Recently we came across a story from last year that we wished we hadn’t missed, but it’s still interesting. The University of Nebraska is using a “mechanical stomach” to save 95 tons of CO2 emissions per year by digesting the food and sending it down the drain instead of sending food waste on long (and emissions heavy) journeys to landfills.
“What a biodigester does is take solid foods that get thrown away and mixes them up into a nutrient-rich liquid that goes down the drain,” said Dave Annis, director of University Dining Services (the man in the featured image). “The simplest way to describe it is that it’s a mechanical stomach, always digesting away.”
Before the university put in the biodigester, campus waste management had to come every day to pick up the food waste. They filled up large bags, which were heavy to carry. Waste management would put the bags in trucks, which weren’t zero emissions vehicles. They then moved from vehicle to vehicle (each of which had emissions of some kind), and ended up in the landfill, where the food waste rots and releases more carbon into the atmosphere. All that seems pretty subpar now that the university has the biodigester.
“The people that were the happiest about it were our facilities people — the people that had to come in a couple times a day and haul away all the big, messy, heavy bags of garbage,” Annis said. “There’s none of that now. After we put the one in Selleck, they were the ones that came to us and said, ‘Well, when are you going to put in the next one? We really like these things.’”
Annis says the biodigester can handle any food waste, totaling up to 400 pounds per day. On the outside, it’s a large metal box, but on the inside is a tank filled with small black pellets. There’s a rotating paddle inside that mixes things up to keep the biodigestion going.
“The first thing we do is introduce a safe, food-grade enzyme to the tank. We let that sit for a few hours to get it started. It’s like using yeast when you’re baking,” Annis said. “Then, you feed it a little bit of starter. We mix five pounds of rice, five pounds of sugar and a little bit of water together. After it’s been digesting that for about six hours, you can just start putting food in. It can digest just about anything. It’s pretty amazing to see a half-eaten hotdog go in there and be gone by the next day.”
At the end of the process, all that’s left is a liquid that the university currently puts down the drain, but they hope to change that. Outdoor compost piles usually end up fertilizing crops or get used for other things, and they hope to do something similar with the biodigester’s output. “There are places that collect that and use it for fertilizer, but we aren’t ready for that yet,” Annis said. “It’s one of those aspirational goals to be able to find a use for what comes out and goes down the drain now and use it for other purposes — sort of closing the circle.”
The biodigester was put in in 2019, and a second unit was added to another dining hall in 2020. Between just these two units, they’ve kept 50,000 pounds of food waste out of the landfill and reduced the campus’ carbon footprint by 95 tons. After seeing these benefits, the university wants to put one of these in every campus dining hall.
“We still have three dining centers that don’t have them,” he said. “We had hoped that we’d have a couple more in over the summer, but COVID sort of changed everyone’s plans, and we just didn’t have the resources at that point to be able to do that. But it’s still on the back burner, and we’ll get to them as soon as we can.”
Why This Matters
This story shows us that there’s often a domino effect for things we do that is hard to consider when we do it. When something gets thrown away, we either put it in the dumpster or take it to the curb ourselves and that’s the last we see of it. In a campus dining hall, the people cleaning up the food waste and bagging it only see the people who pick up the garbage bags, and that’s the end of it as far as their job is concerned.
The downstream impacts still add up, regardless of whether we see them. Bits of food that end up in the garbage ended up adding up to 50,000 pounds (that’s most of a semi-truck load) in just one year at two university dining halls. Food that gets thrown away in other places, like our homes, restaurants, etc probably adds up to an immense amount of material that would dwarf what this article covered.
Moving all of that waste takes a collection truck, then it goes to a sorting facility of some kind (ideally), and then ends up in a larger truck to get to the landfill. Imagine the weight of a whole country’s worth of pizza crusts, watermelon rinds, and hard french fries (among many, many other things). Then, imagine diesel trucks moving that weight around. That’s not so good.
Now, imagine all of that food rotting in a landfill for months or even years. That bit of food you didn’t eat a few months ago and threw away is probably sitting somewhere emitting carbon into the atmosphere as you read this article, along with all of the other bits of food everyone else didn’t eat. That’s not very good at all.
I don’t think we will see home biodigesters that soon, but if everyplace with a high volume of food waste used one, it would make a measurable impact. On top of that, home composting is probably a good option for many people to get some more good out of the carbon emissions instead of just taking up landfill space.
After writing this article, I’m going to be looking for a composter for my yard.
Featured image provided by University of Nebraska. Source: University press release.
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