Sean Sprague/Alamy
Nature sanitises around 38 million tonnes of human waste per year – the equivalent of around £3.2-billion-worth of commercial water treatment.
Alison Parker at Cranfield University in the UK and colleagues looked at 48 cities in Africa, Asia, North America and South America. They analysed how much human waste is produced and where it ends up by reviewing existing data from interviews, observations and direct field measurements.
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The team looked at waste management not connected to sewers. This included pit latrines and septic tanks where waste is primarily contained on-site – in a hole below the ground for pit latrines and in box tanks for septic tanks.