How is wastewater treated?

It’s easy not to think about where our wastewater goes; the process that goes into treating it and returning it into circulation is lengthy and complex. First, wastewater will go down the drain from your toilet bowl or sink and into a pipe that connects into a large sewer pipe under the road. Each sewer is joined to a network that links to a local sewage treatment works.

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Unwanted nasties in the water

When the wastewater arrives at the sewage treatment works, it will be screened to remove items that should not have been flushed away. These include problems such as face wipes, cotton buds, nappies and sanitary towels. However, wastewater treatment workers will also find items as diverse as children’s toys, rags and bottles within the mix. Special equipment is also used to remove the grit, which can accrue in large quantities.

The waterwater then goes to primary treatment stage to remove human waste by separating it into large settlement tanks. The sludge is then pumped away to be treated. The remaining water will pass over the tank and move on to secondary treatment. At this stage, any smaller bits of sludge and the water will be treated to remove any bugs that may be living in it.

The use of good bacteria

At bigger treatment works, the water will pass into aeration tanks where air is added to the water. This encourages the growth of good bacteria, which will break down unwanted bacteria by eating them. Processes like this can also be found in some domestic homes to treat water at the source. Find out more about inline static mixers at sites like

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The final treatment stage sees the treated water passing through a settlement tank. Here, the good bacteria will sink, forming more sludge. This will go on for sludge treatment or be recycled into the earlier treatment stage. The resulting water is clean and passes over a wall at the tank’s top.

At this stage, additional treatments may be carried out if the treated water is returning to a sensitive site, such as a river with protected wildlife. To do this, the water filters through a sandbed, which attracts any final remaining particles and removes them. It is then returned to rivers, where the cycle begins once again and our water continues to be used, cleaned and recycled.

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