Leftover cooking oil is used by Mexico City market vendors as fuel to power local buses

A market vendor fries up a batch of flautas at Mexico City's Churubusco market in January 2022. Some city buses are powered by biodiesel made from oil used in this and other market stalls in the city. (Cody Copeland/Courthouse News)

The plant located at the city’s sprawling wholesale foods market produces over 830 gallons of biodiesel a day and keeps thousands of gallons of used cooking oil from polluting the soil and waterways.

The busy diners at the Churubusco market may not know it, but the same vegetable oil used to fry their lunch could soon power the bus that gets them to work in the near future. 

This market located in the historic neighborhood of Coyoacán is one of several in Mexico City that sell their used cooking oil to a plant that processes it into an additive for biodiesel. The final product is being used in two of the capital’s sundry public transportation networks. 

Designed by researchers at Mexico’s National Polytechnic Institute (IPN), the compact plant occupies a 1,400-square-foot corner of a large bus garage at the city’s sprawling wholesale foods market known as the Central de Abasto (Ceda). 

Here the oil used to fry classic Mexican snack foods called antojitos or garnachas — such delectable and greasy fare as flautas, gorditas and quesadillas (yes, they deep fry them down here) — is put to use rather than wasted. 

It is processed into an organic additive that is mixed at a 20/80 ratio with petroleum-based diesel, which is being used to move buses over the circuitous routes of the city’s Metrobus and Public Transport Network (RTP) systems.

Plant coordinator Rubí Guzmán extolled the virtues of using this biodiesel in such notorious polluters as diesel engines, but said that this particular benefit is actually subordinate to the primary motive for making it out of cooking oil. 

“This is an important step in the transition to the circular economy,” she said. “It’s not necessarily about creating new types of fuels — which is a good thing, of course — but rather about finding solutions to waste materials, which have a huge negative impact on our systems and environment.”

The compact biodiesel plant at Mexico City’s wholesale food market produces over 830 gallons of biodiesel a day from cooking oils collected from city markets. (Cody Copeland/Courthouse News)

The biodiesel produced at the Ceda plant both reduces the amount of diesel being burned in city bus engines and produces less pollution, since it cleans the vehicles’ tanks, injectors, motors, and pipes through its use. 

But the plant’s biggest benefit is that it keeps dirty cooking oil off the streets.

“Here in Mexico City we have a problem with cooking oil not being disposed of properly,” said plant supervisor Mariana Molina. “People throw it in the trash or pour it down the drain, which pollutes bodies of water or the soil or wherever they decide to toss it.”

In addition to the typical problems used cooking oil can cause in plumbing systems, such careless disposal can also cause flooding and, once released into the environment, can suffocate fish and microbes in the ecosystems it contaminates. 

Each day the plant processes around 925 gallons of oil that might have ended up as pollution. With a conversion ratio of just under 90%, the plant’s daily output comes out to more than 830 gallons of biodiesel for use in city buses.

The plant is also highly efficient and creates no waste itself. All residual materials from the process are used in other organic processes, such as the production of biogas, which can be used in water heaters and kitchen stoves. 

The largest secondary material resulting from this process is glycerol, which is used in pharmaceuticals and cosmetics after being refined. Guzmán said that they are looking for the most efficient way to take advantage of this material.

Also on the docket is finding a way to reduce the cost of the final product, which is only slightly cheaper than current diesel prices in Mexico. 

Flora Ng, a chemical engineer at the University of Waterloo in Ontario, Canada, who is experimenting with ways to produce cheaper biodiesel, said that taking used cooking oil as the raw material for the process could offset the cost of production. 

“Feedstock is the major cost of biodiesel production,” said Ng. “Biodiesel produced from waste oil from markets and restaurants should cost less than that produced from food-grade oil feedstock.”

Before and after: a bottle of used cooking oil (left) sits next to one of biodiesel (right) produced in the plant in Mexico City’s wholesale food market. (Cody Copeland/Courthouse News)

However, even though it’s a waste product, used cooking oil is not immune to the law of supply and demand.

Ng added its price “will increase once there is interest to use these wastes as feedstock for biodiesel,” which has been seen in markets from Mexico to Canada. 

Guzmán noted that the Ceda plant isn’t the only business in town in the market for post-garnachas cooking oil. Industries that produce animal feed and artisanal soaps also use it.

Thus, the city is hoping to expand its collection system to make it easy for citizens and others to donate their used oil, to benefit both their plumbing and the environment.

“We want to increase citizens’ ability to donate, as well as big industries,” said Guzmán. “We want them to take responsibility for the waste materials they produce.”

Source: El Universal

The Mexico City Post