The sewerage system simply wasn’t designed to handle
personal products, most of which contain plastic or other insoluble
When flushed down the toilet they can create blockages in the pipes
which are on average only six inches in diameter.
In fact it has been
estimated that over two thirds of all blockages contain disposable
items. These blockages reduce the efficiency of
the system and add to the problem of sewage flowing into our rivers
But how does SRD escape the system?
There are a number of ways that items can 'escape' from sewage systems
and sewage treatment works, finding their way into rivers and the sea
and 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
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 been upgrading
their screens and will have installed 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.
Click the image to open a window with a larger diagram.
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 will end up being washed onto beaches.
In periods of high rain, 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 river and to improve the screens on the overflows.
However, the best way to prevent SRD ending up in rivers or on the
beach is to throw items in the bin instead of in the toilet!