C14.3 - Treating waste water

Question 1

What happens to all the waste that leaves our homes down the drains?
What happens to everything that drains from washing machines, dishwashers, sinks, baths and toilets?

Answer 1

Everything that drains from washing machines, dishwashers, sinks, baths and toilets flows down pipes and enters the larger sewer pipes

Question 2

Sewage

Answer 2

Everything that drains from washing machines, dishwashers, sinks, baths and toilets, along with waste water from businesses and industry

Question 3

What has to be treated at sewage treatment plants?

Answer 3

Everything that drains from washing machines, dishwashers, sinks, baths and toilets, along with waste water from businesses and industry (sewage), together with waste water from farming activities has to be treated at sewage treatment plants

Question 4

Why does everything that drains from washing machines, dishwashers, sinks, baths and toilets, along with waste water from businesses and industry (sewage), together with waste water from farming activities have to be treated at sewage treatment plants?

Answer 4

Everything that drains from washing machines, dishwashers, sinks, baths and toilets, along with waste water from businesses and industry (sewage), together with waste water from farming activities has to be treated at sewage treatment plants, to make it safe before it can be returned to the environment, usually into rivers or piped out to sea

Question 5

1st step of sewage treatment

Answer 5

The 1st step of sewage treatment is:
Screening - Once the sewage arrives at the sewage treatment plant, the first step is to remove large solid objects and grit from the rest of the waste water
The sewage passes through a metal grid that traps the large objects

Question 6

2nd step of sewage treatment

Answer 6

The 2nd step of sewage treatment is:
Primary treatment - In the first circular tank, the solid sediments are allowed to settle out from the mixture
Large paddles rotate, pushing the solids, called sludge, towards the centre of the tank
There the sludge is piped to a storage tank for further treatment

Question 7

In the 2nd step of sewage treatment, what does the watery liquid (effluent) above the sludge do?

Answer 7

In the 2nd step of sewage treatment, the watery liquid (effluent) above the sludge flows into the next tank
Although no solid matter is visible, this effluent still contains many potentially harmful microorganisms

Question 8

3rd step of sewage treatment

Answer 8

The 3rd step of sewage treatment is:
Secondary treatment - In the second tank, useful bacteria feed on any remaining organic matter and harmful microorganisms still present, breaking them down aerobically (in the presence of oxygen)
The tank is aerated by bubbling air through the waste water

Question 9

In the 3rd step of sewage treatment, the tank is aerated by bubbling air through the waste water.
How long can this take?

Answer 9

In the 3rd step of sewage treatment, the tank is aerated by bubbling air through the waste water
This can take from several hours to several days

Question 10

In the 3rd step of sewage treatment, the tank is aerated by bubbling air through the waste water.
This can take from several hours to several days, depending on what?

Answer 10

In the 3rd step of sewage treatment, the tank is aerated by bubbling air through the waste water.
This can take from several hours to several days, depending on the quality of the waste water, size of the tank, rate of aeration and temperature

Question 11

4th step of sewage treatment

Answer 11

The 4th step of sewage treatment is:
Final treatment - In the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated
At this point, the treated waste water is safe enough to be discharged back into rivers

Question 12

In the 4th step of sewage treatment, in the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment.
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated.
At this point, the treated waste water is safe enough to be discharged back into rivers.
However, what can happen if the river is a particularly sensitive ecosystem?

Answer 12

In the 4th step of sewage treatment, in the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated
At this point, the treated waste water is safe enough to be discharged back into rivers
However, if the river is a particularly sensitive ecosystem, the water can be filtered one more time through a bed of sand

Question 13

In the 4th step of sewage treatment, in the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment.
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated.
At this point, the treated waste water is safe enough to be discharged back into rivers.
However, if the river is a particularly sensitive ecosystem, the water can be filtered one more time through a bed of sand.
If necessary, what then can happen?

Answer 13

In the 4th step of sewage treatment, in the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated
At this point, the treated waste water is safe enough to be discharged back into rivers
However, if the river is a particularly sensitive ecosystem, the water can be filtered one more time through a bed of sand
If necessary, the water can then be sterilised by ultraviolet light or by chlorine

Question 14

In the 4th step of sewage treatment, in the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment.
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated.
At this point, the treated waste water is safe enough to be discharged back into rivers.
However, if the river is a particularly sensitive ecosystem, the water can be filtered one more time through a bed of sand.
If necessary, the water can then be sterilised by ultraviolet light or by chlorine.
However, what does the release of chlorine into rivers do?

Answer 14

In the 4th step of sewage treatment, in the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated
At this point, the treated waste water is safe enough to be discharged back into rivers
However, if the river is a particularly sensitive ecosystem, the water can be filtered one more time through a bed of sand
If necessary, the water can then be sterilised by ultraviolet light or by chlorine
However, the release of chlorine into rivers does cause concern

Question 15

In the 4th step of sewage treatment, in the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment.
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated.
At this point, the treated waste water is safe enough to be discharged back into rivers.
However, if the river is a particularly sensitive ecosystem, the water can be filtered one more time through a bed of sand.
If necessary, the water can then be sterilised by ultraviolet light or by chlorine.
However, why does the release of chlorine into rivers cause concern?

Answer 15

In the 4th step of sewage treatment, in the last tank, the useful bacteria are allowed to settle out to the bottom of the tank as a sediment
The sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated
At this point, the treated waste water is safe enough to be discharged back into rivers
However, if the river is a particularly sensitive ecosystem, the water can be filtered one more time through a bed of sand
If necessary, the water can then be sterilised by ultraviolet light or by chlorine
However, the release of chlorine into rivers does cause concern, as toxic organic compounds of chlorine can be formed in the environment

Question 16

What can dried sludge be used as?

Answer 16

Dried sludge can be used as a renewable energy source, along with biogas and biomethane

Question 17

Dried sludge can be used as a renewable energy source, along with biogas and biomethane.
What are all of these made from?

Answer 17

Dried sludge can be used as a renewable energy source, along with biogas and biomethane
All of these are made from sewage

Question 18

What happens when sewage sludge is dried?

Answer 18

When sewage sludge is dried, it takes up a lot less space, so it becomes easier to transport it away from the sewage treatment plant

Question 19

What happens to the sludge separated off during the primary treatment of the sewage?

Answer 19

The sludge separated off during the primary treatment of the sewage is not wasted
After further treatment, most can be dried and used as fertilised

Question 20

The sludge separated off during the primary treatment of the sewage is not wasted.
What can happen after further treatment?

Answer 20

The sludge separated off during the primary treatment of the sewage is not wasted
After further treatment, most can be dried and used as fertiliser on farmland to improve the soil or used as a source of renewable energy

Question 21

The sludge separated off during the primary treatment of the sewage is not wasted.
What does the sludge contain?

Answer 21

The sludge separated off during the primary treatment of the sewage is not wasted
The sludge contains organic matter, including human waste, suspended solids, water and dissolved compounds

Question 22

The sludge separated off during the primary treatment of the sewage is not wasted.
The sludge contains organic matter, including human waste, suspended solids, water and dissolved compounds.
What do microorganisms do to the sludge?

Answer 22

The sludge separated off during the primary treatment of the sewage is not wasted
The sludge contains organic matter, including human waste, suspended solids, water and dissolved compounds
It is digested anaerobically by microorganisms beneath the surface in the treatment tank

Question 23

The sludge separated off during the primary treatment of the sewage is not wasted.
The sludge contains organic matter, including human waste, suspended solids, water and dissolved compounds.
It is digested anaerobically by microorganisms beneath the surface in the treatment tank.
At what 2 temperatures can this biological treatment be carried out?

Answer 23

The sludge separated off during the primary treatment of the sewage is not wasted
The sludge contains organic matter, including human waste, suspended solids, water and dissolved compounds
It is digested anaerobically by microorganisms beneath the surface in the treatment tank
This biological treatment can be carried out at a relatively high temperature of about 55 degrees Celsius or a lower temperature of about 35 degrees Celsius

Question 24

The sludge separated off during the primary treatment of the sewage is not wasted.
The sludge contains organic matter, including human waste, suspended solids, water and dissolved compounds.
It is digested anaerobically by microorganisms beneath the surface in the treatment tank.
This biological treatment can be carried out at a relatively high temperature of about 55 degrees Celsius or a lower temperature of about 35 degrees Celsius.
How long can this take to complete?

Answer 24

The sludge separated off during the primary treatment of the sewage is not wasted
The sludge contains organic matter, including human waste, suspended solids, water and dissolved compounds
It is digested anaerobically by microorganisms beneath the surface in the treatment tank
This biological treatment can be carried out at a relatively high temperature of about 55 degrees Celsius or a lower temperature of about 35 degrees Celsius, which can take up to 30 days to complete

Question 25

The sludge separated off during the primary treatment contains organic matter, including human waste, suspended solids, water and dissolved compounds.
It is digested anaerobically by microorganisms beneath the surface in the treatment tank.
This biological treatment can be carried out at a relatively high temperature of about 55 degrees Celsius or a lower temperature of about 35 degrees Celsius, which can take up to 30 days to complete.
What does the higher temperature have?

Answer 25

The sludge separated off during the primary treatment contains organic matter, including human waste, suspended solids, water and dissolved compounds
It is digested anaerobically by microorganisms beneath the surface in the treatment tank
This biological treatment can be carried out at a relatively high temperature of about 55 degrees Celsius or a lower temperature of about 35 degrees Celsius, which can take up to 30 days to complete
The higher temperature has the benefit of speeding up the breakdown of the organic matter, but energy has to be supplied to heat the sludge

Question 26

What do the breakdown products of the sludge separated off during the primary treatment include?

Answer 26

The breakdown products of the sludge separated off during the primary treatment include biogas

Question 27

Biogas

Answer 27

Biogas is a mixture of methane, carbon dioxide and some hydrogen sulfide

Question 28

The breakdown products of the sludge separated off during the primary treatment include biogas.
What can happen to biogas?

Answer 28

The breakdown products of the sludge separated off during the primary treatment include biogas
Biogas can be burned and used to power the sewage treatment plant or provide electricity for the surrounding area

Question 29

The breakdown products of the sludge separated off during the primary treatment include biogas.
Biogas can be burned and used to power the sewage treatment plant or provide electricity for the surrounding area.
What can also happen to it?

Answer 29

The breakdown products of the sludge separated off during the primary treatment include biogas
Biogas can be burned and used to power the sewage treatment plant or provide electricity for the surrounding area
It can also be further cleaned to make methane, the main gas in natural gas and piped into the gas supply

Question 30

The breakdown products of the sludge separated off during the primary treatment include biogas.
Biogas can be burned and used to power the sewage treatment plant or provide electricity for the surrounding area.
It can also be further cleaned to make methane, the main gas in natural gas and piped into the gas supply.
Alternatively, what can happen to the sludge?

Answer 30

The breakdown products of the sludge separated off during the primary treatment include biogas
Biogas can be burned and used to power the sewage treatment plant or provide electricity for the surrounding area
It can also be further cleaned to make methane, the main gas in natural gas and piped into the gas supply
Alternatively, the sludge can be dried out and turned into a crusty solid ‘cake’ that can be burnt to generate electricity