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The Advantages and Disadvantages of Anaerobic Digestion vs Composting

What are the advantages and disadvantages of anaerobic digestion vs composting is a question asked by a large number of people.

Image illustrates the benefits of Anaerobic digestion vs composting: Making a Comparison. Anaerobic digestion pros and cons.
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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

  1. It is a net energy-producing process which produces renewable energy in the form of biogas.
  2. 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 (pasteurized).
  3. It reduces odour below unprocessed waste odour levels. an example of this is the comparison between manure spreading and the same material spread after anaerobic digestion when it is known as “digestate”.
  4. It is much less likely to cause environmental pollution than spreading untreated organic waste on land.
  5. Provides for efficient resource recovery, and conservation of non‑renewable energy sources.
  6. Lower sludge mass generation when used as a primary water treatment method compared to an aerobic system applied to the same contaminant concentration and flow.
  7. The effect of the fertilizer is longer lasting than for untreated organic waste.

Disadvantages of Anaerobic Digestion

  1. 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.
  2. If run inefficiently AD can cause an odour nuisance.
  3. Does not convert as large a proportion of the carbon in the biomass to biogas as can be achieved using gasification.
  4. It takes longer to start‑up the process due to the slow growth rate of the methane-producing organisms as compared to aerobic systems.
  5. In some applications has higher buffer chemical dosing requirements for pH control to keep the pH for AD within the range of 6.5–8.
  6. Nutrients removal is not as efficient as in aerobic treatment if is used as a water treatment process. Invariably a post‑treatment process will be necessary before any discharge to a watercourse. For such discharges, a secondary process stage will be needed such as membrane filtration, or even further aerobic treatment, in order to meet the river, ditch, or stream discharge consent requirements and protect the aqueous environment.

Advantages of Composting

  1. Lower initial capital investment needed to start of composting facility than is needed for an AD Plant.
  2. A slightly lower level of training is needed to run a composting plant the is required for an AD Plant.
  3. 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.
  4. It has the same advantages as for AD (items 3 to 6 inclusive) over spreading untreated organic waste material on land.

Disadvantages of Composting

  1. If the composted materials contain waste types such as animal or food waste there is a risk that diseases (for example “foot and mouth”) may be spread in the compost. (See our grey box below which explains the difference between “green” and “food” waste compost.)In those circumstances, many countries (such as the UK and EU) the Animal By-products regulations must be complied with for all commercial compost sales/ spreading on land.Like anaerobic digestion, it is necessary to pasteurize the composted material to ensure that all infectious agents have been effectively removed. Commercial composting companies ensure that they meet the relevant regulations by applying the PAS 100 code for Quality Compost.
  2. This can be done by ensuring that it composts rapidly and raises its own temperature, through the heat produced during composting. The required hot temperature must be held constant for a stated minimum time period. Ensuring that every batch self-sanitises itself this way requires very good operating practice. and detailed monitoring to demonstrate successful pasteurisation to the  local environmental regulating body.

3. This disadvantage is the biggest disadvantage of composting! Composting requires the input of quite large energy inputs to fuel and operate the equipment needed to aerate and turn the compost piles.

By comparison anaerobic digestion wins hands-down for “greenness” by providing its own power to do this.

Composting makes no contribution to reducing the carbon footprints of the businesses that use the composting process.

By comparison AD Plants can assist businesses by reducing their carbon footprint.

4. Like AD, if run inefficiently, composting can cause an odour nuisance.


The Difference Between “Green” and “Food” Waste Compost

The are to distinct “Green” and “Food waste” compost types and input materials according to their source.

Green and food derived composts can be used in landscape and regeneration projects. Green compost is solely derived from garden waste and comes from sources such as domestic gardens, municipal parks and recreational areas, and is collected separately from other waste streams.

This compost is usually produced outdoors in open windrows.

Food derived compost contains a mixture of garden and food waste collected separately from other waste streams from households and businesses. This compost is produced in enclosed in-vessel systems and must be compliant with Animal By-Products Regulations (ABPR), as well as the relevant waste legislation. via wrap.org.uk


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

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:

Aerobic digestion - known as composting
Fig. 1 – Schematic Diagram Showing the Aerobic Digestion Process
Anaerobic digestion schematic diagram
Fig. 2 – Schematic Diagram Showing the Anaerobic Digestion Process

(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 (a renewable energy source which burns cleanly), and that
  • biogas plants make more energy than they consume to operate,

are generally the factors that make anaerobic digestion the best, most sustainable, option.


Footnote:

Energy Balance Benefits and Feedstock Issues

Although composting (IVC or in Windrows) and anaerobic digestion (AD) treat similar wastes, they are in fact complimentary and not competing technologies.

From an energy consumption and greenhouse gas emission reduction point of view, there is merit in having an AD stage first following by composting.

The benefit of an AD process is that it produces energy in the form of biogas, whereas composting will generally use energy in the processing stages, in aerating the waste and treating any leachate arising from the process. Although the AD liquor which comes out of an AD plant often needs treating, the energy required is available from the biogas.

The digestate from AD often needs to be matured by composting before it can be applied to land.

Since the AD process has reduced the total amount of material (which has been removed as gas), less energy should be required than if the whole amount of waste was treated through composting.

Notwithstanding these issues, some proportions of materials are inherently better suited to either composting or anaerobic digestion.

For example, high proportions of green waste with much bulky wood material is better suited to composting processes as it is easier to handle and has less gas production. Conversely, high proportions of kitchen waste are better suited to AD processes as the gas production potential is
higher and odour control is easier to achieve.


We hope that you found this article useful. If so, and you have a moment to do this. We would greatly appreciate your comments.

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Comments

  1. Reply

    I liked your site a lot. I’m taking an online course on Water Quality Technology from the UW-Moraine Park and I found this very useful in helping me write a paper on alternate methods of sludge stabilization. Thanks.

    1. Reply

      Thanks for your feedback. It is appreciated, and it is good to hear that you found some useful information for your paper.

        • Vasuki
        • January 16, 2020
        Reply

        I totally disagree with the assumption that aerobic digestion is more expensive, which is far from the truth. Shallow open pits can used in rotation for composting, where earth worms and bacteria will break down organic materials producing valuable organic manure. In most warm climates, aerobic composting can be completed within 2-4 weeks.

    • sami
    • January 2, 2017
    Reply

    why aerobic degradation is faster than anaerobic degradation????????????

      • radimin
      • October 7, 2017
      Reply

      I think that the normally given answer the AD experts will give you is that the methanogenic archaea that do the anaerobic degradation, are a lot slower growing (metabolising) than their aerobic equivalents. I hope that helps you.

    • Peter Ogrady
    • January 28, 2017
    Reply

    The reason that aerobic degradation is faster than anaerobic degradation is that the anaerobic organisms (methanogens) that do the degrading in anaerobic systems are slow growing at normal ambient (atmospheric) temperatures. They grow faster at higher temperatures. If you look on the web you will see that in hot tropical climates it is much more common to see small domestic biogas plants. Those un-insulated tansk don’t work so well in cooler climates.

  2. Reply

    tanks alot it of great help to my project work

    • brodie
    • January 8, 2018
    Reply

    Thank you for posting this great article. I’m a long time reader however I’ve never actually left a comment.
    I’ve bookmarked your site and shared this on Facebook.

    Thanks again for a quality article!

  3. Reply

    Your writing is very well received by me. At first my view was to say that anaerobic digestion was not preferable to composting, now I see that you are telling us the opposite. The fertiliser is a much needed product for farmers I am sure.

    • Alice Araujo
    • May 8, 2018
    Reply

    The Advantages of Anaerobic Digestion are many. Thanks to Brazilian-German Project on energy from Biogas – PROBIOGAS (DKTI). In May 2016, a biogas project based on agricultural residues with a capacity of about 21 MW won an energy auction for the first time. The energy will be priced at EUR 70/MWh, and it will start producing electricity from 2021.

  4. Reply

    Hello there,

    My name is Aly and I would like to know if you would have any interest to have your website here at anaerobic-digestion.com promoted as a resource on our blog alychidesigns.com ?

    We are in the midst of updating our broken link resources to include current and up to date resources for our readers. Our resource links are manually approved allowing us to mark a link as a do-follow link as well.

    If you may be interested please in being included as a resource on our blog, please let me know.

    Thanks,
    Aly

    • Hanno Halonen
    • August 28, 2018
    Reply

    Hi. Thank you for the informative writing and article. Some people are using the heat generated from composting to heat water/interior spaces, so perhaps that could be added to the advances of composting.

    • Baz
    • November 17, 2018
    Reply

    Hello there,

    Would like to know if you would have any interest to have your website here at anaerobic-digestion.com promoted as a resource on our blog. If so mail me to the email I just used for this post.

    We are in the midst of updating our broken link resources to include current and up to date resources for our readers. Our resource links are manually approved.

    If you may be interested please in being included as a resource on our blog, please let me know.

    Thanks

    1. Reply

      Baz – Yes. I mailed you.

    • tam
    • October 31, 2019
    Reply

    what if the organics are out of a MSW material recovery facility with contaminants like glass, plastics etc.
    can I in this case use this contaminated organics in AD or compost ?

      • radimin
      • November 5, 2019
      Reply

      In many countries with good regulation for healthy food production there will be rules for farmers to comply with.

      The use of what was originally from an “MSW material recovery facility” may not be allowed if the compost is to be used in agriculture. It will be expected to have heavy metals too high for this.

      The regulations in the UK, for example, require that the compost which is spread for crop use, will not damage the land for food production.

      Depending on the source of any compost/ matured digestate there may be any one of many contaminants which must not be allowed to build-up in the soil. Before, those are spread on the fields the compost must be tested and shown to comply with the PAS100 standard for the materials in the compost. Plus, the required conditions of pasteurisation must also be complied with.

      “MSW material recovery facility” organic waste fraction may also contain waste covered by the Animal By-products Regulations.

      You mention glass and plastics contamination. These are not specifically banned in the UK. But, many people have said that the UK regulations are out of date and need updating to specifically prohibit plastics in compost spread on agricultural land.

  5. Reply

    It is very misleading to you say compost need to be pasteurised before it can be used. This shows a basic misunderstanding how and why compost is made and used. You also ignore the reduction is emissions from reduced artificial fertiliser use.

      • radimin
      • November 29, 2019
      Reply

      Colin. I think that you needed to read it more carefully, but maybe the fact that I was referring to commercial composting, not garden composting, was not as clear as it could have been. So, I have updated the text to make it clear that my comparison was being made for a disadvantage of food waste composting and mixed food and household waste, and not solely “green” waste.

      Anaerobic digestion also results in reduced artificial fertiliser use so I don’t see why it should be included in a comparison article?

    • R Prakash
    • January 1, 2020
    Reply

    It all depends where are you going the composting. If you are doing Home Composting Aerobic is best.
    Anaerobic creates foul smell and one is dissuaded in doing composting itself. For large community projects, AD could be ok.

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