London’s iconic red double-decker buses will soon run on biofuel derived from coffee waste, if entrepreneur Arthur Kay has anything to do with it. Kay run Biobean, a start-up which gathers coffee waste from chain stores and converts it into liquid fuel.

"We are going through a period of energy divergence where we are moving from a fossil-fuel based society to one that is increasingly diversified. Bio-fuel will be crucial to that," said Kay, noting that, people consume 500,000 tonnes of coffee each year in the UK, which could create enough biofuel to power a city such as Manchester. Heavy traffic and tall buildings contribute to the poor air quality in London, and Kay hopes that his fuel will go some way to reducing the problem.

The exact method used by Biobean to extract the biofuel is patented but involves evaporating the grounds, a process known as hexane extraction. The leftover matter is compressed into logs and pellets which can be used as a wood alternative in fires.