Mad about Science: Trash

By Brenden Bobby
Reader Columnist

Have you ever spent time thinking about where your trash goes? Once you’re done with that Styrofoam tray and plastic wrap that contained your chicken cutlet, where does it go?

The observation of garbage’s life cycle ends for most of us in a large plastic bin that gets dumped into a truck and whisked away to places unknown. Others may transport their trash to a collection facility, like any of the 13 such sites in Bonner County. Regardless, the journey of trash doesn’t end there. Lots of garbage ends up in landfills, which at first glance appear to be giant plots of land in which garbage is dumped — but this is a critical oversimplification of the level of engineering design that goes into a landfill. 

The first and largest issue of digging a hole and filling it with garbage is considering what happens when it rains. Water follows the path of least resistance downward, and, in the case of a giant hole filled with trash, it treats the garbage like a filter and collects every bit of bacteria, organic matter plastic particulates it can on its way into the substrate. This emulsion of garbage juice is called leachate, and it’s something you don’t want making its way into subterranean bodies of water.

Most landfills will compact clay soil to create a watertight membrane at the bottom of the pit to keep garbage juice from leaching into the soil. Some landfills will use a layer of plastic welded together, like a giant contractor bag that creates a membrane through which water cannot pass. Often, both processes will be used. This creates another problem — where does the water go?

It doesn’t go anywhere until it fills the giant bowl, creating a disgusting garbage swamp and breeding ground for bacteria and malodorous aromas in an already vile and disgusting pile of refuse. This problem can be mitigated by lining the basin with perforated pipes that collect leachate for processing. Pumps can also be used at the bottom of the pile to push leachate up the slopes and into its destination to be processed.

Processing leachate is extremely expensive. The cost of maintaining and operating pumps in a mountain of garbage while also making sure it doesn’t leach into the soil elsewhere is tricky. Some sites will create special ponds to allow the water to evaporate and become air moisture as part of the water cycle. Other facilities may use biological components that break down the harmful elements within the leachate. Plants and algae are also similarly used. Some facilities may use a combination of all of these processes to deal with leachate.

At this point, you’ve thrown a giant pile of garbage into a pit and collected the water. What happens when you start running out of space?

Trash is usually not very dense. The things we use and dispose of are often containers meant to hold other objects or a lot of air, so when they’re perforated and damaged they can be mashed down to drive out the air and minimize the physical footprint of the object. This is often done first within your own garbage can. The next step takes place inside the garbage truck, which is equipped with hydraulic presses that mash the collected bags of waste and force out air. Finally, at the landfill, huge tractors with massive crushing wheels repeatedly drive over layers of garbage to further compact it.

The goal of a landfill is to maximize the volume used before running out of space, so maximizing compaction is a vital step to the success of a landfill.

Trash like paper and Styrofoam is very light and likes to blow around in the wind. This spreads the mess to surrounding areas and is something a landfill needs to account for. Many landfills are required to cover garbage at the end of a working day. In some cases, soil is used while others may use huge plastic tarps. This creates a problem when water collects as leachate and cannot penetrate the layers, creating a nasty garbage lasagna with layers of varying densities — not something you want to be driving over in a heavy vehicle.

Eventually, the garbage must be covered once it reaches an unworkable height. This is essentially the same process that happens beneath the landfill to create an impermeable layer that doesn’t allow water into the garbage below. Grass is sown on top to help with erosion control and to hide the pile of filth below.

This still isn’t the end of the process of a landfill. Innumerable microbes trapped beneath the earthy tomb will work for decades to digest the organic trash and generate heat through methane as waste. This must also be carefully released and treated through a number of gas pump systems that carefully release the methane without allowing oxygen into the heap. If it’s not carefully controlled, it presents the chance for a fire or even a methane explosion to occur within the sealed landfill.

In some cases, this excess gas is flared off on site to break the gas down into less environmentally damaging components. In other cases, it can be used as an alternative to natural gas to power tens of thousands of homes per site.

After it’s all sealed up and left to do whatever it is the microbes want to do for three decades, many landfills are prime real estate to become parks. It’s land that can’t be used for anything else, so we might as well let nature take it back over and get some enjoyment from the space, right?

Stay curious, 7B.