Britain's first "number two" bus will take to the road today - powered entirely by human and food waste.
Bio-Bus, a 40-seater shuttle service between Bath and Bristol Airport, can travel up to 186 miles on one tank of gas.
The gas is generated through the treatment of sewage and food waste that is unfit for human consumption.
Engineers believe Bio-Bus could provide a sustainable way of fuelling public transport while improving urban air quality.
The gas produces fewer emissions than traditional diesel engines and is both renewable and sustainable.
It is generated at Bristol sewage treatment works, which is run by GENeco, a subsidiary of Wessex Water.
This week, the company also became the first in the UK to inject gas generated from human and food waste into the national gas grid network.
Mohammed Saddiq, general manager of GENeco, said: "Through treating sewage and food that's unfit for human consumption we're able to produce enough biomethane to provide a significant supply of gas to the national gas network that's capable of powering almost 8,500 homes as well as fuelling the Bio-Bus.
"Gas-powered vehicles have an important role to play in improving air quality in UK cities, but the Bio-Bus goes further than that and is actually powered by people living in the local area, including quite possibly those on the bus itself.
"Using biomethane in this way not only provides a sustainable fuel, but also reduces our reliance on traditional fossil fuels."
The Bio-Bus can travel up to 186 miles on a full tank of gas, which takes the annual waste of around five people to produce.
The annual waste generated from one bus load of passengers would provide enough power for a return journey from Land's End to John O'Groats.
The first passengers to be welcomed aboard the Bio-Bus will be visitors to the UK commuting from Bristol Airport to the historic city of Bath.
Bath Bus Company, which is operating the service, will use the Bio-Bus for its rapidly growing A4 service from Bath to Bristol Airport via South Bristol.
Collin Field, engineering director at Bath Bus Company, said: "Up to 10,000 passengers are expected to travel on the A4 service in a month, which is available not only for airport travel, but also local journeys along the route through Saltford, Keynsham, Brislington, Knowle and Hengrove.
"With so much attention being directed towards improving air quality generally, the public reaction to the appearance of this bus on a service between a World Heritage City and an airport will further focus on the potential for this particular fuel."
Mr Field said the Bio-Bus was being launched at a very "appropriate" time, as the city of Bristol would become the European Green Capital in 2015.
Bristol sewage treatment works processes around 75 million cubic metres of sewage waste and 35,000 tonnes of food waste collected from households, supermarkets and food manufacturers each year.
A total of 17 million cubic metres of biomethane - the equivalent of meeting the power needs of 8,300 homes - is generated each year at the plant through a process known as anaerobic digestion.
Charlotte Morton, chief executive of the Anaerobic Digestion and Bioresources Association, added: "A home generated green gas, biomethane is capable of replacing around 10% of the UK's domestic gas needs and is currently the only renewable fuel available for HGVs.
"The bus also clearly shows that human poo and our waste food are valuable resources.
"Food which is unsuitable for human consumption should be separately collected and recycled through anaerobic digestion into green gas and biofertilisers, not wasted in landfill sites or incinerators."