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Water aeration is the process of increasing or maintaining the oxygen saturation 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 an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
,
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 ...
or
pond A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from tha ...
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 ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
,
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 relative abundance of methane ...
or
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
. 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 ca ...
(DO) is a major contributor to poor water quality. Not only do fish and most other aquatic animals need oxygen, aerobic bacteria 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 occur through a movement of water caused by an incoming
stream A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams ...
,
waterfall A waterfall is a 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 several ...
, or even a strong
flood A flood is an overflow of water ( 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 an area of study of the discipline hydrol ...
. 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 the Greek "limnos" meaning "lake". It is the layer that lies below the thermocline. Typically the hypolimni ...
.


Surface aeration


Low speed surface aerator

The low speed surface aerator is a device for biology aeration with high efficiency. Those 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 motor that powers a rotating impeller. 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 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 definition of ...
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 surface aerators 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 first 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. Surface aerators are 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 first portion of the water column, often leaving the bottom portions unaffected. Low speed surface aerator 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. lot ...
(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 gaseous fuel, such as coal gas, producer gas, biogas, landfill gas or natural gas. In the United Kingdom, the term is unambiguous. In the United States, due to the widespread use of ...
, or an
electric motor An electric motor is an electrical 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 wire winding to generate f ...
. 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.Bolles, Steven A
"Modeling Wastewater Aeration Systems to Discover Energy Savings Opportunities."
Process Energy Services, LLC.


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. 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, porcelain, ...
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 The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
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. 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 as well as other aeration techniques, such as coarse bubble aeration.


Lake destratification

(''See also Lake de-stratification)'' Circulators are commonly used to mix a
pond A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from tha ...
or
lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
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 is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, ...
also can be adversely affected. For fisheries managers, the spatial distribution of
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
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.


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, se ...
, sending dissolved
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
levels plummeting and threatening the species it supports. Two dedicated
McTay Marine McTay Marine was a shipbuilder in Bromborough, Merseyside from 1974 to 2016. History McTay Engineering had been set up in 1963 by James McBurney and Jim Taylor. McTay Engineering specialised in the construction of storage tanks and associated pla ...
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. The dissolved oxygen concentration within
Cardiff Bay Cardiff Bay ( cy, Bae Caerdydd; historically Tiger Bay; colloquially "The Bay") is an area and freshwater lake in Cardiff, Wales. The site of a former tidal bay and estuary, it serves as the river mouth of the River Taff and Ely. The body of ...
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 is using a mobile oxygenation barge built by
McTay Marine McTay Marine was a shipbuilder in Bromborough, Merseyside from 1974 to 2016. History McTay Engineering had been set up in 1963 by James McBurney and Jim Taylor. McTay Engineering specialised in the construction of storage tanks and associated pla ...
with
liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an app ...
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. 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 region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the Eastern Shore of Maryland / ...
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 not ...
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 are a fraction of their 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 process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
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, in exchange the filter feeders keep the water clean and thus clear enough for plants to have sufficient access to sunlight. Researchers have proposed that 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 environm ...
.


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, inc ...
processes use a variety of forms of aeration to support biological oxidative processes. A typical example is activated sludge 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 *
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 ( ; from Greek λίμνη, ''limne'', "lake" and λόγος, ''logos'', "knowledge") is the study of inland aquatic ecosystems. The study of limnology includes aspects of the biological, chemical, physical, and geological characteris ...


References

{{DEFAULTSORT:Water Aeration Aquatic ecology