![Schematic of the Waste Stabilization Pond (WSP)](https://upload.wikimedia.org/wikipedia/commons/2/24/Schematic_of_the_Waste_Stabilization_Pond_%28WSP%29.jpg)
Waste stabilization ponds (WSPs or stabilization ponds or waste stabilization lagoons) are
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 th ...
s designed and built for
wastewater treatment
Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environme ...
to reduce the organic content and remove
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s from
wastewater
Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industr ...
. They are man-made depressions confined by earthen structures. Wastewater or "influent" enters on one side of the waste stabilization pond and exits on the other side as "effluent", after spending several days in the pond, during which treatment processes take place.
Waste stabilization ponds are used worldwide for wastewater treatment and are especially suitable for
developing countries
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
that have warm climates. They are frequently used to treat
sewage
Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residenc ...
and
industrial effluents, but may also be used for treatment of municipal run-off or
stormwater
Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...
. The system may consist of a single pond or several ponds in a series, each pond playing a different role in the removal of
pollutants
A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...
. After treatment, the effluent may be returned to surface water or reused as
irrigation
Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...
water (or
reclaimed water
Water reclamation (also called wastewater reuse, water reuse or water recycling) is the process of converting municipal wastewater
Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produce ...
) if the effluent meets the required effluent standards (e.g. sufficiently low levels of
pathogens
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
).
Waste stabilization ponds involve natural treatment processes which take time because removal rates are slow. Therefore, larger areas are required than for other treatment processes with external energy inputs. Waste stabilization ponds described here use no aerators. High-performance lagoon technology that does use aerators has much more in common with the
activated sludge
The activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. It uses air (or oxygen) and microorganisms ...
process. Such
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 ...
s use less area than is needed for traditional stabilization ponds and are also common in small towns.
Fundamentals
Concept of stabilization
Sewage
Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residenc ...
and many types of
industrial wastewaters contain organic matter. If wastewater is discharged untreated into
surface water
Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean.
The vast majority of surface water is produced by prec ...
bodies (for instance, rivers and lakes), their organic matter serves as food for
microorganisms
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
living in the surface waters. These organisms use the organic matter for energy generation for their growth and reproduction. This is done via their
respiration
Respiration may refer to:
Biology
* Cellular respiration, the process in which nutrients are converted into useful energy in a cell
** Anaerobic respiration, cellular respiration without oxygen
** Maintenance respiration, the amount of cellul ...
, in which they convert the organic matter into carbon dioxide and water. These stable components do not cause water pollution problems. Therefore this is frequently called "stabilization" of the organic matter.
However, these organisms use oxygen in their respiration, thus reducing the oxygen concentration in the surface waters. This is one of the main
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
problems, which may affect the surface water
biota, including fish.
Waste stabilization ponds reproduce these biological phenomena before they take place in the receiving surface water and cause the pollution problems due to oxygen consumption. The ponds receive wastewater, and, by natural processes similar to those that take place in the surface waters, carry out stabilization of the organic matter inside them, as part of the treatment. This is why they received the name of waste stabilization ponds.
Microorganisms
The reactions take place by the joint participation of several microorganisms living within the pond. The organic matter is measured as
biochemical oxygen demand
Biochemical oxygen demand (BOD) is the amount of dissolved oxygen (DO) needed (i.e. demanded) by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period. T ...
(BOD). BOD values in the pond effluent are lower than in the influent, reflecting the removal of organic matter. This pond
biome
A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
uses organic matter from the wastewater as food.
Nutrients are converted to cell material and energy for life processes including reproduction and growth of living cells. Some of these living cells will be consumed by organisms at higher
trophic levels
The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...
within the pond. In ponds, the most important group of microorganisms are
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
, which utilize most of the organic matter from the wastewater, but also consume oxygen.
Algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
are another essential group of microorganisms. They do not depend on the organic material from the influent. Instead, they undertake
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 i ...
, in which they produce the organic matter for their own consumption and, very importantly here, they release oxygen. The excess oxygen released supports the respiration done by the
aerobic organisms
Aerobic means "requiring air," in which "air" usually means oxygen.
Aerobic may also refer to
* Aerobic exercise, prolonged exercise of moderate intensity
* Aerobics, a form of aerobic exercise
* Aerobic respiration, the aerobic process of cell ...
in the pond. Atmospheric
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 as wel ...
is also dissolved into the liquid, which assists in maintaining an aerobic layer on the top of the pond surface.
Oxygen levels
The oxygen concentration varies in the liquid column: Close to the surface, concentrations are high and support the growth of aerobic organisms. Close to the pond bottom, sunlight penetration is low, and thus photosynthetic activity is reduced. This causes oxygen concentrations to be low there. Finally, inside the sediments in the bottom layer, there is no oxygen at all. Here, organic matter is removed by digestion undertaken by
anaerobic organisms.
Removal of pathogens
Pathogens can be efficiently removed in waste stabilization ponds. The process relies mostly on maturation ponds for removal of pathogens, although some removal also takes place in the other ponds of the system. The higher the number of ponds in the series, the more efficient the pathogen removal.
Removal of pathogenic bacteria and
viruses
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
occurs mainly by inactivation. Pathogens are inactivated as a result of a complex interaction of mechanisms that involve pH (the pH value in ponds is high because of algal photosynthesis), temperature,
ultraviolet radiation
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
present in the sunlight that reaches the pond surface and photooxidative reactions taking advantage of high dissolved oxygen concentrations.
[Verbyla, M., von Sperling, M., Ynoussa, M. (2017). Waste Stabilization Ponds. In: J.B. Rose and B. Jiménez-Cisneros, (eds]
Global Water Pathogens Project
(C. Haas, J. Mihelcic and M. Verbyla) (eds)
Part 4. Management of Risk from Excreta and Wastewater
. Michigan State University, E. Lansing, MI, UNESCO.
Protozoan
Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
pathogens are present in the wastewater in the form of cysts or oocysts.
Helminths
Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schi ...
(worms) are present in the form of eggs. The protozoan and helminth pathogens can be removed by the mechanism of sedimentation.
Very high removal efficiencies may be achieved, especially if maturation ponds are part of the treatment system. In that case, the final pond effluent may be in compliance with
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
guidelines for irrigating with treated wastewaster (or "
reclaimed water
Water reclamation (also called wastewater reuse, water reuse or water recycling) is the process of converting municipal wastewater
Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produce ...
").
[WHO (2006)]
WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater - Volume IV: Excreta and greywater use in agriculture
World Health Organization (WHO), Geneva, Switzerland However, sludge (sediment) from the ponds may be heavily contaminated with helminth eggs, which may survive even after several years of storing the sludge inside of the pond.
Types
![Configurations of pond systems](https://upload.wikimedia.org/wikipedia/commons/9/92/Configurations_of_pond_systems.jpg)
Waste stabilization ponds consist of man-made basins comprising a single or several series of anaerobic, facultative or maturation ponds. The presence or absence of oxygen varies with the three different types of ponds, used in sequence. Anaerobic waste stabilization ponds have very little dissolved oxygen, thus anaerobic conditions prevail. The second type of pond, facultative stabilization ponds, sustain an aerobic surface habitat above an anaerobic benthic habitat.
Maturation ponds offer aerobic conditions throughout, from the surface to the bottom.
The main configurations of pond systems are:
* Facultative pond only;
* Anaerobic pond followed by a facultative pond;
* Facultative pond followed by maturation ponds in series;
* Anaerobic pond followed by a facultative pond followed by maturation ponds in series.
If an anaerobic pond is present, part of the
suspended solids
Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to motion of the water. Suspended solids can be removed by sedimentation if their size or density is comparatively large, or by filtration. It ...
from the wastewater settles, thus removing the organic matter (
BOD) contributed by these solids. Additionally, some of the dissolved organic matter is removed by
anaerobic digestion
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the ferm ...
. During the second stage in the facultative pond'','' most of the remaining BOD is removed mainly by the
heterotrophic
A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
bacteria that receive oxygen from the photosynthesis undertaken by algae. The main function of the tertiary stage in maturation ponds is the removal of pathogens, although it may also assist in
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
reduction (i.e.
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
).
However,
nitrogen fixation
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
by algae living in stabilization pond systems may increase nitrogen levels in stabilization pond effluent.
Anaerobic ponds
Anaerobic ponds receive raw
wastewater
Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industr ...
. They have a smaller surface area compared to facultative ponds and are also deeper (usually 3.0 to 5.0 m). The depth decreases the influence of oxygen production by photosynthesis, leading to anaerobic conditions. Depending on loading and climatic conditions, these ponds are able to remove between half to two thirds of the influent BOD. This significantly decreases the load of organic matter that goes to the facultative ponds, and thus decreases their required size.
Anaerobic stabilization ponds have the disadvantage of potentially releasing
malodorous gases. This especially includes
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 unde ...
with an odor of rotten eggs, if the system has operational problems.
The first pond biome in a series of stabilization ponds digests the
putrescible
Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is e ...
solids suspended in the wastewater being treated. Anaerobic ponds allow solids to settle down at the bottom as sludge. This settling removes a portion of the particulate organic material.
A large fraction of the settled solids will accumulate close to the point where wastewater enters the pond. Therefore, anaerobic ponds must be designed to be far deeper than either aerobic or facultative ponds. The depth decreases the oxygen levels so anaerobic bacteria can efficiently digest the waste.
Anaerobic ponds contain anaerobic organisms which are able to break down complex organic waste into basic compounds that are less harmful to the environment.
[Cincinnati, O. (2010, June 29). ]
NEPIS document display
'. Because anaerobic organisms can only thrive in warm temperatures, anaerobic ponds are not suitable in temperate or cold climates.
Sludge accumulates at the bottom of the anaerobic ponds and needs to be removed every few years.
Facultative ponds
![Facultative pond (6898412198)](https://upload.wikimedia.org/wikipedia/commons/7/7e/Facultative_pond_%286898412198%29.jpg)
Facultative stabilization ponds that receive raw wastewater are called primary facultative ponds. If they are receiving wastewater that has already been treated in anaerobic ponds, they are called secondary facultative ponds. Facultative stabilization ponds may also be used for treatment following other types of treatment processes such as upflow anaerobic sludge blanket (UASB) reactors,
oxidation ditches or
aerated lagoons. Compared with anaerobic ponds, facultative ponds are shallower (1.5 to 2.5 m deep) and have much larger surface areas. The surface area is important because it allows atmospheric oxygen to dissolve and sunlight radiation to penetrate the water. This allows for photosynthetic activity to occur which produces more oxygen.
In most ponds both bacteria and algae are needed in order to maximize the decomposition of organic matter and the removal of other pollutants.
Algae produce oxygen (photosynthesis) and also consume oxygen (respiration), but they leave an excess of oxygen that can then be used by aerobic bacteria for respiration and for the processes of oxidation (or stabilization) of the organic matter in the wastewater.
Several types of invertebrates are present in the ponds where they control the population of
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
, which then settles to the bottom.
Heavy algal growth may block sunlight from penetrating into the pond. This decreases the potential for photosynthesis to contribute oxygen to the pond.
In the treatment of sewage, systems composed of anaerobic ponds followed by facultative ponds usually have overall BOD removal efficiencies between 75 and 85%. Higher efficiencies are difficult to achieve because the effluent contains high concentrations of particulate organic matter, in the form of algae, naturally produced during treatment.
The sludge comprising the sediment layer in the pond undergoes anaerobic digestion, and may accumulate for several years without needing removal.
Maturation ponds
Some additional removal of organic matter and other pollutants may be achieved in maturation ponds. These ponds are only included in the treatment line when high efficiencies of pathogen removal are required, either for discharge of the treated effluent in
surface water
Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean.
The vast majority of surface water is produced by prec ...
bodies, or for use for irrigation or
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 ...
. They are usually used after facultative ponds, but may also follow other treatment processes, such as
upflow anaerobic sludge blanket (UASB) reactors. They could also be placed after an
activated sludge
The activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. It uses air (or oxygen) and microorganisms ...
process.
Maturation ponds must be shallow (around 1.0 m depth or less) with a great surface area so that more oxygen can dissolve into the water giving the bacteria enough oxygen to properly function.
Shallow ponds benefit from high photosynthetic activity arising from the penetration of solar radiation. The pH values are high because of intense photosynthesis, and ultraviolet radiation penetration takes place in the upper layers. Both of these factors promote the removal of pathogenic bacteria and viruses. Given the high surface area of the maturation ponds, protozoan cysts and helminth eggs are also removed, with sedimentation as the main mechanism.
Sludge accumulation is very low in maturation ponds.
Very high pathogen removal efficiencies may be achieved, depending on several factors: temperature,
hydraulic retention time (the amount of time the liquid remains in the system - from entrance to exit), the number of ponds in the series, the presence of baffles and the depth of ponds.
Maturation ponds may be used in combination with a
rainwater
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water fo ...
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
to form an ecological, self-purifying irrigation reservoir.
Application and suitability
Waste stabilization ponds are very efficient in their primary objective of removing organic matter and, under some conditions, pathogenic organisms. Their design criteria have changed very little over the years.
Ponds are simple to design, build, operate and maintain, which is very important in remote areas and in
developing countries
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
where sophisticated equipment and highly skilled labor is not easily available. Construction may be done by local contractors in small towns.
Waste stabilization ponds work well in nearly all environments and can treat most types of
wastewater
Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industr ...
.
They are particularly well-suited for tropical and subtropical countries because the intensity of the sunlight and temperature are key factors for the efficiency of the removal processes.
Ponds are used throughout the world. In many countries and regions ponds are the most widely used treatment process. For this reason, they are one of the processes recommended by
WHO
Who or WHO may refer to:
* Who (pronoun), an interrogative or relative pronoun
* Who?, one of the Five Ws in journalism
* World Health Organization
Arts and entertainment Fictional characters
* Who, a creature in the Dr. Seuss book '' Horton He ...
for the treatment of wastewater for reuse in agriculture and aquaculture, especially because of their effectiveness in removing
nematodes
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...
(worms) and
helminth
Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schi ...
eggs.
Ponds cannot achieve very high efficiencies in the removal of organic matter, and usually have low capacities for removing nitrogen and
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
. The effluent usually has high concentrations of
suspended solids
Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to motion of the water. Suspended solids can be removed by sedimentation if their size or density is comparatively large, or by filtration. It ...
, resulting from algal production in the ponds. Therefore, ponds are not a suitable technology in areas where stringent discharge standards exist, unless additional stages of post treatment are included.
Since ponds require large areas, they may not be practical in proximity to towns where land is expensive. A suitable
topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sci ...
and a suitable
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
structure are also desired, in order to reduce construction costs.
Operation and maintenance
![Waste stabilization ponds facultative pond (in Brazil)](https://upload.wikimedia.org/wikipedia/commons/6/61/Waste_stabilization_ponds_facultative_pond_%28in_Brazil%29.png)
Regarding operation and maintenance, the tasks performed by the operational staff are very simple and do not require special skills. Additionally, there is no energy consumption for aeration, no need of heavy equipment maintenance and no frequent sludge removal,
sludge treatment and disposal.
Ponds require very little maintenance, since there is no heavy electric or mechanical equipment that requires attention. The only routine maintenance needed is on the preliminary treatment (cleaning of screens and removal of sand), routine checking of pipes, weirs and other hydraulic structures, and removal of unwanted vegetation growth in embankments.
Sludge removal
Sludge accumulates inside the ponds. It needs to be removed only in the interval of several years. This is an important advantage of the system. However, when removal is necessary, it is usually an expensive and labor-intensive operation. Removal is more frequent in anaerobic ponds (every few years), because of their smaller volume and lower capacity to store the sludge, compared with facultative ponds. In facultative ponds, sludge removal may be necessary only in intervals around 15 to 25 years. In maturation ponds, sludge accumulation is very low.
Sludge removal, also called desludging, may be done in two basic ways: (i) interrupting the operation of the pond for desludging or (ii) keeping the pond in operation while desludging.
In the first case, the influent wastewater to the pond to be desludged is closed. Afterwards, the pond is drained and the bottom sludge is left for open drying for several weeks. During this period, the wastewater to be treated needs to be diverted to other ponds in the system. After the sludge has dried, its removal may be done manually (very laborious in large ponds) or mechanically using tractors or mechanical scrapers. In the second alternative, when the pond is left in operation during desludging, the removed sludge will be wet and will require further drying. This is undertaken outside the pond. Sludge removal can be by suction and pumping using
vacuum trucks (only for small ponds), dredging, pumping from a raft or involving other mechanical equipment. In either case, the amount of sludge to be removed is very high, considering its accumulation over a period of years. This process is very laborious, expensive and requires careful planning.
Costs
In the selection of a wastewater treatment process, besides the technical aspects that are relevant to each alternative, also cost factors play a very important role. The latter can be basically divided into (i) construction costs and (ii) operation and maintenance costs. Waste stabilization ponds are usually considered a cheap alternative in terms of construction costs. However, the final costs will depend essentially on the size of ponds, presence of maturation ponds in the process configuration, topography, soil conditions, groundwater level and land cost.
Because all these elements are site-specific, it is difficult to generalize overall construction costs. In most cases these will be lower compared with other wastewater treatment alternatives.
[Arthur, J.P. (1983). Notes on the design and operation of waste stabilization ponds in warm climates of developing countries. Technical paper No 7. Washington D.C] Depending on the specific situation of the area, construction costs can increase and level up with other technologies.
Waste stabilization ponds are one of the cheapest wastewater treatment processes in terms of operation and maintenance.
Comparison with other infrastructure
The following types of water and wastewater infrastructure may superficially resemble waste stabilization ponds, but are not the same:
*
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 ...
s rely upon mechanical aerators to provide oxygen to stabilize organic matter. Aerated lagoons may be used as the first stage in the treatment line instead of anaerobic ponds to limit release of malodorous gases, but with energy and maintenance requirements causing higher operating costs.
*
Constructed wetland
A constructed wetland is an artificial wetland to treat sewage, greywater, stormwater runoff or industrial wastewater. It may also be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development. ...
s are designed to improve water quality by supporting rooted vegetation arranged to physically remove solids and particulate material while removing soluble nutrients in the water by uptake into plant tissue and supplying oxygen to the water to reduce BOD.
*
Retention basins are used to manage
stormwater
Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...
runoff
Runoff, run-off or RUNOFF may refer to:
* RUNOFF, the first computer text-formatting program
* Runoff or run-off, another name for bleed, printing that lies beyond the edges to which a printed sheet is trimmed
* Runoff or run-off, a stock market ...
to prevent
flooding
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 hydrolog ...
and downstream
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
, and improve
water quality
Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...
in an adjacent
river
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...
,
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 stream ...
,
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 ...
or
bay.
Detention basin
A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of rivers, streams, lakes or bays to protect against flooding and, in some cases, downstream erosion by storing water for a limited period of time. ...
s are similar but are "dry ponds" designed to temporarily hold runoff as a flood control measure.
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Infiltration basin
An infiltration basin (or recharge basin) is a form of engineered sump or percolation pond that is used to manage stormwater runoff, prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. It is ...
s are ponds designed to percolate their contents into underlying permeable soils.
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Settling basin
A settling basin, settling pond or decant pond is an earthen or concrete structure using sedimentation to remove settleable matter and turbidity from wastewater. The basins are used to control water pollution in diverse industries such as agricul ...
s are designed to separate solids from wastewaters without provision for treatment of those solids.
See also
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Industrial wastewater treatment
Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to a sa ...
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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'') a ...
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List of waste water treatment technologies
This page consists of a list of wastewater treatment technologies:
See also
*Agricultural wastewater treatment
* Industrial wastewater treatment
*List of solid waste treatment technologies
* Waste treatment technologies
* Water purification
*S ...
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Natural swimming pond
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Organisms used in water purification
Most organisms involved in water purification originate from the waste, wastewater or water stream itself or arrive as resting spore of some form from the atmosphere. In a very few cases, mostly associated with constructed wetlands, specific orga ...
References
External links
Publications on pondsin the library of the
Sustainable Sanitation Alliance
The Sustainable Sanitation Alliance (SuSanA) is a loose network of organizations who are "working along the same lines towards achieving sustainable sanitation". It began its work in 2007, one year before the United Nations International Year o ...
* Stabilization pond pictures: Enter "pond" into search field o
SuSanA photo database on Flickr
{{pond
Anaerobic digestion
Ponds
Sanitation
Sewerage infrastructure
Water management
Water treatment