NCWR

About NCWR

Wastewater treatment

In a nutshell

In this activity we are informed about the treatment process of the urban wastewater and why is considered as a non-conventional water resource.

a school day

12-13 years old

In the field

Our objectives

In this activity you will:

  • Be informed about the steps followed in a wastewater treatment plant.
  • Find out the uses of the treated wastewater.

Things to use

Notebooks and pens, photo camera

Stop and wonder

Scientists describe the different “types” of water, depending on their origin and uses, giving them different “colors”.

Discuss in your groups the following:


  1. Have you ever heard of “black water”? What do you think it is?
  2. What is the difference between “blackwater” and “grey water”?

Water-readings

The wastewater treatment

” water is the wastewater from the toilet bowls. The wastewater of a city generated from the houses, offices, schools, public buildings, stores, etc. ends up in the sewage system and through its network, to the wastewater treatment plant. There wastewater undergoes certain processes:

  1. Screening: The sewage is led to open tanks that are penetrated vertically by large grates, imagine them as huge combs. These hold large solid debris (e.g. pieces of plastic, wood, cloth, etc).
  2. Primary settlement: After screening, the sewage flows at a slow rate to allow grit- the heavier materials-  to settle in the bottom of the tank, as sludge.
  3. Secondary or biological treatment: The overflowing liquid from the primary settlement moves on to the biological treatment reservoirs (aeration tanks) where intensive aeration is taking place. Wastewater contains both microorganisms and organic matter (carbon). These microorganisms using oxygen, grow rapidly, multiply and feed on the organic substances. So, thanks to the microorganisms, the effluent is cleansed. As they grow , microorganisms tend to joint with each other.
  4. Secondary settlement: The effluent is led to tanks for the remaining solids – sludge together with flocks of microorganisms- to settle down. In fact, a part of them is sent back to the aeration tank to “help” microorganisms to consume the organic matter. The secondary settling tank is also open and slowly filled up so that it overflows. The overflowing fluid is free of organic substances.
  5. Disinfection: To make sure no microorganisms left in the recovered water, we add chlorine, which destroys them.

The “recovered” water, meaning the water resulting from the wastewater treatment is usually led to a water body (sea or river) without causing risks of contamination or pollution. However, this practice is a big waste, since this water is suitable for various uses, after some further treatment (polishing) in order to meet certain quality criteria. For example, it can be used to water the parks of a city, or some crops, as well as for cooling purposes in factories. In addition, the sludge produced during the wastewater treatment can be used as a fertilizer or fuel.

Do you know…


  1. … that wastewater treatment is mandatory for all municipalities in many countries of the Mediterranean? What about your country?
  2. … that many large industries and enterprises (e.g. hotels) throughout the Mediterranean are obliged to process their wastewater at their own treatment facilities?
  3.  … which Mediterranean country uses 80% of the recovered wastewater for irrigation in agriculture? We give you an hint: while this country is almost arid, it has developed such water recovery technology that gradually turns the desert into arable land; it actually exports a lot of vegetables to Europe and elsewhere!

Play & learn

Drag and drop the processes of the wastewater treatment with their proper place in the image. Before you start make sure you have read the previous Water Readings!

 wastewater-treatment quiz-hotspot
1
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10
  • 1 1 intake
  • 2 2 screening
  • 3 3 primary settlement
  • 4 4 secondary/biological treatment
  • 5 5 sludge treatment (digestion)
  • 6 6 secondary settlement
  • 7 7 tertiary settlement
  • 8 8 disinfection
  • 9 9 irrigation with the recovered water
  • 10 10 discharge of the recovered water to the sea

Group activity

Visit to the wastewater treatment plant

Organise a visit to the wastewater treatment plant of your area and collect information about the processes included.

Before your visit:


Observe on the map the area where the wastewater plant is located. Why do you think the particular location was chosen?

During your visit:


  1. Keep notes  and take photos of all the stages.
  2. Do you find any differences between this plant and the general one described in the Water Readings? Is there any step ‘missing’ or ‘new’?
  3. Ask the staff where the recovered water ends up e.g. to the sea or a river  or is it used for a certain purpose (if yes, which one)?
  4. Try to collect information about the sludge produced as well, if it is used somehow.

Water meter

Provided that all quality regulations are followed during the wastewater treatment, how much do you agree with using the recovered water...
not at all a little so and so very very much
for watering the parks and golf courses (if all regulations are followed)

to fertilize tree crops e.g. orange trees, olives (if all regulations are followed)

for watering the school yard (if all regulations are followed)

for toilet flushing (if all regulations are followed)

for cooling purposes in the factories (if all regulations are followed)

Water meter

I liked this activity .. .

Way forward

Dive in…

Rainwater harvesting   

Do you know about grey water?   

Desalination

if you want know about other non-conventional water resources.

Go back to the homepage!

The water basins

Water in the city

Desalination

Do you know about grey water?

Rainwater harvesting

Greywater recycling in practice

Wastewater treatment

The water cycle in a bowl!

Waterworks through time

Climate change challenges

Rainwater Harvesting Systems in practice

Reduce-Reuse-Recycle

Water resources

Where do I begin?

The water basins

In this activity we learn what a water drainage basin is and why it is important for the experts to study it.

Continue!

Water in the city

What is the "urban water cycle"? Which are the important aspects of water management within a city environment?

Continue!

Desalination

Let's find out how sea and brakish water can become a freshwater resource!

Continue!

Do you know about grey water?

Let's find out what "greywater” is and how we can use it!

Continue!

Rainwater harvesting

Can we collect rainwater? And how to use it? Let's find out!

Continue!

Greywater recycling in practice

How a grewywater system is installed? Let's find out!

Continue!

Wastewater treatment

In this activity we are informed about how wastewater is treated and what we can do with the treated wastewater.

Continue!

The water cycle in a bowl!

Let's travel within the water cycle!

Continue!

Waterworks through time

Let's discover the story behind the historic fountains, cisterns and aqueducts of our town!

Continue!

Climate change challenges

Time to discuss about climate change, causes and impact and how we can cope with it.

Continue!

Rainwater Harvesting Systems in practice

What are the various types of rainwater harvesting systems? Let's find out more about them!

Continue!

Reduce-Reuse-Recycle

What is my water footprint and how can I reduce it?

Continue!

Water resources

Discovering the water resources of our region.

Continue!

Where do I begin?

Let's see why it is important to know about water in our region.

Continue!