COLUMBIA – Adam White finds it difficult to explain what his job at the Columbia landfill involves. That’s not surprising, given that his title is bioreactor specialist.
The city landfill was the first in Missouri to implement bioreactor technology, according to the Columbia Public Works Department’s website. The bioreactor speeds up the decomposition of waste and the production of methane gas, which is harvested and piped to the Water and Light Department’s Columbia Energy Center. The center uses that methane gas to produce electricity, which powers homes and businesses in Columbia.
“A lot of people don’t realize all the different aspects (of landfilling),” White said. “There’s a science to it…and sometimes you have to think creatively and out of the box.”
Since it began operating in 2008, the bioreactor has generated about 2.25 percent of the electricity Columbia uses, White said. That’s enough energy to power about 2,250 homes in Columbia, he said.
In traditional landfill cells — which make up the vast majority of Columbia’s 720-acre landfill north of town on Peabody Road — the trash is covered up. These cells, which comprise 102 acres of the landfill area, are known as “dry tombs” because they prevent water or air from reaching the waste. In dry tombs, waste can take decades to decompose.
In a bioreactor landfill cell, on the other hand, water is added to the waste to make it break down and produce gas much faster. Only one of the cells in that 102 acres has been designated as a bioreactor cell, White said.
“The whole idea behind trying to get those elevated moisture levels is to increase the rate of decomposition for that waste,” White said. “So the waste becomes stable at an earlier stage in its life than it would otherwise.”
Turning Trash Into Electric Power
The city of Columbia created a bioreactor cell at its landfill in 2008 as a means of generating methane gas that in turn is used to generate electricity at the Columbia Energy Center. The bioreactor generates about 2.25 percent of the electricity Columbia uses. It also causes trash at the landfill to decompose more quickly.
Here’s a look at how the bioreactor cell works.
Waste is collected to be decomposed in the bioreactor.
Water is pumped across the mound and drains down through the waste. The water causes faster decomposition. It collects at the bottom and is recycled back through the system.
As the waste decomposes, it releases methane, which is brought to a turbine or combustion engine.
Methane powers the turbine or combustion engine, which generates electricity using a green energy source.
White said managing a landfill is complicated. One of his biggest responsibilities is overseeing the injection of moisture into the bioreactor cell, determining how many gallons of liquid should be pumped into the cell from onsite stormwater basins.
White and other landfill workers pump an average of 50,000 to 60,000 gallons of water into the bioreactor cell per day during “injection season,” which runs from spring through fall. He said the temperature of the water must exceed 50 degrees. Otherwise, the bacteria that speed up the decomposition can’t survive, he said.
White also has to determine how much contaminated liquid to remove from trash in the bioreactor cell. Waste that enters the landfill has a natural moisture content of roughly 25 percent, he said. But that moisture is contaminated and can’t be used as part of the bioreactor process. Instead, White said it’s collected from the bioreactor, funneled to a central location and then discharged into the sanitary sewer system for treatment.
White said every day at the landfill is a little different, which is why he likes the job. But he said some days are crappier than others.
“Birds like to sit on top of the handles of the valves I have to adjust … and they poop all over my valves,” he said.
The valves that White tweaks are connected to the gas extraction wells. Using a gas extraction monitor, White can check the amount of methane a landfill cell is producing and make adjustments based on production goals provided by Water and Light. There are 65 valves throughout the landfill, and White checks them all once a week. But he usually knows what each cell will produce.
“They’re like your kids,” he said. “You get to know them and their attitudes.”
White said he also likes his job because he’s able to work on projects from start to finish. After graduating from MU with a degree in soil science, White worked as a consultant for Terracon, an environmental engineering company in Columbia.
“You just get called in for one specific problem, you fix that problem, and then you’re gone,” White said about working with the company. “You never see…how your solution to the problem was implemented.”
At the landfill, however, White is involved with all aspects of a project from design to implementation. Every challenge, he said, is a learning opportunity.
“It’s neat to see what types of little issues arise…and how things can be tweaked to make them work better in the future,” White said. “We can then take those recommendations from what we’ve learned in the field and apply them to the next project that we’re doing that has similar aspects.”
One project White worked on involved the installation of gas collection lines for the bioreactor. Initially, the lines were placed horizontally, but that caused problems when water levels rose in the bioreactor cell. Now the lines slope away from the gas collection point, which slows down water buildup and extends the life of the collection line.
Rick Finely, the landfill and compost operations supervisor who works side by side with White, commented on White's dedication to working at the landfill.
“He can be depended on,” Finely said. “When he says things are going to get done, they get done.”
Supervising editor is Scott Swafford.