The sewerage system simply wasn’t designed to handle personal products, most of which contain plastic or other insoluble materials. 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 and seas.

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 treatment plant.

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!