Anaerobic Digestion Equipment: Complete Guide to AD Plant Systems

Anaerobic digestion equipment is much more than the digester tank itself. A reliable AD or biogas plant depends on an integrated chain of feedstock reception, preparation, pumping, mixing, heating, digestion, gas handling, energy recovery, digestate management, instrumentation and safety systems.

Choosing the wrong item at almost any point in that chain can constrain the whole plant.

A pump that cannot tolerate fibrous material, a mixer that leaves dead zones, inadequate grit removal, poor access for maintenance or an undersized gas-treatment system can all reduce plant availability and profitability.

This guide explains the main categories of anaerobic digestion equipment, what each item does and the engineering considerations that should influence equipment selection.

If you are looking for companies that design, manufacture or supply anaerobic digestion and biogas equipment rather than guidance on selecting the equipment itself, see our separate European biogas companies and anaerobic digestion suppliers list.

Key Takeaways

• An AD plant should be designed as one integrated process system, not as a collection of individually selected machines.
• Important equipment includes feedstock reception systems, depackaging equipment, pumps, mixers, digester tanks, heating systems, gas holders, gas cleaning, CHP or biomethane upgrading, digestate handling and instrumentation.
• Feedstock characteristics should drive equipment selection. Solids content, particle size, fibrous material, grit, packaging contamination and viscosity all matter.
• Reliability, maintainability and access can be as important as nominal equipment efficiency.
• Equipment in biogas areas may need to comply with DSEAR and hazardous-area requirements.
• Modern AD plants increasingly include biomethane upgrading, carbon dioxide recovery and advanced monitoring, not just CHP engines.
• Whole-life cost is more important than lowest purchase price. Energy consumption, wear, downtime, servicing and replacement parts should all be considered.

What Equipment Is Needed for Anaerobic Digestion?

The precise equipment required depends on:

• feedstock type;
• plant throughput;
• solids concentration;
• digester configuration;
• retention time;
• whether wastes or non-wastes are accepted;
• how the biogas will be used;
• how digestate will be stored and used; and
• the site's environmental permit and planning conditions.

However, most commercial plants require equipment in the following broad groups:

1. feedstock reception;
2. contaminant removal and preparation;
3. feed pumping;
4. digester tanks;
5. mixing;
6. heating;
7. biogas collection;
8. gas cleaning;
9. CHP or biomethane upgrading;
10. gas flaring;
11. digestate separation and storage;
12. instrumentation and control; and
13. safety systems.

1. Feedstock Reception Equipment

Feedstock reception is the first process stage and one of the most important.

A well-designed reception system must cope with the physical form, delivery method and contamination level of the incoming material.

Depending on the plant, equipment may include:

• weighbridges;
• tipping halls;
• reception hoppers;
• liquid waste tanks;
• screw conveyors;
• walking-floor systems;
• bucket loaders;
• screening equipment; and
• automated feed dosing systems.

For waste-fed plants, reception areas may also need to contain spills, control odour and prevent cross-contamination.

Feedstock handling equipment should be designed for the actual waste received, not an idealised specification.

Real food waste may contain plastic packaging, cutlery, stones, glass, grit, metal and other contaminants.

2. Depackaging and Contaminant Removal

Where packaged food waste is accepted, depackaging equipment can become one of the most critical items in the whole plant.

The purpose is to separate biodegradable food material from:

• plastic film;
• rigid plastic packaging;
• metal;
• cardboard;
• glass; and
• other non-digestible materials.

Poor depackaging can create several downstream problems:

• plastic contamination in digestate;
• pump blockages;
• ragging;
• grit accumulation;
• higher maintenance requirements; and
• reduced marketability of digestate.

Excessive shredding or grinding can also create very small plastic fragments that are difficult to remove later.

For that reason, equipment should be selected not simply on throughput but also on:

• organic recovery;
• reject cleanliness;
• plastic fragmentation;
• water consumption;
• energy use; and
• maintenance requirements.

3. Anaerobic Digestion Feed Pumps

Pumping thick, heterogeneous organic material is very different from pumping clean water.

Feed pumps may have to handle:

• high solids concentrations;
• fibrous material;
• viscous slurries;
• sand and grit;
• food particles; and
• occasional contaminants.

Common pump types include:

• progressive cavity pumps;
• rotary lobe pumps;
• centrifugal pumps for lower-solids duties; and
• specialist solids-handling pumps.

No pump type is universally best.

The correct choice depends on the duty.

Important selection criteria include:

• flow rate;
• differential pressure;
• solids concentration;
• particle size;
• abrasiveness;
• viscosity;
• fibre content;
• temperature; and
• maintenance access.

A pump that performs well with liquid slurry may be completely unsuitable for thick food-waste pulp.

4. Macerators and Size-Reduction Equipment

Some plants use macerators or other size-reduction equipment before digestion.

Potential benefits include:

• smaller particle size;
• reduced risk of pipe blockage;
• improved pumpability; and
• greater surface area for biological degradation.

However, size reduction should not be treated as automatically beneficial.

Grinding unwanted materials can make contaminants more difficult to remove. It also consumes power and introduces another item requiring maintenance.

The objective should be appropriate feedstock preparation, not simply producing the smallest possible particles.

5. Anaerobic Digester Tanks

The digester vessel is the central biological reactor.

Common configurations include:

• continuously stirred tank reactors;
• plug-flow digesters;
• high-solids or dry digestion systems;
• covered lagoons;
• multi-stage digesters; and
• specialist industrial reactors.

Digester construction materials may include:

• reinforced concrete;
• glass-fused-to-steel;
• stainless steel; and
• other suitably protected steel systems.

Tank selection depends on:

• feedstock;
• process temperature;
• retention time;
• mixing system;
• corrosion environment;
• site conditions;
• design life; and
• maintenance strategy.

A digester is not merely a storage tank. Its geometry affects mixing, heat distribution, sediment accumulation and gas release.

6. Anaerobic Digester Mixing Equipment

Mixing is one of the most important and frequently misunderstood equipment-selection decisions in anaerobic digestion.

Mixing can help:

• distribute incoming feedstock;
• maintain microorganisms in contact with substrate;
• equalise temperature;
• reduce sedimentation;
• limit floating crusts; and
• release biogas from the digesting slurry.

Common systems include:

• submersible mixers;
• side-entry mixers;
• top-entry mixers;
• external pumped recirculation;
• gas mixing; and
• hydraulic mixing arrangements.

More mixing does not automatically produce more biogas.

Excessive mixing can increase parasitic power consumption and, in some circumstances, may disrupt useful microbial associations.

The correct objective is sufficient effective mixing at minimum reasonable energy consumption.

7. Digester Heating Systems

Anaerobic microorganisms require a reasonably stable temperature.

Commercial digesters therefore commonly include heating systems using:

• external heat exchangers;
• recirculation loops;
• internal heating coils; or
• other indirect heating arrangements.

Heat may be supplied from:

• CHP engine cooling water;
• biogas boilers;
• external heat networks; or
• other available heat sources.

Temperature stability is usually more important than continuously chasing an exact theoretical optimum.

Heat exchanger design should take account of fouling, viscosity and the ability to clean the equipment.

8. Gas Holders

Biogas production and gas consumption rarely match perfectly from one moment to the next.

A gas holder provides short-term buffering between production and use.

Common arrangements include:

• double-membrane roofs;
• separate membrane gas holders; and
• other low-pressure storage systems.

The holder should not be regarded as long-term energy storage.

Its role is usually to manage relatively short variations in:

• gas production;
• engine demand;
• upgrader demand; and
• temporary process interruptions.

9. Biogas Cleaning Equipment

Raw biogas may contain contaminants that can damage downstream equipment.

Treatment systems may therefore remove:

• hydrogen sulphide;
• water vapour;
• particulates;
• siloxanes in some applications; and
• other trace contaminants.

Biogas cleaning technologies can include:

• activated carbon;
• biological desulphurisation;
• iron-based media;
• condensate removal;
• gas drying; and
• specialist polishing systems.

Gas treatment should be specified around the requirements of the downstream equipment.

An engine, boiler and biomethane-upgrading unit may each require different gas quality.

10. Combined Heat and Power Equipment

Historically, many UK AD plants used biogas in combined heat and power (CHP) engines.

A CHP installation produces electricity while recovering heat from:

• engine cooling water;
• lubricating systems; and
• exhaust gases.

Useful heat can be returned to the digestion process or supplied to other heat users where appropriate.

For a detailed discussion see our guide to biogas CHP systems, benefits and cost savings.

11. Biomethane Upgrading Equipment

Many newer large AD projects are designed around biomethane production rather than electricity generation.

Biogas upgrading equipment removes most of the carbon dioxide and other unwanted components to produce methane-rich biomethane.

Commercial technologies include:

• membrane separation;
• pressure swing adsorption;
• water scrubbing; and
• chemical absorption systems.

Selection should consider:

• gas flow;
• methane recovery;
• methane slip;
• energy consumption;
• gas specification;
• maintenance requirements;
• turndown capability; and
• availability.

Modern environmental permits in England were updated in February 2026 to include additional provisions for biogas and biomethane treatment and captured carbon dioxide. (gov.uk)

12. Carbon Dioxide Recovery Equipment

Biomethane upgrading creates a carbon-dioxide-rich stream.

Increasingly, developers are considering whether this CO₂ can be:

• purified;
• compressed;
• liquefied;
• temporarily stored; and
• sold for suitable commercial uses.

This represents a significant change from earlier AD plants where separated carbon dioxide was commonly treated simply as an off-gas.

CO₂ recovery can therefore become another process plant within the wider AD installation.

13. Biogas Flares

A flare provides a safe means of destroying biogas when normal gas utilisation equipment is unavailable.

This may occur during:

• commissioning;
• CHP shutdown;
• upgrader maintenance;
• gas-quality problems; or
• other abnormal operating conditions.

A flare is an essential safety and environmental item, not merely an optional backup.

Its capacity should be sufficient for credible gas-production scenarios where normal gas utilisation is unavailable.

14. Digestate Separation Equipment

Digestate can sometimes be used as whole digestate, but many plants separate it into:

• a liquid fraction; and
• a fibrous solid fraction.

Common equipment includes:

• screw presses;
• decanter centrifuges;
• screens; and
• other mechanical separation systems.

Separation may help:

• reduce transport volumes;
• create distinct nutrient fractions;
• improve storage management; and
• prepare material for further nutrient recovery.

Digestate equipment should be selected with the final outlet in mind.

15. Digestate Storage

Digestate storage is not glamorous equipment, but it can determine whether the plant operates successfully.

Storage capacity must take account of:

• seasonal agricultural restrictions;
• weather;
• spreading opportunities;
• land availability;
• nutrient-management requirements; and
• unexpected interruptions.

Insufficient digestate storage can constrain the entire AD plant even when the biological process is performing perfectly.

16. Instrumentation and Process Monitoring

Modern anaerobic digestion plants increasingly depend on instrumentation and data acquisition.

Common measurements include:

• feed rate;
• temperature;
• pH;
• tank level;
• gas flow;
• methane concentration;
• oxygen concentration;
• hydrogen sulphide;
• pressure; and
• electricity and heat production.

Laboratory measurements may additionally include:

• volatile fatty acids;
• alkalinity;
• ammonia;
• dry solids;
• volatile solids; and
• nutrient concentrations.

Instrumentation should provide information that operators can actually use.

Installing more sensors does not automatically improve operation if instruments are unreliable, poorly maintained or generate alarms nobody understands.

17. Control Systems and Automation

AD plants normally include programmable control systems or supervisory control and data acquisition systems.

Automation may control:

• feed dosing;
• pumping;
• mixing;
• temperature;
• gas pressure;
• CHP operation;
• biomethane upgrading;
• flare operation; and
• alarm management.

More sophisticated plants may increasingly make use of:

• advanced process control;
• model-based optimisation;
• soft sensors;
• remote monitoring; and
• digital-twin technology.

For more on this subject see our guide to ADM1, anaerobic digestion modelling and digital twins.

18. Anaerobic Digestion Safety Equipment

Biogas plant equipment must be designed around the hazards of methane, hydrogen sulphide, carbon dioxide, pressure, confined spaces and rotating machinery.

Safety-related equipment may include:

• gas detectors;
• fire detection;
• pressure relief valves;
• vacuum protection;
• emergency shutdown systems;
• ventilation;
• flame arrestors;
• emergency flares;
• safe isolation systems; and
• appropriately rated electrical equipment.

In the UK, potentially explosive atmospheres may require consideration under DSEAR and hazardous-area classification requirements.

Safety equipment should be integral to process design rather than added after the plant layout has been fixed.

How to Specify Anaerobic Digestion Equipment

Buying an item because another AD plant uses the same model is rarely sufficient.

Equipment specification should begin with the process duty.

Feedstock Characteristics

Determine:

• solids content;
• particle size distribution;
• fibre content;
• viscosity;
• abrasiveness;
• contaminants;
• temperature; and
• expected variability.

Normal and Maximum Duty

Equipment should be checked at:

• minimum flow;
• normal flow;
• maximum expected flow; and
• abnormal but credible operating conditions.

Redundancy

Ask what happens if the equipment fails.

A cheap single pump can become extremely expensive if its failure stops the whole plant.

Critical duties may justify:

• duty/standby pumps;
• parallel equipment;
• bypass arrangements; or
• stored critical spares.

Maintenance Access

Equipment inevitably requires maintenance.

Design should therefore consider:

• lifting access;
• isolation valves;
• drainage;
• washdown;
• safe access platforms;
• replacement clearances; and
• confined-space implications.

Equipment that cannot be safely removed and serviced is badly installed even if it performs perfectly when new.

Materials Compatibility

Components may be exposed to:

• hydrogen sulphide;
• moisture;
• ammonia;
• organic acids;
• abrasive solids; and
• cleaning chemicals.

Material selection, coatings and seals should therefore match the service environment.

Energy Consumption

Parasitic power demand can be significant.

Major electrical users may include:

• mixers;
• pumps;
• macerators;
• air compressors;
• biogas upgrading equipment; and
• digestate separation systems.

A lower-capital-cost machine that consumes substantially more energy may have the higher whole-life cost.

Whole-Life Cost Matters More Than Purchase Price

The cheapest anaerobic digestion equipment is not necessarily the least expensive.

Whole-life evaluation should include:

• purchase price;
• installation;
• electrical consumption;
• wear components;
• service contracts;
• spare parts;
• labour;
• downtime;
• replacement frequency; and
• lost biogas production during failure.

Plant availability often matters more economically than small differences in purchase price.

Design the Plant Around the Feedstock

One of the most common conceptual mistakes is to select a standard AD plant and then attempt to force the available feedstock through it.

The better approach is the reverse:

characterise the feedstock first, then design the process and equipment around it.

A slurry-based farm plant, packaged-food-waste facility and industrial wastewater digester may all be called anaerobic digestion plants, but their equipment requirements can be very different.

Equipment for Food Waste AD Plants

Food-waste plants often need particularly robust front-end equipment because of contamination and feedstock variability.

Typical requirements may include:

• enclosed reception;
• depackaging;
• contaminant removal;
• grit management;
• pasteurisation;
• odour extraction;
• high-solids pumping; and
• reliable digestate handling.

Front-end equipment can have a disproportionate effect on downstream reliability.

If contaminants enter the digester, they eventually have to come out somewhere.

Equipment for Farm Anaerobic Digestion Plants

Farm plants processing slurry, manure and silage may require:

• silage clamps;
• solid feed hoppers;
• augers;
• slurry pumps;
• mixers;
• digesters;
• gas holders;
• CHP or upgrading equipment; and
• large digestate stores.

Equipment must tolerate seasonal feed characteristics.

Energy crops such as maize are normally harvested and ensiled, then fed from storage throughout the year rather than supplied as continuously freshly harvested material.

Equipment for Biomethane Plants

Biomethane plants add another substantial layer of equipment beyond conventional digestion.

Depending on the project, this can include:

• fine gas cleaning;
• upgrading;
• compression;
• gas-quality analysis;
• odorisation;
• grid-entry equipment;
• propane addition where required;
• methane-slip control;
• CO₂ treatment; and
• gas metering.

The gas-utilisation system should therefore be considered during initial plant design, not added as an afterthought.

Environmental Permitting Can Influence Equipment Selection

In England, anaerobic digestion equipment is also influenced by the site's environmental permitting regime.

The Environment Agency's current standard rules distinguish between, among others:

• larger AD installations treating more than 100 tonnes per day;
• waste-recovery AD plants below that threshold;
• on-farm AD facilities; and
• sewage-sludge digestion.

The relevant standard rules were updated in February 2026, including changes relating to biogas and biomethane treatment and carbon dioxide capture. (gov.uk)

Equipment therefore needs to be specified not only to perform technically, but also to operate within the authorised process and emissions controls.

Don't Buy Equipment Before Defining the Process

It is tempting to begin a project by obtaining prices for tanks, mixers, pumps and upgrading equipment.

That is often backwards.

A more robust sequence is:

1. define the feedstocks;
2. characterise their physical and biological properties;
3. establish the required throughput;
4. choose the digestion process;
5. develop the mass and energy balance;
6. define gas and digestate outlets;
7. identify the equipment duties;
8. then select suppliers and equipment.

This reduces the risk of creating a plant around a collection of vendor packages that do not integrate properly.

Finding Anaerobic Digestion Equipment Suppliers

Once the process duties and required equipment have been defined, the next stage is identifying appropriate technology providers.

Rather than duplicating a list of manufacturers here, we maintain a separate resource specifically for readers looking for suppliers:

Biogas Companies in Europe – AD Technology Suppliers and Industry Companies

This equipment guide is intentionally focused on what equipment is required and how to select it; the companies page focuses on who supplies it.

Frequently Asked Questions About Anaerobic Digestion Equipment

What equipment is required for an anaerobic digestion plant?

Most plants require some combination of feedstock reception, preparation equipment, pumps, mixers, digesters, heating systems, gas holders, gas cleaning, CHP or biomethane upgrading, flares, digestate handling, instrumentation and safety systems.

What is the most important piece of AD equipment?

There is no single most important machine. The plant performs as a system. A failure in feed preparation, pumping, mixing, heating or gas handling can all stop or constrain production.

What type of pump is used in anaerobic digestion?

Common choices include progressive cavity pumps, rotary lobe pumps and specialist solids-handling pumps. Selection depends on solids concentration, viscosity, particle size, fibres, abrasiveness and required pressure.

What type of mixer is best for an anaerobic digester?

No mixer type is universally best. Selection depends on digester geometry, solids content, rheology, tank dimensions and the required mixing duty. Options include submersible, side-entry, top-entry, pumped recirculation and gas-mixing systems.

Does every AD plant need a CHP engine?

No. Many earlier plants were CHP-based, but numerous newer projects upgrade biogas to biomethane instead. Some plants may use boilers or combinations of different gas-utilisation systems.

Does every biomethane plant need CO2 recovery equipment?

No. Carbon dioxide recovery is an additional option rather than a universal requirement. However, commercial utilisation of separated biogenic CO₂ is attracting increasing interest.

Why is depackaging equipment important?

At food-waste AD plants, poor depackaging can introduce plastic, metal, glass and grit into downstream equipment and digestate. Effective separation can therefore affect both plant reliability and digestate quality.

Should anaerobic digestion equipment be selected on purchase price?

No. Whole-life cost should include power use, wear, servicing, parts availability, labour, downtime and lost production as well as initial price.

What equipment is used to make biomethane?

Biomethane production typically requires biogas cleaning, upgrading, gas analysis, compression and final gas-quality control. Grid-injection projects also require equipment specific to the local gas-network connection.

How do I find anaerobic digestion equipment manufacturers?

For manufacturers and technology providers, see our separate European biogas companies and suppliers guide. Keeping supplier information separate from this equipment-selection guide avoids confusing two different search intents.

Conclusion

The most successful anaerobic digestion plants are not necessarily those containing the most sophisticated equipment.

They are the plants where each piece of equipment has been selected to suit:

• the actual feedstock;
• the process duty;
• the operating environment;
• the maintenance strategy;
• the permit conditions; and
• the equipment immediately upstream and downstream.

That is why anaerobic digestion equipment selection should begin with process engineering rather than equipment catalogues.

A correctly specified pump, mixer, digester, gas-treatment system or digestate separator may appear unremarkable when operating normally.

But that is exactly the point.

Good AD equipment should quietly allow the biological process to remain stable, available and productive for years.

Authoritative Sources and Further Reading

• Environment Agency – Standard Rules Environmental Permitting
• Environment Agency – SR2021 No 6 Anaerobic Digestion Installations
• Environment Agency – SR2021 No 7 Anaerobic Digestion Waste Recovery Operations

This article was substantially rewritten in September 2026 to reflect modern anaerobic digestion equipment, biomethane production, process integration, current environmental permitting and contemporary equipment-selection practice.

In this section we feature the following anaerobic equipment pages:

pH Control Equipment
Anaerobic Digestion Pumps
Anaerobic Digestion Tanks
Biogas Generator Manufacturers
Biogas Holders for Anaerobic Digestion Plants
Heat Exchangers for Anaerobic Digestion Plants
Biogas Analysis and Gas Quality Monitoring Equipment

[First published November 2014. Updated December 2022. Rewritten September 2026.]