Wastewater Treatment Process - United Utilities

Wastewater Treatment Process Supporting Resources – KS3

Copyright © United Utilities Water Limited 2020 1

Contents Location 1: The Inlet.......................................................................................................................................................... 2

Location 2: Screens ........................................................................................................................................................... 5

Location 3: Primary Settlement Tanks .............................................................................................................................. 8

Location 4: Activated Sludge Lanes ................................................................................................................................. 11

Location 5: Final Settlement Tanks ................................................................................................................................. 14

Location 6: Outlet ........................................................................................................................................................... 17

Location 7: Sludge Holding Tanks ................................................................................................................................... 20

Location 8: Sludge Treatment ......................................................................................................................................... 23

Location 9: Renewable Energy Generation Plant ........................................................................................................... 26

Location 10: Solar Panels ................................................................................................................................................ 29

Supporting Resources – KS3


Location 1: The Inlet Introduction

This activity can be used as one of a series as the students explore the water treatment process or as a

standalone activity.

Preparation

Use this activity with the students in a virtual or face to face lesson.

Ways to utilise this resource include:

a) Resource on the whiteboard (teacher demonstration)

b) Pupil activity on laptops or tablets

c) Flipped learning resource (pupils explore before coming to the lesson)

d) Homework activity (pupils explore and have to complete an assignment at home)



Activity

1: The Inlet

Watch the video, look around the image and investigate the inlet. Can you find the

answers to the following questions?

● Where does the sewage that arrives at the inlet come from?

● Why might a property need a septic tank?

● What are the positives and negatives of rainwater entering the collection

of residential and commercial sewage?



Answer Key

1: The Inlet

Watch the video, look around the image and investigate the inlet.

Can you find the answers to the following questions?

● Where does the sewage that arrives at the inlet come from?

Sewage arrives from residential and commercial properties with some

treatment plants able to accept waste from septic tanks collected by tankers.

● Why might a property need a septic tank?

The residence or business is not connected to the sewerage network and

therefore needs a septic tank to store sewage safely before it is taken for

treatment.

● What are the positives and negatives of rainwater entering the collection of

residential and commercial sewage?

Rainwater that enters the sewerage system can help dilute commercial and

residential sewage to aid movement through the system, however, if there is a

sudden influx of rainwater this can overload the system and there could be an

escape of sewage. (The likelihood of an increase in rainwater entering the

system increases with urban creep and increased surface runoff.)



Location 2: Screens

Introduction



Preparation









Activity

2: Screens

Watch the video, look around the image and investigate the screens, detritors and

compactors. Can you find the answers to the following questions?

● What is the function of the screens in this process?

● What sort of separation is involved - mechanical or chemical?

● What is the primary cause of sewer flooding?

● What other objects contribute to blocked sewers?



Answer Key

2: Screens

Watch the video, look around the image and investigate the screens, detritors and

compactors. Can you find the answers to the following questions?

● What is the function of the screens in this process?

To remove large debris and detritus from the sewage inflow that could damage

the treatment works further into the process.

● What sort of separation is involved - mechanical or chemical?

Mechanical separation as the debris is physically removed using screens and

scrapers.

● What is the primary cause of sewer flooding?

Wet wipes are the biggest cause of sewer flooding as they do not degrade.

● What other objects contribute to blocked sewers?

Any rubbish that enters the sewer system can cause blocked sewers.

Particularly household waste such as fats/oils, nappies, cotton wool etc. Plastic

bags and bottles can enter the system when dropped into drains or swept up

by rainwater.



Location 3: Primary Settlement Tanks

Introduction



Preparation









Activity

3: Primary

Settlement

Tanks

Watch the video, look around the image and investigate the primary settlement tanks.


● Why allow the solids to settle? How would this impact the process?

● What is the benefit of adding flocculants (Chemicals) to the process?

● Why does the process use little electricity?



Answer Key

3: Primary

Settlement

Tanks

Watch the video, look around the image and investigate the primary settlement tanks.


● Why allow the solids to settle? How would removing this impact the process?

Natural process of organic solids sinking saves energy. Removing this means

the solids would need to be filtered which is less efficient.

● What is the benefit of adding flocculants (Chemicals) to the process?

Increases size of the organic solids. Solids then settle and can be removed.

● Why does the process use little electricity?

Relies on physical action of the organic solids settling before removal by the

scraper. The biogas produced can be used to create electricity which offsets

energy usage.



Location 4: Activated Sludge Lanes

Introduction



Preparation









Activity

4: Activated

Sludge Lanes

Watch the video, look around the image and investigate the Activated Sludge Lanes.


● Using aerobic bacteria in the Activated Sludge Lanes requires the addition of

what to the process?

● Why does United Utilities keep the bacteria hungry and low on energy?

● Why is the oxygen diffused through the sludge and how does this impact the

efficiency of the process?

● What are United Utilities doing to minimise the amount of additional energy

needed for this process?



Answer Key

4: Activated

Sludge Lanes

Watch the video, look around the image and investigate the Activated Sludge Lanes.


● Using aerobic bacteria in the Activated Sludge Lanes requires the addition of

what to the process?

Aerobic bacteria need oxygen to efficiently breakdown the solids within the

sewage, therefore oxygen needs to be introduced to the system to maximise

the efficiency of the bacteria.

● Why does United Utilities keep the bacteria hungry and low on energy?

By keeping the bacteria hungry they will continue to break down the solid

matter. If the bacteria had enough they would slow down and the process

would lose efficiency.

● Why is the oxygen diffused through the sludge and how does this impact the

efficiency of the process?

Diffusing the oxygen throughout the sludge allows the bacteria to break down

the materials across the whole tank rather than just in a small area if there was

a single source of oxygen. This maximises the efficiency of the bacteria and

increases the amount of sludge that can be treated at any one time.

● What are United Utilities doing to minimise the amount of additional energy

needed for this process?

The distribution of oxygen throughout the activated sludge lanes requires a

large amount of energy. To minimise the amount of energy that United Utilities

needs to use they supplement the energy from the national grid with electricity

generated in their own combined heat and power plant. This offset limits the

reliance on fossil fuel electricity and makes the process more sustainable.



Location 5: Final Settlement Tanks

Introduction



Preparation









Activity

5: Final

Settlement

Tanks

Watch the video, look around the image and investigate the Final Settlement Tanks.


● How is the sludge reused to improve the efficiency of the process?

● Why is it important to allow the sludge to settle for a second time?

● Why is the surface of the settlement tank calmer than that of the active sludge

lanes?



Answer Key

5: Final

Settlement

Tanks

Watch the video, look around the image and investigate the Final Settlement Tanks.


● How is the sludge reused to improve the efficiency of the process?

Bacteria from the active sludge lanes are still present at this stage. By

reintroducing portions of this material back into the active sludge lanes the

levels of bacteria in the active sludge lanes can be maintained. This increases

efficiency as United Utilities can monitor bacteria levels in the reintroduced

sludge rather than adding new bacteria to the lanes with each batch of sludge

processed.

● Why is it important to allow the sludge to settle for a second time?

Allowing a second settlement reduces the energy needed to remove the sludge

as it settles and can be removed easily from the bottom of the tank.

● Why is the surface of the settlement tank calmer than that of the Active sludge

lanes?

The second settlement tanks are not actively agitated by the dispersal of

oxygen, as happens in the active sludge lanes, and so the surface is a lot calmer.



Location 6: Outlet

Introduction



Preparation









Activity

6: Outlet

Watch the video, look around the image and investigate the Final Effluent Outlet. Can

you find the answers to the following questions?

● Why is tertiary treatment needed and what does it entail?

● What is the difference between clean and potable water?

● Why would United Utilities use a gravity fed system to reintroduce water to

the environment?

● Why might water be released into a river or sea and not into a reservoir?

● What systems do United Utilities have in place to ensure minimum impact on

the natural water cycle?



Answer Key

6: Outlet

Watch the video, look around the image and investigate the Final Effluent Outlet. Can you

find the answers to the following questions?

● Why is tertiary treatment needed and what does it entail?

Tertiary treatment is required to remove very fine particulate matter from treated

water. This process involves a fine filter to ensure the particulate is captured and

removed.

● What is the difference between clean and potable water?

Clean water is safe for the environment and can be released into the natural water

cycle via rivers and into the sea. Potable water is classified safe for human

consumption (drinking water) and has undergone further treatment than clean

water.

● Why would United Utilities use a gravity fed system to reintroduce water to the

environment?

Using a gravity fed system means that the water does the hard work instead of using

further energy to pump water to a specific place. United Utilities will use a gravity

fed system to save energy and increase the efficiency of their processes.

● Why might water be released into a river or sea and not into a reservoir?

Releasing water back into a river or the sea means the water is rejoining the natural

water cycle where, once having passed through the water cycle, it will rejoin the

water network after collecting in reservoirs. Whilst recycled potable water is

achievable and clean water can be made potable, this is not standard practice in the

UK. There are additional benefits to the water entering the water cycle before being

made potable again.

● What systems do United Utilities have in place to ensure minimum impact on the

natural water cycle?

Through primary, secondary and tertiary treatment, United Utilities ensure that

human processes integrate into the natural environment. The final effluent output is

safe for the environment due to the processes employed by United Utilities and is

returned in a controlled manner to ensure limited impact on the natural environment.



Location 7: Sludge Holding Tanks

Introduction



Preparation









Activity

7: Sludge Holding Tanks

Watch the videos and scroll around the location.

Find the answers to the following questions:

● Is the sewage broken down by biological or mechanical separation at this stage?

● How can the gases be used to offset the energy needed to treat the sewage?

● What two ways does this process contribute to wider energy use and crop production?



Answer Key

7: Sludge Holding Tanks

Watch the videos and scroll around the location.

Find the answers to the following questions:

● Is the sewage broken down by biological or mechanical separation at this stage? Within the storage tanks the sludge has excess water removed before the sludge is digested. This is a mechanical process.

● How can the gases be used to offset the energy needed to treat the sewage? Gases collected from other parts of the process and stored here can be used to fuel the combined heat and power engines. These engines take a byproduct of the treatment process and use it to provide some of the energy required by the other stages. As the process is refined it will take less external energy to run the processes as more energy can be reclaimed from the process byproducts.

● What two ways does this process contribute to wider energy use and crop production? Excess energy from the combined heat and power engines can be fed back into the national grid supporting energy use across the country. Biosolids can be distributed to agricultural farmers to be used as fertiliser for crop production.



Location 8: Sludge Treatment

Introduction



Preparation









Activity

8: Sludge

Treatment

Watch the video, look around the image and investigate Sludge

Treatment. Can you find the answers to the following questions?

● Identify 3 byproducts from this stage of treatment and a use for each.

● How does increasing the temperature impact the process?

● What is the difference between the bacteria used in this stage and that in the

Active Sludge Process?

● How might United Utilities build a relationship with the local community with

the products produced at this stage?



Answer Key

8: Sludge

Treatment

Watch the video, look around the image and investigate Sludge Treatment. Can you

find the answers to the following questions?

● Identify 3 byproducts from this stage of treatment and a use for each.

Water - it can be reintroduced into the natural water cycle or for irrigation in

farming.

Biogas - this can be used to fuel the combined heat and power engines that can

produce heat and electricity.

Biosolids - these can be used as fertiliser in agriculture.

● How does increasing the temperature impact the process?

Raising the temperature produces a more favourable environment for the

bacteria which increases the rate of digestion.

● What is the difference between the bacteria used in this stage and that in the

Active Sludge Process?

The active sludge lanes use Aerobic bacteria this is why the active sludge lanes

have oxygen distributors. Within the digesters anaerobic bacteria are used to

break down the sludge into the useful byproducts of water, biogas and

biosolids. Anaerobic bacteria do not require oxygen to break down the sludge

effectively.

● How might United Utilities build a relationship with the local community with

the products produced at this stage?

Reaching out to the local farming community, United Utilities can provide

fertiliser for the agricultural industry, which would support local employment

and industry. Additional energy produced by the heat and power engines that

is not used by the plant can be fed back into the National Grid, which would

then be used by local residences and businesses.



Location 9: Renewable Energy Generation Plant

Introduction



Preparation









Activity

9: Renewable

Energy

Generation Plant

Watch the video, look around the image and investigate the Combined Heat and

Power Station. Can you find the answers to the following questions?

● What are the benefits of United Utilities producing its own heat and power?

● How does producing heat and power increase the efficiency of the systems

in place at the Wastewater Treatment Plant?

● What measures are used to limit environmental impact?

● Why would releasing the biogas be an environmental concern and what

measures do United Utilities take to mitigate this?



Answer Key

9: Renewable

Energy

Generation Plant

Watch the video, look around the image and investigate the Combined Heat and

Power Station. Can you find the answers to the following questions?

● What are the benefits of United Utilities producing its own heat and power?

By producing its own heat and power United Utilities can become less

reliant on additional energy from the National Grid. This reduces the

environmental impact of their energy requirements, produces savings for

the company as they are not paying for as much additional energy and

drives efficiencies in the processes in the aim to become self-sufficient for

energy.

● What measures are used to limit environmental impact?

Producing heat and power from biogas reduces the reliance on energy from

fossil fuels for the site, uses the byproducts of the process removing the need

for disposal of these byproducts, and by supplying energy to the national

grid United Utilities contributes to renewable energy production nationally.

● Why would releasing the biogas be an environmental concern and what

measures do United Utilities take to mitigate this?

Methane is a key greenhouse gas and contributes significantly to Global

Warming and Climate Change. Methane is a main component of the biogas

the wastewater treatment process produces. If the biogas were to be

released into the atmosphere it would increase the amount of greenhouse

gases in the atmosphere. To prevent this, biogas is stored securely on site,

used to power combined heat and power engines and, to control the

pressure of the gas, can be burnt in a flare stack to prevent methane release

into the atmosphere.



Location 10: Solar Panels

Introduction



Preparation









Activity

10: Solar Panels

Watch the video on Solar Panels. Can you find the answers to the following

questions?

● What are the advantages of a floating solar array?

● How might a floating solar array impact on the other processes United

Utilities carry out?

● What advantages and disadvantages are there to being the first commercial

scale UK floating solar array?

● What considerations do United Utilities make before investing in floating

solar arrays?



Answer Key

10: Solar

Panels

Watch the video on Solar Panels Can you find the answers to the following questions?

● What are the advantages of a floating solar array?

A floating solar array can use a surface that would otherwise be unusable, by

covering the water’s surface it can inhibit algae growth and reduce water loss

through evaporation. This is particularly useful in countries facing drought or

reduced access to water such as Australia.

● How might a floating solar array impact on the other processes United Utilities

carry out?

The energy produced by the floating solar arrays can be used to power other

United Utilities facilities, it can protect the surface of reservoirs from

evaporation preserving water levels which impacts on United Utilities water

distribution processes.

● What advantages and disadvantages are there to being the first commercial

scale UK floating solar array?

Advantages include developing new technologies making United Utilities a

pioneer in the field and identifying and developing industry knowledge which

informs future strategy.

Disadvantages include the possibility of making mistakes as being the first

means there is no one to identify potential pitfalls. Developing knowledge

requires investment in the production of prototypes and analysis before

producing a scalable process.

● What considerations do United Utilities make before investing in floating solar

arrays?

United Utilities use a simple formula to identify a potential site. Is there a large

enough demand from the site for additional energy? Is there enough space

available to ensure efficiency? Can the solar array be connected to the local

distribution company to ensure the energy produced is utilised correctly?

Documents

Wastewater Treatment Process - United Utilities