Have you ever stopped to consider where the water from your toilet and sinks goes to? It was not long ago that almost every home had a cesspit to collect all household waste, in fact, in many remote communities’ cesspits are still the norm.
There are many myths surrounding our drainage and although the Roman’s did indeed do much for the country, they did not build the foul drainage channels that are still present in the streets below London.
What is Sewerage?
According to SewerHistory.org, the first sewers in London were simply open ditches that drained towards the Thames. The word sewer actually derives from Old French seuwiere, which means to remove water. In modern English, sewerage describers the sewer network and sewage is the waste water within the network.
Modern sewers are kept separate from rainwater drainage and remain fully enclosed between house and treatment work. However, in many cities, including London, parts of the sewerage network are still connected to rainwater runoff, and this is a common cause of sewage overspills.
The History and advances of sewage treatment works
It wasn’t until the late 1850’s that London began to recognize the importance of a fully functioning sewage system. Before this time diseases such as typhoid and cholera claimed thousands of lives as a result of untreated sewerage and un-sanitised water. The Thames resembled an open sewer despite the river supplying the source for the cities drinking water!
The Great Stink of 1858 was The Thames become almost clogged with foul waste and this prompted the government to take action to improve the city’s outdated sewage systems.
In 1859, engineer Joseph Bazalgette began work on the first intercepting underground sewers. This project was not completed until 1868 and it still serves as a foundation in our sewer systems today.
Due to ongoing advances and improvements over the years the sewage treatment works have excelled in the purification and cleaning of waste water. The Thames that was once claimed bare and inhabitable for fish from as recent as the 1950s is now thriving with over a hundred species of fish occupying the river. This is because the water supply is now clean enough to inhabit freshwater ecosystems.
The steps in treating waste water
When used water is expelled through toilet flushing or sink drainage the waste water must go through a cleaning process to transform the water back to its sanitary state so it is acceptable to be re-introduced back into the rivers.
As the used water has become contaminated and unfit for human use it is transferred through the draining system which then connects to underground pipes leading to the sewage system. This sewage water will then be transmitted to the sewage treatment works in preparation for the first stage of the multi cleaning process.
Multi Cleaning Process
- The water will go through a screening process where all items that are actually unsuitable to be flushed such as rags and paper along with other items that are considered non-biodegradable are removed from the water supply. A grit extractor is also used to remove road grit and other inorganic matter
- A primary treatment is then required to remove solid waste from the water this is done by putting the sewage in large settlement tanks. The primary sludge is collected and lays at the bottom of the tank and therefore the waste water on top has a greatly reduced amount of solids than before the primary treatment. The sludge is then pumped away for disposal, further treatment and can be resourced and used as an energy generator and turned into electricity or alternatively can be used as an organic fertilizer.
- Secondary treatment – A biological treatment known as the activated sludge treatment is implemented using oxygen which is pumped into the water providing an environment for good bacteria cells so they can consume the sewage and break down the unwanted microorganisms within the water
- Final treatment – The water containing the good bacteria cells introduced during the secondary treatment are removed again using another settlement tank where the bacteria cells will form a sludge in a similar process to the primary treatment stage.
- If further treatment is required to sanitize the water it will be filtered through a bed of sand which will remove any impurities remaining within the water.
Following the waste water treatment process the now clean water is then put back into rivers and reservoirs and may eventually become a suitable water supply. Current technology does not allow sewage to be converted to drinking water, but researchers in America are working on this.
Future plans for expansion of sewage treatment works and modernization of sewers is likely to further accommodate the Greater London’s population growth, although London’s “super sewer” is probably still several years away.