Aerobic composting is a process that uses microorganisms that require air to break down organic matter into compost. In fact, the word “Aerobic’ literally means “with air”.
The microorganisms that require air in this process include aerobic bacteria, fungi, and physical decomposers.
Aerobic composting produces heat, water, and carbon dioxide (CO2). While CO2 is classified as a greenhouse gas, it is many times less harmful than the methane emitted using anaerobic composting.
Some sources state that the process also produces humus, a stable organic material that takes can take decades or centuries to decay.
However, other scientists have challenged this in recent years, and have even questioned the existence of humus.
What we do know is that aerobic composting changes the form of organic matter into compost which benefits beneficial microbes, soil, and (mostly through an indirect process) plants.
Learn more: How Compost Benefits Soil Structure | Mycorrhizae Fungi
The microorganisms involved in aerobic composting
An aerobic composting process is usually started by bacteria that thrive at lower temperatures. These are called mesophilic bacteria.
As these bacteria become more active, they generate heat. This encourages heat-loving bacteria called thermophilic bacteria.
Fungus also plays an important role, especially when decomposing materials that are harder to break down.
It’s likely that thermophilic fungi play a particularly important role. White rot fungus and Actinomycetes are also thought to play an important role in breaking down lignin-heavy materials.
Aerobic composting can still take place at lower temperatures. In this case, bacteria that prefer lower temperatures (psychrophilic bacteria) play a bigger role.
However, scientists still disagree about how big a role they play in the composting process.
Learn more: The Mind-Boggling Role Of Bacteria In Composting
What are the requirements for Aerobic composting?
The aerobic microorganisms that break down organic require moisture to survive. Bacteria also require moisture to move around the compost heap.
See Moisture In Compost for more information.
Most composters are aware of the need to supply greens (high nitrogen materials) and browns (high carbon materials).
Two of the most important for composters to know about are carbon and nitrogen. Carbon is used as an energy source and a building block. Nitrogen is used to build proteins and other elements. Microorganisms in compost also require phosphorus (P) and potassium (K), although home composters don’t need to worry about including these.
Learn more: The C: N ratio in compost
As you can imagine, a process which is called “with air” composting requires air. The bacteria need oxygen for energy, while fungi and physical decomposers need oxygen to survive.
Insulation can provide warmth. This encourages the bacteria which break down organic material fastest.
This insulation can be provided in a number of different ways. For example, a large heap means the interior of the compost will be insulated by the outer layers, while the straw can be used to provide insulation for a smaller heap.
For the soil
Aerobic composting is a great way to reduce waste and create a soil amendment for gardens and farms. It likely produces a compost higher in nutrients than anaerobic composting.
CO2 is only 1/20th as harmful to the environment as methane (the main by-product of anaerobic degradation).
The heat produced in aerobic composting kills some harmful bacteria and pathogens while supporting the growth of beneficial bacteria species. Pathogen reduction continues while the compost cools down, matures and stabilizes.
In contrast to artificial fertilizers, many of the nutrients in compost are insoluble, rather than soluble. This reduces the leaching of nutrients from the soil which can damage the environment.
Aerobic composting is much faster than anaerobic composting, and the initial stage of composting can take as little as 14 days. However, it is important to allow the compost to mature after the initial hot stage.
There are many ways to facilitate aerobic composting. These include:
The Berkely Method
Developed in the 1950s, this labor-intensive method involves turning compost either every day or other every day. The authors claim finished compost can be produced in as little as 2 weeks, but in reality, the compost is likely to need a maturation phase before being used.
Using compost tumblers
Compost tumblers utilize leverage and design to allow regular turning with less effort. While one independent study by Which suggested that they take longer than a regularly turned compost bin to produce compost, the effort involved is likely to be far less.
Static piles can be constructed in a way that maximizes airflow. This allows aerobic composting to take place with minimal (or sometimes zero) turning.
Learn more: 13 Composting Methods to Choose From | Industrial Composting Technologies
Tools needed for aerobic composting
The tools needed for aerobic composting depend on the accuracy and quantity needed and the purpose you need them for.
A home gardener making their first pile can probably manage with existing equipment such as a garden fork and a pair of shears, while a commercial operation will want industrial equipment well beyond the scope of this article.
If you’re a home gardener with more than a passing interest, I recommend considering a compost thermometer. This helps you know when you need to take action and is an enormously helpful learning tool.
If you have a larger compost pile and have problems turning it, it is also worth investing in a compost fork.
Also see: Tools for Faster, Better Compost
Etymology Side note
If, like me, you’re interested in history, you might want to know that the word Aerobic was coined by Louise Pasteur in 1863. The word was formed from the Greek ‘Aero’ (air) and the word bios (to live).
The Science Of Composting: How Compost Happens
Biocycle: Aerobic Composting and Anaerobic Digestion
On Farm Handbook: Composting Processes and Techniques
Online Etymology Dictionary: Aerobic
Global Composting Solutions: Aerobic v. Anaerobic Composting