Aerated lagoon
Encyclopedia
An aerated lagoon or aerated basin is a holding and/or treatment pond
provided with artificial aeration
to promote the biological oxidation of wastewater
s. There are many other biological processes for treatment of wastewaters, for example activated sludge
, trickling filter
s, rotating biological contactor
s and biofilter
s. They all have in common the use of oxygen
(or air) and microbial action to biotreat the pollutants in wastewaters.
systems where the effluent has the same composition as the mixed liquor in the lagoon. Typically the sludge will have a residence time or sludge age of 1 to 5 days. This means that the chemical oxygen demand
(COD) removed is relatively little and the effluent is therefore unacceptable for discharge into receiving waters. The objective of the lagoon is therefore to act as a biologically assisted flocculator which converts the soluble biodegradable organics in the influent to a biomass which is able to settle as a sludge. Usually the effluent is then put in a second pond where the sludge can settle. The effluent can then be removed from the top with a low COD, while the sludge accumulates on the floor and undergoes anaerobic stabilisation. .
Ponds or basins using floating surface aerators achieve 80 to 90% removal of BOD
with retention times of 1 to 10 days. The ponds or basins may range in depth from 1.5 to 5.0 metres.
In a surface-aerated system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O2
/kW
h. However, they do not provide as good mixing as is normally achieved in activated sludge systems and therefore aerated basins do not achieve the same performance level as activated sludge units.
Biological oxidation processes are sensitive to temperature and, between 0 °C and 40 °C, the rate of biological reactions increase with temperature. Most surface aerated vessels operate at between 4 °C and 32 °C.
grid inside a lagoon. There are two main types of submerged diffused aeration systems for lagoon applications: floating lateral and submerged lateral. Both these systems utilize fine
or medium bubble diffusers to provide aeration and mixing to the process water. The diffusers can be suspended slightly above the lagoon floor or may rest on the bottom. Flexible airline or weighted air hose supplies air to the diffuser unit from the air lateral (either floating or submerged).
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...
provided with artificial 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:...
to promote the biological oxidation of wastewater
Wastewater
Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...
s. There are many other biological processes for treatment of wastewaters, for example activated sludge
Activated sludge
Activated sludge is a process for treating sewage and industrial wastewaters using air and a biological floc composed of bacteria and protozoans.-Purpose:...
, trickling filter
Trickling filter
A trickling filter consists of a fixed bed of rocks, lava, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime to grow, covering the bed of media...
s, rotating biological contactor
Rotating biological contactor
A rotating biological contactor or RBC is a biological treatment process used in the treatment of wastewater following primary treatment. The primary treatment process removes the grit and other solids through a screening process followed by a period of settlement...
s and biofilter
Biofilter
Biofiltration is a pollution control technique using living material to capture and biologically degrade process pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air...
s. They all have in common the use of 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...
(or air) and microbial action to biotreat the pollutants in wastewaters.
Types of aerated lagoons or basins
- Suspension mixed lagoons, where there is less energy provided by the aeration equipment to keep the sludge in suspension.
- Facultative lagoonFacultative lagoonFacultative lagoons are a type of stabilization pond used for biological treatment of industrial and domestic wastewater. Sewage or organic waste from food or fiber processing may be catabolized in a system of constructed ponds where adequate space is available to provide an average waste...
s, where there is insufficient energy provided by the aeration equipment to keep the sludge in suspension and solids settle to the lagoon floor. The biodegradable solids in the settled sludge then degrade anaerobically.
Suspension mixed lagoons
Suspension mixed lagoons flow through activated sludgeActivated sludge
Activated sludge is a process for treating sewage and industrial wastewaters using air and a biological floc composed of bacteria and protozoans.-Purpose:...
systems where the effluent has the same composition as the mixed liquor in the lagoon. Typically the sludge will have a residence time or sludge age of 1 to 5 days. This means that the chemical oxygen demand
Chemical oxygen demand
In environmental chemistry, the chemical oxygen demand test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in surface water or wastewater, making COD a useful measure of water quality...
(COD) removed is relatively little and the effluent is therefore unacceptable for discharge into receiving waters. The objective of the lagoon is therefore to act as a biologically assisted flocculator which converts the soluble biodegradable organics in the influent to a biomass which is able to settle as a sludge. Usually the effluent is then put in a second pond where the sludge can settle. The effluent can then be removed from the top with a low COD, while the sludge accumulates on the floor and undergoes anaerobic stabilisation. .
Methods of aerating lagoons or basins
There are many methods for aerating a lagoon or basin:- Motor-driven floating surface aerators
- Motor-driven submerged aerators
- Motor-driven fixed-in-place surface aerators
- Injection of compressed air through submerged diffusersDiffuser (sewage)An air diffuser or membrane diffuser is an aeration device typically in the shape of a disc, tube or plate, which is used to transfer air and with that oxygen into sewage or industrial wastewater. Oxygen is required by microorganisms/bacteria residents in the water to break down the pollutants...
Floating surface aerators
Biochemical oxygen demand
Biochemical oxygen demand or B.O.D. is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. The term also refers to a chemical procedure for...
with retention times of 1 to 10 days. The ponds or basins may range in depth from 1.5 to 5.0 metres.
In a surface-aerated system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O2
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...
/kW
Kw
kw or KW may refer to:* Kuwait, ISO 3166-1 country code** .kw, the country code top level domain for Kuwait* Kilowatt* Self-ionization of water Kw* Cornish language's ISO 639 code* Kitchener–Waterloo, Ontario, Canada...
h. However, they do not provide as good mixing as is normally achieved in activated sludge systems and therefore aerated basins do not achieve the same performance level as activated sludge units.
Biological oxidation processes are sensitive to temperature and, between 0 °C and 40 °C, the rate of biological reactions increase with temperature. Most surface aerated vessels operate at between 4 °C and 32 °C.
Submerged diffused aeration
Submerged diffused air is essentially a form of a diffuserDiffuser (sewage)
An air diffuser or membrane diffuser is an aeration device typically in the shape of a disc, tube or plate, which is used to transfer air and with that oxygen into sewage or industrial wastewater. Oxygen is required by microorganisms/bacteria residents in the water to break down the pollutants...
grid inside a lagoon. There are two main types of submerged diffused aeration systems for lagoon applications: floating lateral and submerged lateral. Both these systems utilize fine
Fine bubble diffusers
Fine bubble diffusers are a pollution control technology used to aerate wastewater for sewage treatment. They produce a plethora of very small air bubbles which rise slowly from the floor of a wastewater treatment plant or sewage treatment plant aeration tank and provide substantial and efficient...
or medium bubble diffusers to provide aeration and mixing to the process water. The diffusers can be suspended slightly above the lagoon floor or may rest on the bottom. Flexible airline or weighted air hose supplies air to the diffuser unit from the air lateral (either floating or submerged).
See also
- Industrial wastewater treatmentIndustrial wastewater treatmentIndustrial wastewater treatment covers the mechanisms and processes used to treat waters that have been contaminated in some way by anthropogenic industrial or commercial activities prior to its release into the environment or its re-use....
- List of waste water treatment technologies
- Retention basinRetention basinA retention basin is used to manage stormwater runoff to prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. Sometimes called a wet pond or wet detention basin, it is an artificial lake with vegetation around the perimeter, and includes a...
- Rotating biological contactorRotating biological contactorA rotating biological contactor or RBC is a biological treatment process used in the treatment of wastewater following primary treatment. The primary treatment process removes the grit and other solids through a screening process followed by a period of settlement...
- Sewage treatmentSewage treatmentSewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
- Water aeration
- Water pollutionWater pollutionWater pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
External links
- Wastewater Lagoon Systems in Maine
- Aerated, Partial Mix Lagoons (Wastewater Technology Fact Sheet by the U.S. Environmental Protection Agency)
- Aerated Lagoon Technology (Linvil G. Rich, Professor Emeritus, Department of Environmental Engineering and Science, Clemson UniversityClemson UniversityClemson University is an American public, coeducational, land-grant, sea-grant, research university located in Clemson, South Carolina, United States....
)