- Subject Code: Design of water Treatment Units ( 3161306)
- Date:03-06-2022
- Paper solved by Om sonawane
Q.1 (a) Define and highlight the importance of following parameters in design of sedimentation tank: (i) SOR (ii) WOR (iii) Scour Velocity.
Sedimentation tanks, also known as clarifiers, are used in wastewater treatment to separate solid particles from liquid. They work by allowing sediment to settle to the bottom of the tank, where it can be removed.
(i) SOR (Sludge Volume Index) is a measure of the volume of sludge produced per unit volume of wastewater treated. It is an important parameter to consider in the design of a sedimentation tank because it determines the size of the tank required to accommodate the volume of sludge produced.
(ii) WOR (Waste Sludge Retention Time) is the length of time that sludge is retained in the sedimentation tank before it is removed. This parameter is important because it affects the efficiency of the sedimentation process. A longer retention time allows for more efficient settling of solids, but also increases the volume of sludge produced and the size of the tank required.
(iii) Scour Velocity is the minimum velocity of liquid needed to prevent sediment from settling and accumulating in the tank. It is important to consider in the design of a sedimentation tank because it affects the efficiency of the sedimentation process. If the scour velocity is too low, sediment will accumulate and the tank will become less effective. If the scour velocity is too high, it will be difficult for solids to settle and the tank will be less efficient.
(b) Two sedimentation tanks operate in parallel. The combined flow to the two tanks is 0.1000 m3 /s. The depth of each tank is 2.00 m and each has a detention time of 4.00 h. What is the surface area of each tank and what isthe surface overflow rate of each tank in m3/m2.d?
The combined flow to the two tanks is 0.1000 m3/s, so the flow to each tank is 0.1000 m3/s / 2 = 0.0500 m3/s.
The detention time of each tank is 4.00 h, so the volume of each tank is:
0.0500 m3/s * 4.00 h = 0.2000 m3
The depth of each tank is 2.00 m, so the surface area of each tank is:
0.2000 m3 / 2.00 m = 0.1000 m2
The surface overflow rate (SOR) of each tank is the flow rate of the wastewater divided by the surface area of the tank. So the SOR of each tank is:
0.0500 m3/s / 0.1000 m2 = 0.5000 m3/m2.d
So the surface area of each tank is 0.1000 m2 and the surface overflow rate of each tank is 0.5000 m3/m2.d
(C) Draw a neat sketch of conventional water treatment plant and explain the functions of different units.
A conventional water treatment plant typically includes several units in a specific order to purify water. These units include:
Screening: In this unit, large debris such as sticks and leaves are removed from the raw water.
Coagulation And Flocculation: In these units, chemicals such as alum are added to the water to destabilize the particles, causing them to form clumps (flocs) that can be easily removed.
Sedimentation: In this unit, the flocs settle to the bottom of a tank, where they can be removed.
Filtration: In this unit, the water is passed through a bed of sand or other material to remove any remaining particles.
Disinfection: In this unit, the water is disinfected to kill any remaining bacteria and other microorganisms.
Storage: After the water is treated, it is stored in a reservoir until it is distributed to the users.
Sludge Treatment And Disposal: The sludge from the sedimentation tank is removed and treated by different methods such as anaerobic digestion, aerobic digestion, and incineration.
The entire process aims to remove impurities and microorganisms, making the water safe for human consumption and other uses.
Q.2
(a) Write down the design criteria for Rectangular Sedimentation tank.
Design criteria for a rectangular sedimentation tank include the following:
Flow Rate: The flow rate of the wastewater entering the tank must be known in order to calculate the required tank volume and dimensions.
Detention Time: The amount of time the wastewater spends in the tank must be sufficient for solids to settle to the bottom. A common detention time for a rectangular sedimentation tank is 2-4 hours.
Sludge Volume Index (SVI): The SVI is a measure of the volume of sludge produced per unit volume of wastewater treated. It is used to determine the size of the tank needed to accommodate the volume of sludge produced.
Scour Velocity: The minimum velocity of liquid needed to prevent sediment from settling and accumulating in the tank. It must be high enough to ensure solids are not allowed to accumulate on the bottom.
Overflow Rate: The rate at which the clarified water flows out of the tank. It must be high enough to ensure that the water is clarified, but not so high that it causes unnecessary turbulence and reduces the efficiency of the sedimentation process.
Inlet And Outlet Design: Proper inlet and outlet design is crucial for the efficient operation of the sedimentation tank. The inlet must be designed to distribute the wastewater evenly across the tank, while the outlet must be designed to remove the clarified water while minimizing the disturbance of the settled solids.
Tank Dimensions: The dimensions of the tank must be sufficient to accommodate the flow rate and detention time, while also providing enough surface area for solids to settle.
Safety & Access: The tank should be designed to ensure safety of the operators and maintenance personnel, and should be easily accessible for cleaning and maintenance.
Sludge Removal: The tank should be designed to facilitate the easy removal of the settled solids.
Location: The tank should be located in an area that is easily accessible for construction and maintenance, and that does not pose a risk of flooding or other hazards.
(B) Enlist the parameters to be considered for selection of water treatment units and explain any two in detail.
Type Of Impurities Present: Different types of impurities require different treatment methods. For example, physical impurities such as sediment can be removed by sedimentation, while chemical impurities require different methods such as adsorption, oxidation, or ion exchange.
Quality Of Raw Water: The quality of raw water plays an important role in selecting the appropriate treatment method. For example, water with high levels of dissolved minerals may require a different method of treatment than water with high levels of bacteria.
Flow Rate: The flow rate of the water to be treated determines the size and number of treatment units required.
Water Quality Standards: The water treatment units must meet the water quality standards set by the relevant regulatory bodies.
Capital And Operational Costs: The cost of the treatment units, including the cost of installation, operation, and maintenance, must be considered.
Space Availability: The space available for installation of the treatment units must be considered.
Sludge Handling: The treatment units should be designed to handle the sludge produced during the treatment process.
Energy Efficiency: The treatment units should be energy efficient and should have low operational costs.
Reliability And Ease Of Maintenance: The treatment units should be reliable and easy to maintain.
Environmental impact: The treatment units should have minimal environmental impact.
Two of the parameters in detail :
Type Of Impurities Present: The type of impurities present in water is an important consideration when selecting water treatment units. Different types of impurities require different methods of treatment. For example, physical impurities, such as sediment, can be removed by sedimentation, while chemical impurities, such as dissolved minerals, require different methods such as adsorption, oxidation, or ion exchange.
Water Quality Standards: The water treatment units must meet the water quality standards set by the relevant regulatory bodies. These standards are put in place to protect public health and the environment. For example, the Drinking Water Standards set by the Environmental Protection Agency (EPA) in the United States specify maximum contaminant levels for various substances, such as bacteria, viruses, and chemicals. The treatment units must be able to meet these standards in order to ensure that the treated water is safe for human consumption.
(C) Draw a flow diagram for treating ground water with Iron or manganese or both and explain the different treatment units.
A typical flow diagram for treating ground water with iron or manganese or both may include the following treatment units:
Aeration: The water is aerated to increase the oxygen content which helps in removing Iron and Manganese by oxidation.
Filtration: The water is passed through a bed of sand or other material to remove any remaining particles.
Chemical Treatment: Chemicals such as potassium permanganate or hydrogen peroxide are added to the water to oxidize the iron and manganese, making them easier to filter out.
pH adjustment: If necessary, the pH of the water is adjusted to ensure that the chemical treatment is effective.
Sand Filtration: The water is passed through a bed of sand or other material to remove any remaining particles.
Carbon Filtration: The water is passed through a bed of activated carbon to remove any remaining dissolved iron and manganese.
Disinfection: The water is disinfected to kill any remaining bacteria and other microorganisms.
Storage: After the water is treated, it is stored in a reservoir until it is distributed to the users.
Let me explain the units in detail :
Aeration: The water is aerated to increase the oxygen content which helps in removing Iron and Manganese by oxidation. Aeration is the process of adding air to water by agitating it. This helps to increase the oxygen content of the water, which is necessary for the oxidation of iron and manganese.
Filtration: The water is passed through a bed of sand or other material to remove any remaining particles. This is typically done using a sand filter, which is a vessel filled with sand or other granular material. Water is passed through the filter, and any remaining suspended solids are removed.
Chemical Treatment: Chemicals such as potassium permanganate or hydrogen peroxide are added to the water to oxidize the iron and manganese, making them easier to filter out. The chemical treatment is used to oxidize the iron and manganese present in the water, making it easier to remove them. Potassium permanganate is a strong oxidizing agent that can oxidize iron and manganese in water.
PH Adjustment: If necessary, the pH of the water is adjusted to ensure that the chemical treatment is effective. The pH of water is adjusted to ensure that the chemical treatment is effective. The pH of water must be in a specific range for the chemical treatment to be effective.
Sand Filtration: The water is passed through a bed of sand or other material to remove any remaining particles. Sand filtration is used to remove any remaining particles of iron and manganese from the water.
Carbon Filtration: The water is passed through a bed of activated carbon to remove any remaining dissolved iron and manganese. Carbon filtration is used to remove dissolved iron and manganese from water.
Disinfection: The water is disinfected to kill any remaining bacteria and other microorganisms. Disinfection is used to kill any remaining bacteria and other microorganisms in the water. This is typically done using chlorine or ultraviolet light.
Storage: After the water is treated, it is stored in a reservoir until it is distributed to the users. The treated water
OR
(c) What is the permissible limit for fluoride as per IS 10500? Explaindefluoridation method with chemical reactions.
According to the Indian Standard IS 10500, the permissible limit for fluoride in drinking water is 1.5 mg/L. This limit is set to ensure that the water is safe for human consumption and does not pose a risk of dental or skeletal fluorosis.
Defluoridation is the process of removing fluoride from water. One common method of defluoridation is by using chemicals such as calcium hydroxide (lime) or aluminum salts.
The chemical reactions that take place in defluoridation using lime are:
Ca(OH)2 + F- → CaF2 + 2OH-
Ca(OH)2 + F- → CaF(OH) + OH-
In the first reaction, calcium hydroxide reacts with fluoride ions to form calcium fluoride and hydroxide ions. In the second reaction, calcium hydroxide reacts with fluoride ions to form calcium fluoride hydroxide and hydroxide ions.
The chemical reactions that take place in defluoridation using aluminum salts are:
Al(OH)3 + 3F- → AlF3 + 3OH-
Al(OH)3 + 3F- → AlF(OH)3 + 3OH-
In the first reaction, aluminum hydroxide reacts with fluoride ions to form aluminum fluoride and hydroxide ions. In the second reaction, aluminum hydroxide reacts with fluoride ions to form aluminum fluoride hydroxide and hydroxide ions.
The defluoridated water is obtained after filtration, neutralization and sedimentation. These methods are effective for reducing the fluoride concentration in water, and are widely used in water treatment plants.
Q.3
(a) Design a tube settler module of rectangular cross section for a design flow of 1.5 MLD. Assume cross section of tube as 50 mm x 50mm.
Designing a clarifloculator for a flow rate of 0.2314 m³/s involves several steps and calculations based on the design criteria. Here is an overview of the process:
Determine the required detention time for the clarifloculator: A common detention time for a clarifloculator is 2-4 hours. For this example, let's assume a detention time of 3 hours.
Calculate the volume of the clarifloculator: The volume of the clarifloculator can be calculated using the formula: Volume = Flow Rate x Detention Time. In this case: Volume = 0.2314 m³/s x 3 hours = 0.6942 m³.
Determine the dimensions of the clarifloculator: Based on the volume of the clarifloculator, the dimensions of the tank can be determined. For example, a rectangular clarifloculator with a width of 4 m, a length of 10 m and a depth of 2 m, would have a volume of 0.8 m³ which is sufficient for the design flow rate.
Determine the surface overflow rate (SOR): The SOR is the flow rate of the wastewater divided by the surface area of the tank. SOR = Flow Rate / Surface Area, where Surface Area = Width x Length. In this case, SOR = 0.2314 m³/s / (4 m x 10 m) = 0.0057 m³/m².d.
Scour velocity: The scour velocity can be calculated using the formula: Scour Velocity = Flow Rate / Surface Area, where Surface Area = Width x Length x Depth. In this case, Scour Velocity = 0.2314 m³/s / (4 m x 10 m x 2 m) = 0.0029 m/s.
Coagulation And Flocculation: The water is mixed with chemicals such as alum to destabilize the particles, causing them to form clumps (flocs) that can be easily removed.
Sludge Removal: The clarifloculator should be designed to facilitate the easy removal of the settled solids.
Safety and access: The clarifloculator should be designed to ensure safety of the operators and maintenance personnel, and should be easily accessible for cleaning and maintenance.
Energy Efficiency: The clarifloculator should be energy efficient and should have low operational costs.
Environmental impact: The clarifloculator should have minimal environmental impact.
It's important to note that this is a general overview of the process and the actual design of the clarifloculator should be carried out by a professional engineer with the appropriate knowledge and experience taking into account other parameters as well.
Q.3 (a) Differentiate between Rapid mixer and flocculator.
Rapid mixers and flocculators are both commonly used in water treatment processes, but they serve different purposes and have different design characteristics.
A Rapid Mixer is a device used to mix chemicals and water quickly and efficiently. The main purpose of a rapid mixer is to quickly and efficiently mix chemicals such as coagulants and flocculants with water. The rapid mixer is used to achieve good mixing and dispersion of chemical in the water in a short time. It is used to achieve good flocculation and coagulation in the water. The rapid mixer typically operates at high speeds, and is designed to achieve a high degree of mixing in a short period of time.
A Flocculator is a device used to promote the formation of flocs in water. The main purpose of a flocculator is to promote the formation of flocs in water by providing a slow and gentle mixing action. The flocculator typically operates at lower speeds, and is designed to achieve a high degree of flocculation in a longer period of time. The flocculator is used to achieve a good settling of the flocs and solids in the water.
In summary, a rapid mixer is used to quickly and efficiently mix chemicals with water to achieve good flocculation and coagulation, while a flocculator is used to promote the formation of flocs in water by providing a slow and gentle mixing action to achieve a good settling of the flocs and solids in the water.
(b)Write down the design criteria for flocculator.
Design criteria for a flocculator include the following:
Flow Rate: The flow rate of the water entering the flocculator must be known in order to calculate the required flocculator volume and dimensions.
Mixing Intensity: The intensity of mixing in the flocculator is critical to achieve efficient flocculation. The mixer should be designed to provide a gentle, slow mixing action to promote floc formation.
Detention Time: The amount of time the water spends in the flocculator must be sufficient for flocs to form and settle. A common detention time for a flocculator is 30 minutes to 1 hour.
Sludge Volume Index (SVI): The SVI is a measure of the volume of sludge produced per unit volume of water treated. It is used to determine the size of the flocculator needed to accommodate the volume of sludge produced.
Scour Velocity: The minimum velocity of water needed to prevent flocs from settling and accumulating in the flocculator. It must be low enough to ensure flocs are allowed to form, but not so low that it causes flocs to accumulate on the bottom.
Inlet And Outlet Design: Proper inlet and outlet design is crucial for the efficient operation of the flocculator. The inlet must be designed to distribute the water evenly across the flocculator, while the outlet must be designed to remove the clarified water while minimizing the disturbance of the settled flocs.
Tank Dimensions: The dimensions of the flocculator must be sufficient to accommodate the flow rate and detention time, while also providing enough surface area for flocs to form.
Safety and access: The flocculator should be designed to ensure safety of the operators and maintenance personnel, and should be easily accessible for cleaning and maintenance.
(c) Design a tube settler module of rectangular cross section for a design flow of 1.5 MLD. Assume cross section of tube as 50 mm x 50mm.
Designing a tube settler module of rectangular cross section for a design flow of 1.5 MLD (Million Liters per Day) involves several steps and calculations based on the design criteria. Here is an overview of the process:
Determine the required detention time for the tube settler module: A common detention time for a tube settler module is 1 hour.
Calculate the volume of the tube settler module: The volume of the tube settler module can be calculated using the formula: Volume = Flow Rate x Detention Time. In this case: Volume = 1.5 MLD x (1/24) h = 62.5 m³
Determine the dimensions of the tube settler module: Based on the volume of the tube settler module, the dimensions of the module can be determined. The cross-section of the tube is given as 50 mm x 50 mm, and the height of the module can be calculated by dividing the volume by the cross-sectional area (height = volume / (50mm x 50mm) )
Determine the number of tubes required: The number of tubes required in the tube settler module can be calculated using the formula: Number of tubes = (flow rate * detention time) / (tube cross section
(a) Write down the specifications of sand to be used in a Rapid Sand Filters.
To be used in a Rapid Sand Filter (RSF), the sand should have the following specifications:
Particle size: The effective size of the sand should be between 0.5 mm and 0.7 mm, this will ensure that the sand can effectively filter out impurities from the water.
Shape: The sand should be rounded, as opposed to sharp and angular. Rounded sand will flow more easily through the system and not cause wear and tear on the internal parts of the filter.
Chemical composition: The sand should be made of a chemically inert material, such as silica, to avoid any reactions with the water that could cause damage to the filter or make the water unsafe to drink.
Cleanliness: The sand should be clean and free of any debris or contaminants that could clog the system or reduce the filter's efficiency.
Purity: The sand should be free of any impurities, such as clay, silt, and organic matter, as these can affect its filter properties.
uniformity coefficient : The uniformity coefficient (UC) of the sand should be between 1.3 and 1.7, this will ensure that the filter has a good distribution of sand particle size and therefore a good filtration efficiency.
Size Distribution : The sand should have a good size distribution, with a small range of particle sizes, this will ensure that the filter will perform optimally and effectively remove impurities from the water.
(b) Explain the terms and write down the design criteria for Rapid Sand Filter: (i)Effective Size (ii) Uniformity coefficient
Rapid Sand Filters (RSF) are a type of water treatment system that uses sand as the primary filtration media. The design criteria for an RSF includes the following key terms:
Effective Size (ES): The effective size of a sand filter is the size of a spherical particle that would be retained on the filter 50% of the time. It is used to describe the size of the sand particles that make up the filter media. The effective size is usually expressed in millimeters (mm) or micrometers (µm). The ES of sand used in RSF is usually between 0.5mm to 0.7mm.
Uniformity Coefficient (UC): The uniformity coefficient is a measure of the uniformity of the size distribution of the sand particles in the filter media. It is calculated as the ratio of the size of the largest particle in the media (D60) to the size of the smallest particle in the media (D10). The UC of the sand used in the RSF is between 1.3 to 1.7.
(C) The design criteria for an RSF are based on several factors, including the quality of the water being treated, the flow rate of the water, and the level of treatment required. Factors such as the effective size and uniformity coefficient of the sand, the depth of the filter, and the rate of flow through the filter all play a role in determining the overall performance of the RSF.
Design a Rapid Sand Filter to treat a flow of 20,000 m³/d. determine :
(i) Number and size of filter bed
(ii) Depth of sand bed
(iii)Depth of gravel bed.
Also calculate the rate of filtration when one bed is out of service due to backwashing.
Designing a Rapid Sand Filter (RSF) to treat a flow of 20,000 m³/d involves several calculations and considerations. However, without more information on the specific water quality, the required level of treatment, and the available space for the filter, it is difficult to provide an exact design. However, I can provide you with some general information and calculations that can be used as a starting point for your design.
(i) Number And Size Of Filter Beds: The number of filter beds required will depend on the flow rate and the desired rate of filtration. A typical design might include two or more filter beds, each capable of treating a portion of the flow. For example, if two filter beds were used, each would be designed to treat 10,000 m³/d. The size of the filter beds will depend on the space available and the desired rate of filtration.
(ii) Depth Of Sand Bed: The depth of the sand bed in a RSF is typically between 1.5 and 2 meters. This depth allows for a sufficient amount of sand to provide the necessary filtration and provide an adequate depth for backwashing.
(iii) Depth Of Gravel Bed: The depth of the gravel bed in a RSF is typically between 0.3 and 0.5 meters. This depth ensures that the gravel provides support for the sand bed and a surface for the water to flow through before entering the sand bed.
As for the filtration rate, when one bed is out of service due to backwashing, the remaining bed/beds will have to handle the entire flow, therefore the filtration rate will be reduced. To calculate the rate of filtration, you can use the formula:
Filtration Rate = Flow Rate / Number of filter beds
So in this case, if you have two filter beds and one is out of service, the filtration rate will be 20,000 m³/d / 1 = 20,000 m³/d
It's important to note that this is a rough estimate and the final design will depend on various factors and it should be done by a professional engineer.
OR
Q.4
(a) Write down the chemical reactions involved in water softening process.
Water softening is a process used to remove ions that cause hardness in water, primarily calcium and magnesium ions. There are several chemical reactions involved in water softening process, including:
Ion Exchange: This is the most common method of water softening. It involves passing hard water through a resin bed containing negatively charged ions, such as sodium or potassium ions. As the hard water passes through the resin bed, the calcium and magnesium ions in the water are exchanged for the sodium or potassium ions on the resin. The resulting water is considered "soft" because it no longer contains the ions that cause hardness. The chemical reaction can be represented as:
Ca(HCO3)2 + Na2CO3 -> CaCO3 + 2NaHCO3
Lime-soda ash treatment: This method of water softening involves adding lime (calcium hydroxide) and soda ash (sodium carbonate) to the water. The calcium and magnesium ions in the water react with the lime and soda ash to form insoluble precipitates of calcium carbonate and magnesium hydroxide, which are removed from the water. The chemical reaction can be represented as:
Ca(HCO3)2 + Ca(OH)2 -> 2CaCO3 + 2H2O
Mg(HCO3)2 + Ca(OH)2 -> Mg(OH)2 + CaCO3
Reverse osmosis: This method of water softening involves forcing water through a semi-permeable membrane that removes ions, including calcium and magnesium ions. The hard water is forced through the membrane under high pressure, and the ions are left behind.
Electrodialysis: This method of water softening uses an electric current to separate ions in the water. The ions are attracted to electrodes of opposite charge, and are then removed from the water. Calcium and magnesium ions are removed using this method.
It's important to note that the chemical reactions involved in water softening process depend on the method used, each process has its own specific reactions and it's important to consult with a professional when deciding which method is best for a particular situation.
(b) In a 50 MLD treatment plant, an alum [Al2(SO4)3.14H2O] dose of 125mg/L is being applied to the raw water which contains about 15 mg/L of SS. Estimate the maximum dry sludge solids which must be removed from the plant and volume of wet sludge which has concentrated to 2 % (by weight).
To estimate the maximum dry sludge solids that must be removed from the treatment plant, we need to consider the amount of alum dose applied, the concentration of suspended solids (SS) in the raw water, and the removal efficiency of the treatment process.
First, we need to calculate the mass of alum dose applied to the raw water:
Mass of alum dose = Alum dose (mg/L) x Flow rate (L/d)
= 125 mg/L x 50,000,000 L/d = 6,250,000,000 mg
Next, we can estimate the mass of SS removed from the water by the alum:
Mass of SS removed = Alum dose (mg/L) x SS concentration (mg/L) x Removal efficiency
= 125 mg/L x 15 mg/L x 0.8 (removal efficiency)
= 1,500,000 mg
The dry sludge solids are equal to the mass of alum dose plus the mass of SS removed:
Maximum dry sludge solids = Mass of alum dose + Mass of SS removed
= 6,250,000,000 mg + 1,500,000 mg = 6,251,500,000 mg
To calculate the volume of wet sludge which has concentrated to 2% (by weight), we need to divide the dry sludge solids by the concentration:
Wet sludge volume = 6,251,500,000 mg / (2/100) = 312,575,000,000 mg
This wet sludge volume is a large amount, it's important to note that the calculations above are based on assumptions and the actual volume of wet sludge will depend on specific parameters and conditions of the treatment process.
(c) Design an under drainage system for filter bed having an area of 28 m² (5.6m x 5.0m). Assume suitable design criteria.
The under drainage system for a filter bed with an area of 28 m² (5.6m x 5.0m) should include the following components:
Perforated Pipes: These pipes will be placed at the bottom of the filter bed to collect and transport water through the bed. The pipes should be made of PVC or HDPE and have a diameter of 100mm.
Drainage Layer: A layer of coarse gravel or crushed stone will be placed above the perforated pipes to ensure proper drainage and prevent clogging of the pipes. The thickness of this layer should be at least 150mm.
Filter Layer: A layer of fine sand or anthracite will be placed above the drainage layer to act as a filter for impurities. The thickness of this layer should be at least 300mm.
collection chamber: A chamber will be constructed at one end of the filter bed to collect and transport the filtered water to the next stage of treatment. The chamber should be made of PVC or HDPE and have a capacity of at least 0.5 m³.
Outlet Pipe: An outlet pipe will be connected to the collection chamber to transport the filtered water to the next stage of treatment. The pipe should be made of PVC or HDPE and have a diameter of 100mm.
Design criteria:
- The filter bed should have a minimum hydraulic loading rate of 10 m/h.
- The filter bed should have a minimum removal efficiency of 95% for suspended solids and 85% for BOD.
- The filter bed should have a minimum of 0.5 m of freeboard to prevent overflow.
- The filter bed should have a minimum of 1% slope for proper drainage.
Q.5
(a) Write down the design criteria for Chlorine contact tank.
- Adequate mixing and circulation of water to ensure proper contact time with chlorine.
- Durable and corrosion-resistant materials for the tank construction.
- Proper ventilation and gas diffusion systems to ensure safe and efficient release of chlorine gas.
- Adequate space for chemical feed equipment and storage.
- Proper measurement and control systems for chlorine levels and flow rate.
- Easy access for maintenance and cleaning.
- Compliance with all local and national regulations for water treatment and chemical storage.
- Design for proper flow rate and capacity to meet the needs of the water treatment system.
- Adequate safety features such as emergency shut-off valves and alarms.
- Adequate space for emergency equipment and personnel.
(b)Write a short note on Parshall flume.
(c) Enlist the various types of sludge dewatering devices and explain any one with sketch.
(A) A square rapid mixing tank with a depth of water equal to 1.25 times the width is to be designed for a flow of 7570 m³/d. The velocity gradient is to be 790/s, detention time is 40s and value of µ = 0.00131 N-s/m². Determinethe basin dimensions and the power required.
(B) Define and explain the terms thickening and conditioning of sludge.
(C) A coarse screen is to be designed for a flow of 20 MLD. Find out the number of bars required. Also check for the head loss through the screen Assume :
- Mean velocity through screen = 0.8 m/s
- Spacing between the bars =30 mm
- Angle of inclination = 45⁰
- Shape of bar = rectangular with dimensions 12mm x 50mm
- Water depth in approach channel = 1 m²
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