Any water that’s used and then discarded is classed as ‘wastewater’. This can be the straining’s from your saucepan of pasta, the water you send down the bowl every time you flush the toilet, or the millions of gallons used in power stations every day to generate electricity.
Where does wastewater come from?
Both industrial and domestic water ends up in the same place (unless it requires specialist treatment such as water used in some power plants or chemical factories), and essentially, it all goes through the same treatment process. Any water that has already been used for a process, whether that’s on a farm, in your home, or in any business, is classed as wastewater.
Before it can be returned to the environment via rivers or the sea, it’s our responsibility to make sure it’s as clean as it can be. So it’s put through a series of treatment processes to remove as much of the unwanted waste products as possible.
The wastewater treatment process
Wastewater is sent down the sewage network (or delivered in tankers, if your home has a septic tank rather than a sewage connection) and arrives at your local water treatment plant.
These plants are dotted around the country and are operated by each water company. When the water arrives at the plant, the first stage it goes through is the ‘Screening stage’.
Here, the water passes through a series of mesh filters, each one with smaller holes than the last. This screening process filters out large bits of detritus, such as leaves, plants, and more unpleasant matter that shouldn’t have really found its way into the wastewater system in the first place!
After the water has passed through these screens a chemically active form of oxygen is introduced (known as pre-ozonation), which destroys the microscopic organisms and any metals that have made it through the screens.
A chemical is then added to the water to act as a binding agent, which turns the particles and dissolved metals into a sludge. This sludge then settles to the bottom of (appropriately named) settlement tanks, where it is syphoned off. This is known as ‘clarification’.
The result is an (almost) clean water by-product, which is then allowed to filter through beds of sand and gravel, which remove any last particles. The filtered water is now colourless and can go on to further tanks that use carbon filters to remove any pesticide residue. If the water is too acidic or alkaline, pH correction processes restore it to a neutral pH.
If the wastewater has come through lead pipes, (which is the case in some parts of the UK where some sewage systems still have lead piping), then phosphate is added to counteract any lead that may be present in the water.
Finally, the water is chlorinated and passed through a strong ultraviolet light to destroy any remaining microbes, before being allowed to return back into the environment.
Does waste water go back into the drinking supply?
Eventually, recycled wastewater may well find its way back into reservoirs via water courses and rivers. However, wastewater is more often used for commercial and agricultural operations, rather than replenishing the domestic supply.
Why is the process so complex?
Our modern world tends to contaminate wastewater with some very difficult-to-deal-with pollutants. From complex chemicals to micro-plastics, all of these contaminants need to be dealt with before the water is returned to the environment.
Unfortunately, some of these by-products of the modern world are very difficult to deal with, so wastewater has to go through a series of rigid processes to ensure as many of these pollutants are removed as possible.
There are still those that get through, though, and that is why recycled water is used for commercial processes, rather than for drinking water.
We have a responsibility to ensure that the water we put back into the environment is as clean as possible and that our waste and by-products do not go on to enter the food chain, poison our soil, or pollute our seas.