Chapter 9: Water treatment

Question 1

The water treatment process may vary slightly at

Answer 1

different locations

Question 2

The water treatment process may vary slightly at different locations, depending on

Answer 2

the technology of the plant and the water it needs to process, but the basic principles are largely the same.

Question 3

Standard water treatment processes:

Answer 3

1. Coagulation
2. Sedimentation
3. Filtration
4. Disinfection
5. Sludge Drying
6. Fluoridation
7. pH Correction

Question 4

Standard water treatment processes:

Coagulation

Answer 4

During coagulation, liquid aluminium sulfate (alum) and/or polymer are added to untreated (raw) water. When mixed with the water, this causes the tiny particles of dirt in the water to stick together or coagulate. Next, groups of dirt particles stick together to form larger, heavier particles called flocs which are easier to remove by settling or filtration.

Question 5

Standard water treatment processes:

Sedimentation

Answer 5

As the water and the floc particles progress through the treatment process, they move into sedimentation basins where the water moves slowly, causing the heavy floc particles to settle to the bottom. Floc which collects on the bottom of the basin is called sludge, and is piped to drying lagoons. In Direct Filtration, the sedimentation step is not included, and the floc is removed by filtration only.

Question 6

Standard water treatment processes:

Filtration

Answer 6

Water flows through a filter designed to remove particles in the water. The filters are made of layers of sand and gravel, and in some cases, crushed anthracite. Filtration collects the suspended impurities in water and enhances the effectiveness of disinfection. The filters are routinely cleaned by backwashing.

Question 7

Standard water treatment processes:

Disinfection

Answer 7

Water is disinfected before it enters the distribution system to ensure that any disease-causing bacteria, viruses, and parasites are destroyed. Chlorine is used because it is a very effective disinfectant, and residual concentrations can be maintained to guard against possible biological contamination in the water distribution system.

Question 8

Standard water treatment processes:

Sludge Drying

Answer 8

Solids that are collected and settled out of the water by sedimentation and filtration are removed to drying lagoons.

Question 9

Standard water treatment processes:

Fluoridation:

Answer 9

Water fluoridation is the treatment of community water supplies for the purpose of adjusting the concentration of the free fluoride ion to the optimum level sufficient to reduce dental caries. Hunter Water is required to fluoridate water.

Question 10

Standard water treatment processes:

pH Correction

Answer 10

Lime is added to the filtered water to adjust the pH and stabilise the naturally soft water in order to minimise corrosion in the distribution system, and within customers’ plumbing.

Question 11

Wastewater treatment is closely related to

Answer 11

the standards and/or expectations set for the effluent quality.

Question 12

Wastewater treatment is closely related to the standards and/or expectations set for the effluent quality. Wastewater treatment processes are designed to

Answer 12

achieve improvements in the quality of the wastewater

Question 13

The various treatment processes may reduce:

Answer 13

1. suspended solids
2. biodegradable organics
3. pathogenic bacteria
4. nutrients

Question 14

The various treatment processes may reduce:

suspended solids:

Answer 14

(physical particles that can clog rivers or channels as they settle under gravity)

Question 15

The various treatment processes may reduce:

Biodegradable organics

Answer 15

(e.g. BOD) which can serve as “food” for microorganisms in the receiving body. Microorganisms combine this matter with oxygen from the water to yield the energy they need to thrive and multiply; unfortunately, this oxygen is also needed by fish and other organisms in the river. Heavy organic pollution can lead to “dead zones” where no fish can be found; sudden releases of heavy organic loads can lead to dramatic “fishkills”.

Question 16

The various treatment processes may reduce:

Pathogenic bacteria

Answer 16

Pathogenic bacteria and other disease causing organisms These are most relevant where the receiving water is used for drinking, or where people would otherwise be in close contact with it

Question 17

The various treatment processes may reduce:

Nutrients

Answer 17

including nitrates and phosphates. These nutrients can lead to high concentrations of unwanted algae, which can themselves become heavy loads of biodegradable organic load Treatment processes may also neutralize or removing industrial wastes and toxic chemicals.

Question 18

Nutrients, including nitrates and phosphates. These nutrients can lead to high concentrations of unwanted algae, which can themselves become heavy loads of biodegradable organic load Treatment processes may also neutralize or removing industrial wastes and toxic chemicals. This type of treatment should

Answer 18

ideally take place at the industrial plant itself, before discharge of their effluent in municipal sewers or water courses.

Question 19

Widely used terminology refers to three levels of wastewater treatment:

Answer 19

primary, secondary, and tertiary (or advanced).

Question 20

Primary (mechanical) treatment is designed to

Answer 20

remove gross, suspended and floating solids from raw sewage.

Question 21

Primary (mechanical) treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes ……………… to ……………………………………… by …………………. to …………………………..

Answer 21

screening to trap solid objects and sedimentation by gravity to remove suspended solids.

Question 22

Primary (mechanical) treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes screening to trap solid objects and sedimentation by gravity to remove suspended solids. This level is sometimes referred to as

Answer 22

“mechanical treatment”

Question 23

Primary (mechanical) treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes screening to trap solid objects and sedimentation by gravity to remove suspended solids. This level is sometimes referred to as “mechanical treatment”, although chemicals are often used to

Answer 23

accelerate the sedimentation process

Question 24

Primary (mechanical) treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes screening to trap solid objects and sedimentation by gravity to remove suspended solids. This level is sometimes referred to as “mechanical treatment”, although chemicals are often used to accelerate the sedimentation process. Primary treatment can

Answer 24

reduce the BOD of the incoming wastewater by 20-30% and the total suspended solids by some 50-60%.

Question 25

Primary (mechanical) treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes screening to trap solid objects and sedimentation by gravity to remove suspended solids. This level is sometimes referred to as “mechanical treatment”, although chemicals are often used to accelerate the sedimentation process. Primary treatment can reduce the BOD of the incoming wastewater by 20-30% and the total suspended solids by some 50-60%. Primary treatment is usually the

Answer 25

first stage of wastewater treatment

Question 26

Primary (mechanical) treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes screening to trap solid objects and sedimentation by gravity to remove suspended solids. This level is sometimes referred to as “mechanical treatment”, although chemicals are often used to accelerate the sedimentation process. Primary treatment can reduce the BOD of the incoming wastewater by 20-30% and the total suspended solids by some 50-60%. Primary treatment is usually the first stage of wastewater treatment. Many advanced wastewater treatment plants in industrialized countries have started with

Answer 26

primary treatment

Question 27

Many advanced wastewater treatment plants in industrialized countries have started with primary treatment, and have then added other treatment stages as

Answer 27

wastewater load has grown

Question 28

Many advanced wastewater treatment plants in industrialized countries have started with primary treatment, and have then added other treatment stages as wastewater load has grown, as the need for treatment has

Answer 28

increased,

Question 29

Many advanced wastewater treatment plants in industrialized countries have started with primary treatment, and have then added other treatment stages as wastewater load has grown, as the need for treatment has increased, and as resources have become

Answer 29

available.