Lesson 6:
Sedimentation
Objective
In this lesson we will answer the following questions:
Reading Assignment
Read the online lecture.
Lecture
After raw water and chemicals have been mixed and the floc formed, the water containing the floc (because it has a higher specific gravity than water) flows to the sedimentation or settling basin.
Sedimentation is also called clarification. Sedimentation removes settleable solids by gravity. Water moves slowly through the sedimentation tank/basin with a minimum of turbulence at entry and exit points with minimum short-circuiting. Sludge accumulates at the bottom of the tank/basin. Typical tanks or basins used in sedimentation include conventional rectangular basin, conventional center-feed basins, peripheral-feed basin, and spiral-flow basins.
In conventional treatment plants, the amount of detention time required for settling can vary from 2 to 6 hours. Detention time should be based on the total filter capacity when the filters are passing 2 gpm per square foot of superficial sand area. For plants with higher filter rates, the detention time is based on the filter rate of 3 to 4 gpm per square foot of sand area. The time requirement is dependent on the weight of the floc, the temperature of the water, and how still the basin is. Effective sedimentation is critical to optimize pathogen removal and to enhance filter effluent quality.
A number of conditions affect sedimentation: 1) uniformity of flow of water through the basin, 2)stratification of water due to difference in temperature between water entering and water already in the basin, 3) release of gases that may collect in small bubbles on suspended solids, causing them to rise and float as scum rather than settle as sludge, 4) disintegration of previously formed floc, and 5) size and density of the floc.
Sedimentation basins are designed to provide idle conditions, such as a uniform low velocity, proper detention time, no short circuits, and no surface turbulence to the flocculated water for an effective sedimentation. Velocity varies from 1 to 3 ft/minute. Detention time (the time it takes to fill the tank) ranges from 1 to 6 hours, depending on the design of the basin. A short circuit is the flowing of incoming water through the tank, without proper stratification of the water in the basin. Short circuits are generally caused by the stratification of the water in the basin and are common during summer and winter. There should be a proper mixing and baffling of the influent with the water in the basin. Surface turbulence is due to wind action and movements of the equipment. An adequate wind-breaking height of the basin wall above the water surface and the proper maintenance of equipment are very helpful.
Sediments settle to the bottom of the basin, and the effluent is strained from the top. These basins have inlet and outlet valves for flow control, and the bottom floor slopes to a hopper (pit) for the sludge collection. Sedimentation basins are classified as primary and final sedimentation basins, according to their functions. A primary sedimentation basin receives the flocculated water and discharges it to the final sedimentation basin.
Primary Sedimentation Basins
There are two types of primary sedimentation basins: conventional and high rate.
Conventional Basins
Conventional basins are rectangular or circular. Generally, they are 15 to 20 feet deep to allow proper sedimentation by keeping sludge, light floc (above the sludge), and clear water on the top well separated. Thus, carryover of the floc into the effluent is prevented. Detention time of water in these basins is 4 to 6 hours.
A rectangular basin has a horizontal flow from inlet to the outlet . The inlet is at one end and the outlet is at the other. This type of flow is known as a plug flow. Generally, length to width ratio is 20 to 1. Dimensions and proper baffling of these basins allow proper mixing, low velocity, and no short circuits. Sludge is normally collected into a hopper close to the inlet end and is discharged periodically.
A circular basin has the radial flow from a central inlet. It may have a central chemical mixing zone. Sludge scrapers collect the sludge into a central hopper.
High Rate Basins
High rate basins are designed for a better treatment with high load and less detention time. They are compact units. Detention time is generally 1 to 2 hours, as compared to 4 to 6 hours in the conventional basins. These basins consist of tube settler basins, plate settler basins, and solid contact basins.
Tube Settler Basins
Tube settler basins have tubes installed in them to increase the settling surface and adequate baffling for better sedimentation in less space.
Plate Settler Basins
Like tube settlers, plate settler basins have plates instead of tubes for a similar function.
Solid Contact Basins
Solid contact basins are compact units with rapid mixing, coagulation, and sedimentation zones in one unit. They are circular basins. A small percentage of previously formed floc is mixed and recirculated with the coagulating water in the central part for a fast and economical flocculation. This mixture is called slurry. Preformed floc is beneficial by providing the required particulate surface, by providing some of its remaining coagulation capacity, and by acting as a scrubber to remove turbidity from the influent water.
After coagulation and flocculation, the water flows to the sedimentation zone, which is the outer part of the basin. The flocculated water flows under or over a bonnet - (inverted cone) shaped baffle that separates the reaction and sedimentation zones. solids settle to the bottom and are swept by the scrapers into one or more concentrating hoppers. A part of these solids is recirculated and the rest are discharged. There are several different designs of solid contact basins by various companies that are suitable for different types of source water.
Solids-contact units are popular for smaller package-type water treatment plants and also in cold climates where the units have to be inside a building. However, care must be exercised in the operation of these units to ensure that a uniform sludge blanket is formed and is subsequently maintained throughout the solids removal process. The sludge blanket is sensitive to changes in water temperature. Temperature density currents tend to upset the sludge blanket. Loss of the sludge blanket will affect the performance of the filters.
Sedimentation Zones
All sedimentation basins have four zones - the inlet zone, the settling zone, the sludge zone, and the outlet zone. Each zone should provide a smooth transition between the zone before and the zone after. In additon, each zone has its own unique purpose.
Zones can be seen most easily in rectangular sedimentation basins, such as the one shown below:
In a circular clarifier, water typically enters the basin from the center rather than from one end and flows out to outlets located around the edges of the basin; but the four zones can still be found within the clarifier.
Inlet Zone
The two primary purposes of the inlet zone of a sedimentation basin are to distribute the water and to control the water's velocity as it enters the basin. In addition, inlet devices act to prevent turbulence of the water.
The incoming flow in a sedimentation basin must be evenly distributed across the width of the basin to prevent short-circuiting. Short-circuiting is a problematic circumstance in which water bypasses the normal flow path through the basin and reaches the outlet in less than the normal detention time. In addition to preventing short-circuiting, inlets control the velocity of the incoming flow. If the water velocity is greater than 0.5 ft/sec, then floc in the water will break up due to agitation of the water. Breakup of floc in the sedimentation basin will make settling much less efficient.
Two types of inlets are shown below. The stilling wall, also known as a perforated baffle wall, spans the entire basin from top to bottom and from side to side. Water leaves the inlet and enters the settling zone of the sedimentation basin by flowing through the holes evenly spaced across the stilling wall.
The second type of inlet allows water to enter the basin by first flowing through the holes evenly spaced across the bottom of the channel and then by flowing under the baffle in front of the channel. The combination of channel and baffle serves to evenly distribute the incoming water.
Settling Zone
After passing through the inlet zone, water enters the settling zone where water velocity is greatly reduced. This is where the bulk of floc settling occurs and this zone will make up the largest volume of the sedimentation basin. For optimal performance, the settling zone requires a slow, even flow of water. The settling zone may be simply a large expanse of open water. But in some cases, tube settlers and lamella plates, such as those shown below, are included in the settling zone.
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Tube settlers and lamella plates- Water flows up through slanted tubes or along slanted plates. Flow settles out in the tubes or plates and drifts back down into the lower portions of the sedimentation basin. Clarified water passes through the tubes or between the plates and then flows out of the basin. |
Tube settlers and lamella plates increase the settling efficiency and speed in sedimentation basins. Each tube or plate functions as a miniature sedimentation basin, greatly increasing the settling area. Tube settlers and lamella plates are very useful in plants where site area is limited, in packaged plants, or to increase the capacity of shallow basins.
Outlet Zone
The outlet zone controls the water flowing out of the sedimentation basin - both the amount of water leaving the basin and the location in the basin from which the outflowing water is drawn. Like the inlet zone, the outlet zone is designed to prevent short-circuiting of water in the basin. In addition, a good outlet will ensure that only well-settled water leaves the basin and enters the filter. The outlet can also be used to control the water level in the basin. Outlets are designed to ensure that the water flowing out of the sedimentation basin has the minimum amount of floc suspended in it. The best quality water is usually found at the very top of the sedimentation basin, so outlets are usually designed to skim this water off the sedimentation basin.
A typical outlet zone begins with a baffle in front of the effluent. This baffle prevents floating material from escaping the sedimentation basin and clogging the filters. After the baffle comes the effluent structure, which usually consists of a launder, weirs, and effluent piping. A typical effluent structure is shown below:
The primary component of the effluent structure is the effluent launder, a trough which collects the water flowing out of the sedimentation basin and directs it to the effluent piping. The sides of a launder typically have weirs attached. Weirs are walls preventing water from flowing uncontrolled into the launder. The weirs serve to skim the water evenly off the tank.
A weir usually has notches, holes or slits along its length. These holes allow water to flow into the weir. The most common type of hole is the V-shaped notch shown on the picture above, which allows only the top inch or so of water to flow out of the sedimentation basin. Conversely, the weir may have slits cut vertically along its length, an arrangement which allows for more variation of operational water level in the sedimentation basin. Water flows over or through the holes in the weirs and into the launder. Then the launder channels the water to the outlet, or effluent, pipe. This pipe carries water away from the sedimentation basin and to the next step in the treatment process, filtration. The effluent structure may be located at the end of a rectangular sedimentation basin or around the edges of a circular clarifier. Alternatively, the effluent may consist of finger weirs, an arrangement of launders which extend out into the settling basin as shown below.
Sludge Zone
The sludge zone is found across the bottom of the sedimentation basin where the sludge collects temporarily. Velocity in this zone should be very slow to prevent resuspension of sludge. A drain at the bottom of the basin allows the sludge to be easily removed from the tank. Thank tank bottom should slope toward the drains to further facilitate sludge removal.
In some plants, sludge removal is achieved continuously using automated equipment. In other plants, sludge must be removed manually. If removed manually, the basin should be cleaned at least twice per year, or more often if excessive sludge buildup occurs. It is best to clean the sedimentation basin when water demand is low, usually in April and October. Many plants have at least two sedimentation basins so that water can continue to be treated while one basin is being cleaned, maintained, and inspected. If sludge is not removed from the basin often enough, the effective (useable) volume of the tank will decrease, reducing the efficiency of sedimentation. In addition, the sludge built up on the bottom of the tank may become septic, meaning that it has begun to decay anaerobically. Septic sludge may cause taste and odor problems or may float to the top of the water and become scum. Sludge may also become resuspended in the water and be carried over to the filters.
Final Sedimentation Basin
The final sedimentation basin is similar in structure to a conventional primary sedimentation basin. However, it has the provision for adding some chemicals, such as polymer, into the water. This basin provides another step for turbidity removal by the further sedimentation of any carryover turbidity in the effluent of the primary sedimentation basin. Because there is either none or very little floc in the water, a small dose (0.5 mg/L) of a polymer is often used for coagulation of the turbidity. Generally, the final basin has a very small amount of sludge. Final basin effluent is, usually, disinfected with a small amount of chlorine for controlling the biological growth in the filter media. Water from these basins is crystal clear with turbidity less than 1 NTU. It flows to the filters for the final removal of turbidity.
Factors Affecting Sedimentation
Several factors affect sedimentation, including:
To a large extent, a sedimentation basin's efficiency will depend on the efficiency of the preceding coagulation/flocculation process. The size, shape, and density of the floc entering the sedimentation basin will all influence how well the floc settles out of the water. Floc which is too small or too large, is irregularly shaped, or has a low density will not tend to settle out in the sedimentation basin. Even if the coagulation/flocculation process is very efficient, floc can disintegrate on its way to or in the sedimentation basin. Previously formed floc will disintegrate if the water velocity is too high, if there are sharp bends in the pipe at the inlet.
if water is discharged above the sedimentation basin water level...
or if throttle valves are used.
Another major cause of inefficiency in the sedimentation basin is short-circuiting, which occurs when water bypasses the normal flow path through the basin and reaches the outlet in less than the normal detention time. The picture below shows a basin in which the water is flowing primarily through the left half of the basin. (Flowing water is shown as green blobs.) An efficient sedimentation basin would have water flowing through the entire basin, rather than through just one area.
When water in the sedimentation basin short-circuits, the floc does not have enough time to settle out of the water, influencing the economy of the plant and the quality of the treated water.
Short-circuiting in a sedimentation basin can be detected in a variety of ways. If areas of water in the basin do not appear to be circulating, or if sludge buildup on the bottom of the basin is uneven, then tests may be called for. Floats or dyes can be released at the inlet of the basin to determine currents. A variety of factors can cause short-circuiting in a sedimentation basin. Basin shape and design, along with design of the inlet and outlet, can cause short-circuiting. You may remember from the last lesson that a long, thin sedimentation basin is less likely to short-circuit than is a short broad one. Uneven distribution of flow either at the inlet or outlet can also cause short-circuiting. If the weir at the outlet is not level or if some of the notches clog, flow will be uneven and will cause short-circuiting. In addition to the design of the basin, characteristics of the water can also cause short-circuiting. Differences of temperature can cause stratification of the water - separation of water into bands of different temperature. Incoming water will tend to flow through the band of water which corresponds to its own temperature, and will not spread throughout the rest of the basin.
We should note that temperature can cause other problems with sedimentation as well. Cold water prevents floc from settling, so that longer settling times or larger doses of coagulant chemicals are needed.
Gases in the water may cause floating scum, which can carry over into the filters. Sprinkling water on the on the scum may cause the scum to settle, but it is usually a better practice to find and fix the source of the problem. Gases in the sedimentation basin are usually caused by water being introduced in the pump or by a leak in the raw water line.
Another sedimentation basin problem is algal growth. If sedimentation basins have sufficient sunlight, algae will grow on the walls of the basin. These algae can break loose and clog the filter. Algae are best treated with shock chlorination, a method of feeding 5-10 ppm of chlorine into the raw water or of sprinkling HTH around the basin walls just before the plant is shut down for a few hours. The chlorine will kill the algae while the chlorinated water sits in the tank.
A few other factors can also influence sedimentation basin efficiency. Intermittent operation of the basin can cause settling problems. Also, design problems such as excessive surface loading or weir loading can cause problems. We will discuss surface and weir loading in the second half of this lesson.
As mentioned earlier, flocs are formed via the coagulation and flocculation treatment processes. The floc, comprised of organic and inorganic matter, must be removed prior to filtration in order to reduce the turbidity load on the filters. Conventional sedimentation requires the flocculated water to move slowly through a sedimentation tank with a minimum of turbulence at the entry and exit points and a minimum of hydraulic short-circuiting. The weight of the solids at the slow water velocity will allow the solids to settle by gravity to the bottom of the tank prior to the end of the basin. The mass of collected solids is referred to as sludge.
The U.S. Environmental Protection Agency (EPA) has established primary maximum contaminant levels (PMCL) for turbidity at conventional surface water treatment plants. The combined filter effluent must have a turbidity of < 0.3 NTU (nephelometric turbidity units) in 95% or more of the turbidity samples collected each month. In addition, the combined filter effluent must never exceed 1 NTU.
Sedimentation Calculations
Sedimentation, the solid-liquid separation by gravity, is one of the most basic processes of water treatment. In water treatment, plain sedimentation, such as the use of a presedimentation basin for grit removal and a sedimentation basin following coagulation/flocculation, is the most commonly used approach. The two common tank shapes of sedimentation tanks are rectangular and circular. There are certain calculations that need to be performed to ensure that sedimentation is properly occuring, including tank volume, detention time, surface overflow rate, mean flow velocity, weir overflow rate, percent settled biosolids and determining lime dosage.
Tank Volume
For rectangular sedimentation basins use the following equation:
Volume, gal = Length, ft x Width, ft x Depth, ft x 7.48 gal/ft3
Example:
A sedimentation basin is 25 ft wide by 80 ft long and contains water to a depth of 14 ft. What is the volume of water in the basin, in gallons?
Volume, gal = Length, ft x Width, ft x Depth, ft x 7.48 gal/ft3
Volume, gal = 80 ft x 25 ft x 14 ft x 7.48 gal/ft3
Volume, gal = 209,440 gal
For circular clarifiers, use the following equation:
Volume, gal = 0.785 x (Diameter)2 x Depth, ft x 7.48 gal/ft3
Example:
A clarifier has a diameter of 25 ft and contains water to a depth of 18 ft. What is the volume of water in the basin, in gallons?
Volume, gal = 0.785 x (Diameter)2 x Depth, ft x 7.48 gal/ft3
Volume, gal = 0.785 x (25 ft)2 x 18 ft x 7.48 gal/ft3
Volume, gal = 66,058 gal
Detention Time
Detention time for clarifiers varies from 1 to 3 hours. There are a couple of different equations used to determine detention time, depending on the shape of the tank:
Basic equation:
Rectangular basin:
Circular basin:
You'll notice the detentino time equations for rectangular and circular bains basically combine the volume and detention time in one equation.
Example 1:
A sedimentation tank has a volume of 137,000 gal. if the flow to the tank is 121,000 gph, what is the detention time in the tank, in hours?
Example 2:
A sedimentation basin is 60 ft long by 22 ft wide and has water to a depth of 10 ft. If the flow to the basin is 1,500,000 gpd, what is the sedimentation basin detention time?
First, convert the flow rate from gpd to gph so the time units will match:
Now, calculate the detention time:
Surface Overflow Rate
The surface overflow rate is used to determine loading on sedimentation basins and circular clarifiers. Surface overflow rate only measures the water overflowing the process (plant flow only). Surface overflow rate calculations do not include recirculated flows and is determined with the following equation:
Example 1:
A circular clarifier has a diameter of 80 ft. If the flow to the clarifier is 1800 gpm, what is the surface overflow rate in gpm/ft2?
*Remember that the area of a circular clarifier can be determined by 0.785 x (Diameter)2
Example 2:
A sedimentation basin 70 ft by 25 ft receives a flow of 1000 gpm. What is the surface overflow rate in gpm/ft2?
*Remember that the area of a rectangle can be found by length,ft x width, ft
Mean Flow Velocity
The measure of average velocity of the water as it travels through a rectangular sedimentation basin is known as mean flow velocity and is calclated by the following equation:
Flow, ft3/min = Cross-sectional area, ft2 x Volume, ft/min (or Q=AV)
Example:
A sedimentation basin is 60 ft long by 18 ft wide and has water to a depth of 12 ft. When the flow through the basin is 900,000 gpd, what is the mean flow velocity in the basin in ft/min?
*Hint: Because velocity is desired in ft/min, the flow rate in the equation must be expressed in ft3/min:
Now, solve for the velocity, or volume:
Flow, ft3/min = Cross-sectional area, ft2 x Volume, ft/min
84 ft3/min = (18 ft x 12 ft) x Volume, ft/min
To get the velocity on one side by itself to solve you need to move the area to the other side of the equal sign making it 84/(18x12):
So the velocity through the sedimentation basin is 0.4 ft/min.
Weir Loading Rate (Overflow Rate)
Weir loading rate (weir overflow rate) is the amount of water leaving the settling tank per linear foot of weir. The result of this calculation can be compared with design. Normally, weir overflow rates of 10,000 to 20,000 gpd/ft are used in the design of a settling tank. Typically, the weir loading rate is a measure of the flow in gallons per minute (gpm) over each foot of weir. The weir loading rate is determined using the following equation:
Example:
A circular clarifier receives a flow of 3.55 MGD. If the diameter of the weir is 90 ft, what is the weir loading rate in gpm/ft?
First convert the flow from MGD to gpm:
To determine feet of weir for a circular clarifier:
Weir, ft = 3.14 x Diameter
Weir, ft = 3.14 x 90 ft
Weir, ft = 283 ft
Now we can determine the weir loading rate:
Percent Settled Biosolids
The percent settled biosolids test (volume over volume test) is conducted by collecting a 100-mL slurry sample from the solids contact unit and allowing it to settle for 10 iminutes. After 10 minutes, the volume of settled biosolids at the bottom of the 100-mL graduated cylinder is measured and recorded. The equation used to calculate percent settled biosolids is:
Example:
A 100-mL sample of slurry from a solids contact unit is placed in a graduated cylinder and allowed to set for 10 minutes. The settled biosolids at the bottom of the graduated cylinder after 10 minutes is 22 mL. What is the percent of settled biosolids of the sample?
Determining Lime Dosage
mg/L
During the alum dosage process, lime is something added to provide adequate alkalinity (HCO3) int he solids contact clarification process for the coagulation and precipitation of the solids. To determine the lime dose required, in mg/L three steps are required.
In step 1, the total alkalinity required to react with the alum to be added and provide proper precipitation is determined using the following equation:
Total alkalinity required, mg/L = Alkalinity reacting with alum, mg/L + alkalinity in the water, mg/L
*Hint: 1 mg/L alum reacts with 0.45 mg/L alkalinity
Example for Step 1:
Raw water requires an alum dose of 45 mg/L, as determined by jar testing. If a residual 30-mg/L alkalinity must be present in the water to ensure complete precipitation of alum added, what is the total alkalinity required, in mg/L?
First, calculate the alkalinity that will react with 46 mg/L alum:
To get "x mg/L alkalinity" on one side by itself so we can solve for it, multiply both sides by 45 mg/L alum:
x mg/L alkalinity = 0.45 mg/L x 45 mg/L
x mg/L alkalinity = 20.25 mg/L
Now calculate the total alkalinity required:
Total alkalinity required, mg/L = Alkalinity reacting with alum, mg/L + alkalinity in the water, mg/L
Total alkalinity required, mg/L = 20.25 mg/L + 30 mg/L
Total alkalinity required, mg/L = 50.25 mg/L
In step 2, we make a comparison between required alkalinity and alkalinity already in the raw water to determine how many mg/L alkalinity should be added to the water. The equation used to make this calculation is:
Added alkalinity = Total alkalinity required, mg/L - alkalinity in water, mg/L
Example for Step 2:
A total of 44 mg/L alkalinity is requried to react with alum and ensure proper precipitation. If the raw water has an alkalinity of 30 mg/L as bicarbonate, how much mg/L alkalinity should be added to the water?
Added alkalinity = Total alkalinity required, mg/L - alkalinity in water, mg/L
Added alkalinity = 44 mg/L - 30 mg/L
Added alkalinity = 14 mg/L alkalinity to be added
In step 3, after determining the amount of alkalinity to be added to the water, we determine how much lime (the source of alkalinity) must be added. We accomplish this by using the ratio including 1 mg/L reacts with 0.45 mg/L alkalinity:
Example for Step 3:
It has been calculated that 16 mg/L alkalinity must be added to a raw water. How much mg/L lime will be required to provide this amount of alkalinity? (1 mg/L alum reacts with 0.45 mg/L alkalinity and 1 mg/L alum reacts with 0.35 mg/L lime).
First determine the mg/L lime required by using a proportion that relates bicarbonate alkalinity to lime:
Then cross-multiply:
0.45x = 16 mg/L x 0.35 mg/L
Now get x on one side by itself by dividing both sides by 0.45:
So your system needs 12.4 mg/L of lime to provide the appropriate amount of alkalinity.
lb/day
After th elime has been determined in terms of mg/L, it is a fairly simple matter to calculate the lime dose in lb/day, which is one of the most common calculations in water treatment. To convert from mg/L to lb/day lime dose, we use the following equation:
Lime, lb/day = Lime, mg/L x Flow, MGD x 8.34 lb/gal
Example:
The lime dose for a raw water has been calculated to be 15.2 mg/L. If the flow to be treated is 2.4 MGD, how many lb/day lime will be required?
Lime, lb/day = Lime, mg/L x Flow, MGD x 8.34 lb/gal
Lime, lb/day = 15.2 mg/L x 2.4 MGD x 8.34 lb/gal
Lime, lb/day = 304 lb/day lime
g/min
To convert from mg/L lime to g/min lime, use the following equation:
*Hint: 1 lb - 454 g
Example:
A total of 275 lb/day lime will be required to raise the alkalinity of the water passing through a solid contact clarification process. How many g/min lime does this represent?
Review
Sedimentation removes settleable solids by gravity. Water moves slowly through the sedimentation tank/basin with a minimum of turbulence at entry and exit points with minimum short-circuiting. Sludge accumulates at the bottom of the tank/basin. Typical tanks or basins used in sedimentation include conventional rectangular basin, conventional center-feed basins, peripheral-feed basin, and spiral-flow basins. In conventional treatment plants, the amount of detention time required for settling can vary from 2 to 6 hours. Detention time should be based on the total filter capacity when the filters are passing 2 gpm per square foot of superficial sand area. Sediments settle to the bottom of the basin, and the effluent is strained from the top. These basins have inlet and outlet valves for flow control, and the bottom floor slopes to a hopper (pit) for the sludge collection. Sedimentation basins are classified as primary and final sedimentation basins, according to their functions. A primary sedimentation basin receives the flocculated water and discharges it to the final sedimentation basin. Sedimentation, the solid-liquid separation by gravity, is one of the most basic processes of water treatment. In water treatment, plain sedimentation, such as the use of a presedimentation basin for grit removal and a sedimentation basin following coagulation/flocculation, is the most commonly used approach. The two common tank shapes of sedimentation tanks are rectangular and circular. There are certain calculations that need to be performed to ensure that sedimentation is properly occuring, including tank volume, detention time, surface overflow rate, mean flow velocity, weir overflow rate, percent settled biosolids and determining lime dosage.
Assignment
Please complete the math worksheet for this lesson. You must be logged into Canvas to complete this assignment. Make sure you choose the appropriate semester.
Quiz
Answer the questions in the Lesson 6 quiz. You will need to log into Canvas to take the quiz. You may take the quiz 3 times, if needed, and an average will be taken from your attempts for final grade calculation. Make sure you choose the appropriate semester.
