Types of Settling Tanks
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Questions and Answers

What is the main difference between intermittent sedimentation tanks and continuous flow type tanks?

  • The water in intermittent tanks is brought to complete rest while in continuous flow tanks, the flow velocity is only reduced. (correct)
  • Intermittent tanks have radial or spiral flow, while continuous flow tanks have horizontal flow.
  • Continuous flow tanks store water for a certain period while intermittent tanks keep water in complete rest.
  • Intermittent tanks have circular plans while continuous flow tanks have long rectangular plans.

    • Why are long rectangular settling basins generally preferred over circular tanks?

  • Circular tanks are easier to control flow for large volumes.
  • Long rectangular tanks allow for easier sludge scraping.
  • Long rectangular tanks with horizontal flow are hydraulically more stable. (correct)
  • Circular tanks are hydraulically more stable.

    • What is the function of the sludge zone in a long rectangular settling tank?

  • To uniformly distribute flow over the cross section.
  • To collect sludge below the settling zone. (correct)
  • To collect and discharge clarified effluent.
  • To facilitate sludge scraping.

    • What type of flow occurs in the inlet zone of a long rectangular settling tank?

    <p>Horizontal flow</p> Signup and view all the answers

    What mechanism is used to pull settled material into a sludge hopper in long rectangular settling basins?

    <p>Slow moving mechanical sludge scraper</p> Signup and view all the answers

    Why is the bottom of a long rectangular settling basin slightly sloped?

    <p>To facilitate sludge scraping</p> Signup and view all the answers

    What is the purpose of constructing a baffle close to the inlet in a settling basin?

    <p>To decrease inlet velocities</p> Signup and view all the answers

    Why are peripheral weirs not acceptable in settling basins?

    <p>They increase short-circuiting</p> Signup and view all the answers

    In circular settling basins, how does the horizontal velocity of water change as you move from the center to the perimeter?

    <p>It decreases</p> Signup and view all the answers

    What is the equation for the vertical settling velocity of a particle in a settling basin?

    <p>$vt= \frac{(\rho_p - \rho)gd^2}{18\mu}$</p> Signup and view all the answers

    What is the relationship between the retention time in the settling zone and the depth of a settling basin?

    <p>Direct relationship</p> Signup and view all the answers

    What is the overflow rate q0 used as a design factor for in settling basins?

    <p>$\frac{Q}{As}$</p> Signup and view all the answers

    What is the recommended detention period for coagulated sedimentation in a settling basin?

    <p>2 to 2.5 hours</p> Signup and view all the answers

    What is the general ratio of tank dimensions (L:B) recommended for a rectangular settling basin?

    <p>~3:1</p> Signup and view all the answers

    What is the typical depth range for circular settling basins?

    <p>2.5m to 5.0m</p> Signup and view all the answers

    What is the recommended surface overflow rate for thoroughly flocculated water in a settling basin?

    <p>24000 to 30000 L/d/m2 tank area</p> Signup and view all the answers

    What is the surface area of the rectangular sedimentation tank designed to treat 2.4 million litres of raw water per day?

    <p>100 m2</p> Signup and view all the answers

    What is the relationship between the length (L) and breadth (B) of the rectangular sedimentation tank designed in the given text?

    <p>L = 3B</p> Signup and view all the answers

    What is the main reason that makes colloidal particles difficult to separate from water?

    <p>Small size</p> Signup and view all the answers

    'Lyophobic' colloids can be best described as:

    <p>Solvent hating</p> Signup and view all the answers

    'Lyophilic' colloids are:

    <p>Solvent loving</p> Signup and view all the answers

    What is the phenomenon called where colloidal particles have constant motion due to bombardment by molecules of the dispersion medium?

    <p>Brownian motion</p> Signup and view all the answers

    'Flocculation' can be best described as:

    <p>Agglomeration of destabilized particles into compact flocs</p> Signup and view all the answers

    'Coagulation' involves:

    <p>'Particle transport' and 'Particle destabilization'</p> Signup and view all the answers

    'Electrical Double Layer' in a colloidal dispersion contains counter ions to:

    <p>Balance the electrical charge on the particle</p> Signup and view all the answers

    'Destabilization of Colloidal Dispersion' can be achieved by changing the characteristics of:

    <p>'Medium' and 'Colloid particles'</p> Signup and view all the answers

    What is the purpose of Rapid or Flash mixing in water treatment?

    <p>To disperse coagulant rapidly and uniformly through water</p> Signup and view all the answers

    Which type of flocculation refers to contacts between colloidal particles due to Brownian motion?

    <p>Perikinetic flocculation</p> Signup and view all the answers

    How is the velocity gradient (G) estimated in systems with spatial changes in fluid velocity?

    <p>$G=(P/μV)1/2$</p> Signup and view all the answers

    Which mechanism is responsible for destabilization through charge neutralization in water treatment?

    <p>Adsorption and charge neutralization</p> Signup and view all the answers

    What is necessary for sweep-floc coagulation to occur during water treatment?

    <p>Amorphous metal hydroxide precipitation</p> Signup and view all the answers

    What does the Jar Test primarily aim to determine?

    <p>The optimum operating conditions for water treatment</p> Signup and view all the answers

    In Perikinetic flocculation, how do colloidal particles come into contact for flocculation?

    <p>Due to Brownian motion</p> Signup and view all the answers

    What role do salts of Al(III) and Fe(III) play in water and wastewater treatment?

    <p>They act as coagulants</p> Signup and view all the answers

    'Orthokinetic flocculation' refers to the contact between colloidal particles due to:

    <p>Mechanical agitation</p> Signup and view all the answers

    What is the main method of cleaning rapid sand filters?

    <p>Agitating and backwashing</p> Signup and view all the answers

    What is the primary principle behind slow sand filtration?

    <p>Combination of processes including straining, adsorption, and bacteriological action</p> Signup and view all the answers

    Which material forms a thin layer on the sand surface in slow sand filters during the initial purification process?

    <p>Organic matter</p> Signup and view all the answers

    What purpose does the 'Schmutzdecke' serve in slow sand filtration?

    <p>Provides living quarters for micro-organisms</p> Signup and view all the answers

    How does the rate of filtration compare between slow sand filters and rapid sand filters?

    <p>RSF has a smaller rate than SSF</p> Signup and view all the answers

    Which factor influences the flexibility of rapid sand filters in meeting demand variations?

    <p>Filter sand size</p> Signup and view all the answers

    What is the main post-treatment requirement for water from rapid sand filters to ensure safety?

    <p>Disinfection</p> Signup and view all the answers

    How is clean water headloss typically managed in slow sand filters compared to rapid sand filters?

    <p>Initial loss is higher in SSF than RSF</p> Signup and view all the answers

    What is the variation in depth between the base material in slow sand filters and rapid sand filters?

    <p>Base material is deeper in slow sand filters compared to rapid sand filters</p> Signup and view all the answers

    What is the Carman-Kozeny equation used to calculate?

    <p>Head loss</p> Signup and view all the answers

    When should a filter be backwashed?

    <p>When the floc starts to break through the filter and the turbidity in the effluent increases</p> Signup and view all the answers

    What can happen if a filter backwash rate is too high?

    <p>Media will be washed from the filter into the troughs and out of the filter</p> Signup and view all the answers

    What is Air Binding in rapid gravity filters?

    <p>When air gets trapped in the filter causing it to stop functioning</p> Signup and view all the answers

    What is a remedial measure to prevent cracking of filters and formation of mud balls?

    <p>Washing off particles with a caustic soda solution</p> Signup and view all the answers

    What does a long filter run without backwashing lead to?

    <p>Packing down of the filter media making it difficult to expand during backwash</p> Signup and view all the answers

    What does the Reynolds number (Ng) represent in the Carman-Kozeny equation?

    <p>Flow regime character</p> Signup and view all the answers

    Why is backwashing needed?

    <p>To remove suspended floc and decrease turbidity in effluent</p> Signup and view all the answers

    What effect does air binding have on a rapid gravity filter?

    <p>Stops proper functioning by trapping air</p> Signup and view all the answers

    What is the purpose of the jar testing apparatus?

    <p>To determine optimal operating conditions for water treatment</p> Signup and view all the answers

    In the jar test procedure, what is the purpose of turning off the mixers and allowing containers to settle?

    <p>To measure the final turbidity</p> Signup and view all the answers

    What is the main function of slow sand filters in water treatment?

    <p>To remove suspended particles and bacteria</p> Signup and view all the answers

    Which basic filtration mechanism occurs due to the force of gravity and settling velocity of particles?

    <p>Sedimentation</p> Signup and view all the answers

    What does the term 'effective size' refer to in the context of filter materials?

    <p>The size that allows 10% of sand to pass through a sieve</p> Signup and view all the answers

    What is the role of gravel in a filtration system using sand as the filter media?

    <p>To support the layers of sand for effective filtration</p> Signup and view all the answers

    When measuring and expressing the uniformity of particle sizes in sand, what does the uniformity coefficient represent?

    <p>The ratio of sieve size for 60% particles to effective size</p> Signup and view all the answers

    What type of coal-stone is used to make anthrafilt as an alternative to sand filter media?

    <p>Anthracite coal-stone</p> Signup and view all the answers

    What is the purpose of adjusting pH levels and coagulant dosages in jar testing?

    <p>To determine optimal operating conditions for water treatment</p> Signup and view all the answers

    Why is it important to allow containers to settle before measuring final turbidity in jar testing?

    <p>To separate floc formations from water samples</p> Signup and view all the answers

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