Paddlewheel Aerator
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Water aeration is the process of increasing or maintaining the
oxygen saturation Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is Dissolution (chemistry), dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the g ...
of water in both natural and artificial environments. Aeration techniques are commonly used in pond, lake, and reservoir management to address low oxygen levels or algal blooms.


Water quality

Water aeration is often required in water bodies that suffer from hypoxic or anoxic conditions, often caused by upstream 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 A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...
,
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...
or
pond A pond is a small, still, land-based body of water formed by pooling inside a depression (geology), depression, either naturally or artificiality, artificially. A pond is smaller than a lake and there are no official criteria distinguishing ...
or by surface agitation from a fountain or spray-like device to allow for oxygen exchange at the surface and the release of gasses such as
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
,
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
or
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...
. Decreased levels of
dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can ...
(DO) is a major contributor to poor water quality. Not only do fish and most other aquatic animals need oxygen,
aerobic bacteria An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. The ability to exhibit aerobic respiration may yield benefits to the aerobic organism, as aerobic respiration yields more energy than anaerobic ...
help 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 methods

Any procedure by which oxygen is added to water can be considered a type of water aeration. There are many ways to aerate water, but these all fall into two broad areas – surface aeration and subsurface aeration. A variety of techniques and technologies are available for both approaches.


Natural aeration

Natural aeration is a type of both sub-surface and surface aeration. It can occur through sub-surface aquatic plants. Through the natural process of photosynthesis, water plants release oxygen into the water providing it with the oxygen necessary for fish to live and aerobic bacteria to break down excess nutrients. Oxygen can be driven into the water when the wind disturbs the surface of the water body and natural aeration can also occur through a movement of water caused by an incoming
stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...
,
waterfall A waterfall is any point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf. Waterfalls can be formed in seve ...
, or even a strong
flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...
. In large water bodies in temperate climates, autumn turn-over can introduce oxygen rich water into the oxygen-poor
hypolimnion The hypolimnion or under lake is the dense, bottom layer of water in a thermally- stratified lake. The word " hypolimnion" is derived from . It is the layer that lies below the thermocline. Typically the hypolimnion is the coldest layer of a la ...
.


Surface aeration


Low speed surface aerator

The low speed surface aerator is a device for biology aeration with high efficiency. These devices are often in steel protected by epoxy coating and generate high torque. The mixing of water volume is excellent. The common power is going from 1 up to 250kw per unit with an efficiency (SOE) around 2 kgO2/kw. Low speed aerator are used mostly for biology plant aeration for water purification. The higher the diameter, the higher the SOE and mixing.


Fountains

A fountain consists of a means of spraying the water upwards into the air. Typically this may be done using a motor that powers a rotating
impeller An impeller, or impellor, is a driven rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid. Strictly speaking, propellers are a sub-clas ...
. The impeller pumps water from the first few feet of the water and expels it into the air. This process utilizes air-water contact to transfer oxygen. As the water is propelled into the air, it breaks into small droplets. Collectively, these small droplets have a large
surface area The surface area (symbol ''A'') of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the d ...
through which oxygen can be transferred. Upon return, these droplets mix with the rest of the water and thus transfer their oxygen back to the ecosystem. Fountains are a popular method of providing surface aeration because of the aesthetic appearance that they offer. However, most fountains are unable to produce a large area of oxygenated water. Also, running electricity through the water to the fountain can be a safety hazard.


Floating surface aerators

Floating surface aerators work in a similar manner to fountains, but they do not offer the same aesthetic appearance. They extract water from the top 1–2 feet of the water body and utilize air-water contact to transfer oxygen. Instead of propelling water into the air, they disrupt the water at the water surface. Floating surface aerators are also powered by on-shore electricity. The effectiveness of a surface aerator is limited to a small area as they are unable to add circulation or oxygen to much more than a 3-metre radius. This circulation and oxygenating is then limited to the uppermost portion of the water column, often leaving the bottom portions unaffected. Low speed surface aerators can also be installed on floats.


Paddlewheel aerators

Paddlewheel aerators also utilize air-to-water contact to transfer oxygen from the air in the atmosphere to the water body. They are most often used in the
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. Nelu ...
(rearing aquatic animals or cultivating aquatic plants for food) field. Constructed of a hub with attached paddles, these aerators are usually powered by a tractor power take-off ( PTO), a
gas engine A gas engine is an internal combustion engine that runs on a fuel gas (a gaseous fuel), such as coal gas, producer gas, biogas, landfill gas, natural gas or hydrogen. In the United Kingdom and British English-speaking countries, the term is ...
, or an
electric motor An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a electromagnetic coil, wire winding to gene ...
. They tend to be mounted on floats. Electricity forces the paddles to turn, churning the water and allowing oxygen transfer through air-water contact. As each new section of water is churned, it absorbs oxygen from the air and then, upon its return to the water, restores it to the water. In this regard paddlewheel aeration works very similarly to floating surface aerators.


Subsurface aeration

Subsurface aeration seeks to release bubbles at the bottom of the water body and allow them to rise by the force of buoyancy. ''Diffused aeration systems'' utilize bubbles to aerate as well as mix the water. Water displacement from the expulsion of bubbles will cause a mixing action to occur, and the contact between the water and the bubble will result in an oxygen transfer.


Jet aeration

Subsurface aeration can be accomplished by the use of
jet aerators {{more citations needed, date=January 2021 Jet aerators are applied across a wide range of water, wastewater and biosolids treatment applications. Their primary purpose is to transfer oxygen to the liquid or sludge. A Jet aerator works through aspi ...
, which aspirate air, by means of the Venturi principle, and inject the air into the liquid.


Coarse bubble aeration

Coarse bubble aeration is a type of subsurface aeration wherein air is pumped from an on-shore
air compressor An air compressor is a machine that takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a Pneumatics, pneumatic device that energy conversion, converts mechanical power (from ...
. through a hose to a unit placed at the bottom of the water body. The unit expels ''coarse bubbles'' (more than 2mm in diameter), which release oxygen when they come into contact with the water, which also contributes to a mixing of the lake's stratified layers. With the release of large bubbles from the system, a turbulent displacement of water occurs which results in a mixing of the water. In comparison to other aeration techniques, coarse bubble aeration is very inefficient in the way of transferring oxygen. This is due to the large diameter and relatively small collective surface area of its bubbles.


Fine bubble aeration

Fine bubble aeration is an efficient way to transfer oxygen to a water body. A compressor on shore pumps air through a hose, which is connected to an underwater aeration unit. Attached to the unit are a number of diffusers. These diffusers come in the shape of discs, plates, tubes or hoses constructed from glass-bonded silica, porous
ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...
plastic, PVC or perforated membranes made from EPDM (ethylene propylene diene Monomer) rubber. Air pumped through the diffuser membranes is released into the water. These bubbles are known as ''fine bubbles''. The EPA defines a fine bubble as anything smaller than 2mm in diameter. This type of aeration has a very high oxygen transfer efficiency (OTE), sometimes as high as 15 pounds of oxygen / (horsepower * hour) (9.1 kilograms of oxygen / (kilowatt * hour)). On average, diffused air aeration diffuses approximately 2–4 cfm (cubic feet of air per minute) (56.6-113.3 liters of air per minute), but some operate at levels as low as 1 cfm (28.3 L/min) or as high as 10 cfm (283 L/min). Fine bubble diffused aeration is able to maximize the surface area of the bubbles and thus transfer more oxygen to the water per bubble volume. Additionally, smaller bubbles take more time to reach the surface so not only is the surface area maximized but so are the time each bubble spends in the water, allowing it more opportunity to transfer oxygen to the water. As a general rule, smaller bubbles and a deeper release point will generate a greater oxygen transfer rate. One of the drawbacks to fine bubble aeration is that the membranes of ceramic diffusers can sometimes clog and must be cleaned in order to keep them working at their optimum efficiency. Also, they do not possess the ability to mix the water column as well as other aeration techniques, such as coarse bubble aeration.


Lake destratification

Circulators are commonly used to mix a
pond A pond is a small, still, land-based body of water formed by pooling inside a depression (geology), depression, either naturally or artificiality, artificially. A pond is smaller than a lake and there are no official criteria distinguishing ...
or
lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...
and thus reduce thermal stratification. Once circulated water reaches the surface, the air-water interface facilitates the transfer of oxygen to the lake water.
Natural resource Natural resources are resources that are drawn from nature and used with few modifications. This includes the sources of valued characteristics such as commercial and industrial use, aesthetic value, scientific interest, and cultural value. ...
and environmental managers have long been challenged by problems caused by thermal stratification of lakes. Fish die-offs have been directly associated with thermal gradients, stagnation, and ice cover. Excessive growth of plankton may limit the recreational use of lakes and the commercial use of lake water. With severe thermal stratification in a lake, the quality of
drinking water Drinking water or potable water is water that is safe for ingestion, either when drunk directly in liquid form or consumed indirectly through food preparation. It is often (but not always) supplied through taps, in which case it is also calle ...
also can be adversely affected. For fisheries managers, the spatial distribution of
fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
within a lake is often adversely affected by thermal stratification and in some cases may indirectly cause large die-offs of recreationally important fish. One commonly-used tool to reduce the severity of these lake management problems is to eliminate or lessen thermal stratification through aeration. Many types of aeration equipment have been used to reduce or eliminate thermal stratification. Aeration has met with some success, although it has rarely proved to be a panacea.


Large-scale projects


Thames oxygenation barges

During heavy rain, London's sewage storm pipes overflow into the
River Thames The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, s ...
, sending dissolved
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
levels plummeting and threatening the species it supports. Two dedicated McTay Marine vessels, oxygenation barges ''Thames Bubbler'' and ''Thames Vitality'' are used to replenish oxygen levels, as part of an ongoing battle to clean up the river, which now supports 115 species of fish and hundreds more invertebrates, plants and birds.


Cardiff Bay

The dissolved oxygen concentration within
Cardiff Bay Cardiff Bay (; colloquially "The Bay") is an area and freshwater lake in Cardiff, Wales. The site of a former tidal bay and estuary, it is the river mouth of the River Taff and River Ely, Ely. The body of water was converted into a lake as part ...
are maintained at or above 5 mg/L. Compressed air is pumped, from five sites around the Bay, through a series of steel reinforced rubber pipelines, laid on the beds of the Bay and Rivers Taff and Ely. These are connected to approximately 800 diffusers. At times this is insufficient and the Harbour Authority uses a mobile oxygenation barge built by McTay Marine with
liquid oxygen Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear cyan liquid form of dioxygen . It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which is ongoing. Physical ...
stored in a tank. Liquid oxygen is passed through an electrically heated vapouriser and the gas is injected into a stream of water which is pumped from, and returned to, the bay. The barge is capable of dissolving up to 5 tonnes of oxygen in 24 hours.


Chesapeake Bay

Similar options have been proposed to help rehabilitate the
Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula, including parts of the Ea ...
where the principal problem is lack of filter-feeding organisms such as
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but no ...
s responsible for keeping the water clean. Historically the Bay's oyster population was in the tens of billions, and they circulated the entire Bay volume in a matter of days. Due to pollution, disease and over-harvesting their population is a fraction of historic levels. Water that was once clear for meters is now so turbid and sediment-ridden that a wader may lose sight of their feet before their knees are wet. Oxygen is normally supplied by submerged aquatic vegetation via
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
but pollution and sediments have reduced the plant populations , resulting in a reduction of dissolved oxygen levels, rendering areas of the bay unsuitable for aerobic aquatic life. In a symbiotic relation the plants provide the oxygen needed for underwater organisms to proliferate, and in exchange the filter feeders keep the water clean and thus clear enough for plants to have sufficient access to sunlight. Researchers have proposed oxygenation through artificial means as a solution to help improve water quality. Aeration of hypoxic water-bodies seems an appealing solution and it has been tried successfully many times on freshwater ponds and small lakes. However no one has undertaken an aeration project as large as an
estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime enviro ...
. A 353-hectare portion of the bay connected to the Rock Creek has been aerated using pipes since 2016. The system started as a large-bubble system intended mainly for de-stratification, creating a 74-ha oxic zone. It was upgraded in 2019 to fine-bubble injectors to provide more oxygen directly.


Water treatment aeration

Many
water treatment Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, ...
processes use a variety of forms of aeration to support biological oxidative processes. A typical example is
activated sludge The activated sludge process is a type of biological wastewater treatment process for treating sewage or Industrial wastewater treatment, industrial wastewaters using aeration and a biological floc (biofilm), floc composed of bacteria and protozoa ...
which can use fine or coarse bubble aeration or mechanical aeration cones which draw up mixed liquor from the base of a treatment tank and eject it through the air where oxygen is entrained in the liquor.


See also

*
Aerated lagoon An aerated lagoon (or aerated pond) is a simple wastewater treatment system consisting of a pond with artificial aeration to promote the biological oxidation of wastewaters. There are many other aerobic biological processes for treatment of waste ...
*
Lake ecosystem A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems (''lentic'' ref ...
*
Limnology Limnology ( ; ) is the study of inland aquatic ecosystems. It includes aspects of the biological, chemical, physical, and geological characteristics of fresh and saline, natural and man-made bodies of water. This includes the study of lakes, ...


References

{{DEFAULTSORT:Water Aeration Aquatic ecology