Live Updates arrow
Account Login
search-button
menu-button menu-button-close
search-icon
Close
Accessibility tools

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.

background

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.

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

The water treatment process

Water is essential to every aspect of our lives. Here you can learn more about the water cycle and our water treatment process before it goes into supply.

How we treat drinking water Flow and spill reporting

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
1
2
3
4
5
6
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 remaining impurities through additional filtration, disinfection with chlorine or UV light technology. Potentially harmful nutrients, like nitrate and phosphorus, are also removed so that wastewater returning to the environment is much cleaner and doesn't disrupt the ecosystems of our rivers, lakes, and seas.

graphic illustrating sludge treatment in the wastewater process

Sludge treatment

Remember the sludge from the earlier stage of the process? 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 treatment of sludge is call bioresources and the solid materials we end up with are called biosolids. These can then be used by farmers as fertilisers.

Bioresources
Landscape shot of a river

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 re-joins the natural water cycle. The water you're using today would have once been rain, groundwater, and even river water.

graphic illustrating the wastewater treatment process
hotspot-icon
hotspot-icon
hotspot-icon
hotspot-icon
hotspot-icon
hotspot-icon
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 remaining impurities through additional filtration, disinfection with chlorine or UV light technology. Potentially harmful nutrients, like nitrate and phosphorus, are also removed so that wastewater returning to the environment is much cleaner and doesn't disrupt the ecosystems of our rivers, lakes, and seas.

graphic illustrating sludge treatment in the wastewater process

Sludge treatment

Remember the sludge from the earlier stage of the process? 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 treatment of sludge is call bioresources and the solid materials we end up with are called biosolids. These can then be used by farmers as fertilisers.

Bioresources
Landscape shot of a river

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 re-joins the natural water cycle. The water you're using today would have once been rain, groundwater, and even river water.

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.

The challenges with our coastal treatment sites

We operate in one of the most unique and challenging regions in the country, with over 40% of our customers living along the coast—more than any other UK water company.

That means many of our treatment sites are right by the sea—where it’s 43% more expensive to operate due to corrosion, planning constraints and tighter environmental standards.

This video explains how we’re tackling these challenges head-on, upgrading our wastewater treatments sites and investing in our future plans.  

wastewater treatment works final treatment process
Play The challenges with our coastal treatment sites Video