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What Happens to Sewage After You Flush?

What Happens to Sewage After You Flush?


The famous line in Finding Nemo, ‘all drains lead to the ocean’ has been a much-used quote, but is it an accurate statement? To answer that question, we need to look at the different types of waste leaving our properties, the treatment it requires, and where it ends up.

‘Wastewater’ is any leftover water that is flushed through your pipes from washing your clothes, flushing the toilet, or draining the sink. All wastewater is referred to as sewage (even though it’s not all human excrement).

Where Does Waste Water Go?

All the waste water from your property travels the same route through the sewer pipes whether it comes from a domestic or commercial property. All wastewater is flushed into the sewer system. The pipes from your home join up with the larger pipe on your street and then flow into even bigger sewer pipes (some are bigger than a London bus!). These sewer pipes transport wastewater to the treatment plant.

Why Does Sewage Need to be Treated?

Several decades ago, the way sewage was dealt with was very simple: it was thrown onto the streets. However, this caused significantly high pollution levels and was a dangerous health concern for many people.

Sewage is eventually sent into our rivers and oceans, so it is essential it is properly treated to avoid posing a health risk to humans and aquatic life. Treating sewage helps get rid of dangerous germs and remove items accidentally flushed into the pipes, such as plastic wrappers, cosmetics, and cigarette butts.

Treating sewage can be a time-consuming process and often takes a couple of days. However, it can be faster if miscellaneous items are not flushed down the toilet, only to be painstakingly fished out during the treatment stage.

There are Two Classes of Sewage Treatment

Sewage treatment really comes down to two different classes; sanitary sewers and storm sewers. Storm sewers tend to be less polluted because they only carry materials that are washed away from the surface during rainy or stormy weather. However, sanitary sewers contain human waste, dirty water from washing machines and sinks, and many other unpleasant substances. So, it is extremely important this wastewater is properly treated before being released back into our rivers and oceans.

The wastewater that leaves your property to be treated must pass through a variety of treatment methods and pass water-qualify testing before being sent back into our rivers and oceans. The treatment process for sewage happens in numerous stages, these are outlined below.

First, You Flush the Toilet

When you flush your toilet, the first thing it does is wash all the sewage into the sewer pipes under your house. The sewage travels along these pipes, joining larger pipes under the street and flowing all the way to the nearest treatment plant.

The Pre-Treatment Stage

The very first stage of treatment after you’ve flushed involves screening the sewage for the removal of large items, such as rags, wet-wipes, sanitary items, and other debris pieces. To remove all these items, the sewage is essentially sent through a large sieve. All the things that shouldn’t be put down the drain get taken out during this process.

Primary Stage of Sewage Treatment

The sewage is sent through several series of filters at the treatment plant to filter out the large pieces, separating the liquid and the sludge so that the solid leftovers can be taken to landfill. During this stage, large scrapers move around tanks, pushing the collected sludge into the middle where it can be easily removed. The water then moves to the top for the next part of the process.

The Second Stage of Sewage Treatment

In this stage of sewage treatment, nasty odours and bacteria are removed from the water and sludge through a process called aeration, where oxygen is introduced to help break down bacteria and organic matter. At the end of this thorough process, the sewage is usually regarded as safe for release back into a natural watercourse. However, it is common for the sewage to go through a final treatment to ensure all the dangerous bacteria has been removed.

The Final Treatment Stage

This final stage involves further aeration, followed by an oxygen-depleted stage to help reduce nitrogen and phosphorous to make the sewage clean and ready for release back into the waterways. Depending on the treatment plant and the methods they use, this stage can also involve using a UV light and chlorination treatment to remove any bacteria that remains.

Waste Ends Up in the Ocean

Although there are some companies that collect energy from wastewater during the treatment process, generally our treated wastewater ends up back in the oceans. However, it is only released once it has been strictly regulated and approved by the Environment Agency to ensure it meets all the high-quality standards.

And if you’re worried about the effect on marine life, there’s no need to be because incredibly, the waste water that is returned to the oceans is so well-treated that it actually improves water quality and keeps fish and aquatic life healthy. And eventually, this water will form clouds, fall back down as rain and potentially find its way back into your home’s waterworks where it will be treated before coming out of your kitchen tap!

Now, when you flush the toilet you know a little bit more about where your waste goes and where it eventually ends up!

Let’s finish on a fun fact: London tap water has been through 7 people before it reaches you!