Oxygen is an important factor in composting. Like most living beings, the aerobic microorganisms that turn food and garden waste into compost require oxygen to support their life. They get it from air that flows through the compost pile or that is trapped in the spaces within it.
But how do you get air into a compost pile? One common way is just to turn the pile over with a bulldozer or a specialized compost pile turning machine. This is simply the big mechanized version of what many people do when they dig and turn their backyard composting. Doing this moves and traps air in the spaces between the food and yard waste. Another way that composting facilities get air into compost piles is by pumping air directly into the pile. Some municipal and industrial composting facilities do this by building the pile of compostable material on top of a solid pad with air channels in it. Once the pile is complete, air is pumped into the channels and forced to rise up into the compost pile. Air blowing through the pile of compostable material from the bottom meets the oxygen needs of the microorganisms. This helps them to grow and consume the food and yard waste material that they turn into rich compost.
Compost facility operators face challenges if there is not enough air in the compost pile. This can happen if the pile is too wet and is turning to sludge. That can lead to aerobic microorganisms dying off and the composting process stopping. Quite often in this situation the aerobic microorganisms will be replaced by anaerobic microorganisms which can thrive without oxygen. The waste will start to break down again – but with one very noticeable difference. The smell.
Anaerobic decomposition of food and yard waste almost always produces a pungent odour. So, if a compost operation is beginning to stink you can tell that the process has lost its aerobic microorganisms and they have been replaced by the anaerobic kind.
By the way, if you are in the market for microorganisms, whether the aerobic or anaerobic kinds, you can buy them. However, composting system operators seldom need to go shopping for them. There are so many microorganisms already living in the soil and in the air that a composting operation, or an anaerobic digestion system, will usually get started by itself, once you build the pile, with microorganisms that are naturally occurring on the fresh fruit and vegetable waste and on the yard waste that is put into the pile.
For more information:
Compost Fundamentals: Aerobic Decomposition. Washington State University.
Greens and Browns: Aerobic & Anaerobic Composting. Oregon State University.
Types of Composting and Understanding the Process. US Environmental Protection Agency.