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Questions and Answers
What is the primary purpose of a sedimentation tank in water treatment?
What is the term for the process of suspended particles settling to the bottom of a liquid and forming a sediment?
What type of forces resist the movement of particles in a fluid?
What is the purpose of coagulation in water treatment?
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What is the term for the combining of suspended particles to form larger particles, or flocs?
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What is the purpose of rapid sand filtration in water treatment?
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What is the term for the phase of the water that leaves the top of the sedimentation tank?
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What is the force that causes particles to move in a uniform manner in a direction?
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What is the term for the process of adding chlorine to the water to kill bacteria and other microorganisms?
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What is the zone in the sedimentation tank where the suspended particles settle to the bottom?
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Study Notes
Coagulation and Sedimentation
- Coagulation consists of three parts: addition of coagulant, flocculation, and clarification/sedimentation.
- Sedimentation aided with coagulation is used to remove suspended particles and colloidal particles present in water.
- Commonly used coagulants include Aluminium sulphate (alum), Ferrous Sulphate, Ferric sulphate, and Sodium sulphate.
Electrical Double Layer (EDL)
- When a charged particle is placed in a suspension with ions, it attracts counter ions (opposite charged ions) by electrostatic attraction.
- A gradient of counter ions is established, driving them away from the surface.
- The formation of EDL occurs via attraction of oppositely charged counterions by the primary surface charge, followed by diffusion of the counterions away from the surface.
- EDL leads to a net electrostatic repulsion/attraction between colloids.
Methods to Destabilize Colloids (Coagulation Processes)
- Methods to destabilize colloids include coagulation processes.
Settling Velocities
- Settling velocity (𝑣) is 100 m/day, with a settling velocity of 7.769 m/day in 38.85% of cases.
Types of Settling
- Type I: Discrete particle settling
- Type II: Flocculent particle settlement, where particles settle with interaction with neighboring particles
- Type III: Hindered or Zone settling
- Type IV: Compression settling
Coagulation-Flocculation
- Coagulation-flocculation is a pre-treatment process.
- Post-treatment processes include rapid sand filtration and chlorination.
Plain Sedimentation Tank
- Plain sedimentation tank is a solid-liquid separation process where a suspension is separated into two phases: clarified supernatant (overflow) and concentrated sludge (underflow).
- The process involves settling, where particles experience a force due to gravity or centrifugal motion, and tend to move in a uniform manner in the direction of that force.
- There are three zones in a plain sedimentation tank: sludge zone, settling zone, and water level.
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Description
Test your knowledge of coagulation and sedimentation processes in water treatment, including settling velocity, coagulants, and removal of suspended particles. This quiz covers key concepts in civil engineering and environmental engineering.
