Composting vs. Anaerobic Digestion

Most of us have heard of ‘composting’ as the mainstream way to recycle organic waste, and while the composting process is effective, there are other methods that may be more efficient. Not mentioned as often, but is certainly up and coming, is biogas production for renewable energy. These two methods of organic waste disposal are similar in ways, and each offer their own pros and cons. Their main difference is their way of decomposition, as they utilize different bacteria to breakdown and therefore release different gases in the process. This starts with anerobic and anaerobic – what is the difference? Let’s get into it!

Aerobic vs. Anaerobic

To start, lets first discuss the difference between aerobic and anaerobic. Very simply put, anerobic means ‘with oxygen’ and anaerobic means ‘without oxygen.’ Given this, during the composting process, organic matter (biomass, food waste, manure, leaf/yard waste etc.) must be exposed to oxygen to create the fertilizer, whereas in the biogas process, the breakdown process is controlled in an anaerobic environment using an anaerobic digester.


Composting is the natural aerobic breakdown of organic matter, to create a nutrient dense fertilizer to put back into your garden to feed and nurture soils. For composting, it is essential that the organic waste is exposed to oxygen to assist in the disintegration of the material. There is a fine science to creating and producing the perfect compost for use of fertilization, requiring 4 key elements: nitrogen, carbon, oxygen, and water. Given this, composting requires balancing nutrients, regulating temperature and moisture, as well as consistent aeration (to encourage an aerobic environment). When the degrading biomass is exposed to oxygen, it helps to reduce the amount of emitted greenhouse gases, as they are not getting ‘trapped’ and the material is able to ‘breathe.’ With the proper balance of  nutrients and proper aeration, composting does not emit significant greenhouse gas emissions. However, there are off-gases from the composting process that are not collected and emitted into the atmosphere. That is where the biogas process using anaerobic digestion becomes superior.

Pros to Composting:

  • Anyone can do it – it only takes a back yard composter to start this process
  • Low buy in, for both commercial and residential applications
  • Great basic way to start diverting food waste scraps from your home kitchen
  • Can become a fun hobby for gardening enthusiasts
  • Yield a high nutrient fertilizer for home and commercial gardens/crop growing

Cons to Composting:

  • Does ultimately release some greenhouse gases, especially in large or commercial scale facilities, even with capture methods in place

Anaerobic Digestion & Biogas

Anaerobic digestion and the biogas process is part of a biological waste treatment method used in waste treatment plants everywhere in the world. Since anerobic digestion already occurs in nature (and in landfills and livestock management systems), using an anaerobic digester to produce biogas is simply better utilization of an already available renewable natural resource. Biogas is produced only after the organic waste (food waste, manure, etc) is broken down by natural bacteria from the anerobic digestion process. Using an anaerobic digester creates a controlled environment for organic waste to be broken down so that the contents can be optimized and contained.

The break down of steps are as follows:

  1. Liquid organic waste, animal manure and/or solid organic waste is led into a digester where an anaerobic process using bacteria ferments the wastes and produces biogas as a gaseous biproduct.
  2. The remaining non-digestible solids in the digester are collected as a high nutrient ‘sludge’ or ‘compost’ that can later be returned to the ground as fertilization.
  3. This biogas produced is further processed, resulting in a gas consisting of about 50% methane, 50% carbon dioxide. This is similar in chemical composition to natural gas obtained from the oil and gas fields.
  4. Once the methane and carbon dioxide are filtered and cleaned, the gases can be stored under high pressures in cylinders or pumped directly back into the grid for use in both renewable electricity and renewable natural gas.

Pros to Anaerobic Digestion/Biogas:

  • Yield two useful bioproducts (RNG & fertilizer)
  • Captures all greenhouse gases (and turns them into a renewable resource)

Cons to Anaerobic Digestion/Biogas:

  • Can only be done on a commercial scale
  • Very costly to start and maintain

Organics in the Landfill

Although this is aside from composting and anaerobic digestion, organics in the landfill decompose in an anaerobic environment, which makes them so problematic. To really get the full scope of composting and anaerobic digestion (and why these processes are so important), we can’t leave out what happens when you throw your organics into the landfill.

Organics that are disposed of in the landfill are problematic for multiple reasons, but the most worrisome being the uncontrolled released of methane (one of the most harmful greenhouse gases contributing to climate change). Naturally when organic matter decomposes, it undergoes aerobic decomposition (needing oxygen to break down- ‘i.e composting’). When organic/biomass waste goes to the landfill, it inevitably gets buried under massive amounts of other trash, cutting off it’s regular supply of oxygen. With its limited supply to oxygen, coupled with its inability to be aerated, the organic waste then ends up undergoing anaerobic decomposition (which allows the food waste to be broken down by organisms that can live without free-flowing oxygen). This creates and releases uncontrolled amounts of unfiltered, raw ‘biogas’ into the atmosphere. Landfills are the third-largest source of human-generated methane emissions in North America.


Both composting and anaerobic digestion far exceed throwing organic waste into the landfill. However, for large scale organic waste disposal, composting alone falls short in comparison to the production of biogas. All food waste that enters our facility is sent to local biogas facilities to create renewable natural gas. This way of food waste disposal is superior to any other disposal method for organic waste because it provides two biproducts – biogas to energy and high nutrient fertilizer. The additional benefit to an anaerobic digester/biogas facility is that all the off-gases are captured (& turned into a renewable product) and nothing is released into the environment. All other forms of decomposition of food waste/organic matter/biomass emit greenhouse gas emissions, some more then others, but ultimately biogas is the most environmentally friendly way to dispose of organic waste.


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