Solid waste disposal| Aquatic and Terrestrial Pollution| AP Environmental science| Khan Academy

Time for a little trash talk. The United States produces more solid waste each year than any other nation, and as we make more and more trash, we're running out of places to put it. There are two main types of solid waste: industrial solid waste and municipal solid waste. Industrial solid waste comes from industries like factories, mines, and farms. Municipal waste, on the other hand, comes from homes and workplaces like offices. It's basically the stuff you'd put in your trash can or dumpster, like paper, plastic bags, cardboard, food waste, cans, bottles, and yard waste.

Suppose you're on a picnic with your friends. Being an AP Environmental Science student and all, you brought reusable utensils. You see an old empty potato chip bag on the ground. You're able to identify it as a fine specimen of municipal solid waste. You decide to pick it up and put it in the trash, but now that it's in the trash, where will it go? Most likely, it'll end up in a landfill, just like more than half of the United States' municipal solid waste. To store so much waste, landfills have to be really big.

One kind of landfill is an open dump, which is a large field or pit filled with trash. Let’s think about the pros of an open dump. For one thing, they're really big, so they allow a lot of people to get rid of a lot of waste. This is why they're often used near big cities with large populations. They're also pretty inexpensive to maintain, and they do a great job at keeping waste away from people's homes and workplaces.

But if we take a closer look at open dumps, we can see that there are some potential problems too. First off, open dumps can be smelly, which could be unpleasant for the people who live around them. Because open dumps are uncovered and uncompacted, the wildlife and the weather could spread the waste into the surrounding environment. The trash in open dumps can emit dangerous gases and even catch on fire, so we could add gases and fires to our list of cons, because these could be dangerous to wildlife.

Another problem happens when it rains. The water seeps into the landfill, and as it goes through, it gets contaminated with toxic materials like heavy metals from electronics or waste from discarded prescription drugs. This contaminated water that comes out of the landfill is called leachate. When you think about it, the word leachate makes sense, because the root word "leech" means that this water absorbs and carries some of the dissolved waste material with it. Leachate can be dangerous because it can seep into the soil and contaminate groundwater that people rely on for drinking, so this can make the water supply toxic to humans.

Another problem with open dumps is that they require a lot of land, which means they cause habitat destruction. Another kind of landfill is a sanitary landfill. You may be thinking, how could a landfill—a pit of trash—be sanitary? Well, sanitary landfills have something that open dumps don't: a liner, which is a layer of clay or plastic that keeps the trash in. Every day when trash is put in a landfill, it's covered by a layer of construction debris or low-quality soil, and then it's compacted into a cell. The process repeats with all of its tightly sealed and compacted cells, making it very hard for water to get into the landfill.

So sanitary landfills keep the environment inside really dry. But over time, rainwater will eventually infiltrate the layers and form leachate. The tightly sealed cells prevent water from leaving too, so leachate can build up inside the landfill. Some sanitary landfills are built with double liners and pipes so that leachate can be stored and treated. If you went inside a sanitary landfill, you wouldn't be able to breathe—not because it would be super smelly. This is because the cells are sealed up so tightly that it's hard for oxygen to get in and circulate.

The environment inside is mostly anaerobic, which means that there is little oxygen. You see, the prefix "an-" means not or without, and the word "aerobic" means involving or requiring oxygen. So the word "anaerobic" describes a place without oxygen. Aerobic decomposition, which is a process of decay that takes place in aerobic environments and involves microorganisms that need oxygen to survive, can't occur. Instead, anaerobic decomposition, which is decay by microorganisms that don't need oxygen, takes place. This process produces methane, a greenhouse gas that contributes to global warming.

It could take several decades or even hundreds of years for the tightly compacted waste in a sanitary landfill to decompose, so this type of landfill can contribute to global warming for a long time. So, what are the pros and cons of sanitary landfills compared with open dumps? Sanitary landfills are less smelly and less likely to catch on fire. Because sanitary landfills keep the waste inside covered and compacted, we don't have the same problem of the wildlife and the weather moving around the waste.

But no landfill is perfectly sealed, so leachate can still seep out. Adding and compacting layers of trash causes dust and noise. Also, remember that the anaerobic decomposition in sanitary landfills produces methane, a greenhouse gas. But some sanitary landfills capture the methane emitted by the decomposition so that it can be burned to generate electricity. This can capture 60 to 90 percent of the methane produced by the landfill, so that methane capture could be a pro because it generates electricity.

Sanitary landfills are really expensive, so they're a lot more common in more economically developed countries, and like open dumps, they require a lot of land. One way to reduce the amount of material that needs to be landfilled is by burning it in an incinerator. This reduction in the volume of the waste is really helpful in areas with limited land space, so reducing the volume of trash is one of incineration's pros. Modern high-tech waste-to-energy incinerators have another pro: they can produce electricity and sell it to consumers.

Some of the cons of burning trash are that it emits CO2, ash waste, hazardous gases, and other air pollutants. Incinerators could be built to help reduce these emissions by using a series of filters to remove mercury and dioxins from the exhaust gases. Another way to lessen the danger of burning trash is by sorting out the hazardous materials before the incineration. But these safety features, like the filters and the sorting, make waste incineration much more expensive.

Despite all these ways of getting rid of waste, we're still having trouble finding places to put it. The landfill near my home filled up, so my county transfers its waste to a sanitary landfill in a neighboring state. This transportation burns fossil fuels and produces greenhouse gases. But what could we do with the landfills that are already filled up? Some old landfills are mined for valuable metals and recyclable materials. My home state of Virginia turned an old closed landfill in Virginia Beach into a public park called Mount Trashmore Park. It's actually one of the most popular parks in the area, so if you ever feel like picnicking on a landfill, that might be the one to try.