Biogas can be one of the most useful forms of renewable energy because it does something that wind turbines and solar panels cannot do: it can produce renewable energy while treating organic wastes that society must deal with anyway.
Food waste, manure, sewage sludge, agricultural residues and other biodegradable materials naturally decompose. When that decomposition takes place without oxygen, microorganisms produce a methane-rich gas.
Anaerobic digestion captures that gas rather than allowing its energy value to go to waste.
But describing biogas simply as “green energy” misses an important point.
Not all biogas is equally sustainable.
The environmental case is strongest when anaerobic digestion uses unavoidable wastes and residues, captures methane that might otherwise reach the atmosphere, recycles nutrients and produces useful renewable gas.
The case becomes much more complicated when agricultural land is used specifically to grow energy crops for digesters.
Understanding that distinction is becoming increasingly important as the biogas and biomethane industries expand.
What Is Biogas?
Biogas is a combustible gas produced when microorganisms break down biodegradable organic matter in the absence of oxygen. This biological process is called anaerobic digestion (AD).
Raw biogas normally contains primarily:
- methane (CH4);
- carbon dioxide (CO2);
- water vapour; and
- small quantities of gases and contaminants such as hydrogen sulphide.
The methane is the valuable energy component.
Biogas can be burned in boilers to produce heat, used in combined heat and power (CHP) engines to generate electricity and heat, or upgraded by removing much of the carbon dioxide and other impurities.
The upgraded gas is generally known as biomethane or, particularly in North America, renewable natural gas (RNG).
Biomethane can potentially substitute for fossil natural gas in gas grids, industrial processes, heating and transport.
For readers looking for a more detailed introduction to the gas itself, see our separate guide to What Is Biogas?
Is Renewable the Same as Sustainable?
No. This is an important distinction when discussing biogas.
Biogas is renewable because its organic feedstocks can be replenished within relatively short biological cycles. Unlike fossil natural gas, its carbon does not principally come from geological reserves accumulated over millions of years.
But being renewable does not automatically make every method of producing biogas sustainable.
Sustainability asks a different question: What are the overall environmental, economic and resource consequences of producing that renewable energy?
A biogas plant using unavoidable food waste, manure or sewage sludge may recover energy from material that already requires treatment while also capturing methane and recycling nutrients.
A plant supplied primarily by purpose-grown energy crops may also produce renewable biogas, but its wider sustainability depends on factors such as land use, competition with food production, fertiliser use, soil impacts, transport and the greenhouse-gas emissions associated with growing the feedstock.
Similarly, methane leakage, excessive transport distances or poorly managed digestate can reduce the environmental benefits of an otherwise renewable biogas system.
So two different questions need two different answers:
Is biogas renewable? Generally, yes.
Is biogas sustainable? It can be highly sustainable, particularly when produced from wastes and residues, but the answer depends upon how the feedstock is obtained and how the complete anaerobic digestion system is designed and operated.
For a fuller explanation of why biogas is classified as renewable energy, read our separate article: Is Biogas Renewable? Unveiling the Truth Behind Its Sustainability.
Why Can Biogas Be Sustainable?
The sustainability argument for biogas rests on much more than the fact that methane can be burned to produce energy.
Its greatest environmental value often comes from combining several functions within one system.
An anaerobic digestion plant can:
- treat biodegradable waste;
- capture methane;
- generate renewable energy;
- reduce reliance on fossil fuels;
- stabilise organic material;
- recycle nutrients through digestate;
- reduce uncontrolled decomposition of organic wastes; and
- potentially reduce greenhouse-gas emissions.
This combination makes anaerobic digestion fundamentally different from many other renewable-energy technologies.
A solar farm principally produces electricity.
A wind turbine principally produces electricity.
A well-designed waste-fed anaerobic digestion plant can simultaneously provide waste treatment, renewable-energy production and nutrient recycling.
That is one reason anaerobic digestion has become an important component of many circular-economy strategies.
Does Burning Biogas Produce Carbon Dioxide?
Yes.
Any claims you read that suggest that biogas produces “no carbon emissions” are misleading.
When methane is burned, carbon dioxide is produced. The important distinction is where the carbon originated and what would otherwise have happened to the organic material.
Much of the carbon in food, crops and other recently produced biological materials is part of the relatively short-term biogenic carbon cycle. Plants absorb carbon dioxide while growing, that carbon enters organic materials, and some of it is eventually returned to the atmosphere.
This differs from extracting coal, oil and fossil natural gas containing carbon that has been stored underground for geological periods and adding that carbon to the active atmosphere.
However, this does not mean that every biogas plant is automatically carbon-neutral.
The complete greenhouse-gas balance can be affected by:
- feedstock production;
- transport;
- plant energy consumption;
- methane leakage;
- digestate storage and application;
- displaced fossil fuels;
- alternative waste-management methods; and
- land-use changes associated with growing feedstocks.
For this reason, sustainability should be assessed across the whole anaerobic digestion system, not merely at the point where biogas is burned. This is where AD plant developers should carry out a life cycle assessment of their product and use that to review the sustainability of the project over its design life.
Avoiding Methane Emissions Can Be Particularly Important
Methane is a powerful greenhouse gas.
Organic materials can generate methane when they decompose under anaerobic conditions in places such as manure stores, lagoons, landfills and other unmanaged environments.
Capturing that methane and using it as an energy source can therefore provide two benefits.
The energy can substitute for fossil energy, while methane that might otherwise have escaped to the atmosphere can be captured.
This is one reason that anaerobic digestion of manures and suitable organic wastes can have substantial climate benefits.
However, the same principle makes methane leakage from biogas plants particularly important.
Digesters, pipework, gas holders, pressure-relief systems, upgrading equipment and digestate storage all need to be properly designed, operated and maintained.
Producing renewable methane makes little environmental sense if an avoidable proportion of that methane is then allowed to escape. See our article, and our views on fugitive emissions.
Biogas Turns Waste Into a Resource
One of the strongest arguments for anaerobic digestion is that huge quantities of biodegradable material are generated regardless of whether society wants to produce renewable energy.
People will continue to generate sewage.
Livestock will continue to produce manure.
Food manufacturers will continue to generate organic residues.
Households, shops, restaurants and commercial kitchens will continue to produce unavoidable food waste.
These materials require management.
Anaerobic digestion provides an opportunity to recover value from them.
Instead of regarding organic material purely as a waste requiring disposal, AD can recover energy and nutrients from it.
This is the principle behind the frequently used description of anaerobic digestion as a circular-economy technology.
Food Waste and Anaerobic Digestion
Food waste is particularly suitable for anaerobic digestion because much of it is readily biodegradable and capable of producing useful quantities of biogas.
Where food cannot reasonably be prevented, redistributed or used for human consumption, anaerobic digestion can provide an effective recycling route.
Separate collection is important.
Cleaner source-separated food waste generally provides a better feedstock than mixed municipal waste containing plastics, metals, glass and other contaminants.
Packaged commercial food waste may also require depackaging before digestion.
The objective should be to recover the biodegradable fraction while minimising contamination of both the digester feed and the resulting digestate.
The Food-versus-Fuel Problem
The sustainability argument becomes less straightforward when crops are deliberately grown primarily to feed anaerobic digesters.
Maize and other energy crops can produce high biogas yields and provide operators with predictable feedstocks.
But agricultural land is finite.
Using productive land to grow energy crops can potentially compete with food production, affect crop rotations, increase fertiliser and pesticide requirements, alter soil management and create indirect land-use effects.
This creates an important distinction between two models of anaerobic digestion.
One model asks:
“What crop should we grow to produce the most biogas?”
The other asks:
“What unavoidable organic wastes and residues do we already have, and how much useful renewable energy can we recover from them?”
From a resource-efficiency perspective, these are very different propositions.
The long-term credibility of anaerobic digestion may increasingly depend upon prioritising wastes, residues, manures and genuinely sustainable feedstocks rather than allowing renewable-energy incentives to encourage unnecessary competition with food production.
Biogas and Energy Security
Biogas also has an energy-system characteristic that distinguishes it from wind and solar power.
Gas can be stored.
Solar generation depends on sunlight and wind generation depends on weather conditions. Biogas production is biological and comparatively continuous, while stored biogas or biomethane can be used when energy is required.
Biomethane can also make use of existing gas infrastructure where suitable networks and injection facilities are available.
This makes renewable gas potentially valuable in an energy system containing increasing amounts of intermittent renewable electricity.
Biogas should not be regarded as a replacement for wind or solar power.
The technologies can complement one another.
Biogas Versus Fossil Natural Gas
Biomethane can be processed to achieve characteristics sufficiently similar to fossil natural gas for injection into gas networks, subject to the applicable gas-quality requirements.
This creates an important opportunity.
Instead of replacing every piece of equipment that currently relies on gaseous fuel, some applications may be progressively decarbonised by replacing a proportion of fossil natural gas with renewable biomethane.
This may be particularly valuable for applications where direct electrification is difficult or expensive.
Nevertheless, biomethane supplies are finite.
There is not an unlimited quantity of sustainable organic waste available.
Renewable gas should therefore be regarded as a valuable resource that needs to be used where it delivers strong environmental and economic benefits, rather than as justification for unlimited continuation of fossil-gas consumption.
What About Digestate?
Energy is only one product of anaerobic digestion.
After microorganisms have broken down the biodegradable feedstock, a nutrient-containing material known as digestate remains.
Where its quality is suitable and regulations permit its use, digestate can return nutrients and organic matter to agricultural land.
This can reduce reliance on manufactured fertilisers and help close nutrient cycles.
But digestate is not automatically an environmental benefit.
Poor storage or inappropriate application can cause:
- ammonia emissions;
- odour;
- nutrient losses;
- water pollution; and
- greenhouse-gas emissions.
Contaminants entering with feedstocks can also affect digestate quality.
Once again, the environmental performance of anaerobic digestion depends upon the whole system.
What Are the Disadvantages of Biogas?
Biogas has genuine environmental advantages, but it also has limitations.
Anaerobic digestion plants require significant capital investment and competent operation.
Feedstock supplies must be reliable.
Digesters contain large biological populations that can be disrupted by unsuitable feedstocks, toxic substances, temperature changes, overloading or poor process control.
Biogas itself contains methane and therefore presents fire and explosion hazards.
Hydrogen sulphide can be toxic and corrosive.
Odour, vehicle movements, noise and visual impact can create local concerns.
Digestate requires appropriate storage, transport and outlets.
Methane leakage can substantially reduce climate benefits.
Poorly selected feedstocks can undermine sustainability.
None of these disadvantages means anaerobic digestion should not be used.
They demonstrate why an AD plant should be regarded as an integrated biological, mechanical, environmental and energy system, rather than simply as a tank that produces gas.
Is Biogas Better Than Hydrogen?
Biogas and hydrogen are sometimes presented as competing fuels, but this is an oversimplification.
They have different characteristics, production routes and potential applications.
Biomethane has the significant advantage of being compatible with much existing natural-gas infrastructure and equipment when upgraded to the required specification.
Hydrogen may become increasingly important in particular industrial, energy-storage and transport applications.
Future low-carbon energy systems are unlikely to depend upon one universal fuel.
Electricity, biomethane, hydrogen and other energy carriers may each be valuable where their particular characteristics are most useful.
The relevant question is therefore not simply “Which fuel wins?”
It is:
“Which energy source delivers the greatest benefit for this particular application?”
Can Algae and Other New Feedstocks Produce Biogas?
Anaerobic digestion is not limited to conventional agricultural and food wastes.
Researchers and commercial developers have investigated many potential feedstocks, including algae, seaweed and other forms of biomass.
Some may eventually become useful components of the renewable-gas sector.
But novel feedstocks should be judged using the same principles as conventional ones.
How much land, water, energy and nutrients are required to produce them?
How easily can they be harvested and processed?
What is their net energy yield?
What happens to the digestate?
And, most importantly, do they provide a better environmental outcome than alternative uses of those resources?
The fact that a material can produce methane does not automatically make it a sustainable feedstock.
So, Is Biogas Really Sustainable?
The answer is yes — when it is produced and used well.
Biogas is particularly compelling when anaerobic digestion:
- treats unavoidable organic wastes and residues;
- captures methane that might otherwise escape;
- replaces fossil energy;
- recycles nutrients;
- controls methane leakage;
- produces a useful, clean digestate; and
- avoids unnecessary competition with food production.
The sustainability case becomes weaker when feedstocks require intensive production, productive agricultural land is diverted unnecessarily from food, methane is allowed to escape, digestate is poorly managed or large amounts of energy and resources are consumed merely to keep the process operating.
The question should therefore not be:
“Is anaerobic digestion sustainable?”
A better question is:
“Under what circumstances does anaerobic digestion deliver the greatest environmental benefit?”
For waste food, manure, sewage sludge and many other unavoidable biodegradable residues, the answer can be compelling.
These materials already exist.
We have to manage them somehow.
If anaerobic digestion can safely convert them into useful renewable gas while recycling nutrients and preventing uncontrolled methane emissions, it can turn an environmental liability into a valuable resource.
That is where the strongest future for sustainable biogas lies.
[Published April 2022. Updated and rewritten August 2026.]
Although it retains the same name, biogas is a greener alternative to conventional natural gas.
I made my very own biogas right at home by using a simple biogas system that I developed for a very low cost. I really use the biogas to power a pair of very inexpensive motors.