LONDON — It was part of the imagery of much earlier times: a red double-decker bus nudging through London streets shrouded in smog created in part by its own exhaust fumes.
Such was the vehicle’s lumbering notoriety that a musical duo popular in the 1950s and ’60s, Flanders and Swann, composed a tongue-in-cheek panegyric to the “London Transport diesel-engined 97-horsepower omnibus.” They called their song “A Transport of Delight.”
On Monday, though, the city’s 9,500 buses — still mostly painted red — laid claim to a fresher narrative.
While the worst smogs, or “pea soupers,” have long dispersed, London still chokes on high levels of pollution. Seeking to curb toxic diesel fumes, transportation officials and companies are hunting for new sources of energy for the buses.
The latest idea? Coffee grounds.
On Monday, in a much-hyped debut, a company called Bio-bean, in partnership with the oil giant Royal Dutch Shell, introduced relatively small amounts of oil produced from coffee grounds into the mix of diesel and biofuels mandated by the city authorities.
The first batch of 6,000 liters, or about 1,580 gallons, would power one bus for a year, Bio-bean said in a news release. According to official figures in 2015, London’s buses used 240 million liters of diesel fuel a year.
Given the tiny proportion of coffee-based oil in the bus fuel, there was no immediate, empirical indication that the noisome whiff of central London’s air would turn into the alluring aroma of, say, a Roman cafe, or even a Starbucks. Coffee-based oil does have a strong smell of coffee, Bio-bean said, “but once it is processed, distilled, blended and mixed with mineral diesel, that odor is removed.”
Despite their traditional penchant for tea, Londoners drink an average of 2.3 cups of coffee a day, producing about 200,000 tons of used grounds, the news release said. Bio-bean collects that waste from coffee shops and factories and processes the sludge into oil.
“It’s a great example of what can de done when we start to reimagine waste as an untapped source,” Arthur Kay, the company’s founder.
At present, according to Transport for London, which operates London’s public transportation system, the city authorities want to ensure that increasing numbers of buses are fueled by a blend of diesel and biofuels made of products such as waste cooking oil and tallow from meat processing companies.
Additionally, more than a sixth of the bus fleet is powered by hybrid engines, and that proportion is set to grow. The authorities also want to convert the 300 single-deck buses to run on electricity or hydrogen, which emit no exhaust fumes, Transport for London said.
For years, the British authorities offered lower vehicle taxes to motorists using low-carbon diesel engines. But in recent years, London and many other European capitals have become alarmed by concentrations of harmful nitrogen oxides in the city’s air. And a backlash against diesel has grown with the scandal over secret efforts by several major carmakers, Volkswagen in particular, to circumvent emissions controls.
“We’ve got a health crisis in London caused directly by the poor-quality air,” Mayor Sadiq Khan said in October. “Roughly speaking, more than 9,000 Londoners die prematurely because of the poor-quality air.”
His remarks were made as the authorities introduced a charge for people driving into the city center in vehicles powered by engines that do not meet the latest European Union emissions standards, usually older diesel-powered models.
The so-called T-charge, meaning Toxicity Charge, is 10 pounds, or roughly $13 a day, in addition to the so-called congestion charge levied on drivers since 2003, which now stands at £11.50 a day, Monday through Friday.
That has brought the potential costs for a weekday drive into the city center to £21.50, approaching $30 — far more, in fact, than the cost of a latte or a double espresso.