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Dissolved Air Flotation (DAF) is primarily employed for the removal of suspended matter, rather than dissolved substances, from water.
Answer: True
Explanation: The primary function of Dissolved Air Flotation (DAF) is the separation and removal of suspended solids and oils, not dissolved chemical species.
In the DAF process, air is dissolved into water after it has been released into the flotation tank.
Answer: False
Explanation: Air is dissolved into water under pressure within a dedicated vessel (like an air drum) *before* it is released into the flotation tank, where the pressure drop facilitates bubble formation.
The formation of tiny bubbles in the DAF process occurs when air-saturated water is subjected to increased pressure.
Answer: False
Explanation: Bubble formation occurs when air-saturated water, previously under pressure, is released into the lower pressure environment of the flotation tank. The pressure reduction, not an increase, triggers the release of dissolved air as bubbles.
The principle of flotation in DAF relies on air bubbles reducing the density of suspended particles below that of water.
Answer: True
Explanation: By adhering to suspended particles, the air bubbles increase the overall buoyancy of the particle-bubble complex. This effectively reduces the apparent density, causing the particles to float to the surface.
The material removed from the DAF tank is the clarified effluent, while clean water exits as froth.
Answer: False
Explanation: The froth layer, consisting of the removed suspended matter and attached bubbles, is skimmed from the surface. The clean water that exits the tank after this process is known as the clarified effluent.
In drinking water treatment using DAF, clarified water is withdrawn from the top layer of the tank after froth removal.
Answer: False
Explanation: In DAF systems for drinking water treatment, the clarified water, free of suspended matter, is withdrawn from the bottom layer of the DAF tank, after the froth has been removed from the surface.
Dissolved Air Flotation is classified as a chemical precipitation process.
Answer: False
Explanation: Dissolved Air Flotation is classified as a physical separation process, relying on the principles of buoyancy and adhesion, rather than chemical precipitation.
The fundamental principle of DAF involves using large, slow-moving bubbles to lift particles.
Answer: False
Explanation: The fundamental principle of DAF relies on the generation and utilization of numerous *tiny*, rapidly forming bubbles, which efficiently attach to suspended particles to facilitate flotation.
Pressure in the DAF process is primarily used to facilitate the skimming of froth from the surface.
Answer: False
Explanation: Pressure in the DAF process is critical for dissolving air into the water. This air-saturated water, upon release to atmospheric pressure, forms the bubbles necessary for flotation, not for skimming.
The transition from a pressurized state to atmospheric pressure is irrelevant to bubble formation in DAF.
Answer: False
Explanation: The transition from a pressurized state to atmospheric pressure is the fundamental mechanism by which dissolved air is released from supersaturated water, leading to the formation of the fine bubbles essential for the DAF process.
The term 'clarified effluent' refers to the concentrated froth layer removed from the DAF tank surface.
Answer: False
Explanation: The clarified effluent is the treated water that remains in the tank after the froth layer (containing the removed suspended matter) has been skimmed off. It represents the purified output of the DAF process.
What is the principal objective of the Dissolved Air Flotation (DAF) process in water treatment?
Answer: To separate and remove suspended particulate matter, including oils and solids, from water.
Explanation: The core purpose of DAF is the physical separation and removal of suspended materials, such as oils and solids, from water by utilizing buoyancy.
How are the tiny air bubbles, essential for the DAF process, generated?
Answer: By releasing pressurized, air-saturated water, causing dissolved air to form bubbles due to a pressure drop.
Explanation: The generation of fine bubbles is achieved by releasing air-saturated water from a pressurized state into atmospheric pressure. This pressure differential causes the dissolved air to rapidly form bubbles.
In the DAF process, what happens to the air-saturated water when it enters the flotation tank?
Answer: The pressure drop causes the dissolved air to form tiny bubbles.
Explanation: Upon entering the flotation tank at atmospheric pressure, the previously pressurized air-saturated water undergoes a pressure reduction, triggering the release of dissolved air as numerous fine bubbles.
What is the significance of the pressure reduction valve just before the float tank?
Answer: It causes the pressure drop that leads to the formation of fine air bubbles.
Explanation: The pressure reduction valve controls the release of air-saturated water from the pressurized system into the flotation tank, inducing a pressure drop that is critical for the formation of fine bubbles.
Which statement best describes the DAF process's classification?
Answer: A physical separation process.
Explanation: DAF is categorized as a physical separation process, utilizing principles of buoyancy and adhesion to remove suspended matter from water.
What is the state of the water exiting the DAF tank after the froth removal?
Answer: Clarified effluent, free of most suspended matter.
Explanation: Following the removal of the froth layer, the water remaining in the DAF tank is significantly clarified, meaning it is largely free of suspended matter and suitable for further treatment or discharge.
The DAF process is fundamentally based on the principle of:
Answer: Using fine air bubbles to increase particle buoyancy.
Explanation: The core principle of DAF involves attaching fine air bubbles to suspended particles, thereby increasing their buoyancy and causing them to float to the surface for removal.
What does the term 'suspended matter' refer to in the context of DAF treatment?
Answer: Solid particles or oil droplets dispersed in the water but not dissolved.
Explanation: Suspended matter encompasses solid particles and oil droplets that are dispersed within the water but remain undissolved, representing the primary target contaminants for DAF removal.
The air drum in a DAF system is where compressed air is released directly into the main flotation tank.
Answer: False
Explanation: The air drum is a pressure vessel where a portion of the treated water is saturated with compressed air. This air-saturated water is then released into the main flotation tank, causing bubbles to form due to the pressure drop, rather than releasing compressed air directly.
Parallel plate packing, or lamellas, are used in DAF units to decrease the surface area available for separation.
Answer: False
Explanation: Parallel plate packing, also known as lamellas, is incorporated into DAF units specifically to increase the effective surface area available for separation, thereby enhancing the efficiency of the process.
Circular DAF systems typically require a longer residence time than rectangular systems.
Answer: False
Explanation: Circular DAF systems are generally more efficient and require a shorter residence time (approximately 3 minutes) compared to rectangular systems, which typically need a longer residence time (20-30 minutes).
A spiral scoop is a feature commonly found in rectangular DAF systems to aid froth removal.
Answer: False
Explanation: A spiral scoop is a feature specifically associated with circular DAF systems, designed to facilitate the efficient removal of the froth layer.
The image captioned 'A typical dissolved air flotation unit (DAF)' shows a specialized DAF model designed for deep-sea applications.
Answer: False
Explanation: The image depicts a standard, typical Dissolved Air Flotation (DAF) unit, representative of common industrial and municipal applications, not a specialized model for deep-sea use.
A DAF unit with a capacity of 20 m³/h might be shown alongside associated equipment like a flocculant preparation station.
Answer: True
Explanation: It is common for DAF units, such as one with a 20 m³/h capacity, to be depicted alongside auxiliary equipment like flocculant preparation systems, which are integral to the overall treatment process.
Modern DAF units utilizing parallel plate technology are typically very large and require extensive space.
Answer: False
Explanation: Modern DAF units incorporating parallel plate technology are designed to be compact, offering a smaller footprint compared to older or non-lamella designs, thus requiring less extensive space.
A skimming device in a DAF system is responsible for pumping the clarified water out of the tank.
Answer: False
Explanation: A skimming device is specifically designed to remove the froth layer, which contains the floated suspended matter, from the surface of the DAF tank. Clarified water is typically withdrawn from the bottom.
Parallel plate settlers (lamellas) increase the efficiency of DAF units by reducing the surface area for particle settling.
Answer: False
Explanation: Parallel plate settlers, or lamellas, enhance DAF efficiency by significantly increasing the effective surface area available for separation, thereby promoting more effective particle flotation.
How is the floating material (froth) removed from the DAF tank?
Answer: It is skimmed off the surface by a mechanical device.
Explanation: A mechanical skimming device is employed to continuously remove the layer of froth that accumulates on the water surface, thereby extracting the floated suspended matter from the DAF unit.
What advantage do parallel plate settlers (lamellas) offer in DAF units?
Answer: They provide a larger surface area, enhancing separation efficiency.
Explanation: By installing parallel plates (lamellas), the effective surface area within the DAF unit is substantially increased, leading to improved efficiency in separating suspended particles from the water.
Compared to rectangular DAF systems, circular DAF systems are generally characterized by:
Answer: Shorter residence times and higher efficiency.
Explanation: Circular DAF systems typically exhibit greater operational efficiency and require less time for treatment (shorter residence time) compared to their rectangular counterparts.
What is the function of the 'air drum' in the DAF process?
Answer: To saturate a portion of the treated water with compressed air under pressure.
Explanation: The air drum serves as a pressure vessel where a portion of the treated water is saturated with compressed air, preparing it to generate the fine bubbles necessary for flotation when released.
What does the image of a modern DAF unit with parallel plate technology suggest about its design?
Answer: It is designed to be compact.
Explanation: The integration of parallel plate technology in modern DAF units contributes to a more compact design, optimizing space utilization while maintaining high separation efficiency.
What is the primary role of the 'skimming device' in a DAF system?
Answer: To remove the froth layer accumulated on the surface.
Explanation: The skimming device is engineered to mechanically collect and remove the froth layer, which contains the floated suspended solids and oils, from the surface of the DAF tank.
Which component is responsible for saturating water with air under pressure in the DAF system?
Answer: The air drum.
Explanation: The air drum is specifically designed as a pressure vessel to saturate a portion of the treated water with compressed air, a critical step in preparing it for bubble generation.
How do circular DAF systems typically differ from rectangular ones in terms of operational characteristics?
Answer: Circular systems are generally more efficient and require less time (residence time).
Explanation: Circular DAF units are typically characterized by higher efficiency and shorter required residence times compared to rectangular designs, often leading to a more compact operational footprint.
What is the purpose of the 'flotation tank basin' in a DAF unit?
Answer: To contain the water where the separation process (flotation) occurs.
Explanation: The flotation tank basin serves as the primary vessel where the DAF separation process takes place, allowing air bubbles to lift suspended particles to the surface for removal.
Ferric chloride, a chemical additive sometimes employed in DAF pre-treatment, functions primarily as a flocculant.
Answer: False
Explanation: Ferric chloride is classified as a coagulant, used to destabilize and aggregate colloidal particles. Flocculants, such as polymers, are then used to bind these destabilized particles into larger flocs.
Nucleation sites are essential for the DAF process as they are the primary locations where air is dissolved into the water.
Answer: False
Explanation: Nucleation sites are crucial for bubble formation, but they are surfaces where bubbles *initiate* and grow, not where air is dissolved into the water. Air dissolution occurs under pressure in vessels like the air drum.
Nucleation sites are surfaces where the *dissolution* of air into water is initiated.
Answer: False
Explanation: Nucleation sites are surfaces where the *formation* of air bubbles is initiated, typically on suspended particles. Air dissolution occurs under pressure in specialized vessels.
The primary objective of using coagulants like ferric chloride is to create large, easily removable flocs directly.
Answer: False
Explanation: Coagulants, such as ferric chloride, primarily destabilize colloidal particles by neutralizing their surface charges. Flocculants are then used to bind these destabilized particles into larger, removable flocs.
A flocculant's role is to break down large particle clusters into smaller ones for easier bubble attachment.
Answer: False
Explanation: Flocculants function by binding smaller, coagulated particles together to form larger, more buoyant clusters (flocs), which are then more effectively captured by air bubbles for flotation.
What is the purpose of adding a coagulant, like ferric chloride, before water enters a DAF tank?
Answer: To help aggregate very small colloidal particles, making them easier to flocculate.
Explanation: Coagulants destabilize the surface charges of very small colloidal particles, initiating the aggregation process that is essential for subsequent flocculation and effective flotation.
What is the role of nucleation sites in the DAF process?
Answer: They are surfaces that initiate the formation of air bubbles, often on suspended particles.
Explanation: Nucleation sites provide the necessary surfaces for the rapid formation and growth of air bubbles as dissolved air is released from supersaturated water, typically occurring on the surfaces of suspended particles.
How does the addition of a flocculant modify the suspended matter in the DAF process?
Answer: It helps bind coagulated particles into larger, more buoyant clusters.
Explanation: Flocculants act as bridging agents, binding destabilized particles together to form larger, more cohesive flocs that are readily captured by air bubbles and floated.
What is the main difference in function between a coagulant and a flocculant in DAF pre-treatment?
Answer: Coagulants neutralize charge, while flocculants bind particles into larger clusters.
Explanation: Coagulants destabilize particles by neutralizing their surface charges, while flocculants then bind these destabilized particles into larger, more manageable clusters (flocs).
Dissolved Air Flotation is commonly employed in the paper milling industry for wastewater treatment.
Answer: True
Explanation: The paper milling industry is one of the key sectors that utilizes Dissolved Air Flotation (DAF) for effective wastewater treatment.
DAF systems are particularly beneficial for drinking water sources with high turbidity but low natural color.
Answer: False
Explanation: DAF systems are particularly advantageous for drinking water sources characterized by low turbidity but high natural color, or those prone to unicellular algal blooms, rather than high turbidity.
Which of the following industries commonly employs Dissolved Air Flotation for wastewater treatment?
Answer: Oil refineries and paper mills.
Explanation: DAF technology is widely adopted in sectors such as oil refining and paper manufacturing due to its effectiveness in treating the specific types of wastewater generated in these industries.
What specific challenge in drinking water treatment is DAF particularly suited for?
Answer: Addressing unicellular algal blooms and high natural color.
Explanation: DAF is highly effective in treating drinking water sources prone to unicellular algal blooms and those exhibiting high natural color, contributing significantly to water quality improvement.
How does the DAF process contribute to meeting environmental regulations?
Answer: By removing oils and solids before discharge, preventing contamination.
Explanation: DAF facilitates compliance with environmental regulations by effectively removing pollutants such as oils and suspended solids from industrial wastewater prior to discharge, thereby preventing contamination of receiving water bodies.
What is a potential benefit of using DAF in industrial settings beyond simple wastewater treatment?
Answer: Recovering valuable materials from the waste stream.
Explanation: In certain industrial applications, DAF can be utilized not only for wastewater treatment but also for the recovery of valuable materials present in the waste stream, such as oils or specific solids.