What Happens to Garbage: Insights into the Burning of Waste

What Happens to Garbage?

by Christina De La Rocha

Anyone who has ever had pets or kept chickens quickly realizes that what separates humans from the beasts isn’t the opposable thumb, it’s the ability to clean up a mess. Honestly, where would civilization be if we didn’t have sewage treatment plants and garbage trucks? Especially, maybe, the latter; in these days of planned obsolescence and widespread overconsumption, dealing with trash matters. Think about how much garbage you generate, even if you’re mostly just buying food, clothes, and the basic necessities for keeping your home and yourself clean. For one thing: all that packaging!

And yet, despite the literal tons of trash each of us will generate over the course of our lives, does any of us really know what happens to all of that garbage once we’ve disposed of it? Never mind the toys from your childhood and the computers you’ve owned down through the years, what has happened to all the tissues you’ve tossed into the trash after blowing your nose? Do you have any idea what fate awaits your dental floss?

Until last week Monday, I was pretty sure most of the non-compostable, non-recyclable garbage I’m producing now was going to landfill. Then I got schooled by a brief tour of the local garbage-burning facility.

Yeah, spoiler alert! It’s getting burned. But that turns out to be an interesting story.

Where I live now—which is in the state of Schleswig-Holstein, in Germany—there’s curbside pickup of four different types of household waste: compostables, paper and cardboard, plastic and metal recyclables, and garbage. The compostables get composted and sold back to people needing garden soil, compost, or mulch. As for the cardboard and paper, at this point, I can only presume that they truly do get recycled.

When it comes to the other recycling, I’ve long been skeptical. Because what people here stuff into the recycling bins here is 80% wish-cycling (things like clingfilm, candy wrappers, plastic bags, multi-component packaging, and bottles and cans that haven’t been cleaned) and only 20% actual recyclables (like detergent, shampoo, and single-use plastic beverage bottles), I assumed that most of the “recycling” instead gets burned to produce heat or electricity. And, again, I wrongly assumed that when we put out the trash once a month, it was being picked up and taken to landfill.

As I said, Reader, I have been schooled. By our tour of the local garbage-burning facility.

What Happens to Garbage: Tall grey building with some silos and smoke emitting from chimneys, under a dark blue evening sky
The exterior view of the garbage-burning facility in Kiel, Germany.

The core of our local garbage-burning facility consists of a reservoir that garbage trucks can dump their garbage into, provided they pay a fee. A huge metal grabber, hanging off the arm of a crane, drops down and grabs clawfuls that it feeds into one of two funnels that lead into a multi-chambered furnace.

Each stage of the furnace is a bit hotter than the one before. Because, yeah—or so I am guessing—you don’t want an explosion because you dumped wet garbage straight into a furnace whose temperature is 800–900°C (1470–1650°F). The exhaust from the burning of the garbage runs through filters, to minimize the release of pollutants. By-products of the burning are collected and sold, including the ash. The heat produced by burning the garbage does two things: it turns turbines to generate electricity and it is delivered directly to homes and businesses for heating.

Good on you, garbage!

I swear, I’m now so proud of my trash.

A grey chute leads to an orange pit with a large mechanical claw
A massive grabber, on the hunt for a handful of trash, reaches down into the reservoir that garbage trucks tip their contents into.

One of the first things we learned during our tour, is that thanks to the excess of filters in the exhaust lines, our local garbage-burning facility has the country’s lowest emissions of pollutants like particulates, chlorine, sulfur dioxide, nitrogen oxides, and mercury. These filters have to be constantly refreshed and cared for, even as the furnaces keep working. Aside from a week or two of downtime in the summer for maintenance on various aspects of the facility, it burns garbage 24/7.

One filter captures chlorine, a trace component of trash, but not something you want to be releasing into the atmosphere all the time. Ultimately, the chlorine accumulates in a big tank of hydrochloric acid, which is then sold to a company that sells it on, presumably after refining it. There are tons of uses of hydrochloric acid in science and industry and I’ve certainly bought some at the local DIY store to dissolve some of the carbonates encrusting our tea kettle, faucets, and shower (our water is so hard, I swear you could break your teeth on it).

Another filter collects sulfur, which comes out of the furnace as sulfur dioxide (SO2), one of the major components of acid rain (a devastating environmental problem we’re cutting down on by using of filters in exhaust lines of, for instance, fossil fuel-burning power plants). Then there’s a more general filter to catch things that didn’t get caught in the first two filters and to serve as backup for those times when one of the other filters is overwhelmed or is otherwise not working properly.

A grey chute leads to an orange pit with a large mechanical claw
I have to honestly say, since everyone here in Germany watches Tatort (a police procedural tv drama) every Sunday evening, we were all dying to know what the craziest thing was that the garbage trucks had ever delivered. Meaning, you know, how many bodies had shown up down through the years? But the answer, apparently, was none.

Sadly, though, our local garbage-burning facility isn’t fitted for carbon capture, so it vents all of its carbon dioxide to the atmosphere. Anyway, at the moment, it’s not clear where they could send capture carbon to be stored, although the carbon dioxide could be sold to, for instance, the beverage industry, which needs carbon dioxide to carbonate drinks.

Given the trouble and expense of carbon capture and then use or storage, the managers of our local garbage-burning facility would prefer it if the trash that we throw away was stuff that was made renewably. By this they mean stuff made out of materials that were made recently out of plants instead of stuff made out of plastic and other synthetics.

While it’s true that things like cotton, wood, and wool have a carbon dioxide footprint associated with their production—tractors burn fossil fuels, pesticides are made out of fossil fuels using energy produced by burning fossil fuels, and so on—burning the biological material returns carbon dioxide to the atmosphere that a plant somewhat recently removed.

Meanwhile, burning plastics that have been made from petroleum is, for all intents and purposes, burning fossil fuels. That’s definitely something to think about the next time you go shopping for clothes, home decor, and kitchen utensils that are likely to end up in the garbage (and possibly incinerated) within just a few years.

The claw has grabbed a handful of garbage
The claw, now filled with trash, is on its way to feed the funnel that feeds the chute that feeds the furnace.

Speaking of plastic, I was sort of wrong about the fate of my wish-cycling. The garbage-burning facility doesn’t burn the non-recyclable recycling. That stuff is almost pure plastic, which, being spun from fossil fuels, is incredibly energy-dense. A load of pure plastic burns way too fast and hot for the furnaces that run electricity-generating turbines and feed the district heating that keeps at least 10,000 local buildings (such as houses and apartment buildings) supplied with warmth.

Instead, after the actual recyclables are sorted out of the recycling that has been collected, the non-recyclable remnants are shipped off to companies that make cement. For them, the hotter their fuel burns, the better, because they need hot furnaces. To make cement, these comanies need to heat calcium carbonate (CaCO3) to 2000°C (3600°F) for several hours.

This forces the calcium carbonate to give off carbon dioxide (CO2) to become into calcium oxide (CaO), better known as lime, one of the major components of cement. This energy-intensive calcining is the main reason that cement production is a major source of anthropogenic carbon dioxide to the atmosphere.

In an orange space, a claw sits over metal hardware and garbage
A claw, currently not in use, resting above one of the funnels that is well-stocked up with trash.

Another thing we learned during our tour is that there are bus drivers, train drivers, crane drivers, and, related to that last one, people who drive the claws that pickup the garbage from the reservoir and drop it into the funnels that feed the chute that feeds into the multi-chambered furnace. The flow into the furnace has to be fairly constant, so it’s a job that requires continuous vigilance… over the entirety of an 8-hour shift. You can’t stuff too much garbage into the funnel all at once and you can’t let it get empty.

Zoomed out: there are more claws and a deep pit containing garbage, all orange
The view from the one of the two claw-driving rooms that wasn’t in use at the time. Note the claw dropping garbage into the funnel.

The view from the seat the claw drivers sit in is fantastic (there are two claw-driving booths, one on each end of the reservoir, even if sometimes only one claw is in use at a time). The central room, eerily yellow under the sodium lamps that are always on, is not just full of the refuse of a good portion of the households in the state of Schleswig-Holstein, it’s full of birds. As we ogled the operation, occasionally rooks, which were faster than my photo-trigger finger, came swooping down from whatever hidden rafters they were perched on.

The facility manager said they come in with the trucks—like, literally inside them—that tip in the garbage. In tumbles a load, complete with a bird that is almost certainly, at that point, dazed and confused.

How sad for the birds, I thought. But don’t worry, the facility manager assured us. Look at the square holes there, high in the walls. They’re there to let air in and birds out. But apparently, the birds prefer to stay. It’s always warm inside the reservoir room and there’s plenty of food.

A claw hangs in mid-air in the orange space, with garbage below
In this photo, you can almost make out the person driving the claw. You can also see the square holes in the wall where air can get in (and birds can get out).

Sadder is the case for the cats that come in with the deliveries from time to time. Not so much in the regular garbage trucks, which generally don’t slow down or get quiet enough for cats to want to jump inside. But in the containers that people can order and leave open for a while and fill up—when they need to empty out a house, for instance. Sometimes cats will wander in and settle down and then, boom, the container gets shut and hauled off to the garbage-burning facility.

I suspect the story doesn’t end well for those cats. The facilities manager didn’t offer any encouraging words about ground floor exists for unexpected feline guests. And I’d guess they don’t have any as they probably don’t want rats getting in.

The claw has decended and grabbed a handful of garbage
Imagine spending the rest of your life stuck down there.

What comes out the other end of the furnace is a lot of ash… and things that don’t burn all the way. Wood, for instance, tends to char on the outside and then not burn at all on the inside. Metal things—I saw a few strainers and a spatula, for instance—don’t melt. The furnace isn’t hot enough and they aren’t in there long enough. Even chicken bones make it through intact (although the birds tend to get to these first and strew them about the facility).

So, after enough ash accumulates, it gets trucked away and sieved into various fractions. What can be used for making roads gets sold to companies that make roads. Metal gets sent to metal recyclers. I’m not sure what happens to the chicken bones, though.

In a separate part of the orange space, a different type of claw is moving ash and metal
Ashes to ashes, dust to dust… and metal utensils.

As I mentioned earlier, the chlorine that was collected by the filters gets turned into hydrochloric acid and sold on. Meanwhile, the sulfur dioxide gets turned into gypsum and used as a building material (like drywall). Meanwhile, the electricity and heat generated by the burning of the garbage gets sold to local consumers, meaning that the garbage-burning facility not only gets rid of garbage, it recycles some useful materials out of it, and serves as a powerplant.

That was definitely something I did not know before, although I drive past the garbage-burning facility all the time (it’s right off the highway, at the edge of town). But I like the step the garbage-burning facility represents on our road to zero waste societies. What a step up from just piling up garbage in a garbage dump!

I definitely won’t ever look at anything I throw into the garbage in quite the same way again.