Water Treatment: Coagulation and Flocculation

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the main purpose of a jar test?

To determine the velocity gradient of a fluid

To determine the proper coagulant and coagulant aid, and chemical dosage required (correct)

To measure the size of flocs in a fluid

To measure the turbidity removal of a fluid

What does the velocity gradient (G) measure?

The relative velocity of two fluid particles per unit distance (correct)

The dynamic viscosity of a fluid

The size of flocs in a fluid

The power input of a mixing system

What is the formula to calculate the power input (P) for mixing by impellers?

P = KT n^2 Di^3 μ (correct)

P = D^2 n ρ / μ

P = C1 Ga log (h+C2)/C2

P = G^2 μ V

What is the condition for laminar flow in a mixing system?

NRe < 20 Signup and view all the answers

What is the formula to calculate the power input (P) for pneumatic mixing?

P = C1 Ga log (h+C2)/C2 Signup and view all the answers

What is the purpose of a velocity gradient in a baffle basin?

To measure the degree of mixing Signup and view all the answers

What happens to colloids when they undergo destabilization?

They aggregate in size and start to settle Signup and view all the answers

What is the purpose of adding Ca(OH)2 or NaHCO3 during the coagulation process?

To overcome the problem of reduced pH Signup and view all the answers

What is the reaction between aluminum sulfate and bicarbonate ions?

Al2(SO4)3.14 H2O + 6HCO3- → 2Al(OH)3 + 6CO2 + 14H2O + 3SO4-2 Signup and view all the answers

What is the reaction between ferrous sulfate and calcium hydroxide?

2 FeSO4.7H2O + 2 Ca(OH)2 + 0.5 O2 → 2Fe(OH)3 + 2 CaSO4 + 13 H2O Signup and view all the answers

What is the range of pH required for ferric sulfate coagulation?

pH 4 to 12 Signup and view all the answers

What type of mixing is required for coagulation?

Rapid mixing Signup and view all the answers

What is the purpose of coagulation?

To aggregate colloids and form larger flocs Signup and view all the answers

What is the type of agitator commonly used in coagulation and flocculation?

Mechanical agitators Signup and view all the answers

What is the primary goal of the coagulation/flocculation process in water treatment?

To reduce turbidity in water Signup and view all the answers

What is turbidity a measure of in a water sample?

The amount of suspended solids Signup and view all the answers

What is the role of a coagulant in the coagulation process?

To cause small particles to come together to form large particles Signup and view all the answers

What is the purpose of adding alum (Aluminum sulfate) to water during the coagulation process?

To cause small particles to come together to form large particles Signup and view all the answers

What are non-settleable solids?

Solids that can not settle down by virtue of gravity Signup and view all the answers

What is the process by which colloids can be destabilized?

Charge neutralization Signup and view all the answers

What is the role of positively charged ions in the coagulation process?

They destabilize the colloids Signup and view all the answers

What is the result of removing turbidity from water?

All of the above Signup and view all the answers

Study Notes

Coagulation and Flocculation

The main goal of coagulation/flocculation process is to reduce turbidity in water, which is a measure of the amount of suspended solids in water sample that cause cloudiness.
Turbidity affects taste, odor, and disinfection rates of water, as lower turbidity allows for higher rates of disinfection.

Coagulants

A coagulant is a chemical that is added to water to cause small particles to come together and form large particles that can settle due to gravity.
Typical coagulants include Alum (Aluminum sulfate) and Ferric sulfate (Fe2(SO4)3).

Coagulation

Coagulation is a chemical process in which a coagulant is added to water and suspended by rapid mixing to aggregate dispersed non-settleable solids by destabilization.
The process involves destabilization of colloids, which are particles that stay in suspension due to repulsive forces.
Positively charged ions (e.g., Na+, Mg2+, Al3+, Fe3+) can neutralize the colloidal negative charges and thus destabilize them, allowing them to aggregate and settle.

Theory of Coagulation

Destabilization of colloids can be achieved through charge neutralization or bridging with organic polymers.
Colloids can be destabilized by adding positively charged ions or polymers that react with the colloidal surface, allowing them to aggregate and settle.

Coagulants Properties

Aluminum sulfate (Alum):
- Consumes 6 moles of bicarbonate (HCO3-) per 1 mole of alum.
- Can lower pH if alkalinity is not enough.
- Can be overcome by adding Ca(OH)2 or NaHCO3 (Soda Ash).
Ferrous sulfate:
- Forms a dense, quick-settling floc (Fe(OH)3).
- Requires pH to be raised to 9.5.
- Can be oxidized to form Ferric sulfate (Fe2(SO4)3) at pH 4.
Ferric sulfate:
- Forms a floc that can settle quickly.
- Requires pH to be in the range from 4 to 12.
Ferric chloride:
- Forms a floc that can settle quickly.
- Requires pH to be in the range from 4 to 12.

Coagulation and Flocculation Process

Coagulation involves rapid mixing to form microflocs, while flocculation involves gentle mixing to form larger flocs.
Agitation devices include mechanical agitators, pneumatic agitators, and baffle basins.

Jar Test

A laboratory technique used to determine the proper coagulant and coagulant aid, as well as the chemical dosage required.
Variables include speed of rotation, time of settling, dosage, size of flocs, turbidity removal, color removal, and pH.

Mixing and Agitation

Velocity gradient (G) measures the degree of mixing, with higher G values indicating more intense mixing.
Velocity gradient can be calculated using power input, tank volume, and dynamic viscosity.
Mixing can be achieved through impellers, pneumatic agitation, or baffle basins, each with its own unique characteristics and design equations.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about the importance of coagulation and flocculation in water treatment, including reducing turbidity, improving taste and odor, and enhancing disinfection.