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The wastewater treatment process

We recycle wastewater from almost two million homes before returning it to rivers and the sea. Learn more about our wastewater treatment process.

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Where does wastewater come from?

Wastewater comes from water used in homes and businesses and from rain falling on roofs or the roads and pavements. 

Whether it's from flushing the loo, washing dishes in a busy restaurant or from a nearby farm or factory, it all follows the same route.

It makes it way down pipes and drains into our underground sewer network. Sewers carry the water, now called sewage, to one of our wastewater treatment works.

As well as wastewater, other items often find their way into our sewer network. Fat, oil and grease poured down sinks or unflushable items, such as wet wipes and sanitary products all cause blockages and increase the risk of flooding.

 

The wastewater treatment process

Wastewater treatment sites move the water through a specific process to clean and purify it before it’s returned to the environment. Learn more about this fascinating process.

graphic illustrating the wastewater treatment process
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Graphic showing the screening step of the wastewater treatment process

Screening

As wastewater enters into the treatment plant it goes through large screens. These filter out large objects including sticks, rubbish, and anything else non-biodegradable.

wastewater treatment works final treatment process

Primary treatment

Next, the wastewater flows into large settling tanks. Here, gravity works its magic. Solids will settle at the bottom, forming a layer of sludge. Oils and grease float to the top, forming scum. Both sludge and scum are then removed for further processing, leaving relatively clean water in the middle.

Graphic showing the secondary treatment in the wastewater process

Secondary treatment

In the next phase, the wastewater moves into big tanks called aeration tanks. Air is continually pumped into these tanks, providing oxygen that breaks down any invisible dirt, effectively cleaning the water. The water then flows into a secondary settling tank, where the heavy microorganisms settle out, leaving even cleaner water.

calm river surrounded by greenery

Final treatment

The final cleaning stage then removes any final impurities. This could include additional filtration, disinfection with chlorine or UV light, and sometimes nutrient removal to prevent water pollution when the treated water is released. The result is water that’s safe to return to rivers, lakes, and oceans.

graphic illustrating sludge treatment in the wastewater process

Sludge treatment

Remember the sludge from the first stage of the treatment? This goes on its own adventure. Large tanks known as digesters, use bacteria to break sludge down – this produces methane gas, which we collect and use to generate electricity. The solid materials we end up with are called biosolids. These can then be used by farmers as fertilisers.

graphic illustrating the wastewater treatment process
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Graphic showing the screening step of the wastewater treatment process

Screening

As wastewater enters into the treatment plant it goes through large screens. These filter out large objects including sticks, rubbish, and anything else non-biodegradable.

wastewater treatment works final treatment process

Primary treatment

Next, the wastewater flows into large settling tanks. Here, gravity works its magic. Solids will settle at the bottom, forming a layer of sludge. Oils and grease float to the top, forming scum. Both sludge and scum are then removed for further processing, leaving relatively clean water in the middle.

Graphic showing the secondary treatment in the wastewater process

Secondary treatment

In the next phase, the wastewater moves into big tanks called aeration tanks. Air is continually pumped into these tanks, providing oxygen that breaks down any invisible dirt, effectively cleaning the water. The water then flows into a secondary settling tank, where the heavy microorganisms settle out, leaving even cleaner water.

calm river surrounded by greenery

Final treatment

The final cleaning stage then removes any final impurities. This could include additional filtration, disinfection with chlorine or UV light, and sometimes nutrient removal to prevent water pollution when the treated water is released. The result is water that’s safe to return to rivers, lakes, and oceans.

graphic illustrating sludge treatment in the wastewater process

Sludge treatment

Remember the sludge from the first stage of the treatment? This goes on its own adventure. Large tanks known as digesters, use bacteria to break sludge down – this produces methane gas, which we collect and use to generate electricity. The solid materials we end up with are called biosolids. These can then be used by farmers as fertilisers.

Re-joining the water cycle

After all of these treatment steps, the clean water is finally ready to re-join the environment. It’s released into nearby rivers, lakes, or oceans, where it then rejoins the natural water cycle. The water you're using today would have once been rain, groundwater, and even river water. 

Wastewater treatment plants play a crucial role in maintaining public health and protecting the environment, ensuring that our water resources remain safe and sustainable for future generations. 

It's worth remembering that water is a finite resource and so we all need to do our bit to limit the amount we use. 

Your wastewater

Each day we treat 1,522 million litres of wastewater, roughly the same amount of water to flush the toilet over 187,500 times, but did you know......

An illustrated outline of a toilet

4.7 million

We treat wastewater from over 4.7 million customers.

An illustrated outline of a water drop with waves in it

363

We have 363 wastewater treatment works and 3,519 pumping stations across our region

An illustrated outline of a water pipe

40,058km

Your wastewater arrives at the wastewater treatment works through a 40,058km long sewer network.

Your wastewater

Each day we treat 1,522 million litres of wastewater, roughly the same amount of water to flush the toilet over 187,500 times, but did you know......

An illustrated outline of a toilet

4.7 million

We treat wastewater from over 4.7 million customers.

An illustrated outline of a water drop with waves in it

363

We have 363 wastewater treatment works and 3,519 pumping stations across our region

An illustrated outline of a water pipe

40,058km

Your wastewater arrives at the wastewater treatment works through a 40,058km long sewer network.