of oxygen per hour will really only provide
35% of the advertised SOTR or around 1.05 pounds of oxygen per hour
(3 lbs x 35 percent = 1.05 lbs).
If a pond temperature
is 68°F (20°C) and the dissolved oxygen level is 7 Parts Per Million
(PPM) or 7 mg/l, an aerator system or diffuser that is rated at 3
pounds of oxygen per hour will really only provide 19% of the advertised
SOTR or around 0.57 pounds of oxygen per hour (3 lbs x 19 percent
= 0.57 lbs).
of advertised oxygen transfer actually transferred to a pond
based on water temperature and the dissolved oxygen level
prior to adding the aeration device.
Dissolved Oxygen Level
in Water Being Aerated (mg/L or PPM)
Low oxygen concentrations can be damaging to a variety of critical
life stages of aquatic animals, including larval invertebrates, and
fish eggs and fry.
Like temperature, organisms differ in their tolerance to low dissolved
The ideal dissolved oxygen level for fish is between 7 and 9 milligrams
per liter (mg/L); most fish cannot survive at levels below 3 mg/L
of dissolved oxygen.
Some published guidelines suggest dissolved oxygen concentrations
must not decline below 5 mg/L and should not average less than 6.5
mg/L over a seven-day period. However, the guidelines also require
that dissolved oxygen concentrations remain above 9.5 mg/L in areas
where early life stages of aquatic biota, particularly fish, are present.
Anoxic (depleted oxygen) conditions can result in fishkills, which
is particularly common during harsh winters with extended ice-cover.
When fish are not a concern such as a wastewater treatment facility
or leachate pond, where the main concern is to ensure the BOD is adequately
addressed by the chosen aeration system, different criteria will apply
and take a priority role in importance when deciding if bottom diffusers,
surface aerators or some sort of jet or aspiration aerator or paddlewheel
type aerator will make the most sense.
Air Aerators Systems
These aerators are also called lake-bed aerators or bottom-mount diffusers
and basically use a shore-mounted air blower or compressor type air
pump to push air into multiple diffusers placed at the bottom of a
pond, lake or wastewater tank.
aeration is probably the most common form of aeration in ponds and
lakes and can also be effective in wastewater basins and holding tanks.
Air is forced through a diffuser system which breaks up the airflow
into bubbles. Depending on the matrix or make-up of the diffuser the
bubbles will be fine bubbles less than 0.5 millimeters in diameter
or more coarse bubbles above 2 millimeters
Some of the more popular aeration systems in North America harness
the efficiency of the disc diffusers as part of their bottom mount,
or lake-bed, diffuser system. Diffuser discs come in various sizes;
the most common sizes are the 9 inch diffuser disc and the 12 inch
diffuser disc. These diffuser discs can be arranged on proprietary
weighted bases according to manufacturer or individually weighted
or affixed via lengths of weighted airline to mainline header systems
with valves tapped-off a main header. Diffuser discs have an integrated
check-valve system to prevent backflow of liquids into feeder lines.
Fine Bubble diffuser
discs membranes are made of EPDM (ethylene propylene diene monomer),
silicone or PTEE (PolyTetraFluoro Etyhylene) layered combinations.
Lake and pond diffuser assemblies typically use EPDM diffuser discs
as they are generally used in fairly benign, low-organic situations
in fairly clean waters so they are able to resist fouling quite well.
Wastewater systems, leachate ponds, compost reduction basins or storm
water retention ponds often have higher levels of organics and dirty
effluent which can cause issues with these diffusers and a more specialized
diffuser is needed.
407510 Dissolved Oxygen Meter
Dual display provides O2 or dissolved oxygen and temperature
readings Measures dissolved oxygen in water from 0 to 20.00mg/L
and oxygen in air from 0 to 100% Resolution: 0.1mg/L DO,
0.1% O2 Automatic temperature compensation Min/Max/Average
systems for wastewater treatment
Aeration is one of the important processes employed in
activated sludge process of the biological treatment units
of wastewater. In this process the level of dissolved
oxygen in the effluent is raised to the required amounts
to decompose organic matters present in the effluent and
thereby to reduce the BOD (biochemical oxygen demand)
of the effluent by a physical means called “aeration process”.
The aeration process consumes as much as 60-80% of total
power requirements of wastewater treatment plants. Therefore,
the efficiency in design of aeration process is required
so that wastewater treatment and its power consumption
can be economized.
Technology, Third Edition: An Introduction for Environmental
Scientists and Engineers
Water and wastewater engineering is one of the world's
biggest and most interdisciplinary industries, employing
chemists, microbiologists, botanists, zoologists as well
as engineers, computer specialists and a range of different
management professionals. This accessible student textbook
provides a broad overview of the sector, introducing the
reader to the key concepts of water technology by explaining
the fundamentals of hydrobiology, aquatic ecosystems,
water and supply and wastewater treatment. In 2000 the
Water Framework Directive came into force - this is the
most substantial piece of EC water legislation to date.
Professor Gray uses the Water Framework Directive as the
unifying theme of this new edition taking into account
the implications of compliance and practice, as well as
discussing the topical issue of sustainable principles
in water management. . Covers water quality and regulation
. Deals with water quality assessment, management and
treatment . Includes a new chapter on sustainability within
Lake and Pond
Lake and Pond Management Guidebook is the successor to
the best-selling Lake Smarts: The First Lake Maintenance
Handbook, the "bible" for small-scale lake and pond improvements,
published by the Terrene Institute in 1993. Completely
revised and updated, now published by Lewis Publishers,
this guidebook contains over 300 ideas and projects including
step-by-step practical, low-cost solutions to a wide range
of problems that lake management professionals face everyday.
Coverage includes shoreline buffer installation, fisheries
management, reducing nuisance algal growth, controlling
exotic aquatic plants, lakeside wastewater treatment systems,
small scale dredging, and more.
Principles and Practice, Volume 11 (Water Quality Management
The immense environmental challenges facing the world
now and in years to come can only be met through marshaling
the talents of the best environmental engineers and scientists,
and through the use of innovative, cost-effective solutions.
Written by three leading aeration experts, Aeration: Principles
and Practice, covers the principles and practice of aeration,
a unit process critical to the performance of activated
sludge treatment and to the budget of wastewater plants.
This reference presents the state of the art in aeration,
using examples from a variety of facilities in the USA
and Europe. The authors investigate conventional and deep-tank
aeration systems for BOD removal and nitrification, as
well as high-purity oxygen systems. Operating and capital
costs, as well as energy use data are presented together
with design information allowing the adaptation of new
aeration technologies to plants of diverse size. Both
practitioners and advanced students of wastewater management
will appreciate the detailed presentation of oxygen transfer
principles, especially as they are illustrated in numerous
applications. With the information presented in this book
engineers and managers will be able to understand and
monitor the efficiency of existing aeration systems and
to develop strategies for process improvement.
Ecological Bases for Lake and Reservoir Management (Developments
Ecological Bases for Lake and Reservoir Management provides
a state-of-the-art review of the range of ecologically-based
techniques necessary for the holistic management of lakes
and their catchments. Most of the methods, case studies
and national policies reviewed are directed towards management
of the largest problem - eutrophication - with the emphasis
on the multiple-scale approach needed for successful management
and restoration. Case studies come from the USA and ten
European countries, and range from single lakes through
to lake districts and national inventories. Several essays
precede the practical chapters with thought-provoking
comments on the political, social and economic climate
of water management.
for a Small Lake (The Expanded Guide to Lake and Watershed
expanded guide to New York State lake and watershed management,
2nd edition. Lake associations and citizens play a vital
role in protecting and restoring our lakes and waterways.
This book is an introduction to understanding and managing
lakes. Lakes and their watersheds are natural treasures
for us to use and protect. Together these rich resources
supply abundant water to support thriving communities,
provide recreational opportunities, and spur economic
growth in an area. For many communities, the tax base
and economy are dependent on having clean water. Even
when a lake is healthy, its users cannot afford to wait
for a disaster before acting to keep it healthy and its
water clean for current and future generations. This publication
offers guidance for lakeshore residents, local officials,
and agencies interested in water resources by providing:
* An introduction to lake ecology * Descriptions of lake
restoration and watershed management techniques *A special
section about relevant New York State laws and regulations
* Guidance for preparing a watershed management plan Diet
fir a Small Lake was prepared by the New York State Federation
of Lake Associations, Inc (NYSFOLA) in collaboration with
the New York STate Department of Environmental Conservation
(DEC) and is the culmination of several years of collaboration
on lake management issues. It replaces and expands the
information presented in the first edition.
Establishing a SOTR (Standard Oxygen Transfer Rating) rating for a
diffuser device or to pinpoint a precise SAE (Standard Aeration Efficiency)
for a bottom mounted or lake-bed diffuser aeration system is not easy.
(Standard Aeration Efficiency) of air diffusers is generally between
0.5 and 1.5 pounds per horsepower per pound (1.0 - 2.0 lb/O2/hp-hr).
High efficiency air stones which can create finer bubbles have higher
SAE closer to 3.0 pounds of oxygen per horsepower per hour. Understanding
the needs of your aquatic system will help you best choose the diffuser
system that will be most cost-effective for your project. Depth of
the diffuser placement will dictate the PSI (Pounds per Square Inch)
requirements of your compressor or blower. Compressors and blowers
have limited airflow and pressure thresholds and tubing lengths can
further impact the final diffuser performance. In deeper ponds and
lakes over 10 foot depth the best aeration efficiency and oxygen transfer
will be with a bottom mount diffuser system. Rotary vane or piston
compressors can provide adequate airflow in the most common situations
and if higher airflow and pressure is necessary then a rotary screw
compressor. It is important to recognize and understand the differences
between reciprocating, carbon vane, rotary centrifugal, regenerative
blower and rotary screw compressors as they all have specific strengths
To maximize the efficiency of a diffuser system and to get the most
pounds of oxygen per horsepower per hour from the diffuser you need
to ensure the air blower system is tailored to your specific job.
One interesting benefit of using land-based blowers or air compressor
systems for pond aeration is the reduced underwater noise levels of
diffuser systems when compared to surface aerators. More and more
research is focused on understanding the impact of extraneous noise
on aquatic creatures. Measurements conducted under water are raising
red flags about the noise produced by devices such as paddle wheels,
agitators, airlifts and drilled pipe homemade DIY diffusers or spargers.
In non-living systems (cement basins or oil field tailing ponds) this
extraneous noise is not an issue.
Another benefit of bottom-mount diffusers, because the air supply
blower or compressor is onshore and often hundreds of feet from the
diffuser, is that there is much less audible noise in the water column
to disrupt fish or aquatic life. Reducing the noise that is pushed
into the pond through an aeration device can improve the health of
the fish stocks and general well-being of the pond. Some pond and
lake owners, especially fish clubs or conservation groups have reported
that diffused air is the only aeration method they can use that will
not disrupt breeding. The situations and considerations are virtually
endless, so take some time to research the best aeration method for
your particular application beyond looking at the Oxygen Transfer.
Rates of Diffuser Aeration Systems
One of the most popular ways of comparing diffusers is to use the
pumping rate of the diffuser based on the CFM airflow (cubic feet
per minute) through the diffuser at different depths. Diffusers will
circulate more gallons per minute as the depth of the diffuser placement
increases even with the same CFM flow. By measuring the Gallons Per
Minute of pumping it is possible to establish how many diffusers are
required and the CFM needed to circulate a given volume of water.
Establishing concrete results is not easy. Testing of diffusers is
often paid for by the manufacturer of the system and the data released
are usually the results that show the product in the best possible
light featuring the highest oxygen transfer rates and the best aeration
Per Minute Pumping Rate
Based on listed CFM airflow per diffuser and depth of diffuser
Increasing the CFM will increase the pumping capacity of the
diffuser but every diffuser type has limitations and backflow
headloss equations to consider. Wastewater and tank diffusers
are not considered in this chart as they are more specialized.
This chart should be used as a general guide only without scientific
acknowledgment or reference. Data is condensed estimations based
on manufacturer claims.
our selection of Aeration Diffusers | Air
If a diffuser placed at 5 foot depth is rated to pump or circulate
500 gallons per minute with airflow of 2 CFM, the same diffuser at
a depth of 12 feet might have a pumping capacity of 1500 gallons per
minute with the same airflow of 2 CFM. This is why bottom mounted,
lake-bed diffusers are typically used in deeper situations.
If you need to aerate a large pond that has 2.3 million gallons (approximately
an acre sized pond average 7 feet deep) and you want to do a complete
turnover of the total pond volume every 24 hours, you need to look
at the pumping rates of your chosen diffuser at depth and determine
how many diffusers will do the job.
If each of your diffusers has a rated pumping capacity of 1000 Gallons
Per minute with 2 CFM (Cubic Feet per Minute) of airflow then that
single diffuser would theoretically be able to do a complete pond
turnover in around 38.5 hours. (2,300,000 gallons divided by 1000
gallons per minute = 2300 minutes = 38.3 hours to pump 2.3 million
If you used two diffusers for a total pumping capacity of 2000 gallons
per minute you would be able to do a full volume mix of the pond in
1150 minutes or 19.2 hours.
If you used three diffusers for a total pumping rate of 3000 gallons
per minute you could do the complete pond turnover in 767 minutes
or 12.8 hours. So with three diffusers and 6 CFM you can pump the
full volume of an acre pond in close to 12 hours.
Keep in mind that the depth and shape of your pond will have an impact
on total pumping rates and just how thorough the mixing of the pond
is; stagnant pools can exist in ponds where the water won't be moved
unless correct placement of the diffuser takes these dead zones into
bubbles are better bubbles
Let's have a brief lesson in fine bubbles, it will be fun (well...not
exactly) and you will get a short course in why smaller is sometimes
better especially when it comes to diffuser bubbles!
Lesson 1 - Let's take a fairly large bubble as far as aeration
goes. Our large galloping bubble that is 0.8" in diameter, just
over 3/4 of an inch, or 20 mm has a full volume of 1.64 cubic inches
or 4.19 cubic centimeters. This same glorious orb has a surface area
of 5 inches or 12.6 square centimeters and that is what we can define
as a coarse bubble!
Lesson 2 - Now a coarse diffuser like an airstone would create
large bubbles like in lesson one but if we could use the same volume
of air but break that large sphere into smaller ones we could greatly
increase the available surface area which in turn enhances and embellishes
the aeration transfer capacity of the same air volume! If we replaced
that one large 3/4" wide bubble with tiny bubbles or micro-bubbles
that were 1/16 of an inch or 3 mm in diameter we could fit 296 of
these fine bubbles into the larger one of lesson 1! The combined surface
area of those 296 bubbles works out to over 33 square inches or 84
square centimeters! This is close to 7 times the total surface area...and
the surface is where the oxygen transfer occurs.
Lesson 3 - Now since the surface area is close to 7 times greater
we can theoretically aerate 7 times as much water with the same compressor
or blower or air pump depending on whether we have a fine bubble diffuser
or a coarse bubbler. Same air pump, totally different efficiency!!
Surface aerators usually consist of a submersed motor suspended from
a float that drives an angled prop to create a frothing oxygen transfer
boil on the surface. In smaller ponds and aquaculture tanks these
are often retail units between ½ HP and 5 HP. Larger models up to
300 HP are used by commercial applications and wastewater treatment.
A basic calculation for oxygen transfer requirements or inadequate
surface aerator is to allow at least ½ HP of an efficient surface
aerator for every million gallons of pond volume. This is only a guide
used in smaller ponds. High density fish ponds or ponds with a higher
BOD should calculate at least ¾ HP per million gallons.
The most efficient small-scale surface aerators will have an oxygen
transfer rate based on standard aeration efficiency (SAE) of 3 pounds
per hour per horsepower. This oxygen transfer rate will depend on
motor efficiency and important factors like pond depth and temperature.
As we see in the chart below, a manufacturer's listed oxygen transfer
rate of 3 pound per hour per horsepower will depend on the starting
oxygen rate (either PPM or mg/litre) of the water. If this surface
aerator is put into a pond that has an existing Dissolved Oxygen (D.O)
rate of 5 PPM or 5 milligrams per litre and the temperature of the
water is 59 degrees F (15 degrees Celsius) the actual oxygen transfer
rate of the quoted 3 pounds per HP per hour aerator will only be 46%
of the listed efficiency or 1.38 pounds of oxygen per hour per horsepower
The pumping rates of surface aerators and fountains are usually somewhat
lower than bottom diffuser systems. A typical medium sized surface
aerator from 1 to 7.5 HP which uses a propeller system and a float
will circulate anywhere from 200 to 3000 gallons per minute. The energy
required to run a 7.5 HP surface aerator to move 3000 gallons per
minute would be more than would be required for a diffuser system
which might be able to move the same volume of water with a 1/3 HP
air pump and three diffusers.
A surface aerator would be a poor choice for a large or deep pond.
It will continue to pump basically the same water over and over again,
adding no oxygen where it is needed, because it is not moving water
away from the aerator. Paddlewheels or aspirator type surface systems
would be better suited when the movement of the oxygenated water away
from the aeration device is important.
For the smaller scale surface aerator we use Kasco Marine surface
aerators or Aquamaster Surface Aerators or Scott Aerators or any of
the many popular retail brands.The typical application include commercial
aquaculture, agricultural ponds, industrial plants, municipal waste
water and backyard ponds. These units are typically selected for surface
aeration when a decorative fountain pattern is neither necessary nor
desired, many pond aerators are self-contained, lightweight units
that float at the surface with a single power cord returning to shore
and two or three mooring lines anchoring the unit. The units are easily
installed and maintained by a single person and have proven to be
an excellent choice for both continuous duty pond and lake aeration
and supplemental aeration for unique applications.
Wheel Surface Aerators
Paddlewheel aerators are surface aerators consisting some sort of
motor, electric, diesel, gas powered or tractor power takeoff that
is attached to a floating structure and paddles attached to the motor
hub or shaft which spin and splash at the water surface to create
aeration. By increasing the diameter of the paddles the oxygen transfer
rate can be increased; other important variables are the specific
depth of the blades as well of the angle of the paddles. By increasing
motor speed and hub rotation the oxygen transfer rate is also incrementally
A tractor powered takeoff (PTO) can have very high SOTR (Standard
Oxygen Transfer Rate) as much as 90 pounds of oxygen per hour which
means they can be important as an emergency aeration supply but the
drive-train and drive-shaft of such systems drain efficiency and they
are not at all energy efficient beyond emergency aeration. The more
efficient three-phase or 3-phase power paddle wheel aerators have
a SAE of between 3.5 and 6 pounds of oxygen per HP per hour. This
high SAE, combined their ability to de-stratify through rapid circulation
makes this type of aerator very popular with aquaculture around the
and Jet Aerators
This is another surface mounted aeration device that is very good
at adding aeration and circulation to a pond or basin. They use a
submersed propeller that creates a vacuum effect and draws air through
intake ports into a hollow shaft that is dispersed in a large plume
of fine bubbles (about 2 mm in diameter) throughout the water. The
angle of attack can be adjusted with simple altering of the float
brackets. The aspiration propeller aerators are extremely quiet as
there is no water boil at the surface like a standard surface aerator;
all of the mixing is below the surface. Motors can range from 1 to
100 HP and above. Multiple units can be deployed in basins to ensure
there are no stagnant dead spots. This creates a flow linkage that
disperses and mixes the oxygen evenly through the pond and ensures
an effective circulation. The SAE is approximately 2.0 - 3.0 LB/O2/hp-hr.
Using a dissolved oxygen meter is the most accurate way to ensure
your pond is getting the oxygen it requires to remain healthy.
407510 Dissolved Oxygen Meter
Dual display provides O2 or dissolved oxygen and
temperature readings Measures dissolved oxygen in water
from 0 to 20.00mg/L and oxygen in air from 0 to 100% Resolution:
0.1mg/L DO, 0.1% O2 Automatic temperature compensation
Oxygen DO Meter Kit By Sper Scientific
.O., ppm and mg/L: 0~19.99 Resolution: 0.01 Accuracy:
±1.5% F.S. Automatic temperature compensation 5 YR Warranty
Dissolved Oxygen 110 Meter, with Probe
Independent 100% and zero adjustment calibrations, and
auto-calculation of offset values for accuracy Automatic
temperature compensation (ATC) for ease of use Stores
and recalls up 100 dissolved oxygen (DO) readings with
corresponding temperature for reliability during field
use Water-resistant keypad for meter protection Dual-line,
LCD display of mg/L (ppm) or % saturation, plus temperature
in degrees C or F for flexibility of use
to Compare and Analyze Aerator Performance
Choosing your aeration system involves understand the demands and
desired results. Mechanically adding aeration to reach the oxygen
requirements of any aquatic system, natural or wastewater requires
a complete understanding of which oxygen diffusion type will be the
most cost and efficient to ensure correct circulation and mixing to
support the biological oxygen demand or the pounds of fish in the
pond. As we discussed; depending on the application you are considering
and the actual need for oxygen in your system there are two common
ways of describing any aerator performance. To best evaluate the cost
per year and efficiency use the oxygen transfer rates (SOTR and SAE)
to evaluate the cost and efficiency of the system.
The standard oxygen transfer rate (SOTR) is the amount of oxygen added
to water in 1 hour under a standard set of conditions. These conditions
are usually based on testing results that use oxygen deprived water
at a measured temperature as a baseline to which the aeration product
(diffuser, surface aerator or diffuser tubing) is added with a certain
airflow or horsepower rating to measure the amount of oxygen that
is transferred. The units of SOTR are pounds O2/hour, which can be
multiplied by 0.45 to derive the metric equivalent in kg O2/hour.
Standard aeration efficiency (SAE) is the standard oxygen transfer
rate divided by the power requirement in horsepower (hp). Units of
SAE are pounds O2/hp·hour, which can be multiplied by 0.61 to derive
SAE in metric units of kg O2/kW·hour.
Aerators transfer less oxygen under actual pond conditions than under
the standard conditions of aerator performance so SOTR and SAE values
are best used to only compare similar styles of aerators as an aid
in selecting the correct equipment to purchase rather than as design
criteria for pond use. When interpreting comparisons between aeration
systems and diffusers, small differences in SOTR and SAE test values
may not be meaningful because test conditions may vary and effect
Good SAE values and system dependability and durability are most important
when selecting aerators for general day-today use. The right aerator
for the job is one that delivers the required rates of oxygen transfer
at the lowest energy cost and has a low maintenance schedule.
Any design consideration for the ideal aeration system must evaluate
SAE and not only SOTE (Standard Oxygen Transfer Efficiency). SOTE
(standard oxygen transfer efficiency) is linked directly to bubble
size and bubble ascent velocity, as well as layout/configuration of
the diffuser or diffuser tubing in a tank or pond or basin. The SAE
depends on the total wire to water power and needs to be considered.
If an evaluation of the merits of an aerator were based on the SOTE
only, this would omit consideration of the pump required for diffuser
aerators, just as it would omit the head loss of some bubble diffusers.
oxygen-transfer rates and water-circulating capabilities of emergency
aerators for fish ponds
Oxygen-transfer rates (tap water, 0 mg/l dissolved oxygen, 20°C) for
four tractor powered emergency aerators tested in a 820-m3 pond were:
blower-fan aerator, 12.2 kg O2/h; Crisafulli® pump and sprayer, 12.3
kg O2/h; Airmaster® aerator (centrifugal pump and sprayer), 21.3 kg
O2/h; paddlewheel aerator, 26.3 kg O2/h. Times required for aerators
to homogeneously mix salt in a 6000-m3 pond were: blower-fan aerator,
96 min; Crisafulli pump and sprayer, 94 min; paddlewheel aerator,
53 min; and Airmaster aerator, 38 min. The Airmaster aerator and the
paddlewheel aerator did not differ in their abilities to transfer
oxygen and circulate pond water (P > 0.05); they were both superior
to the blower-fan aerator and the Crisafulli pump and sprayer (P <
0.01). ? Research supported by USDA Special Grant No. 82-CRSR-2-10161
Available at: http://dx.doi.org/10.1016/0044-8486(84)90302-8
of Lagoon Aeration
There are many factors that will act to hinder the transfer of the
oxygen load in a wastewater lagoon system. All of these factors must
be considered to ensure that sufficient air is added to allow the
necessary pounds of oxygen per day to be transferred. Some of these
factors include: Biological activity in the ponds is optimized when
a minimum dissolved oxygen saturation concentration of 2.0 ppm is
maintained at all times. The aeration equipment should be sized for
this basis. The atmospheric pressure at the treatment plant site is
an important factor in determining how much oxygen can be transferred.
It is more difficult to transfer oxygen at higher elevations than
at sea level because of changes in the local air pressure. The maximum
allowable oxygen saturation concentration that can occur at the field
temperature and lagoon depth conditions must be considered. The maximum
amount of oxygen that water can hold at 20 degrees Celsius is 9.09
ppm. As the water temperature increases in the summer months, lesser
concentrations of oxygen can be held by the warmer water. Having determined
the standard oxygen requirement of a pond system, it is next important
to consider how much air volume in SCFM (standard cubic feet per minute)
will be needed to deliver that mass of oxygen. Each cubic foot of
air added to the lagoon will contain about 0.0173 pounds of oxygen.
The oxygen transfer efficiency (OTE) of a diffuser system is a function
of its depth in the ponds. Typically, an OTE of about 1.6% per foot
of depth is found for fine bubble diffusers in a pond setting. For
a lagoon with ten feet of depth, a transfer efficiency of about 16%
could be expected. This means that 16% of the air added at a depth
of ten feet will actively be transferred into the water while eighty-four
percent will be excess and will bubble to the surface. This seems
like an excessive air loss rate, but it is the best now available
with current technology.
Available at: http://www.lagoonsonline.com/aerationmain.htm
: Water Aeration
Water aeration is often required in water bodies that suffer from
anoxic conditions, usually caused by adjacent human activities such
as sewage discharges, agricultural run-off, or over-baiting a fishing
lake. Aeration can be achieved through the infusion of air into the
bottom of the lake, lagoon or pond or by surface agitation from a
fountain or spray-like device to allow for oxygen exchange at the
surface and the release of noxious gasses such as carbon dioxide,
methane or hydrogen sulfide. Dissolved oxygen (DO) is a major contributor
to water quality. Not only do fish and other aquatic animals need
it, but oxygen breathing aerobic bacteria decompose organic matter.
When oxygen concentrations become low, anoxic conditions may develop
which can decrease the ability of the water body to support life.
Aeration speeds up this process of oxidizing organic and mineral pollution.
In fact, if there is sufficient aeration, the fish will be able to
survive, where before they suddenly died. By pumping compressed air
out to the bottom of a lake, lagoon or pond with the use of a diffuser,
the rising air bubbles and the friction caused in the water will bring
bottom water to the surface where it is exposed to the atmosphere.
Large volumes of water thus release noxious gases to the atmosphere,
water picks up oxygen while circulating at the surface.
Natural bacteria are stimulated by aeration and circulation and they
will feed on muck, organics and the food that normally feeds algae
blooms or aquatic plants growth. Using aeration and bacteria is often
a safe and sound form of pollution removal.
Available at: http://en.wikipedia.org/wiki/Water_aeration
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