With the world's population growing, there's more and more waste being produced each year. All this week Nel's been looking into the inventive solutions people have been coming up with to put what we throw away to good use.
Back in the Victorian times, raw sewage went straight into the streets, the sea, and rivers. Not only did that create a huge stink but it caused a lot of diseases.
The answer was to put in a new underground sewer system.
Billions of litres of sewage is treated around the UK every day but not all of it is going to waste.
Find out more: How London's Great Stink led to today's sewers