Call it alchemy, Baton Rouge style.

Engineers are turning the Capital City's trash into fuel that helps power petrochemical plants along the Mississippi River which make the raw materials used to produce all kinds of goods, from plastic containers to car parts.

But first, the garbage needs time to ferment. After five years at the parish landfill, garbage starts giving off combustible gases that are being captured and sold to the plants. As the trash heap grows ever higher, the city-parish is preparing to install more pumps to extract methane gas bubbling underneath the mammoth pile.

The additional pumps mean that even more of the coffee grounds, food scraps and other trash that Baton Rougeans have thrown out over the years will soon be helping to meet the energy needs of the city's sprawling petrochemical plants.

As waste breaks down, it naturally releases gases such as methane. Typically, that gas would have to be burned off. But five years ago, the East Baton Rouge landfill west of Baker began capturing the gas so it could be sold to nearby industrial facilities.

Approximately 75 pumps collect the gas and spirit it to a plant at the landfill where the methane is cooled and condensed, explained Jason Dayton, plant manager for Advanced Disposal Services, the private company contracted to extract and sell methane at the city-parish landfill.

Five miles of underground pipelines deliver the methane to BASF and ExxonMobil, which can burn it in place of natural gas. Most of the methane goes to Exxon, where it's used to run the boilers at the polyolefins plant to make plastic products such as containers and auto parts, according to the company.

When the program started five years ago, Exxon estimated that recycling the gas would have an effect equal to taking 59,000 cars off the road or planting 73,000 acres of pine forest.

As the landfill has grown, operations have expanded, adding about 12 more pumps in 2015, with another dozen planned to be installed soon, said city-parish environmental coordinator Sarah Boudreaux.

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When the program started, the boilers at the Exxon polyolefins plant were using landfill methane to provide 45 percent of the fuel, and the amount has since risen to 54 percent, said spokeswoman Stephanie Cargile.

"The Polyolefins Plant is taking all of the gas that the landfill has offered to ExxonMobil. Our ability to take additional supply and the benefits to the environment will continue to increase over the life of landfill as it matures and produces additional methane," she wrote in an email to The Advocate.

Several years ago, the price of natural gas made it lucrative to begin selling landfill methane, according to Boudreaux.

Although few places like East Baton Rouge and Jefferson parishes decided to cash in by capturing and selling their methane, Boudreaux said, most other places just flare theirs off. The Baton Rouge operation was the first time Exxon had ever used landfill gas to help meet its power needs, according to the company

"We're hardly ever flaring. ... (The plants) basically want everything we can give them," Boudreaux said.

The city-parish gets a cut of the sales, which don't amount to much, but Boudreaux said the city-parish was mostly motivated by a desire to recycle. Exxon even won an Energy Efficiency Award from the American Chemical Council, the company pointed out.

Contracting with Advanced Disposal also means the company maintains all the methane pumps, removing that burden from the city-parish, Boudreaux said. Dayton, the plant manager, makes sure all the pumps are in good order and properly pressurized, and he keeps the plant running and oversees the flare that's used on the rare occasions when the landfill has excess methane.

Though the city-parish is preparing to add more methane pumps, Boudreaux expects to just sell more gas to the companies already connected to the landfill via existing pipelines. Another potential customer could theoretically try to hook up, but installing new pipelines is a legally tedious process due to all the property and infrastructure the pipeline would have to cross, she said.

Follow Steve Hardy on Twitter, @SteveRHardy.