UN World Toilet Day is upon us yet again! This year’s theme focuses on wastewater, and the aim by 2030, as part of the Sustainable Development Goals, is to reach everyone with sanitation, and halve the proportion of untreated wastewater, as well as to increase recycling and safe reuse. For this to be achieved, all human waste from the toilet needs to be contained, transported, treated and disposed of in a safe and sustainable way. For billions of people around the world, sanitation systems either don’t exist or are ineffective, which means human waste gets out and fatal diseases spread, and progress in health and child survival is seriously undermined.
The 2017 World Toilet Day theme – wastewater
The call of nature is one thing that unites us all, but depending on where we live, it’s not always possible to dispose of bodily waste in a safe and responsible manner. In order to achieve the Sustainable Development Goals, everyone’s waste from the toilet needs to take a four step journey:
- Containment – waste must be deposited into a hygienic toilet, and then stored in a sealed tank or pit. It must not come into human contact.
- Transport – pipes need to move the waste to the treatment stage.
- Treatment – the waste then needs to be processed into treated wastewater and waste products that can be safely returned to the environment.
- Disposal or reuse – waste that’s been safely treated can then be used to generate energy or as a fertilizer for food production.
What happens after you flush the toilet?
In the UK, we are lucky enough to have access to a toilet in our homes, workplace, schools and hospitals, and it’s something that the majority of us take for granted. But the stark reality is that 2.3 billion people across the globe are still without access to a safe, hygienic toilet. A toilet is something they rarely, if ever, get to use.
So, for those who do have access to this basic luxury, have you ever wondered what happens after you flush the toilet? We know it’s not something we like to think about, as most of us just flush and forget! But there’s actually an incredible journey your bodily waste goes on once you’ve flushed the loo.
Into the sewers
Once you’ve flushed the toilet, the waste leaves your home and enters into the sewer system. It then joins other wastewater and is carried to a sewage treatment plant.
The wastewater is then screened to remove large objects, which is usually stuff that shouldn’t be there such as nappies. Sand and grit is also filtered out, while oil and grease is skimmed off the surface of the wastewater.
The primary treatment stage
Now the proper treatment of the wastewater can begin. The filtered wastewater is stored into settlement tanks, and is gently mixed to add oxygen and to encourage small particles of contaminant to form bigger clumps, which are called flocs. Once the flocs are heavy and large enough, they fall to the bottom of the tank, where sludge is formed. Scrapers push this sludge to the middle of the tank, and it is then pumped away for further treatment.
The secondary treatment stage
Although still brown, the slightly clean water then goes through a secondary treatment phase. Certain bacteria is added, which feeds on the dangerous pathogens that are present in the faeces-filled wastewater. As the bacteria relies on oxygen, air is added so they can multiply. Once the pathogens are broken down, the bacteria has done their job. Now, the water can be moved to another tank where it is filtered and disinfected, and can be pumped back into our homes.
But what happens to the sludge?
Once the sludge has left the settlement tanks, it is dried using centrifuges – these spin incredibly fast, forcing the solids in one direction and the liquid in the other. Once the amount of liquid has reduced, the sludge enters a thermal hydrolysis plant, where it is boiled under high pressure, before it is quickly decompressed.
Once this phase of the treatment process has been completed, the extremely hot sludge is cooled. Bacteria is then added, which break down the sludge and produce methane as a by-product. This gas can be used to generate electricity and heat.
The now sterile sludge is dried, most of which goes to the agricultural industry, where it is used as a fertilizer.
How toilets could produce electricity, yes really!
Without toilets and the sewer system, cities would become unlivable in no time at all. Just take a look at these shocking figures to give you an idea of the amount of bodily waste that London sewers alone have to deal with.
London sewers manage a staggering 1.25 billion kilograms of faeces, which is equivalent to the weight of 2,174 Airbus A380 jumbo jets, and around 6 billion litres of urine, enough to fill 2,400 Olympic sized swimming pools! Source Forbes.com
Here’s some examples of how electricity has been produced from human waste.
Scientists from the University of Bath, Queen Mary University of London and the Bristol Robotics Laboratory, developed a fuel cell that can be powered by urine, but this on its own didn’t produce a huge amount of power. So, they found a way to increase the power output by ten times, by using a catalyst made from glucose and ovalbumin (a protein found in egg white).
In 2015, the scientists teamed up with Oxfam to demonstrate a prototype of the fuel cell. This lead on to a urine powered toilet being built on the campus of the University of the West of England, which proved that the electric produced by the cell was enough to power the lights in the toilet cubicle. This innovative technology could make a significant difference to communities that live off-grid.
Grand Junction, Colorado, USA – human waste is transformed into renewable natural gas, which is used to fuel road sweepers and rubbish trucks.
Stockholm, Sweden – increasing numbers of buses, taxis and cars run on biogas that’s been extracted from the treatment of food waste and sewage.
Bristol, UK – the No.2 bus is powered by gas rich in methane that’s been extracted from processed human faeces! The bus fuels up at the local sewage plant, and the gas is then compressed into a liquid before being injected into the engine. The bus can travel an impressive 190 miles on a full tank, which is equivalent to the waste produced by five people in year.
So, next time you’re sat on the toilet, give some thought to how your bodily waste can be used to help the protect environment.
More stories on human waste and what we need to do with it
Hi, I’m Liz, an interiors blogger. My main focus area is the bathroom, where I aim to inspire anyone who’s planning and designing a new bathroom – you’ll find plenty of tips, how-to guides and a wealth of ideas!