Aerobic composting
Aerobic composting is the principle at work in aboveground composting environments — whether it takes place in a freestanding pile or in a container that provides air circulation, such as a bin with open sides or a tumbler with aeration holes.
As long as plenty of air is available, aerobic decomposers work faster and more efficiently than their anaerobic counterparts, providing you with finished compost on a faster timetable. However, as organisms deplete the supply of oxygen from the existing spaces and pores between bits of organic matter, the decomposition process slows.
To keep your decomposers working at maximum speed, you may want to incorporate some type of aeration aid during your initial pile construction. One way to do this is to pile organic materials on top of a recycled shipping pallet. The pallet sits several inches above the ground's surface, allowing air to flow beneath it.
If you notice your compost pile shrinking, you can reenergize your aerobicizers by giving your pile a fresh infusion of oxygen in a couple ways:
Turn your pile completely: Fork a freestanding heap to an adjacent spot or turn the contents of one bin into another. If using a tumbler, give it a spin.
Stir organic matter regularly: Use a pitchfork or an aerating tool to stir things up.
If your compost is emitting a bad odor, like rotten eggs or ammonia, it's too wet or wasn't thoroughly mixed. A well-constructed compost pile doesn't smell bad. In fact, it emits a refreshing earthy aroma, like kicking up leaves during a walk through the woods.
Aboveground aerobic decomposers can withstand higher temperatures than their anaerobic counterparts, and they generate heat as a byproduct of their activity. Not all aboveground piles are "hot," but when conditions are to the decomposers' liking, temperatures in your pile heat up sufficiently to kill weed seeds and pathogens.