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A marine outfall (or ocean outfall) is a pipeline or tunnel that discharges municipal or industrial
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, industrial ...
,
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 lan ...
,
combined sewer overflow A combined sewer is a type of gravity sewer with a system of pipes, tunnels, pump stations etc. to transport sewage and urban runoff together to a sewage treatment plant or disposal site. This means that during rain events, the sewage gets dilut ...
s (CSOs), cooling water, or
brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for b ...
effluents from
water desalination Desalination is a process that takes away mineral components from saline water. More generally, desalination refers to the removal of salts and minerals from a target substance, as in soil desalination, which is an issue for agriculture. Saltwa ...
plants to the sea. Usually they discharge under the sea's surface (submarine outfall). In the case of municipal wastewater, effluent is often being discharged after having undergone no or only primary treatment, with the intention of using the assimilative capacity of the sea for further treatment. Submarine
outfall An outfall is the discharge point of a waste stream into a body of water; alternatively it may be the outlet of a river, drain or a sewer where it discharges into the sea, a lake or ocean. In the United States, industrial facilities that disch ...
s are common throughout the world and probably number in the thousands. The light intensity and salinity in natural sea water disinfects the wastewater to ocean outfall system significantly. More than 200 outfalls alone have been listed in a single international database maintained by the Institute for Hydromechanics at Karlsruhe University for the International Association of Hydraulic Engineering and Research (IAHR) /
International Water Association The International Water Association (IWA) is a nonprofit organization and knowledge hub for the water sector, connecting water professionals and companies to find solutions to the world's water challenges. The IWA is headquartered in London, UK, ...
(IWA) Committee on Marine Outfall Systems.Outfalls Database
Click on "Activities", then "Outfalls repository", then "database", then "Output"
The world's first marine outfall was built in
Santa Monica Santa Monica (; Spanish: ''Santa Mónica'') is a city in Los Angeles County, situated along Santa Monica Bay on California's South Coast. Santa Monica's 2020 U.S. Census population was 93,076. Santa Monica is a popular resort town, owing to ...
, United States, in 1910. In Latin America and the Caribbean there were 134 outfalls with more than 500 m length in 2006 for wastewater disposal alone, according to a survey by the Pan American Center for Sanitary Engineering and Environmental Sciences (CEPIS) of
PAHO The Pan American Health Organization (PAHO) is an international public health agency working to improve the health and living standards of the people of the Americas. It is part of the United Nations system, serving as the Regional Office for ...
. According to the survey, the largest number of municipal wastewater outfalls in the region exist in Venezuela (39), Chile (39) and Brazil (22). The world's largest marine outfall stems from the Deer Island Waste Water Treatment Plant located in
Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- most p ...
, United States. Currently, Boston has approximately 235 miles of combined sewers and 37 active CSO outfalls. Many outfalls are simply known by a public used name, e.g. Boston Outfall.OUTFALLS DATABASE AND INFORMATION EXCHANGE


Advantages

The main advantages of marine outfalls for the discharge of wastewater are:Beder, Sharon

Ph.D. Thesis, UNIVERSITY OF NEW SOUTH WALES, AUSTRALIA 1989, Chapter 8: The 'Science' and 'Metaphysics' of Submarine Outfalls
*the natural dilution and dispersion of
organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
,
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 ger ...
and other pollutants *the ability to keep the sewage field submerged because of the depth at which the sewage is being released *the greater die-off rate of pathogens due to the greater distance they will have to travel to shore. They also tend to be less expensive than advanced wastewater treatment plants, using the natural assimilative capacity of the sea instead of energy-intensive treatment processes in a plant. For example, preliminary treatment of wastewater is sufficient with an effective outfall and diffuser. The costs of preliminary treatment are about one tenth that of secondary treatment. Preliminary treatment also requires much less land than advanced wastewater treatment.


Disadvantages

Marine outfalls for partially treated or untreated wastewater remain controversial. The design calculation and computer models for pollution modeling have been criticized, arguing that dilution has been overemphasized and that other mechanisms work in the opposite direction, such as
bioaccumulation Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost or eliminated ...
of
toxins A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849 ...
,
sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...
of
sludge Sludge is a semi-solid slurry that can be produced from a range of industrial processes, from water treatment, wastewater treatment or on-site sanitation systems. For example, it can be produced as a settled suspension obtained from conventiona ...
particles and agglomeration of sewage particles with grease. Accumulative mechanisms include slick formation, windrow formation, flocculate formation and agglomerated formation. Grease or wax can interfere with dispersion, so that bacteria and viruses could be carried to remote locations where the concentration of bacterial predators would be low and the die-off rate much lower.


Technology

Outfalls vary in diameter from as narrow as 15 cm to as wide as 8 m; the widest registered outfall in the world with 8 m diameter is located in
Navia (Spain) Navia is a municipality in the Autonomous Community of the Principality of Asturias, Spain. It lies on the Cantabrian Sea, and is bordered by the municipalities of Villayón to the south, Valdés to the east, and Coaña to the west. It is also ...
for the discharge of industrial wastewater. Outfalls vary in length from 50 m to 55 km, the longest registered outfalls being the
Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- most p ...
outfall with a length of 16 km and an industrial outfall in
Ankleshwar Ankleshwar (sometimes written Ankaleshwar) is a city and a municipality in Bharuch district in the state of Gujarat, India. The city is located 14 kilometres from Bharuch. Ankleshwar Industrial Association (AIA) is the largest organisation of ...
(India) with a length of 55 km. The depth of the deepest point of an outfall varies from 3 m to up to 60 m, the deepest registered outfall being located in Macuto, Vargas (Venezuela) for the discharge of untreated municipal wastewater. Outfall materials include
polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bott ...
, stainless steel,
carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...
,
glass-reinforced plastic Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth ...
,
reinforced concrete Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having hig ...
,
cast iron Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
or tunnels through rock. Common installation methods for pipelines are float and sink, bottom pull and top pull.


Examples

Submarine outfalls exist, existed or have been considered in the following locations, among many others: ;Africa *
Casablanca Casablanca, also known in Arabic as Dar al-Bayda ( ar, الدَّار الْبَيْضَاء, al-Dār al-Bayḍāʾ, ; ber, ⴹⴹⴰⵕⵍⴱⵉⴹⴰ, ḍḍaṛlbiḍa, : "White House") is the largest city in Morocco and the country's econom ...
(Morocco). * Cape Town (South Africa). ;Asia *
Manila Bay Manila Bay ( fil, Look ng Maynila) is a natural harbor that serves the Port of Manila (on Luzon), in the Philippines. Strategically located around the capital city of the Philippines, Manila Bay facilitated commerce and trade between the Phili ...
(Philippines). *
Mumbai Mumbai (, ; also known as Bombay — the official name until 1995) is the capital city of the Indian state of Maharashtra and the ''de facto'' financial centre of India. According to the United Nations, as of 2018, Mumbai is the second-m ...
(India). * Mutwall ( Sri Lanka). * Wellawaththa (Sri Lanka). *
Lunawa Lunawa is a suburb in Sri Lanka lying on the coast just south of the capital, Colombo. Lunawa is a suburb of Moratuwa in the Colombo District of the Western Province. The main sources of income in this city are carpentry and fishing. There are al ...
(Sri Lanka). ;Oceania *
Anglesea, Victoria Anglesea is a town in Victoria, Australia. It is located on the Great Ocean Road in the Surf Coast Shire local government area. In the , Anglesea had a population of 2,545 people. Originally known as Swampy Creek, the area's name was change ...
. *
Geelong Geelong ( ) (Wathawurrung: ''Djilang''/''Djalang'') is a port city in the southeastern Australian state of Victoria, located at the eastern end of Corio Bay (the smaller western portion of Port Phillip Bay) and the left bank of Barwon River, ...
,
Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seyche ...
. *
Sydney Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mountains ...
;Europe * Barcelona, Spain * Costa do Estoril (Portugal) *
Marmara Sea The Sea of Marmara,; grc, Προποντίς, Προποντίδα, Propontís, Propontída also known as the Marmara Sea, is an inland sea located entirely within the borders of Turkey. It connects the Black Sea to the Aegean Sea via the ...
near Istanbul (Turkey) *
San Sebastián San Sebastian, officially known as Donostia–San Sebastián (names in both local languages: ''Donostia'' () and ''San Sebastián'' ()) is a city and municipality located in the Basque Autonomous Community, Spain. It lies on the coast of the ...
(Spain) *
Split Split(s) or The Split may refer to: Places * Split, Croatia, the largest coastal city in Croatia * Split Island, Canada, an island in the Hudson Bay * Split Island, Falkland Islands * Split Island, Fiji, better known as Hạfliua Arts, enterta ...
(Croatia) *
Thames Estuary The Thames Estuary is where the River Thames meets the waters of the North Sea, in the south-east of Great Britain. Limits An estuary can be defined according to different criteria (e.g. tidal, geographical, navigational or in terms of salini ...
downstream of London (UK) * Edinburgh, Scotland. ;North America *
Honolulu Honolulu (; ) is the capital and largest city of the U.S. state of Hawaii, which is in the Pacific Ocean. It is an unincorporated county seat of the consolidated City and County of Honolulu, situated along the southeast coast of the island o ...
(USA) *
New York Bight The New York Bight is the geological identification applied to a roughly triangular indentation, regarded as a bight, along the Atlantic coast of the United States that extends northeasterly from Cape May Inlet in New Jersey to Montauk Point ...
(USA) *
Southern California Bight The Southern California Bight is a 692-kilometer-long (430 mi) stretch of curved coastline that runs along the west coast of the United States and Mexico, from Point Conception in California to Punta Colonet in Baja California, plus the area of ...
(USA). and *
Victoria, British Columbia Victoria is the capital city of the Canadian province of British Columbia, on the southern tip of Vancouver Island off Canada's Pacific coast. The city has a population of 91,867, and the Greater Victoria area has a population of 397,237. The ...
, (Canada). *
Santa Monica Santa Monica (; Spanish: ''Santa Mónica'') is a city in Los Angeles County, situated along Santa Monica Bay on California's South Coast. Santa Monica's 2020 U.S. Census population was 93,076. Santa Monica is a popular resort town, owing to ...
, United States (world's first) *
Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- most p ...
, United States (world's largest) *The city of
San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United States ...
used Pacific Ocean dilution of primary treated effluent into the 21st century. ;Latin America and the Caribbean *
Cartagena, Colombia Cartagena ( , also ), known since the colonial era as Cartagena de Indias (), is a city and one of the major ports on the northern coast of Colombia in the Caribbean Coast Region, bordering the Caribbean sea. Cartagena's past role as a lin ...
*
Ipanema Beach Ipanema () is a neighbourhood located in the South Zone of the city of Rio de Janeiro, Brazil, between Leblon and Arpoador. The beach at Ipanema became known internationally with the popularity of the bossa nova jazz song, "The Girl from Ipa ...
beach from
Rio de Janeiro Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a b ...
( Brazil). This outfall, built in 1975, discharges untreated wastewater through a pipe with a diameter of 2.4m and a length of 4,775m at a depth of 27m. * Sosua (Dominican Republic).


Controversies

In the 1960s the city of
Sydney Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mountains ...
decided to build ocean sewage outfalls to discharge partially treated sewage 2–4 km offshore at a cost of US$300 million. In the late 1980s, however, the government promised to upgrade the coastal treatment plants so that sewage would be treated to at least secondary treatment standards before discharge into the ocean. The submarine outfall in
Cartagena, Colombia Cartagena ( , also ), known since the colonial era as Cartagena de Indias (), is a city and one of the major ports on the northern coast of Colombia in the Caribbean Coast Region, bordering the Caribbean sea. Cartagena's past role as a lin ...
was financed with a loan by the
World Bank The World Bank is an international financial institution that provides loans and grants to the governments of low- and middle-income countries for the purpose of pursuing capital projects. The World Bank is the collective name for the Interna ...
. It was subsequently challenged by residents claiming that the wastewater caused damage to the marine environment and to fisheries. The case was taken up by the
World Bank's Inspection Panel The Inspection Panel is an independent accountability mechanism of the World Bank. It was established in September 1993 by the World Bank Board of Directors, and started operations on August 1, 1994. The Panel provides a forum for people who bel ...
, which contracted two independent three-dimensional modeling efforts in 2006. Both "confirmed that the 2.85km long submarine outfall (was) adequate."World Bank Inspection Panel Progress Report on Cartagena Water Supply, Sewerage and Environmental Management Project
/ref> For disposal into the ocean, environmental
treaty A treaty is a formal, legally binding written agreement between actors in international law. It is usually made by and between sovereign states, but can include international organizations, individuals, business entities, and other legal pers ...
requirements have to met. As international treaties often manage water over countries' borders, wastewater disposal is easier in bodies of water found entirely under the jurisdiction of one country.


References


Sources


IWA Committee on Marine Outfall Systems

Salas, Henry J.:Submarine outfalls a viable alternative for sewage discharge of coastal cities in Latin America and the Caribbean
Lima; CEPIS, 2000


External links


IAHR/IWA Committee on Marine Outfall Systems
{{Wastewater Waste treatment technology Environmental engineering Hydrology Hydraulics Oceanography