This is a magazine article with the title: The Magic of Combined Anaerobic Digestion with Composting of Municipal Solid Waste
This downloadable article was first written in 2004, at a very different stage in the development of modern anaerobic digestion.
At that time, anaerobic digestion was still a relatively unfamiliar technology to many people working in municipal and commercial organic waste management. Composting attracted far more attention, while AD outside the sewage treatment sector was still regarded by many as specialised, experimental or difficult to justify economically.
Only a small number of agricultural biogas plants were operating in the UK, many of them developed by pioneering farmers, while sewage treatment works remained the most familiar application of anaerobic digestion.
Online information about AD was also much more limited than it is today. When I originally wrote this article in 2004, relatively few detailed articles about anaerobic digestion were available on the web and search interest in the subject was very small by present-day standards.
The article was therefore written primarily for an audience already familiar with composting.
Its central argument was that anaerobic digestion should not necessarily be seen as a competitor to composting. The two technologies can be complementary: anaerobic digestion can recover renewable energy from readily biodegradable organic matter, while aerobic composting can provide a useful downstream treatment or maturation stage for suitable solid material.
Why This Article Was Written
In the early 2000s, the economics of anaerobic digestion were very different.
Energy was relatively cheap, renewable-energy incentives were far less developed, and there was little of today’s policy emphasis on biomethane, food-waste recycling, renewable gas, energy security and decarbonisation.
For many waste managers, composting was the established biological treatment technology.
One practical way to explain the potential of anaerobic digestion was therefore to show how it could be incorporated alongside an existing composting operation.
That was the purpose of this article.
A Note About the Term “Anaerobic Co-Digestion”
The terminology used around anaerobic digestion has become much more standardised since this article was first written.
Today, anaerobic co-digestion normally means the simultaneous digestion of two or more different biodegradable feedstocks within the same anaerobic digester.
Examples include:
- food waste with animal manure or slurry;
- food waste with sewage sludge;
- crop residues with manure;
- food-processing residues with an established AD feedstock; and
- other compatible combinations of organic materials.
That is different from the process combination discussed in this older article.
Combining anaerobic digestion with aerobic composting is better described today as an integrated AD and composting system.
In such a system, anaerobic digestion and composting remain separate biological processes:
- anaerobic digestion takes place without oxygen and produces biogas and digestate;
- composting is an aerobic process requiring oxygen; and
- the solid fraction of digestate, or other suitable organic material, may subsequently be composted or matured aerobically.
For the modern definition and current discussion of co-digestion, see:
Anaerobic Co-Digestion: Feedstock Combinations and Why They Work
From Unusual Idea to Established Practice
One of the interesting things about revisiting this article more than two decades later is how much the anaerobic digestion sector has changed.
In 2004, the idea of combining AD with other organic-waste treatment systems still needed considerable explanation.
Today, anaerobic digestion is a mainstream treatment option for food waste, agricultural residues, sewage sludge and many industrial organic wastes.
Similarly, the concept of co-digesting different feedstocks is no longer unusual. Anaerobic co-digestion has become a normal part of modern AD design and operation.
The discussion has therefore moved on from:
“Can different organic materials be digested together?”
to much more practical questions such as:
- which feedstocks are genuinely complementary;
- what proportions should be used;
- how rapidly a new feedstock can safely be introduced;
- how contaminants and inhibitors should be controlled;
- how co-digestion affects digestate quality; and
- whether the plant permit allows the proposed feedstocks to be accepted.
Why Keep This Older Article Available?
I have chosen to retain this download because it captures an important stage in the development of the waste anaerobic digestion industry.
It shows how AD was being explained to composting operators and waste-management professionals at a time when the technology was still far less familiar than it is today.
The underlying engineering idea remains valid:
anaerobic digestion and composting can be highly complementary technologies when they are used in the right sequence and for the right materials.
The terminology has changed, the economics have changed and the industry has matured, but the basic concept of integrating anaerobic and aerobic biological treatment remains relevant.
Download the Original Article
The downloadable PDF below preserves the original article, which was first written in 2004 and later updated in 2014.
Please read it as a historical technical article. Some terminology reflects the way these processes were described at the time and should not be taken as the current industry definition of anaerobic co-digestion.
This is a downloadable single article with the above title. Printable Version
Price: Free (Acrobat file download)
Downloads from 1 February 2009 to February 2012 = 1537
Further Reading
- What Is Anaerobic Digestion? – our main guide to the AD process, feedstocks, biogas and digestate.
- Anaerobic Co-Digestion: Feedstock Combinations and Why They Work – the modern meaning of co-digestion and why complementary feedstocks can improve process performance.
- Co-Digestion of Food Waste and Sewage Sludge – a practical example of modern anaerobic co-digestion.
Historical note: This article was originally written by Steve Last in 2004, during the early development of modern waste anaerobic digestion, and was subsequently updated in 2014.
[This page was published 2012. Updated September 2026.]
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It’s important to make the solid waste with an economic value
The PDF file titled in “The Magic of Combined Anaerobic Digestion with Composting of Municipal Solid Waste” is not available. Please send it to me on my email.
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