Math Is Fun Forum

Detergent

Gist

A detergent is a cleaning agent, often called a "surfactant," that uses molecules with both water-loving (polar) heads and oil-loving (non-polar) tails to lift dirt, grease, and oil from surfaces, suspending them in water so they can be rinsed away. Unlike traditional soaps, detergents are synthetic, work effectively in hard water, and are formulated into various products like laundry liquids, dishwasher tabs, and shampoos, containing additional ingredients for foaming, softening, or scent

Detergent products on the market can be categorized into powder detergents, liquid detergents, detergent bars, detergent pods, etc. The primary purpose is to remove dirt, stains, sweat, oils, pathogens, and other contaminants from fabrics, leaving them clean, fresh, and often pleasantly scented.

Summary

A detergent is a product for cleaning that contains surfactants plus other components. Detergents comprise surfactants as main functional components to remove hydrophobic grease or dirt by dispersing them in water. They often further comprise water (to facilitate application), builders (to soften water), enzymes (for breaking down proteins, fats, or starches), and dyes or fragrances (to improve the user's sensory experience).

Common surfactants used in detergents are alkylbenzene sulfonates, which are soap-like compounds that are more soluble than soap in hard water, because the polar sulfonate is less likely than the polar carboxylate of soap to bind to calcium and other ions found in hard water.

Definitions

The word detergent is derived from the Latin adjective detergens, from the verb detergere, meaning to wipe or polish off. Detergent can be defined as a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. However, conventionally, detergent is used to mean synthetic cleaning compounds as opposed to soap (a salt of the natural fatty acid), even though soap is also a detergent in the true sense. In domestic contexts, the term detergent refers to household cleaning products such as laundry detergent or dish detergent, which are in fact complex mixtures of different compounds, not all of which are by themselves detergents. Detergency is the ability to remove unwanted substances termed 'soils' from a substrate (e.g., clothing).

Details

Key Takeaways:

* Laundry detergents clean fabrics. Surfactants are the key ingredient that allows detergents to remove dirt and stains by interacting with both oil and water.
* Modern detergents contain a mixture of surfactants, enzymes and other ingredients to tackle various stains and fabric care needs.
* The choice between powder and liquid detergents often comes down to personal preference, although environmental considerations and packaging waste are increasingly important factors for consumers.

Nothing beats the feeling of putting on a clean T-shirt, especially after a shower. It leaves you feeling fresh and ready to take on the day. And where do these clean T-shirts come from? Ah, yes -- the laundry, that household chore that never seems to go off of your to-do list. Even the numbers agree: The average American family does about 300 loads of laundry per year [source: Wall Street Journal].

You may find yourself constantly putting clothes and sheets in the wash because, put simply, people are dirty. We sweat, shed skin cells and come into contact with food, dirt and many more particles every day. Consequently, we need a way to effectively get clothes and fabrics clean to maintain personal hygiene and keep up the appearance of garments. But what exactly is going on in that washing machine to get our clothes and fabrics clean? The secret is laundry detergent.

Prior to the invention of laundry detergents, Americans used soap flakes to wash clothes. However, in the 1930s, the first laundry detergent, Dreft by Procter & Gamble, hit the market. Later, in 1943, Procter & Gamble produced Tide, which could get out tougher stains due to the use of some very unique chemical ingredients. Since the 1930s and 1940s, laundry detergent has become a household necessity that is used around the world to clean fabrics. So how exactly do laundry detergents get your clothes clean? In this article we are going to get to the bottom of what happens when detergents enter your washing machine.

Surfactants: Laundry Detergent's Cleaning Power

All laundry detergent ingredients have a job to do, but the one group that's really crucial to getting your clothes clean are surfactants. The word surfactant stems from the combination of words "surface-active agents." Surface-active agents get their name from their unique chemical structure, which allows them to interact with two different types of surfaces, such as oil and water. The tail of a surfactant molecule is hydrophobic, or not attracted to water. What the hydrophobic end is attracted to is grease and dirt. The head of the surfactant molecule, on the other hand, is hydrophilic -- it's attracted to water [source: Silberberg].

So when a greasy piece of clothing is immersed in water with detergents containing surfactant, the tail of the surfactant molecules attach to the grease, and the head end of the molecule is attracted to the water. When the washing machine agitates the clothes, the molecules form tiny spheres, which stay suspended in the water and are rinsed away when the water is drained. Therefore, the prime benefit of surfactants is their ability to draw grime out of clothing while making sure it doesn't return to the fabrics.

Essentially, there are four main types of surfactants, with the first three used the most in laundry detergents, and their actions depend on their interactions with ions. Ions are charged particles due to the gain or loss of electrons. Ions can be positive such as calcium, Ca2+, or negative such as chloride, Cl-.

* Anionic surfactants are negatively charged in solution. However, they do not work as well by themselves in hard water. This is because hard water has many positively charged ions presents such as calcium (Ca2+) and magnesium (Mg2+). Since anionic surfactants are negative they are attracted to the positive ions and bind, making them unable to bind to other molecules in solution.
* Nonionic surfactants have no charge. Therefore, they are not as easily impaired under hard water conditions, since they are not attracted to the positive ions.
* Cationic surfactants are positively charged in solution. They help the anionic surfactant molecules pack in at the water/dirt interface thereby allowing the anionic surfactants to pull more dirt away.
* Amphoteric or zwitterionic surfactants are both positively and negatively charged. These surfactants are very mild and are often found in gentler cleansers such as hand soaps, shampoos and cosmetics. [source: Silberberg].

Additional Components of Laundry Detergent

Although surfactants are at the heart of laundry detergent's ability to clean fabrics, other ingredients can help detergents clean better, brighten clothes or smell better. As described previously, some types of surfactants typically do not work well in hard water due to the excess positive ions present. Additives called builders can help detergents to work better under hard water conditions. Builders accomplish this feat by removing calcium (Ca2+) and magnesium (Mg2+) ions in hard water by binding to them. This allows the surfactants, especially anionic surfactants, to bind to more grime, rather than the positively charged ions in the wash water. Builders also are bases, so they work to neutralize acid and can help disrupt chemical bonds. Another benefit of adding builders to laundry detergents is that manufacturers can use less surfactant, since the builders make the surfactant more efficient. Some examples of builders include sodium tripolyphosphate (STTP) and zeolites [source: EPA].

Detergents can also include components that make clothes whiter or brighter. The most common whitening agents are bleaches. Bleaches contain peroxides, which can oxidize fabrics [source: EPA]. Fluorescent whiteners and brighteners are also added to some laundry detergents because they minimize the yellowing of fabrics. These additives work by absorbing ultraviolet light and emitting back visible blue light, which can mask the yellow that may make colors appear faded and whites appear dingy.

Enzymes are naturally occurring biologic agents present in many detergents in varying concentrations. These enzymes are typically classified into the following categories and are similar to the enzymes used by your body to digest food:

Proteases: help break down proteins
Lipases: help break down fat
Amylases: help break down starches [source: Basketter]

These enzymes help break down food particles that are present on clothing by catalyzing, or speeding up, the decomposition process. A point to consider is that enzymes are biological products that can break down over time. Therefore, detergents can also contain enzyme stabilizers, which protect the enzymes and help them function.

Some other components include fragrance and coloring, which give laundry detergents their distinctive scents and appearance. Detergents sometimes contain trace amounts of dye, which is not enough to dye your actual clothing. However, on top of making your laundry detergent more visually appealing, dyes can show you when there is still detergent left on your clothes after the wash cycle.

Lastly, fillers help dilute and distribute the active ingredients to their proper dosages. Powder and liquid detergents use different fillers. The major filler in powder detergents is sodium sulphate, which provides the granular powdery texture. The primary filler in liquid detergents is water.

Powder vs. Liquid Detergents

Laundry detergent manufacturers have come a long way since the first box of Tide was produced more than 60 years ago. Currently, the two main types of laundry detergent are powders and liquids. For the most part, powder and liquid detergents share the same active ingredients except for the filler used. Additionally, powder and liquid detergents both have pros and cons, and since they have similar cleaning power, people usually choose which type to use based on personal preference.

Here are some of the advantages and disadvantages of using powdered detergents:

Pro: They're generally cheaper.
Pro: The cardboard packaging is more eco-friendly.
Con: Some people think they don't dissolve as well in water. This may have been a problem with some of the first powdered detergents, but these days, most powders are designed to readily dissolve in water.
Con: Sodium sulphate can wreak havoc on septic systems.
Con: Powders contain more chemicals compared with liquids, due to the filler.

People may or may not use liquid detergents for an entirely different set of reasons:

Pro: The detergent is already pre-dissolved.
Pro: You can pre-treat stains by pouring it directly onto clothes.
Con: They're usually more expensive than powdered detergent.
Con: They have plastic packaging, which is less eco-friendly.

Environmental Considerations with Laundry Detergent

Even though detergents do a tremendous job of getting rid of the dirt and grime in our fabrics, at what cost does this come? Considering the toxicities of their chemical ingredients and carbon cost of production, it's not surprising that some people have concerns about the impacts of laundry detergents on the environment.

Their carbon footprint alone is significant by many people's standards. Carbon footprints are an indicator of the amount of carbon dioxide (CO2) produced while making, shipping and using a product. According to the Wall Street Journal, the carbon footprint of using UK detergent brand Tesco, varies from 1.3 pounds (0.6 kilograms) to 1.9 pounds (0.9 kilograms) per load, depending on the form of the detergent that's used. To put this in perspective, it is estimated that for every mile an average car travels, 1 pound (0.5 kilograms) of CO2 is emitted. Recall that American families on average do 300 loads of laundry per year. This means that the carbon footprint of laundry detergents for one year of laundry is approximately 480 pounds (218 kilograms) per year, or about 10 pounds (4.5 kilograms) per week. So, while this may not seem like a lot, especially if your car produces about 5 tons of CO2 per year, this number only reflects the laundry detergent. It does not factor in the extra energy requirements of running the washer and dryer [source: Wall Street Journal].

Now, add to that the toxic effects of the chemical components in detergents. According to the EPA, some of the major concerns about the chemical ingredients used in laundry detergents include the following:

* Toxicity to aquatic organisms and algae
* Persistence in the environment
* Eutrophication of fresh water, particularly by phosphate-based detergents (now, phosphates have been replaced by zeolites which may be alleviating this problem)
* Health problems in people, such as cancer [source: EPA]

Another concern relating to laundry detergent is that it can make the wash water acidic, and depending on where that water runs to, it could further impact the environment, having effects similar to acid rain.

Green Laundry Detergent Options

Given some of these environmental considerations about laundry detergents, there are some greener options available to today's consumer. Most detergents marketed as environmentally friendly don't include perfumes or dyes, and they're typically phosphate free, biodegradable, and they haven't been tested on animals.

One eco-conscious option is detergent designed to work well in cold water. On average, 80 to 85 percent of the total energy used washing a load of clothes goes to heating up the water [source: Sabaliunas et al.]. Washing in cold water saves energy, which can translate to savings on your household energy bills, too.

Another environmental approach is to use concentrated formulas, which cuts down on packaging and on the amount of water it takes to make the detergent. According to Proctor & Gamble spokeswoman Carol Berning, concentrated detergents require "less plastic for bottles, less corrugated cardboard for crating, and less gasoline used, because we need less trucks to move the shipments" [source: Consumer Reports]. The cold water and concentrated options that different companies manufacture may be one step to greener washing practices. However, even in these forms, the detergents still contain some potentially environmentally hazardous chemicals.

An additional green choice -- for the benefit of the environment and you wallet -- could be making your own laundry detergents. There are a variety of recipes out there, with the common ingredients of water, bar soap, borax and washing soda. Some environmental benefits of making your own laundry detergent are that they typically use fewer chemicals and additives, and they can save on packaging. However, be aware that clothing washed with homemade detergent may also require bleaching, and it may not get stains out as well as some of the commercially produced detergents.

Clearly, detergents are chemically complex products that are continually being improved upon, whether it is boosting their stain-fighting powers or making them greener.

Additional Information

Soap and detergent are substances that, when dissolved in water, possess the ability to remove dirt from surfaces such as the human skin, textiles, and other solids. When soap and water are not available for hand washing or when repeated hand washing compromises the natural skin barrier (e.g., causing scaling or fissures to develop in the skin), hand sanitizers—coming in foam, gel, or liquid form—have been recommended.

The seemingly simple process of cleaning a soiled surface is, in fact, complex and consists of the following physical-chemical steps:

* Wetting of the surface and, in the case of textiles, penetration of the fibre structure by wash liquor containing the detergent. Detergents (and other surface-active agents) increase the spreading and wetting ability of water by reducing its surface tension—that is, the affinity its molecules have for each other in preference to the molecules of the material to be washed.
* Absorption of a layer of the soap or detergent at the interfaces between the water and the surface to be washed and between the water and the soil. In the case of ionic surface-active agents (explained below), the layer formed is ionic (electrically polar) in nature.
* Dispersion of soil from the fibre or other material into the wash water. This step is facilitated by mechanical agitation and high temperature; in the case of hand soap, soil is dispersed in the foam formed by mechanical action of the hands.
* Preventing the soil from being deposited again onto the surface cleaned. The soap or detergent accomplishes this by suspending the dirt in a protective colloid, sometimes with the aid of special additives. In a great many soiled surfaces the dirt is bound to the surface by a thin film of oil or grease. The cleaning of such surfaces involves the displacement of this film by the detergent solution, which is in turn washed away by rinse waters. The oil film breaks up and separates into individual droplets under the influence of the detergent solution. Proteinic stains, such as egg, milk, and blood, are difficult to remove by detergent action alone. The proteinic stain is nonsoluble in water, adheres strongly to the fibre, and prevents the penetration of the detergent. By using proteolytic enzymes (enzymes able to break down proteins) together with detergents, the proteinic substance can be made water-soluble or at least water-permeable, permitting the detergent to act and the proteinic stain to be dispersed together with the oily dirt. The enzymes may present a toxic hazard to some persons habitually exposed.

If detached oil droplets and dirt particles did not become suspended in the detergent solution in a stable and highly dispersed condition, they would be inclined to flocculate, or coalesce into aggregates large enough to be redeposited on the cleansed surface. In the washing of fabrics and similar materials, small oil droplets or fine, deflocculated dirt particles are more easily carried through interstices in the material than are relatively large ones. The action of the detergent in maintaining the dirt in a highly dispersed condition is therefore important in preventing retention of detached dirt by the fabric.

In order to perform as detergents (surface-active agents), soaps and detergents must have certain chemical structures: their molecules must contain a hydrophobic (water-insoluble) part, such as a fatty acid or a rather long chain carbon group, such as fatty alcohols or alkylbenzene. The molecule must also contain a hydrophilic (water-soluble) group, such as ―COONa, or a sulfo group, such as ―OSO3Na or ―SO3Na (such as in fatty alcohol sulfate or alkylbenzene sulfonate), or a long ethylene oxide chain in nonionic synthetic detergents. This hydrophilic part makes the molecule soluble in water. In general, the hydrophobic part of the molecule attaches itself to the solid or fibre and onto the soil, and the hydrophilic part attaches itself to the water.

Four groups of surface-active agents are distinguished:

* Anionic detergents (including soap and the largest portion of modern synthetic detergents), which produce electrically negative colloidal ions in solution.
* Cationic detergents, which produce electrically positive ions in solution.
* Nonionic detergents, which produce electrically neutral colloidal particles in solution.
* Ampholytic, or amphoteric, detergents, which are capable of acting either as anionic or cationic detergents in solution depending on the pH (acidity or alkalinity) of the solution.

The first detergent (or surface-active agent) was soap. In a strictly chemical sense, any compound formed by the reaction of a water-insoluble fatty acid with an organic base or an alkali metal may be called a soap. Practically, however, the soap industry is concerned mainly with those water-soluble soaps that result from the interaction between fatty acids and alkali metals. In certain cases, however, the salts of fatty acids with ammonia or with triethanolamine are also used, as in shaving preparations.

River Congo - The Deepest River In The World

Gist

The Congo River is Africa's second-longest (4,700 km) and the world's deepest river (>220 m), flowing in a massive arc through Central Africa to the Atlantic Ocean. It crosses the equator twice, drains the world's second-largest rainforest, and features enormous discharge volume. Key features include the Inga Falls, major biodiversity, and essential, yet challenging, navigation for transport.

The Congo River can tick a lot of impressive feats off its list: it is Africa's most powerful river, the second most voluminous river in the world, the fifth longest, and the deepest. It even passes through the second-largest rainforest in the world.

Summary

Congo River is a river in west-central Africa. With a length of 2,900 miles (4,700 km), it is the continent’s second longest river, after the Nile. It rises in the highlands of northeastern Zambia between Lakes Tanganyika and Nyasa (Malawi) as the Chambeshi River at an elevation of 5,760 feet (1,760 metres) above sea level and at a distance of about 430 miles (700 km) from the Indian Ocean. Its course then takes the form of a giant counterclockwise arc, flowing to the northwest, west, and southwest before draining into the Atlantic Ocean at Banana (Banane) in the Democratic Republic of the Congo. Its drainage basin, covering an area of 1,335,000 square miles (3,457,000 square km), takes in almost the entire territory of that country, as well as most of the Republic of the Congo, the Central African Republic, eastern Zambia, and northern Angola and parts of Cameroon and Tanzania.

With its many tributaries, the Congo forms the continent’s largest network of navigable waterways. Navigability, however, is limited by an insurmountable obstacle: a series of 32 cataracts over the river’s lower course, including the famous Inga Falls. These cataracts render the Congo unnavigable between the seaport of Matadi, at the head of the Congo estuary, and Malebo Pool, a lakelike expansion of the river. It was on opposite banks of Malebo Pool—which represents the point of departure of inland navigation—that the capitals of the former states of the French Congo and the Belgian Congo were founded: on the left bank Kinshasa (formerly Léopoldville), now the capital of the Democratic Republic of the Congo, and on the right bank Brazzaville, now the capital of the Republic of the Congo.

The Amazon and the Congo are the two great rivers of the world that flow out of equatorial zones where heavy rainfall occurs throughout all or almost all of the year. Upstream from Malebo Pool, the Congo basin receives an average of about 60 inches (1,500 mm) of rain a year, of which more than one-fourth is discharged into the Atlantic. The drainage basin of the Congo is, however, only about half the size of that of the Amazon, and the Congo’s rate of flow—1,450,000 cubic feet (41,000 cubic metres) per second at its mouth—is considerably less than the Amazon’s flow of more than 6,180,000 cubic feet (175,000 cubic metres) per second.

While the Chambeshi River, as the remotest source, may form the Congo’s original main stream in terms of the river’s length, it is another tributary—the Lualaba, which rises near Musofi in southeastern Democratic Republic of the Congo—that carries the greatest quantity of water and thus may be considered as forming the Congo’s original main stream in terms of water volume.

When the river first became known to Europeans at the end of the 15th century, they called it the Zaire, a corruption of a word that is variously given as nzari, nzali, njali, nzaddi, and niadi and that simply means “river” in local African languages. It was only in the early years of the 18th century that the river was first called the “Rio Congo,” a name taken from the kingdom of Kongo that had been situated along the lower course of the river. During the period (1971–97) when the Democratic Republic of the Congo was called Zaire, the government also renamed the river the Zaire. Even during that time, however, the river continued to be known throughout the world as the Congo. To the literary-minded the river is evocative of the famous 1902 short story “Heart of Darkness” by Joseph Conrad. His book conjured up an atmosphere of foreboding, treachery, greed, and exploitation. Today, however, the Congo appears as the key to the economic development of the central African interior.

Details

The Congo River, formerly also known as the Zaire River, is the second-longest river in Africa, shorter only than the Nile, as well as the third largest river in the world by discharge volume, following the Amazon and Ganges–Brahmaputra rivers. It is the world's deepest recorded river, with measured depths of around 220 m (720 ft). The Congo–Lualaba–Luvua–Luapula–Chambeshi River system has an overall length of 4,700 km (2,900 mi), which makes it the world's ninth-longest river. The Chambeshi is a tributary of the Lualaba River, and Lualaba is the name of the Congo River upstream of Boyoma Falls, extending for 1,800 km (1,100 mi).

Measured along with the Lualaba, the main tributary, the Congo River has a total length of 4,370 km (2,720 mi). It is the only major river to cross the equator twice. The Congo Basin has a total area of about 4,000,000 sq km (1,500,000 sq mi), or 13% of the entire African landmass.

Name

The name Congo/Kongo originates from the Kingdom of Kongo once located on the southern bank of the river. The kingdom in turn was named after the indigenous Bantu Kongo people, known in the 17th century as "Esikongo". South of the Kingdom of Kongo proper lay the similarly named Kakongo kingdom, mentioned in 1535. Abraham Ortelius labelled "Manicongo" as the city at the mouth of the river in his world map of 1564. The tribal names in Kongo possibly derive from a word for a public gathering or tribal assembly. The modern name of the Kongo people or Bakongo was introduced in the early 20th century.

The name Zaire is from a Portuguese adaptation of a Kikongo word, nzere ("river"), a truncation of nzadi o nzere ("river swallowing rivers"). The river was known as Zaire during the 16th and 17th centuries; Congo seems to have replaced Zaire gradually in English usage during the 18th century, and Congo is the preferred English name in 19th-century literature, although references to Zahir or Zaire as the name used by the inhabitants remained common. The Democratic Republic of the Congo and the Republic of the Congo are named after it, as was the previous Republic of the Congo which had gained independence in 1960 from the Belgian Congo. The Republic of Zaire during 1971–1997 was also named after the river's name in French and Portuguese.

Basin and course

The Congo's drainage basin covers 4,014,500 sq km (1,550,000 sq mi),[6] an area nearly equal to that of the European Union. The Congo's discharge at its mouth ranges from 23,000 to 75,000 {m^3}/s (810,000 to 2,650,000 cu ft/s), with an average of 41,000 {m^3}/s (1,400,000 cu ft/s). The river transports annually 86 million tonnes of suspended sediment to the Atlantic Ocean and an additional 6% of bedload.

The river and its tributaries flow through the Congo rainforest, the second largest rainforest area in the world, after the Amazon rainforest in South America. The third-largest river in the world by discharge volume (at mouth 41,860 m3/s), following the Amazon (219,530 {m^3}/s) and Ganges–Brahmaputra–Meghna (total discharge at delta 43,950 {m}^3/s) rivers;[8] the second-largest drainage basin of any river, behind the Amazon; and is one of the deepest rivers in the world, at depths greater than 220 m (720 ft). Because its drainage basin includes areas both north and south of the Equator, its flow is stable, as there is always at least one part of the river experiencing a rainy season.

The sources of the Congo are in the highlands and mountains of the East African Rift, as well as Lake Tanganyika and Lake Mweru, which feed the Lualaba River, which then becomes the Congo below Boyoma Falls. The Chambeshi River in Zambia is generally taken as the source of the Congo in line with the accepted practice worldwide of using the longest tributary, as with the Nile River.

The Congo flows generally toward the northwest from Kisangani just below the Boyoma Falls, then gradually bends southwestward, passing by Mbandaka, joining with the Ubangi River and running into the Pool Malebo (Stanley Pool). Kinshasa (formerly Léopoldville) and Brazzaville are on opposite sides of the river at the Pool, where the river narrows and falls through a number of cataracts in deep canyons (collectively known as the Livingstone Falls), running by Matadi and Boma, and into the sea at Muanda.

Lower Congo constitutes the "lower" parts of the great river; that is the section of the river from the river mouth at the Atlantic coast to the twin capitals of Brazzaville and Kinshasa. In this section of the river, there are two significant tributaries, both on the left or south side. The Kwilu River originates in the hills near the Angolan border and enters the Congo some 100 km upstream from Matadi. The other is the Inkisi River, that flows in a northerly direction from the Uíge Province in Angola to the confluence with the Congo at Zongo some 80 km (50 mi) downstream from the twin capitals. Because of the vast number of rapids, in particular the Livingstone Falls, this section of the river is not operated continuously by riverboats.

Drainage basin

The Congo basin covers ten countries and accounts for about 13% of Africa. The highest point in the Congo basin is in the Ruwenzori Mountains, at an altitude of around 4,340 m (14,240 ft) above sea level.

Economic importance

Although the Livingstone Falls prevent access from the sea, nearly the entire Congo above them is readily navigable in sections, especially between Kinshasa and Kisangani. Large river steamers worked the river until quite recently. The Congo River still is a lifeline in a land with few roads or railways. Railways now bypass the three major falls, and much of the trade of Central Africa passes along the river, including copper, palm oil (as kernels), sugar, coffee, and cotton.

Hydroelectric power

The Congo River is the most powerful river in Africa. During the rainy season over 50,000 cubic metres (1,800,000 cu ft) of water per second flows into the Atlantic Ocean. Opportunities for the Congo River and its tributaries to generate hydropower are therefore enormous. Scientists have calculated that the entire Congo Basin accounts for 13 percent of global hydropower potential. This would provide sufficient power for all of Sub-Saharan Africa's electricity needs.

Currently, there are about 40 hydropower plants in the Congo Basin. The largest are the Inga dams, about 200 kilometres (120 mi) southwest of Kinshasa. The project was launched in the early 1970s, when the first dam was completed. The plan (as originally conceived) called for the construction of five dams that would have had a total generating capacity of 34,500 megawatts (MW). To date only the Inga I and Inga II dams have been built, generating 1,776 MW.

In February 2005, South Africa's state-owned power company, Eskom, announced a proposal to expand generation through improvements and the construction of a new hydroelectric dam. The project would bring the maximum output of the facility to 40,000 megawatts (MW). It is feared that these new hydroelectric dams could lead to the extinction of many of the fish species that are native to the river.

Natural history

The current course of the Congo River formed between 1.5 and 2 million years BP, during the Pleistocene. It is likely that during this period many upper tributaries of the Congo were captured from adjacent river basins, including the Uele and upper Ubangi from the Chari system and the Chambeshi River alongside a number of upper Kasai River tributaries from the Zambezi system.

The Congo's formation may have led to the allopatric speciation of the bonobo and the common chimpanzee from their most recent common ancestor. The bonobo is endemic to the humid forests in the region, as are other iconic species like the Allen's swamp monkey, dryas monkey, aquatic genet, okapi, and Congo peafowl.

In terms of aquatic life, the Congo River Basin has a very high species richness and among the highest known densities of endemics. As of 2009, almost 800 fish species have been recorded from the Congo River Basin (not counting Lake Tanganyika, which is connected but ecologically very different), and large sections remain virtually unstudied. For example, the section in Salonga National Park, which is about the size of Belgium, had still not been sampled at all in 2006. New fish species are scientifically described with some regularity from the Congo River Basin, and many undescribed species are known.

The Congo has by far the highest diversity of any African river system; in comparison, the next richest are the Niger, Volta and Nile with about 240, 140 and 130 fish species, respectively. Because of the great ecological differences between the regions in the Congo basin—including habitats such as river rapids, deep rivers, swamps, and lakes—it is often divided into multiple ecoregions (instead of treating it as a single ecoregion). Among these ecoregions, the Livingstone Falls cataracts has more than 300 fish species, including approximately 80 endemics while the southwestern part (Kasai River basin) has more than 200 fish species, of which about a quarter are endemic.

The dominant fish families—at least in parts of the river—are Cyprinidae (carp/cyprinids, such as Labeo simpsoni), Mormyridae (elephant fishes), Alestidae (African tetras), Mochokidae (squeaker catfishes), and Cichlidae (cichlids). Among the natives in the river is the huge, highly carnivorous giant tigerfish. Three of the more unusual endemics are the whitish (non-pigmented) and blind Lamprologus lethops, which is believed to live as deep as 160 metres (520 ft) below the surface, Heterochromis multidens, which is more closely related to cichlids of the Americas than other African cichlids, and Caecobarbus geertsii, the only known cavefish in Central Africa. There are also numerous endemic frogs and snails. Several hydroelectric dams are planned on the river, and these may lead to the extinction of many of the endemics.

Several species of turtles and the slender-snouted, Nile and dwarf crocodile are native to the Congo River Basin. African manatees inhabit the lower parts of the river.

Flooding

The Democratic Republic of Congo (DRC) and Republic of Congo (RoC) have historically experienced recurrent flooding along the Congo River and its main tributaries during the rainy season, causing erosion and landslides, and negatively impacting human settlements, agriculture, and public health. The Congo River is expected to be increasingly impacted by climate change as temperatures rise and rainfall increases both in intensity and seasonal duration.

From October 2019 to January 2020, heavy rains affected 16 of the 26 provinces of the DRC and eight out of 12 departments of the RoC, leading to the 2019–2020 Congo River floods. The rains caused the overflow of the Congo River and Ubangi rivers, floods and landslides throughout the DRC and RoC and led to the displacement of hundreds of thousands of people.

Additional Information

The Congo River (also known as Zaire River) is the largest river in Africa. Its overall length of 4,700 km (2,922 miles) makes it the second longest in Africa (after the Nile). The river and its tributaries flow through the second largest rain forest area in the world, second only to the Amazon Rainforest in South America.

The river also has the second-largest flow in the world, behind the Amazon, and the second-largest watershed of any river, again trailing the Amazon. Its watershed is a little larger than that of the Mississippi River. Because large parts of the river basin sit north and south of the equator, its flow is steady, as there is always at least one river having a rainy season. The Congo gets its name from the old Kingdom of Kongo which was at the mouth of the river. The Democratic Republic of the Congo and the Republic of the Congo, both countries sitting along the river's banks, are named after it. From 1971 to 1997, the Democratic Republic of the Congo was called Zaire and its government called the river the Zaire River.

The sources of the Congo are in the Highlands and mountains of the East African Rift, as well as Lake Tanganyika and Lake Mweru, which feed the Lualaba River. This then becomes the Congo below Boyoma Falls. The Chambeshi River in Zambia is usually taken as the source of the Congo because of the accepted practice worldwide of using the longest tributary, as with the Nile River.

The Congo flows mostly west from Kisangani just below the falls, then slowly bends southwest, passing by Mbandaka, joining with the Ubangi River, and running into the Pool Malebo (Stanley Pool). Kinshasa (formerly Léopoldville) and Brazzaville are on opposite sides of the river at the Pool, where the river narrows and falls through a few cataracts in deep canyons (collectively known as the Livingstone Falls), running by Matadi and Boma, and into the sea at the small town of Muanda.

History of exploration

The mouth of the Congo was visited by Europeans in 1482, by the Portuguese Diogo Cão, and in 1817, by a British exploration under James Kingston Tuckey that went up the river as far as Isangila. Henry Morton Stanley was the first European to travel along the whole river.

Economic importance

Although the Livingstone Falls stop ships coming in from the sea, almost all of the Congo is navigable in parts, especially between Kinshasa and Kisangani. Railways cross the three major falls that interrupt navigation, and much of the trade of central Africa passes along the river. Goods include copper, palm oil, sugar, coffee, and cotton. The river can also be valuable for hydroelectric power, and Inga Dams below Pool Malebo have been built.

In February of 2005, South Africa's state owned power company, Eskom, said that they had a proposal to increase the amount of electric power that the Inga can make through improvements and the building of a new hydroelectric dam. The project would bring the highest output of the dam to 40 GW, twice that of China's Three Gorges Dam.

Geological history

In the Mesozoic period before the continental drift opened the South Atlantic Ocean, the Congo was the upper part of a river about 12,000 km (7,500 miles) long that flowed west across the parts of Gondwanaland, now called Africa and South America.

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