Field of wheat being blown by the wind

Anaerobic Digestion vs. Composting

Millions of tons of food go unused every year and landfills receive far more food products than any other material. As we move to more sustainable ways of living, how we dispose of our organic waste can have a real impact on the environment and society. 

On a consumer level, there are many ways of diverting some of this waste: using more of the food item, donating leftover/extra food to those who need it more, and/or feeding pets or livestock with scraps.

Yet there’s often still food left over or food past its expiration date which, especially at larger scales, needs somewhere to go. This is where some interesting ways of breaking down organic waste into useful products comes into play: composting and anaerobic digestion.

Breaking it Down

Anaerobic digestion and composting are ways of utilizing bacteria to process biodegradable materials. These processes both offer considerable environmental benefits compared to depositing organic material in landfills, where uncaptured methane production escapes into the atmosphere to contribute to greenhouse gas effects. 

These processes speed up the natural decomposition process and create new end products that can be used for energy or fertilizer. By recycling food waste into reusable byproducts, we can minimize the buildup of solid waste in the environment and minimize contributions to global warming. There is simply no doubt that either option is far superior to sending food to the landfill to rot!

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What’s the Difference?

While it is true that both of these techniques utilize microorganisms to proceed, the distinction between the two is centered around the use of the term “aerobic.” Aerobic means “with oxygen” and comes from the Greek words for air (aero) and life (bios). Anaerobic means “without oxygen,” so as you might imagine, the presence of oxygen plays a pretty big role in the difference between the two methods. 

Composting is the decomposition of organic matter in the presence of oxygen while anaerobic digestion is the decomposition of organic matter without oxygen. Both processes require moisture, but each requires a different kind of bacteria to convert organic matter into gaseous products. Anaerobic digestion relies on bacteria that thrive when oxygen is not present, while composting utilizes bacteria that use oxygen to grow. The end products of composting is primarily solid fertilizer and heat, whereas anaerobic digestion creates a renewable energy source known as biogas in addition to a liquid fertilizer.

Anaerobic Digestion vs Composting

Anaerobic Digestion

Anaerobic digestion is a naturally-occurring process, and is one of the most promising methods of sustainable waste processing available to us. It reduces the accumulation of waste while also providing environmentally-friendly products which get the most value out of the food being discarded. 

For example, it’s already used extensively in the United States to break down sewage at waste water treatment facilities and contribute to the power generated by utility providers. Other countries such as Sweden are already using biomethane as a vehicle fuel. The gas can also be used for heating or generating electricity, opening up a world of potential applications. 

Anaerobic digestion happens in a tightly sealed container which is heated and filled with organic matter mixed with water. The chemical reaction to convert organic matter into biogas occurs in three main steps:

  1. Bacteria break down animal and plant matter into simple molecules (think of sugars like glucose!).
  2. Bacteria continue to break those molecules down into organic acids (these molecules are smaller than sugars, think of vinegar!).
  3. Bacteria finally convert these organic acids into biogas, which consists of methane and carbon dioxide.

The end products include biogas and a mixture of solid and liquid wastes. This biogas can then be cleaned to become “biomethane,” a near-pure source of renewable energy. In addition to being an incredible source of renewable energy, anaerobic digestion also:

  • Sanitizes the organic waste, eliminating the spread of diseases
  • Is much less likely to cause environmental pollution through untreated waste
  • Produces versatile fertilizer
  • Creates renewable energy streams, helping the economy and businesses

However, this system is more complex and may require more initial startup costs and/or time. This solution isn’t for everyone, but offers significant benefits to businesses who can opt in to this sustainable and safe energy recycling. 


Composting, on the other hand, is easy to do with very little setup or training. The average homeowner could create an open compost bin practically anywhere on his or her property and get to composting right away.

As waste is piled up on the compost heap, the natural composting process oxidizes the various organic matter into a combination of carbon dioxide and nutrient rich fertilizer. This is an example of clean source recycling and a much better option than throwing organic waste in the trash as a beneficial byproduct can be obtained at the end of the process. 

Yet there are some major drawbacks. 

While composting produces solid fertilizer, the carbon dioxide byproduct lacks the versatility or energy of biomethane. In addition, if the compost pile is not regularly monitored and turned over, the heat within the pile will not be sufficient to eliminate any diseases or pathogens in the organic waste. This raises major issues if the composter spreads fertilizer with E. coli bacteria over his or her fields without ever knowing it. Another issue if the pile is not turned over is that methane will be released into the environment as the waste degrades: you’ve essentially created a tiny landfill!

Composting was originally popularized as a simple way of discarding organic matter. While there’s no doubt it’s an improvement over discarding waste at the landfill, composting offers no source of renewable energy. It requires significant monitoring and tending to decompose waste properly, and doesn’t create end products that can be as widely (and safely) used as anaerobic digestion does. 

The Cleaner Organic Waste Process

After reviewing the processes and outputs of the two systems, it’s pretty clear that anaerobic digestion is the much more efficient, clean, and more energy-rich option for organic waste decomposition. It has positive long-term effects on the environment as well as the greater economy compared to composting, and runs on its own without the need for daily manual mixing. 

Have Questions About Anaerobic Digestion? IREA is Here to Help.

IREA develops customized renewable energy solutions and has spent decades working with governments and agencies across the world to identify the best options. Currently, we have several anaerobic digestion projects that process animal waste, food waste, and farm waste into renewable energy and fertilizer for our clients.  

Explore these projects at or contact us to learn more about how anaerobic digestion can benefit you: (202) 957-4131.

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