Dear Science,

I've always been the conscientious kind of consumer who separates her trash and recyclables. Recently, I have also started making sure I buy only biodegradable things: cardboard containers, the corn-based plastic alternatives, paper instead of plastic if I can help it. Well, you get the picture. These days, most of my trash is as biodegradable as I can make it. Here's a logical problem, though: If I put all this wonderful biodegradable trash in a trash bag, isn't it just going to stay in the landfill forever, trapped inside a plastic bag, with nowhere to biodegrade? Should I try to bury it someplace, instead?

Thanks,

Trashed

Your suspicion is mostly correct. Entombed deeply in a landfill, your biodegradable trash is forced to degrade without oxygen, creating copious amounts of methane gas. Methane is a potent greenhouse gas, far worse than carbon dioxide. If you're sending something to a landfill, it's better for the planet if it never degrades.

A landfill is intended to be a place without time, where trash is meant to stay isolated from the surrounding air, water, and soil—somewhat like the Republican plan for America, through immigration reform (a completely sealed USA). Degrading isn't in the plan; it happens anyway, just in a different way.

I now need your close attention. Put your biodegradable cardboard container on your lawn and it will eventually get wet. Microbes will start to eat it. Inside each microbe cell, the carbon and hydrogen chains of the cardboard are steadily stripped down to more and more basic carbon molecules as the cell busily collects energetic electrons released during this metabolic degradation. These electrons are shoved into the mitochondrion of the cell, where most of the energy is captured and used as fuel for the cell. Eventually the cell must do something with these electrons. Free electrons are the nuclear waste of a cell, the nasty by-product of a very efficient energy source. Left to roam about, the electrons are likely to shred up something important. Almost all cells eventually dump these waste electrons onto a passing oxygen molecule, creating carbon dioxide. (Plants, during photosynthesis, do the opposite: They store energy by stealing electrons from carbon dioxide to build up carbon and hydrogen chains, releasing oxygen as a waste product.)

Your same biodegradable container interred in a landfill will inevitably get wet. Microbes will attempt to break down the hydrocarbon molecules, like they would on your lawn, but no longer have oxygen. Instead of the more efficient, free-electron-generating but oxygen-requiring metabolism, these microbes must stop somewhere before carbon dioxide. Generally this is at methane, a carbon and four hydrogen atoms. The methane bubbles out of the landfill and contributes to climate change.

Where should your biodegradable waste go? Ideally into a compost pile, where plenty of oxygen encourages healthy degradation. If you live in Seattle, put it in your yard-waste container and the city will do this for you.

Oxidatively phosphorylatingly yours,

Science

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