Pond Aeration
Encyclopedia
Oxygen saturation
Oxygen saturation or dissolved oxygen is a relative measure of the amount of oxygen that is dissolved or carried in a given medium. It can be measured with a dissolved oxygen probe such as an oxygen sensor or an optode in liquid media, usually water.It has particular significance in medicine and...
of the water.
Water quality
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 lakeLake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
, lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
or pond
Pond
A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens, water features and koi ponds; all designed for aesthetic ornamentation as landscape or architectural...
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
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
or hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
.
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
Aeration
Aeration is the process by which air is circulated through, mixed with or dissolved in a liquid or substance.-Aeration of liquids:-Methods:Aeration of liquids is achieved by:...
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.
Aeration methods
Any procedure by which oxygen is added to water can be considered a type of water aeration. This being the only criterion, there are a variety of ways to aerate a pond. There are two categories of pond aeration: surface aeration and subsurface aeration.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, pond plants restore oxygen to the water, and thus aerate the pond, 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 pond and natural aeration can occur through a movement of water caused by an incoming stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
, waterfall
Waterfall
A waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.-Formation:Waterfalls are commonly formed when a river is young. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens...
, or even a strong flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
.
Fountains
Fountains aerate by pulling water from the surface of the water (usually the first 1–2 feet) and propelling it into the air. Some fountains incorporate the use of a draft tube, which extends deeper and is able to pull water from approximately six feet below the surface, so as to achieve more water circulation.A fountain consists of a motor that powers a rotating impeller
Impeller
An impeller is a rotor inside a tube or conduit used to increase the pressure and flow of a fluid.- Impellers in pumps :...
. 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
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...
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 pond’s 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 an 3 metre radius. This circulation and oxygenating is then limited to the first portion of the water column, often leaving the bottom portions unaffected.Paddlewheel aerators
Paddlewheel aerators also utilize air-to-water contact to transfer oxygen from the air in the atmosphere to the pond. They are most often used in the aquacultureAquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
(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
Power take-off
A power take-off or power takeoff is a splined driveshaft, usually on a tractor or truck, that can be used to provide power to an attachment or separate machine. It is designed to be easily connected and disconnected...
), a gas engine
Gas engine
A gas engine means an engine running on a gas, such as coal gas, producer gas biogas, landfill gas, or natural gas. In the UK, the term is unambiguous...
, or an electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
. 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 pond. 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 pond and allow them to rise by the force of gravity. Diffused aeration systems utilize bubblesLiquid bubble
A bubble is a globule of one substance in another, usually gas in a liquid.Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.-Common examples:...
to aerate as well as mix the pond. Water displacement from the expulsion of bubbles can cause a mixing action to occur, and the contact between the water and the bubble will result in an oxygen transfer.
Coarse bubble aeration
Coarse bubble aeration is a type of subsurface aeration wherein air is pumped from an on-shore air compressorAir compressor
An air compressor is a device that converts power into kinetic energy by compressing and pressurizing air, which, on command, can be released in quick bursts...
. 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 pond’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 pond. 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 ceramicCeramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
plastic, or perforated membranes made from EPDM (ethylene propylene diene Monomer) rubber
EPDM rubber
EPDM rubber , a type of synthetic rubber, is an elastomer which is characterized by a wide range of applications. The E refers to ethylene, P to propylene, D to diene and M refers to its classification in ASTM standard D-1418. The M class includes rubbers having a saturated chain of the...
. With EPDM rubber units, there are approximately eight thousand holes per disk through which air is diffused. Air pumped through the diffuser membranes is released into the water at a rate of roughly 30-50 thousand bubbles per second. These bubbles are known as fine bubbles. The EPA
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
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. On average, diffused pond aeration diffuses approximately 2-4 cfm (cubic feet of air per minute), but some operate at levels as low as 1 cfm or as high as 10 cfm.
By releasing millions of fine bubbles instead of fewer coarse bubbles, fine bubble diffused aeration is able to maximize the surface area of the bubbles and thus transfer more oxygen to the pond per bubble. Additionally, smaller bubbles take more time to reach the surface so not only is the surface area maximized but so are the number of seconds each bubble spends in the water, allowing it more time 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.
Windmills may also be used to power fine bubble aerators.
Solar Panels may also be used to power fine bubble aerators and offer many advantages over other aeration methods including;
• Solar pond aerators can be used in remote locations, far from any electrical outlets.
• Once you have a solar pond aerator installed, you will not have to pay for the energy needed to run it.
• As long as they can receive plenty of sunlight, these aerators will work just as well as other aerators.
Circulators
The primary function of circulators is to circulate and mix the water body, which can reduce pond stratification. Once the circulation reaches the surface, the movement of water causes a transfer of oxygen to occur. In the case of circulators, oxygen transfer is a side-effect and is minimal in comparison to alternative methods of aeration.Oxygenation barges
During heavy rain, London's sewage storm pipes overflow into the River ThamesRiver Thames
The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...
, sending dissolved oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
levels plummeting and threatening the species it supports. Two dedicated McTay Marine
McTay Marine
-Facilities:The McTay Marine shipyard is located at Bromborough on the South bank of the River Mersey, in the North West of England. The purpose built facilities are arranged on a site with ramped slipway facilities directly into the River Mersey...
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
Cardiff Bay is the area created by the Cardiff Barrage in South Cardiff, the capital of Wales. The regeneration of Cardiff Bay is now widely regarded as one of the most successful regeneration projects in the United Kingdom. The Bay is supplied by two rivers to form a freshwater lake round the...
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
-Facilities:The McTay Marine shipyard is located at Bromborough on the South bank of the River Mersey, in the North West of England. The purpose built facilities are arranged on a site with ramped slipway facilities directly into the River Mersey...
with liquid oxygen
Liquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
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.