It is also a perfectly reasonable question.

Anaerobic digestion plants handle organic materials. Depending on the plant, these may include food waste, manure, slurry, crop residues, food-processing wastes and other biodegradable materials. Some of them can produce extremely unpleasant odours if they are stored or handled badly.

So let's start with an honest answer.

Yes, the materials handled at an anaerobic digestion plant can smell. But that does not mean that a properly designed and operated AD plant should cause an unacceptable smell beyond its site boundary.

Those are two very different things.

Where Does the Smell From an AD Plant Actually Come From?

Interestingly, the sealed anaerobic digester itself should not normally be the main source of odour.

The biological process takes place inside enclosed tanks or vessels because the microorganisms need oxygen-free conditions. The biogas produced is also valuable, so operators have every reason to keep the digestion system gas-tight.

The greater potential for odour generally arises around the handling of materials before and after digestion.

Potential sources can include:

• delivery and unloading of food waste and other odorous feedstocks;
• feedstock reception and storage;
• depackaging and preprocessing equipment;
• open doors and poorly contained reception areas;
• spillages;
• digestate storage and handling;
• solid-liquid separation equipment;
• maintenance operations;
• abnormal operating conditions; and
• the application of digestate to agricultural land.

The precise risks depend heavily on the type of AD plant.

A farm digester processing mainly slurry and crops presents a different odour-control challenge from a commercial food-waste AD plant receiving packaged and potentially decomposing food from many sources.

What Does Digestate Smell Like?

Digestate is the material remaining after anaerobic digestion has converted part of the biodegradable organic matter into biogas.

It can certainly have a noticeable odour, but it is misleading to say that all digestate invariably smells extremely unpleasant.

The character and strength of the odour depend on such factors as the original feedstock, digestion conditions, process stability, storage, subsequent treatment and how the digestate is handled.

Digestate may also be separated into liquid and solid fractions, creating materials with different handling characteristics.

The important point is that digestate remains an organic material containing valuable plant nutrients. It therefore needs to be stored and applied responsibly.

Good AD Plant Design Starts With Containment

One of the fundamental principles of odour control is straightforward:

Don't allow odorous air to escape uncontrolled in the first place.

At facilities handling particularly odorous wastes, reception and processing operations can be carried out within enclosed buildings.

Air can be extracted from these areas so that the building is maintained under suitable containment conditions rather than allowing contaminated air to escape through doors and openings.

The extracted air can then be treated using an appropriate odour-abatement system before discharge.

Depending on the application, such systems may include biofilters and other biological, chemical or physical treatment technologies.

There is no single odour-control technology which is automatically correct for every AD plant. The system needs to be designed for the characteristics and loading of the air requiring treatment.

An Odour-Control System Also Has to Keep Working

Installing an odour-control system is not enough.

Fans fail. Ductwork deteriorates. Filters require maintenance. Doors are left open. Feedstocks change. Operators may receive unexpectedly odorous loads.

That is why good odour management combines engineering with operating discipline.

Operators need to understand where odour could arise, monitor the important parts of the process and have procedures for responding when something goes wrong.

This is particularly important because some of the worst odour incidents at waste-treatment facilities occur during abnormal rather than routine operation.

What Does the Environment Agency Require?

Environmental regulation has developed considerably since I first wrote this article.

In England, the Environment Agency published updated guidance on odour management in December 2025.

For regulated activities, operators are expected to assess their odour risks and use appropriate measures to prevent odour pollution or, where prevention is not practicable, minimise it.

Anaerobic digestion is specifically included among the activities for which an Odour Management Plan (OMP) may be required as part of environmental permitting.

An OMP is not supposed to be a vague statement saying that an operator will try not to create smells.

It should identify the potentially odorous materials and processes on the site and explain how risks will be controlled.

This can include:

• feedstock and waste inventories;
• maximum storage times;
• storage conditions;
• process controls;
• containment;
• air extraction and abatement;
• monitoring;
• performance standards;
• record keeping;
• responses to abnormal conditions; and
• contingency arrangements.

The Environment Agency's current permit requirements are aimed at preventing odour at levels likely to cause pollution outside the permitted site boundary.

If a facility does cause odour pollution, the regulator can require further controls and changes to operating practices. Serious or persistent failures can lead to stronger regulatory action.

What Should Local Residents Look For in a Planning Application?

If you live near the site of a proposed anaerobic digestion plant, I don't think it is helpful simply to be told that "AD plants don't smell".

A better approach is to look at what is actually proposed.

Some useful questions are:

• What feedstocks will the plant accept?
• Will particularly odorous materials be unloaded indoors?
• How will reception buildings be contained and ventilated?
• How will extracted air be treated?
• How long can incoming material remain in storage?
• How will digestate be stored?
• What happens if the odour-abatement equipment fails?
• How close are the nearest homes and other sensitive receptors?
• Is there a credible Odour Management Plan?

Those questions tell you considerably more about the likely risk than simply knowing that the development is called an "anaerobic digestion plant".

Visit an Existing AD Plant

There was one suggestion in the original version of this article that I still think has considerable merit.

If you are concerned about a proposed AD plant, find an established plant of a similar type and visit the surrounding area.

You obviously should not enter private operational premises without permission, but it may be possible to experience conditions from public roads or other legitimate public locations.

Ideally, don't just visit one plant once. Weather conditions, wind direction and plant operations vary.

Nevertheless, seeing an operating AD facility can be much more informative than trying to imagine one from drawings in a planning application.

My Own Experience of AD Plant Odour

In the area where I lived when I originally wrote this article, there were several anaerobic digestion plants relatively close by.

My personal experience was that I did not routinely detect odour from those plants beyond their sites.

On occasions when I did notice agricultural odours in the surrounding countryside, the source was not necessarily the AD plant at all. Normal agricultural operations can themselves generate substantial odour.

That is only my personal observation. It is not evidence that every AD plant is odour-free.

There have unquestionably been AD facilities where poor design, inappropriate feedstock management, equipment problems or inadequate operation have resulted in legitimate complaints from neighbours.

That is precisely why odour needs to be considered seriously during design, permitting and operation.

So, Do Anaerobic Digestion Plants Smell?

The most accurate answer is:

The materials handled at anaerobic digestion plants can be highly odorous, but a well-designed and well-operated AD plant should control those emissions rather than routinely subject its neighbours to them.

It would therefore be wrong to dismiss residents' concerns about odour.

But it is equally wrong to assume that because anaerobic digestion involves decomposing organic material, every AD plant must inevitably make the surrounding area smell.

The questions that matter are about feedstock, design, containment, abatement, management, monitoring and operator competence.

That is where residents, planners and regulators should concentrate their attention.

Steve Last
Chartered Civil & Environmental Engineer (MICE)
Chartered Waste Manager (MCIWM)
Chartered Environmentalist (CEnv)

Updated September 2026. This article was originally published many years ago (on 8 January 2015) and has been substantially revised to reflect current anaerobic digestion practice and Environment Agency odour-management guidance.

Further reference: Environment Agency, Odour management: comply with your environmental permit, published December 2025.

   

There is a very large number appearing increasingly often in discussions about the future of anaerobic digestion in Britain.

64 TWh of biomethane a year by 2050.

The Parliamentary Office of Science and Technology (POST) highlighted this figure in its recent briefing on upscaling anaerobic digestion. One of the National Energy System Operator's Future Energy Scenarios suggests that UK biomethane production could need to reach around 64 TWh annually by 2050.

POST describes that as approximately a tenfold increase from current biomethane production levels.

That sounds like extremely good news for the UK anaerobic digestion industry.

And potentially it is.

But there is a question which I think needs asking before we start mentally filling the British countryside with another generation of digesters:

What are we going to put into them?

Building Digesters Is Only Half the Problem

An anaerobic digestion plant isn't like a wind turbine.

Once a wind turbine has been built, nobody needs to find thousands of tonnes of wind and deliver it to the site every year.

An AD plant is fundamentally different.

Every digester requires a continuing supply of suitable organic feedstock. That supply has to remain available not just when the plant is commissioned, but year after year if the investment is to succeed.

The UK already has hundreds of AD plants competing for food waste, agricultural residues, industrial organic wastes, crops, slurries and other suitable materials.

Expanding biomethane production several times over therefore isn't simply an engineering challenge.

It is a feedstock challenge.

There Is Plenty of Organic Material — But Not All of It Is Available Feedstock

POST notes that the UK produces around 10.2 million tonnes of food waste annually.

England's requirement for separate weekly household food-waste collections should make considerably more source-separated organic material available for treatment, and anaerobic digestion is an obvious destination for much of it.

Agriculture offers further possibilities through manures, slurries, crop residues and other organic materials.

But theoretical quantities should never be confused with economically available feedstock.

Material may be dispersed across too large an area. It may already have another use. Transport may make collection uneconomic. Seasonal availability can create difficulties. Contamination can make apparently attractive waste streams unsuitable.

And where several AD plants are seeking the same material, something else happens:

the feedstock acquires a value.

Competition for Food Waste Is Already Important

This is particularly relevant to food-waste AD.

As more separately collected food waste becomes available under Simpler Recycling, it is tempting to assume that this automatically creates an enormous supply of cheap feedstock for new digesters.

I wouldn't make that assumption.

Established food-waste AD operators already have collection networks, contracts, depackaging systems, tankage and relationships with waste producers.

If new biomethane plants are constructed in the same catchments, competition for dependable feedstock may increase.

A developer therefore needs to know considerably more than how many tonnes of organic waste theoretically arise within 30 miles of a proposed site.

They need to know who controls it, what it currently costs, who else wants it and whether it can realistically be contracted for the life of the project.

I have discussed this problem in more detail here:

Finding the Right Feedstock for Anaerobic Digestion Plants

What About Energy Crops?

Purpose-grown crops can provide predictable feedstock and high biogas yields, which is precisely why crops such as maize became important to parts of the European AD industry.

But increasing their use substantially brings the familiar food-versus-fuel and land-use debate straight back into the discussion.

There are also policy constraints.

The Green Gas Support Scheme requires supported biomethane plants to meet sustainability requirements intended to encourage the use of wastes and residues.

So a theoretical shortage of waste feedstock cannot simply be solved by planting unlimited areas of energy crops.

And Feedstock Isn't the Only Constraint

Even where suitable feedstock can be secured, Britain will not obtain a tenfold increase in biomethane simply by ordering more digesters.

Projects also require suitable sites, planning permission, environmental permits, finance, gas-grid connections or alternative biomethane outlets, digestate storage and dependable agricultural outlets for the resulting nutrients.

Anyone who has developed an AD project will recognise that some of these constraints can take longer to resolve than designing the digester itself.

That is particularly relevant at present because developers are reporting increasing difficulty obtaining planning permission for completely new AD plants on some greenfield and farm locations.

64 TWh Isn't the Only Estimate

There is another important point which can easily disappear when large numbers are quoted.

The 64 TWh figure is a scenario rather than a guaranteed government target.

The UK Government has also referred to its 2023 Biomass Strategy, which estimated around 30–40 TWh of biomethane production by 2050 across its illustrative scenarios.

In September 2026, the Department for Energy Security and Net Zero confirmed that it is considering this evidence while developing future policy for biomethane.

So the precise number remains uncertain.

What seems much less uncertain is the direction of travel: Britain expects biomethane to play a substantially larger role in its future energy system.

The Opportunity Is Real — But So Are the Practical Limits

I remain enthusiastic about the potential for UK biomethane.

It converts organic wastes into useful renewable gas, recycles nutrients through digestate and can make use of much of the country's existing gas infrastructure.

It also offers something increasingly important in a world of volatile international energy markets: domestically produced renewable gas.

I recently looked at that energy-security argument in more detail here:

How UK Biomethane Could Cut Gas Prices and Boost Energy Security

But ambitious biomethane scenarios need to be tested against what can actually be delivered.

That means asking some rather less glamorous questions:

Where is the feedstock?
Who controls it?
How far will it travel?
Where will the digestate go?
Can the project obtain planning permission?
Where will the biomethane be used?
And will the economics still work when competing plants are bidding for the same organic material?

Those questions don't undermine the case for expanding anaerobic digestion.

They are what determine whether that expansion will actually happen.

Steve Last
Chartered Civil & Environmental Engineer (MICE)
Chartered Waste Manager (MCIWM)
Chartered Environmentalist (CEnv)

Sources: Parliamentary Office of Science and Technology, Upscaling Anaerobic Digestion, July 2026; Department for Energy Security and Net Zero, Parliamentary Written Answer on domestic renewable gas production, 7 September 2026.

   

For many years, Australia has had plenty of potential for biogas but relatively little visibility as a biomethane market.

That is beginning to change.

I have been watching developments in anaerobic digestion and biogas internationally for many years, and Australia is now one of the countries I think is particularly worth watching.

The important change is not simply that more people are talking about biogas. It is the increasing interest in upgrading biogas to biomethane so that renewable gas can potentially replace fossil natural gas in applications where direct electrification may be difficult.

Why Australia Has Considerable Biomethane Potential

Australia has many of the ingredients needed for a substantial biogas and biomethane industry.

These include agricultural residues, livestock manures, food and beverage processing wastes, municipal organic wastes, sewage sludge and other biodegradable materials that can potentially be treated through anaerobic digestion.

Historically, the economics of biogas projects have often centred on using the gas locally, particularly for heat or combined heat and power.

Biomethane changes the possibilities.

Raw biogas typically contains methane together with a substantial proportion of carbon dioxide and smaller quantities of other gases and contaminants. By removing carbon dioxide and treating the gas to the required specification, the methane-rich product can potentially be used much more like conventional natural gas.

That opens possibilities including gas-network injection, industrial energy use and renewable transport fuel.

Renewable Gas Can Do Something Electricity Cannot Always Do Easily

I am wary of arguments that present renewable gas and electrification as though one must defeat the other.

They solve different problems.

Where electricity can efficiently replace fossil fuel use, electrification may make excellent sense. But some industrial processes, heavy transport applications and existing gas infrastructure present more difficult decarbonisation challenges.

In those circumstances, biomethane produced from appropriate wastes and residues may have a valuable role.

It also has the advantage that anaerobic digestion does more than produce energy. Properly designed projects can simultaneously provide organic-waste treatment and produce digestate containing plant nutrients and organic matter.

From Individual Projects to an Industry

The interesting question for Australia is therefore no longer simply:

"Can biomethane be produced here?"

Clearly it can.

The more important question is whether individual projects will develop into a sufficiently connected market involving reliable feedstock supplies, gas upgrading, appropriate standards, infrastructure, investment and long-term demand for renewable gas.

That transition from a collection of projects to an established industry is what makes the present period interesting.

I recently updated my longer article examining the subject, including Australian biomethane projects, policy and the developing renewable-gas market:

Biomethane in Australia: Projects, Policy and the Emerging Renewable Gas Market

I expect this will be a page that needs updating again as the Australian market develops.

Bringing This Old AD News Blog Back to Life

I have also decided to start posting here again after neglecting this blog for a while.

Rather than duplicate the longer articles published elsewhere, I intend to use this blog for shorter observations on anaerobic digestion, biogas and biomethane developments that I think are worth drawing attention to.

There is certainly no shortage of developments to discuss.

Steve Last
Chartered Civil & Environmental Engineer (MICE)
Chartered Waste Manager (MCIWM)
Chartered Environmentalist (CEnv)

   

 Make no mistake, there have been significant advancements in food waste depackaging and separation equipment in recent years. 

The industry is moving away from first-generation equipment, which consisted of repurposed machines originally designed for MSW sorting, milling, pulping, paper, and card and shredding, and toward purpose-built models that are the result of many years of innovative design.

List Criteria: Depackaging and Separation Machines

We looked for the following characteristics in the listed equipment:

1. Acceptance of a diverse range of biowastes, ranging from OFMSW (Organic Fraction of Municipal Solid Waste) to "Out of Specification." Food-processing-industry-related products
2. Off-the-shelf, tried-and-true designs are preferred over one-of-a-kind, custom-designed prototype equipment.
3. A process philosophy which avoids creating microplastics.

In contrast to suppliers who offer separate units for each function, such as bagging, the new generation of this equipmentis integrated and carries out multiple functions in a single process stage.

such as bag opening and shredding followed by separation and sometimes multiple other units

Suitability for the equipment to be used in conjunction with the anaerobic digestion process.

The best depackaging equipment will separate and capture organic packaging materials from food waste, and also separate and recycle as much of the reject material (e. g. plastics) as possible.

Subject to regulatory requirements, operators of the new generation of this equipment will be able to benefit from green credentials. These come from reclaiming the organic content of food waste and incorporating it into the highest purity quality, natural compost and sustainable soil products.

In the post CPO26 era, all businesses must not only act in a sustainable way but also make plans and publish targets to decarbonise their whole organisations by 2050 or earlier. One way to do this for any organisation which produces food waste, and even some other previously unused organic materials, is to carry out their own in-house depackaging and separation.

An example of government involvement in this process is the US Food Waste Management Program. This scheme is addressing a major issue of our time that directly affects the human and ecological balance of the environment. That is by reducing methane emissions while also creating renewable energy to displace the use of fossil fuels.

There is no doubt that climate change can be reduced by reducing food waste, and recycling more. Where unavoidable waste still occurs it makes sense to channel it back into the circular economy. 

Efficiently depackaging food waste is a key component in this area.

According to the USDA, food waste represents 30 % of all American food manufactured. This can be due primarily to over-consumption in the homes and subsequently. In food production, there are evidently still many wastes generated in even the most sophisticated manufacturing facilities.

We have compiled our waste depackaging and separation equipment supplier list as a resource for all organic waste/ biowaste processors in the hope that we can assist in the selection of the most suitable equipment for their purchasing decisions.

For our list go to our list of food waste depackaging and separation suppliers here.

   

New digester mixing technology has helped a prominent food waste-to-energy plant enhance its biogas production by an average of more than 43%.

Biogas yields have been improved by Landia and Hayley Group working together closely.

Hayley Group, an engineering component supplier, was consulted about the availability of an alternative, superior mixing system for its customer's second digester; mixers that, unlike those in the first tank, would eliminate typical biogas process problems such as foam, blocking, and crusting – and in doing so, help boost the levels of methane in the gas.

Hayley Group’s Engineer, Rob Bentley, said:

“We constantly look to help customers improve efficiencies. This project is of particular note because, with the new, superior mixing system, the increase per cubic metre in gas from the second digester is over 40%. This is extremely encouraging, to say the least, especially when you consider that the second digester also has 10% less capacity than the older first tank”.

Visit: www.blog.anaerobic-digestion.com/digester-mixing