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Waste Cooking Oil From Mexico City's Restaurants Could Power the City's Buses

Biodiesel from the waste cooking oil produced by the capital city's restaurants could help to power the cities public transit system, and reduce emissions in the process.
(Photo: otnaydur/Shutterstock)

(Photo: otnaydur/Shutterstock)

There are more than 1,500 restaurants in the area of Mexico City known as Delegación Cuauhtémoc, an expanse that encompasses the downtown region of the metropolis. A team of researchers from the Universidad Nacional Autónoma de México and Ambientalis Environmental Consulting set out to find if waste cooking oil—the part of cooking oil that’s left unsuitable for human consumption by the deep frying process—might instead be suitable as the raw material for biofuel used by public transit in the bustling city.

Oil and grease don’t break down easily once they hit the environment outside our kitchens; they clog drains, block sewers, and pollute soils and waterways. But a relatively simple process can transform vegetable oil into biodiesel, which can be blended with regular diesel and used as fuel in many of today’s diesel-powered vehicles. The authors of the recent study, published last week in Waste Management & Research, looked at what effect cooking oil-based biodiesel, collected from markets and restaurants in Mexico City, might have on vehicle emissions.

A waste cooking oil collection program could be a powerful weapon for the city in its decades-long battle against air pollution.

In separate trials, the team fed three different fuels to six buses—a 100 percent petro-diesel as a baseline, and two blends of 10 percent and 20 percent biodiesel. Three of the buses had engines that met the United States Environmental Protection Agency’s emissions standards for 1998 (EPA-98); the other three had engines that met the agency’s updated 2004 standards (EPA-04). Loaded with water containers to simulate the weight of passengers, the buses drove a regular, 8.3-kilometer route with 22 stops, in regular traffic conditions. A Ride-Along-Vehicle-Emissions-Measuring system on the buses collected measurements of carbon dioxide, carbon monoxide, nitrogen oxide, and particulate matter emissions while the buses puttered through the city for 45 minutes.

The study found that, in the EPA-04 buses, the 10-percent biodiesel blend reduced particulate matter emissions by 66 percent, and the 20-percent blend reduced emissions of the pollutant by 36 percent compared to controls. Further, nitrogen oxide emissions decreased by four percent from controls when the 10-percent biodiesel fuel was used, and eight percent for the 20-percent biodiesel fuel. CO2 emissions were reduced by six percent and five percent, respectively. Interestingly, in buses with EPA-98 engines and earlier, the biodiesel blends actually increased emissions of particulate matter and nitrogen oxide.

The authors state that, given an average annual distance traveled by the city’s buses of 73,000 kilometers, and an average fuel economy of two kilometers traveled per liter of gas, a 10-percent biodiesel blend from waste cooking oil produced in the city could power thousands of public buses. If adopted, a waste cooking oil collection program could thus be a powerful weapon for the city in it's decades-long battle against air pollution, keeping more than 16,000 tons of CO2 out of the air.

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