What are the advantages and disadvantages of anaerobic digestion vs composting is a question asked by a large number of people. Many of our readers who are familiar with composting, but who are thinking more widely about the subject of recycling organic waste and have just heard about Anaerobic Digestion want to know the anaerobic digestion pros and cons.
If this is you, read on while we answer the question: “Which is best, anaerobic digestion, or the much simpler and lower capital cost method of composting?”
First of all the two processes are very much the same. The crucial difference is that composting is the decomposition of organic matter in the presence of air (oxygen) and anaerobic digestion (AD) is the decomposition of organic matter, without air (and most importantly oxygen) present.
Now we make the case for each process by listing the advantages and disadvantages of anaerobic digestion vs composting below:
Advantages of Anaerobic Digestion
- It is a net energy producing process which produces renewable energy in the form of biogas.
- It produces a liquid and a fibrous fertilizer.
- It sanitizes the feedstock/ waste which is put through it, as long as the temperature is held above a required temperature for a pre-defined time period.
- It reduces odour below unprocessed waste odour levels.
- It is much less likely to cause environmental pollution than spreading untreated organic waste on land.
- The effect of the fertilizer is longer lasting than for untreated organic waste.
Disadvantages of Anaerobic Digestion
- When carried out at a commercial scale on farms and at wastewater treatment works (WwTWs) it requires a high level of investment in large tanks and other process vessels.
- If run inefficiently AD can cause an odour nuisance.
Advantages of Composting
- Lower initial capital investment needed to start of composting facility than is needed for an AD Plant.
- A slightly lower level of training is needed to run a composting plant the is required for an AD Plant.
- It produces a solid output/ fertilizer only. For some this will be an advantage, but in general this digestate product is a neutral factor, neither positive or negative for composting.
- It has the same advantages as for AD (items 3 to 6 inclusive) over spreading untreated organic waste material on land.
Disadvantages of Composting
- Like anaerobic digestion, it is necessary to pasteurize the composted material to ensure that all infectious agents have been effectively removed. This requires very good operating practice and detailed monitoring to demonstrate to regulating bodies.
- This is the biggest disadvantage! Composting requires the input of quite large energy inputs to aerate and turn the compost piles. By comparison anaerobic digestion wins hands-down for “greenness”, and it makes no contribution to reducing the carbon footprints of businesses that use the composting process. By comparison AD Plants can assist businesses by reducing their carbon footprint.
- Like AD, if run inefficiently Composting can cause an odour nuisance.
We also found the following blog articles which discuss anaerobic digestion vs composting as follows, which you might find interesting to read:
Anaerobic Digestion – an Alternative to Composting (Ground To Ground Blog)
Similar to composting, in AD bacteria consume organic waste such as food scraps, silage, and animal waste and generate an environmentally benign byproduct that can be used as a natural fertilizer. Unlike composting, however, AD also produces biogas, which consists of about 2/3 methane (CH4). Natural gas is methane with a small amount of other trace gases, so biogas can be used as fuel like natural gas. … via.ADAlternativeToComposting
What’s the Difference Between Anaerobic Digestion and Aerobic Decomposition
Yes, one is with and the other without oxygen, and both divert waste from the landfill—but in terms of the end products, what is the advantage of anaerobic digestion? Simply put, does society face a shortage of compost or renewable energy?
In San Francisco, the green compost bins are ubiquitous. Even the food trucks are required to place bins alongside their trucks for compost, recyclables, and trash. Result: the city is diverting an enormous amount of trash from the landfill to help meet its zero-waste goal and producing lots of compost in the process – a process which also produces a lot of carbon dioxide, “the primary greenhouse gas emitted through human activities,” according to the EPA.
A few cities are taking an alternative, more expensive approach to diverting this organic waste called anaerobic digestion and in the process also producing biomethane that is captured for use in electricity generation or used as a transportation fuel. And from a “carbon intensity” perspective, this biogas, also called renewable natural gas, scores at the bottom of carbon intensity chart for California’s Low Carbon Fuel Standard, i.e. it is one of the cleanest of all transportation fuels…. Pop Quiz Difference
Anaerobic Digestion vs Composting: Another Way to Compare the “Aerobic” Process of Composting with “Anaerobic” Digestion is to compare the simplified process diagrams which we show below:
(Source: Advanced Biological Treatment of Municipal Solid Waste, Defra UK, 2007)
Anaerobic Digestion vs Composting – Conclusion
There are advantages to both anaerobic digestion and composting, and certainly applying either before green garden waste, or other organic waste is spread on the land, is better than not processing these materials at all.
On balance the preferred process is anaerobic digestion.
The primary reason that anaerobic digestion is considered more sustainable than composting is that composting requires an energy input to carry out the process. The energy is used in the power needed to turn the compost piles during composting. The fact that anaerobic digestion produces biogas is a renewable energy source which burns cleanly, and that biogas plants make more energy than they consume to operate, is generally the factor that makes anaerobic digestion the best most sustainable option.
We hope that you found this article useful. If so, and you have a moment to do this. We would greatly appreciate your comments.