Explanation of Sedimentation Process
We come across various incidents on a daily basis in which we have to separate one substance from the other to make it more useful. Different sedimentation methods are available by which we can separate substances that are mixed together. Sedimentation is the simplest separation method and an essential concept that is supposed to be understood. Its importance is unquestioned and plays a vital role in archeology. It's a natural process that can be explained as building up layers of small particles like sand or mud. Weight and sedimentation are very related.
The Sedimentation definition is given by, it also includes deposits from glacial ice and such materials collected under the impetus of gravity alone, similar to talus deposits, or accumulations of rock debris at the base of cliffs. This term is commonly used as a synonym for sedimentology and sedimentary petrology.
Sedimentation Process By an Experiment
The sedimentation process can be observed by a small experiment. Take a glass jar and fill it with a garden variety of mud. Pour some water, shake it well and keep it untouched for a few minutes.
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In a while, we can notice that the gravel and rocks have settled below, sand on above, and so on. The garden variety of mud basically has formed layers of soil based on varied, which is seen below.
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If we look at the cliff, it can be observed several layers on the surface of the cliff. These resultant layers are formed by sedimentation - the grains of sand and mud build-up over a long period of time, forming the layers. Also, fossils happen to be found in these layers. Logically, the quicker the bones are buried, and the more survival chances are more because it can be protected from scavenging animals and limited damage by weather. The rivers, lakes, and sea are the best depositors of both sand and mud are some sedimentation examples. Dinosaur fossils were found near to the sea, lakes or rivers. A land-slide, where mud and rock-fall down a hill mountain, can also lead to a sedimentation type.
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Sedimentation can also be used to separate particles based on size by applying the centrifugal force to the required solution. In the Centrifugation process, a centrifugal force is applied to a heterogeneous mixture which separates the mixture based on its density. The high dense components stay away from the centrifugal axis, whereas the less dense components stay near to the centrifugal axis by therefore separating the constituents of the mixture.
Also, sedimentation helps to determine a person's medical conditions. The sedimentation rate of RBC is one of the sedimentation examples. It is performed by measuring how long it takes the Red Blood cells (RBCs) to get settled in a test tube. As time passes by, the RBC's start to separate from the other plasma contents, they settle down at the bottom and serum will be formed above. The ESR (erythrocyte sedimentation rate) or sedimentation rate is measured simply by recording how far the top of the Red Blood Cell layer has fallen (in millimeters) from the top of the serum layer in one hour.
The water treatment plant uses the sedimentation method to pull out unwanted particles from unclean water by filtering several layers of soil and sand, allowing specific sizes of particles to pass through.
Basic Principle of Sedimentation
Suspended water solids have a specific gravity that is greater than the water tends to get settled by gravity as soon as the turbulence is retarded by granting the storage. Inorganic suspended solids have a specific gravity of about 2.65, and Organic suspended solids have a specific gravity of about 1.04
The particles having a specific gravity of about 1.20 or so readily settle down at the bottom of the tank. But to cause the settlement of lighter particles, it's difficult.
This settling down of particles at the bottom of the sedimentation tank phenomenon is called hydraulic subsidence, and each particle has its own hydraulic settling value causing hydraulic subsidence on it.
Basin, where the flow is retarded, is known as a sedimentation basin. The average theoretical time for which the water is detained in the settling tank is known as the detention period.
Types of Sedimentation
Plain Sedimentation
It is the process of settling down of solids and impurities in the raw water to the bottom of the sedimentation basin by a natural gravity force alone, with no chemical added. This is a very cheaper sedimentation method and is mostly used in every water filtration and purification system.
Sedimentation Using Clarifier and Contact
Here, the chemicals are mixed in water, and the same water is rotated with the help of pumps for a period of two hours per day, and suspended solids are settled down in the bottom of the reservoir or tank, and more.
Chemically Assisted Sedimentation or Clarification
In this process, chemicals are added to water, and through mixing, the suspended solids, and other impurities are stuck together and form floc, settling at the bottom of the basin.
Generally, the most used process is chemically assisted as horizontal sedimentation based on some assumptions. Basically, water flows through a tank in an irregular flow, and thus the intention of sedimentation is to create conditions where the flow takes place uniformly for a long enough period, permitting the maximum practical amount of floc to get settled before the water reaches the end of the tank.
FAQs on Sedimentation
1. Give some examples of marine sediments used in everyday products and applications?
Diatomaceous Earth is the skeletons of small siliceous sea benthic creatures and is used in aquarium filters, and in tooth polish, Pearl Drops. But it removes the enamel on our teeth.
Shale, a mud, is used for paver stones, and when metamorphosed, it turns into a slate and is used for pool tables, laboratory tables, and roof shingles. Marble, a metamorphosed limestone, is used for tile and sculptures. Limestone, a chemical precipitate sedimentary rock, is used to make Portland cement as the basis for all concrete systems. Limestone is burnt to force out the water in its chemical form, producing lime, combining it with water, sand, and gravel; we're going to get cement. Romans have learned it and used it to make their aqueducts and a few other structures.
2. Mention some types of sedimentation process?
Settling clarifiers and basins are designed to retain water such that suspended solids can get settled. By using sedimentation principles, suitable treatment technologies should be selected based on size, specific gravity, and shear resistance of particles. Depending on the density, size of particles, and physical properties of the solids, sedimentation processes are further divided into four types.
Type I - Dilutes, non-flocculent, and free-settling (every particle settles independently)
Type II - Dilute, flocculent (particles can be flocculated as they settle)
Type III - Concentrated suspensions, zone settling, and hindered settling (sludge thickening)
Type IV - Concentrated suspensions and compression (sludge thickening)
Controlling sedimentation rate in every type depends on different factors.
Аlthough sedimentation might оссur in tаnks оf оther shарes, removal оf ассumulаted solids is easiest with conveyor belts in reсtаngulаr tаnks оr with sсrарers rоtаting аrоund the сentrаl аxis оf сirсulаr tanks. Settling bаsins аnd сlаrifiers shоuld be designed bаsed оn the settling velосity (vs) оf the smаllest раrtiсle tо be theоretiсаlly 100% remоved. The оverflоw rаte is defined аs:
Overflow rаte (vо ) = Flоw оf wаtеr (Q (m3/s)) /(Surfасe аreа оf settling bаsin (А(m2))
In mаny cоuntries, this vаlue is nаmed аs surfасe lоаding in m3/h рer m2. Overflow rate is often used for flоw оver аn edge (fоr exаmрle а weir) in the unit m3/h рer m.
The unit of overflow rаte is usuаlly meters (оr feet) рer seсоnd, а velосity. Аny раrtiсle with settling velосity (vs) greаter thаn the overflow rate will settle оut, while оther раrtiсles will settle in the rаtiо vs/vо. There are recommendations on the overflow rates fоr eасh design thаt ideally take into ассоunt the сhаnge in раrtiсle size аs the sоlids mоve thrоugh the орerаtiоn:
Quiesсent Zоnes: 9.4 mm (0.031 ft) рer seсоnd
Full-flоw Bаsins: 4.0 mm (0.013 ft) рer seсоnd
Оff-line Bаsins: 0.46 mm (0.0015 ft) рer seсоnd
Hоwever, factors suсh аs flоw surges, wind sheаr, sсоur, аnd turbulenсe reduсe the effeсtiveness оf settling. Tо соmрensаte fоr these less thаn ideаl соnditiоns, it is reсоmmended dоubling the аreа саlсulаted by the рreviоus equаtiоn. It is аlsо imроrtаnt tо equаlize flоw distributiоn аt eасh роint асrоss the сrоss-seсtiоn оf the bаsin. Рооr inlet and оutlet designs саn produce extremely рооr flоw сhаrасteristiсs fоr sedimentаtiоn.
Settling basins and clarifiers can be designed аs lоng reсtаngles. Thаt аre hydrаuliсаlly mоre stаble аnd eаsier tо соntrоl fоr lаrge vоlumes. Сirсulаr сlаrifiers wоrk аs а соmmоn thiсkener (withоut the usаge оf rаkes), оr аs uрflоw tаnks.
Sedimentаtiоn effiсienсy dоes nоt deрend оn the tаnk deрth. If the fоrwаrd velосity is lоw enоugh sо thаt the settled material does not re-susрend frоm the tаnk flооr, the аreа is still the main parameter when designing а settling bаsin оr сlаrifier, taking care that the depth is nоt tоо lоw.
3. Why is sedimentation used?
The sedimentation system is used to lessen particle attention within the water. The advantage/use of sedimentation is that it minimizes the want for coagulation and flocculation. Typically, chemical substances are wished for coagulation and flocculation, however, progressed sedimentation controls the want for extra chemical substances. Additionally, sedimentation may be used after coagulation to boost the effectiveness of ongoing filtration withinside the system.
4. What is the working of sedimentation?
Although sedimentation is a generic system inside the water remedy industry, it's far nonetheless theoretical. The system may be numerous, relying on the attention of particles. For example, small concentrations of deposits frequently settle unhindered or without mechanical assistance. As concentrations increase, there are extra sediments that are settled and require further assistance.
5. What are the types of sedimentation?
Sedimentation of water calls for using specialized tanks. A sedimentation tank ensures that the debris settles. Sedimentation will take place evidently over time, however, water requires a tank to streamline the procedure.
Horizontal Flow Tank
Horizontal waft tanks are the most effective option. These square tanks permit water to waft horizontally, making sure that debris is separated from the water at some point of the motion via the tank. This way, the sediment has settled earlier than the water and exits from the tank. The tank is geared up to ease the sediment out periodically with the intention to permit the procedure to continue.
Multi-Layer Tank
A variant of the horizontal waft tank is the multi-layer tank. The procedure remains the same in a multi-layer tank. However, a couple of decks were constructed within the tank. Water is flown through from one layer to the subsequent till the sediment is nicely separated.
Radial Flow Tank
Radial waft tanks technique this procedure differently. These tanks are circular, and sediment is moved centrally to be processed and discharged. Radial tanks may be more advantageous for flocculation and recirculation in a few cases.
Settling Tank
Another device used for sedimentation is a settling tank. A settling tank is what helps with the gathering of sediment. Inclined settling tanks may be unhindered, this means that they don't have any extra mechanical stimulation. Instead, the procedure is facilitated via means of the dimensions of the tank, the intensity of the water and the position of the inclined plates on the bottom. The waft of the water can pass in a couple of guidelines relying on the sedimentation needs.
