Types of Settling Tanks

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?

Horizontal flow (A) Signup and view all the answers

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

Slow moving mechanical sludge scraper (D) Signup and view all the answers

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

To facilitate sludge scraping (B) Signup and view all the answers

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

To decrease inlet velocities (D) Signup and view all the answers

Why are peripheral weirs not acceptable in settling basins?

They increase short-circuiting (B) 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?

It decreases (C) Signup and view all the answers

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

$vt= \frac{(\rho_p - \rho)gd^2}{18\mu}$ (D) 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?

Direct relationship (C) Signup and view all the answers

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

$\frac{Q}{As}$ (C) Signup and view all the answers

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

2 to 2.5 hours (C) Signup and view all the answers

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

~3:1 (D) Signup and view all the answers

What is the typical depth range for circular settling basins?

2.5m to 5.0m (B) Signup and view all the answers

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

24000 to 30000 L/d/m2 tank area (A) 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?

100 m2 (C) 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?

L = 3B (D) Signup and view all the answers

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

Small size (D) Signup and view all the answers

'Lyophobic' colloids can be best described as:

Solvent hating (C) Signup and view all the answers

'Lyophilic' colloids are:

Solvent loving (B) 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?

Brownian motion (C) Signup and view all the answers

'Flocculation' can be best described as:

Agglomeration of destabilized particles into compact flocs (C) Signup and view all the answers

'Coagulation' involves:

'Particle transport' and 'Particle destabilization' (B) Signup and view all the answers

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

Balance the electrical charge on the particle (A) Signup and view all the answers

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

'Medium' and 'Colloid particles' (B) Signup and view all the answers

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

To disperse coagulant rapidly and uniformly through water (C) Signup and view all the answers

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

Perikinetic flocculation (A) Signup and view all the answers

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

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

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

Adsorption and charge neutralization (D) Signup and view all the answers

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

Amorphous metal hydroxide precipitation (A) Signup and view all the answers

What does the Jar Test primarily aim to determine?

The optimum operating conditions for water treatment (A) Signup and view all the answers

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

Due to Brownian motion (A) Signup and view all the answers

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

They act as coagulants (A) Signup and view all the answers

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

Mechanical agitation (A) Signup and view all the answers

What is the main method of cleaning rapid sand filters?

Agitating and backwashing (A) Signup and view all the answers

What is the primary principle behind slow sand filtration?

Combination of processes including straining, adsorption, and bacteriological action (B) 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?

Organic matter (A) Signup and view all the answers

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

Provides living quarters for micro-organisms (A) Signup and view all the answers

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

RSF has a smaller rate than SSF (D) Signup and view all the answers

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

Filter sand size (A) Signup and view all the answers

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

Disinfection (A) Signup and view all the answers

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

Initial loss is higher in SSF than RSF (D) Signup and view all the answers

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

Base material is deeper in slow sand filters compared to rapid sand filters (D) Signup and view all the answers

What is the Carman-Kozeny equation used to calculate?

Head loss (A) Signup and view all the answers

When should a filter be backwashed?

When the floc starts to break through the filter and the turbidity in the effluent increases (A) Signup and view all the answers

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

Media will be washed from the filter into the troughs and out of the filter (A) Signup and view all the answers

What is Air Binding in rapid gravity filters?

When air gets trapped in the filter causing it to stop functioning (D) Signup and view all the answers

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

Washing off particles with a caustic soda solution (D) Signup and view all the answers

What does a long filter run without backwashing lead to?

Packing down of the filter media making it difficult to expand during backwash (A) Signup and view all the answers

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

Flow regime character (C) Signup and view all the answers

Why is backwashing needed?

To remove suspended floc and decrease turbidity in effluent (A) Signup and view all the answers

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

Stops proper functioning by trapping air (D) Signup and view all the answers

What is the purpose of the jar testing apparatus?

To determine optimal operating conditions for water treatment (D) 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?

To measure the final turbidity (B) Signup and view all the answers

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

To remove suspended particles and bacteria (A) Signup and view all the answers

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

Sedimentation (D) Signup and view all the answers

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

The size that allows 10% of sand to pass through a sieve (D) Signup and view all the answers

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

To support the layers of sand for effective filtration (B) Signup and view all the answers

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

The ratio of sieve size for 60% particles to effective size (D) Signup and view all the answers

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

Anthracite coal-stone (D) Signup and view all the answers

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