The sewerage process
The sewerage system simply wasn’t designed to handle personal products (known as Sanitary Related Debris – SRD), most of which contain plastic or other insoluble materials.
When flushed down the toilet they can create blockages in pipes which are, on average, only 15cm in diameter. In fact it has been estimated that three-quarters of all blockages contain disposable items.
These blockages reduce the efficiency of the waste system and in times of flooding can also mean that SRD reaches our rivers, canals and seas.
How does this waste escape the system?
Sewage treatment process diagram (pop-up window)
There are a number of ways that personal products put down the toilet can 'escape' from sewage systems and sewage treatment works and find their way into rivers and the sea, possibly ending up on beaches.
During normal weather conditions, items such as tampons, cotton buds and condoms, which are flushed down the toilet, will remain in the sewers and eventually end up at a sewage treatment plant.
Personal products escape the screens
One of the treatment processes at the beginning of sewage works is called screening. Screens come in a range of sizes and shapes and their main function is to remove solid matter.
Many works have upgraded their screens and will have installed a 6mm or even 3mm bar or mesh. 6mm bar screens will remove any objects that exceed 6mm in one dimension. A 3mm mesh screen will remove any objects that exceed 3mm in two dimensions.
It is therefore possible that items such as panty liners will be able to slip through a bar screen (although a mesh screen would catch them).
Condoms and cotton buds can be particularly difficult to remove because they can squeeze through virtually anything.
If the items that get through the screens then carry on through the rest of the treatment works, they can end up in the wastewater flowing into rivers or the sea and be washed onto beaches.
Combined sewer overflows
In periods of high rainfall, items can escape from the sewers through what are called Combined Sewer Overflows (CSOs). These overflows are designed to prevent sewers flooding (which can lead to houses flooding or sewage escaping onto the streets).
When it is raining heavily, sewage diluted by rainfall, but otherwise untreated, is released from the CSOs directly into rivers. Items that have been flushed down toilets can also escape directly into rivers. Currently there is a huge programme of investment to upgrade CSOs to reduce the frequency with which they discharge to rivers and to improve the screens on the overflows.
Combined sewer overflows - Water UK briefing
The best way to prevent SRD ending up in rivers or on the beach is to throw personal products in the bin instead of down the toilet!
About the campaign
What's the problem?
Bag It & Bin It home
Think before you flushHand wipes flushed down the toilet are causing an increase in blocked sewers, with very unhappy consequences...
Campaign logoBag It & Bin It logos are available here. Please feel free to use these to create your own signs or posters.
