Water treatment

Question 1

What is water softening?

Answer 1

Processes that remove the hardness of water

Question 2

What is purification?

Answer 2

the removal of organic matter and microorganisms in water

Question 3

What is clarification?

Answer 3

the precipitation of solids in water

Question 4

What is temporary water hardness

Answer 4

the easiest form of hardness to remove, it refers to water containing bicarbonates of Ca and Mg or limestone (Calcium carbonate)

Question 5

What are the salts that refer to temporary hardness?

Answer 5

CaCO3 (calcium carbonate)
Ca(HCO3)2 (calcium bicarbonate)
MgCO3 (magnesium carbonate)
Mg(HCO3)2 (magnesium bicarbonate)

Question 6

What is permanent hard water?

Answer 6

refers to water that contains sulphates and chlorides of calcium and magnesium

Question 7

Which salts refer to permanent hardness

Answer 7

MgSO4 (magnesium sulphate)
CaSO4 (calcium sulphate)
MgCl2 (magnesium chloride)
CaCl2 (calcium chloride)

Question 8

How does the ion exchange process occur?

Answer 8

1. Hard water is sent in a tank containing zeolite
2. Ions are exchanged to remove salts from water
3. Process is switched over to another tan while the (Z) is being regenerated in the first tank

Question 8

What is the ion exchange process

Answer 8

The process whereby cations are exchanged to remove impurities in water

Question 9

What are the chemical reactions that occur during ion exchange?

Answer 9

1. Na2Z + MgCl = MgZ + 2NaCl
2. Na2Z + MgSO4 = MgZ + NaSO4
3. Na2Z + CaCl2 = CaZ + 2NaCl
4. Na2Z + CaSO4 = CaZ + NaSO4

Question 10

What is zeolite (Z) ?

Answer 10

Any large group of materials consisting of hydrated silicates of sodium, magnesium etc. used as cation exchangers

Question 11

How is zeolite reclaimed?

Answer 11

The tank containing MgZ and CaZ is treated with a concentrated solution of sodium chloride which transfers sodium ions back to the zeolite to begin the process again

MgZ + 2NaCl = Na2Z + MgCl2
Ca2 + 2NaCL = Na2Z + CaCl2

Question 12

What is the hydrogen- ion exchange process

Answer 12

the process whereby hydrogen ions are used to remove all cations

Question 13

How is hydrogen resin regenerated after the ion exchange process

Answer 13

it is regenerated with sulfuric acid

Question 14

What is the lime soda process

Answer 14

a method of water softening that uses lime (calcium hydroxide) and soda ash (sodium carbonate) to remove hardness-causing minerals, primarily calcium and magnesium, from water.

Question 14

What are the requisites from municipalities regarding safe water supply?

Answer 14

Freedom from pathogenic microbes
Freedom from suspended solids
Water must be soft
Water must be colourless
Water must be odorless

Question 15

How is water treated to improve its quality?

Answer 15

water is aerated to remove iron, odor and taste
water is softened
carbon removes odors and improves flavour
chlorine is added to destroy microorganisms

Question 16

what is phosphate conditioning?

Answer 16

Adding phosphates, like sodium phosphate, to boiler water to prevent scale formation and maintain proper pH levels. This process helps to control hardness, regulate alkalinity, and reduce corrosion by forming easily removable sludge or by buffering the water’s

Question 17

What is silica removal?

Answer 17

Silica removal (Si02) is the deduction of the concentration of silica in water
Silica removal in water treatment can be achieved through various methods, including lime softening and reverse osmosis

Question 18

What is desalting?

Answer 18

a process of removing salts and other impurities from a solution

Question 19

What is reverse osmosis ?

Answer 19

Reverse osmosis (RO) is a filtration process that removes impurities from water by forcing it through a semi-permeable membrane. It works by applying pressure to push water molecules through the membrane while blocking contaminants like salts, bacteria, and chemicals.

Question 20

What is distillation?

Answer 20

the process involving the conversion of a liquid into vapour that is subsequently condensed back to liquid form to remove all ions in water

Question 21

How are impurities measured in wastewaters?

Answer 21

1. The amount of suspended solids
2. Biochemical oxygen demand: the amount of oxygen required by a microbial population to stabilise biodegradable organic material

Question 22

How is sewage water treated?

Answer 22

• Preliminary Treatment – Removes large debris
• Primary Treatment – Uses sedimentation tanks to separate solids and liquids
• Secondary Treatment – Microorganisms break down organic matter via activated sludge
• Tertiary Treatment – chlorine is used to destroy microbes, liquids are discharged into nearby streams
• Sludge Treatment – Processes solid waste for disposal, energy production, or conversion into fertilizer

Question 23

How is industrial waste treated?

Answer 23

Limestone is used to absorb oil or dewatered for reuse Brine is diluted then added to high water flows Organic compounds require special handling before they are disposed of

Question 24

How is water treated (fresh water source)

Answer 24

[Screening] - large particles are removed ↓ [Coagulation/Flocculation]- coagulants are added to the water to precipitate suspended solids ↓ [Sedimentation]- sediments in the water form and descend to the bottom of the tank ↓ [Filtration]- water passes through sand/carbon filters that remove small solids ↓ [Chlorination]- water is chloronated to kill microorganisms ↓ [pH Adjustment / Fluoridation] ↓ [Storage / Distribution]

Question 25

What occurs when silica removal is not required?

Answer 25

Silica is often not removed in water because it: It’s not toxic at normal levels Removing it is expensive. When silica removal is not required, the system consists of: a hydrogen cation exchanger unit and a weakly basic anion exchanger unit then it is followed by a degasifier by aeration to remove CO2 from the bicarbonates that formed in the first step

Question 26

When silica removal is required

Answer 26

It can be removed by activated magnesia or by using dolomitic lime. The system may consist of a hydrogen exchanger and a strongly basic unit (magnesia/dolomitic lime). The degassifier removes the CO2 formed by the bicarbonates from the first step

Question 27

Why would we be required to remove silica in water

Answer 27

In industrial processes (like power plants or boiler systems), silica can cause scaling (build-up of deposits). In semiconductor manufacturing, even tiny amounts of silica can interfere with purity.