Wastewater treatment…
a simple process, right?

Without suitable treatment, the wastewater we produce every day would damage the water environment and create public health problems. This is far from a simple process but it is a very clever one.

used for Screening

Our liquid storage tanks form part of an important process of screening the wastewater, during necessary maintenance works. First, large objects that may cause a blockage are removed (things that really shouldn’t have been put down the drain, such as nappies, wet wipes, and even sometimes things like bricks, bottles and rags). Special equipment is then used to filter out grit, which often washes into the sewer with wastewater.

Did you know?
Every year, 65,000 blockages are caused by people putting the wrong things down the drain… Oops!

Primary treatment tanks

Wastewater is then separated from human waste by putting it into large settlement tanks where solids sink to the bottom. This is called ‘sludge’. This sludge is separated and pumped away for further treatment. The clean water is then ready for the next stage of the process.

Did you know?
Waste sludge is used to generate renewable energy, which powers Sewage Treatment Processing sites? In 2019, Thames Water alone self-generated over 23% of their electricity needs, the equivalent of £37 million in electricity.

Secondary treatment tanks (Aeration lanes)

Once the larger, visible bits of sludge are removed, it’s then important to remove the smaller and sometimes invisible organisms as well. Air is pumped into the water into rectangular tanks called ‘aeration lanes’. This is a process that allows the good bacteria to break down and eat the harmful bacteria. The goodbacteria continues to eat the nasty bacteria until the nasty bugs have gone.

Did you know?
Every day in the UK about 347,000 kilometers of sewers collect over 11 billion litres of wastewater. This water is treated at about 9,000 sewage treatment works before the cleaned, treated effluent is discharged to inland waters, estuaries, and the sea.

Final settlement tanks

The treated water then passes through a final settlement tank. This is where the good bacteria sink to the bottom to form more sludge. This sludge is recycled into secondary treatment tanks. The clean water isonce more filtered slowly through a bed of sand, catching any remaining particles.

Generating power

The collected sludge is treated and put to good use. It is recycled for farmers’ agricultural fertiliser and used to generate energy.

Anaerobic digestion is a process that heats up the sludge to high temperatures, which allows the bacteriato break down the waste. This creates biogas, creating heat which can be turned into electricity. Thermal destruction is the process of drying the sludge into blocks called ‘cake’, again being heated and turned into electricity.

Did you know?
Sewage Treatment Works have been generating electricity from waste for over 50 years.

Returning water to rivers

Once the wastewater is clean, it can be safely returned to local rivers and streams. This process is strictly regulated by The Environment Agency to make sure it meets their high-quality standards. The ‘sludge cake’ remaining after energy production is also used as fertiliser for farmers.
For further information on how to reduce liquid storage tank footprint, liquid storage tanks for screening or environmental storage tanks, please call the team on 01264 243 116.
The Sewage treatment Process – Thames Water.
© Crown Copyright DEFRA Sewage treatment in the UK

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