AD Certification Scheme: ADCS UK Requirements, Audits and International Expansion

The AD Certification Scheme provides an independent assessment of the safety, environmental and operational performance of anaerobic digestion plants.

For operators, ADCS certification offers more than a badge for the company website. The audit can expose weaknesses in management systems, staff competence, maintenance, process monitoring, environmental controls and day-to-day operating practices before those weaknesses contribute to an accident, pollution incident or prolonged plant failure.

The original UK scheme has also developed beyond its early years. Alongside ADCS UK, a separate ADCS International framework now provides a globally applicable approach that can be adapted to different national regulatory settings.

This guide explains:

• what the AD Certification Scheme covers;
• who can apply;
• how the audit and certification process works;
• the current published ADCS UK charges;
• how certification is maintained;
• the difference between ADCS and other standards; and
• how ADCS International extends the idea beyond the United Kingdom.

Originally published in 2018 and subsequently expanded with news of early certified plants. Completely rewritten and updated in September 2026 to cover the current AD Certification Scheme UK and ADCS International.

What Is the AD Certification Scheme?

The AD Certification Scheme, normally abbreviated to ADCS, is an industry-led certification programme created specifically for anaerobic digestion plants.

ADCS UK was developed by the Anaerobic Digestion and Bioresources Association (ADBA) with input from AD operators, developers, regulators, insurers, professional organisations and other industry stakeholders.

It forms part of ADBA’s wider Best Practice Programme and is intended to help operators:

• improve health and safety;
• manage environmental risks;
• demonstrate legal and operational awareness;
• improve plant reliability and performance;
• identify weaknesses through independent assessment; and
• provide greater confidence to employees, regulators, insurers, investors and other interested parties.

The scheme was established in 2017. Granville EcoPark in Northern Ireland became the first plant certified under ADCS UK in January 2018.

Why Does the Anaerobic Digestion Industry Need Its Own Certification Scheme?

An anaerobic digester is not just a tank in which microorganisms produce biogas. A commercial AD facility combines biological treatment, gas production, pressure systems, mechanical equipment, electrical installations, feedstock reception, digestate management and potentially hazardous substances.

The risks can include:

• methane leaks, fires and explosions;
• hydrogen sulphide exposure;
• confined spaces and oxygen-deficient atmospheres;
• pressure-system failures;
• vehicle and machinery accidents;
• biological process instability;
• digestate or feedstock spills;
• odour and other emissions;
• water pollution;
• failure to comply with permit conditions; and
• inadequately trained or supervised personnel.

Legal compliance remains the operator’s responsibility whether or not the plant participates in ADCS. However, the scheme brings numerous aspects of good AD operation together within one sector-specific assessment framework.

ADCS does not replace an operator’s legal duties. It provides an independent way to assess whether appropriate systems, procedures and evidence are in place within the scope of the scheme.

What Does ADCS UK Assess?

According to the current scheme material, ADCS UK assesses plants against 12 criteria. These overlap with relevant elements of standards and regulatory requirements including ISO 45001, ISO 14001, environmental permitting, animal by-product controls, digestate requirements and PAS 110 where applicable.

The assessment extends beyond the possession of policies and certificates. An auditor needs evidence that the plant’s systems are understood, maintained and followed in practice.

The principal areas fall into three broad groups.

1. Health and safety performance

Health and safety assessment may include evidence concerning:

• the identification and control of hazards;
• risk assessments and safe systems of work;
• staff responsibilities and supervision;
• training, competence and refresher training;
• contractor and visitor management;
• emergency planning;
• fire and explosion precautions;
• gas detection;
• confined-space controls;
• maintenance safety and isolation procedures; and
• incident reporting and corrective action.

Simply possessing a generic risk assessment is not enough. It must reflect the actual plant, equipment, feedstocks, work activities and people exposed to the risks.

2. Environmental performance

The environmental part of the scheme considers how the operator identifies and controls risks to land, air and water.

Relevant evidence may include:

• environmental permits and other authorisations;
• site drainage and containment arrangements;
• feedstock acceptance procedures;
• spill prevention and response;
• odour management;
• emissions and leakage controls;
• digestate storage and management;
• monitoring and record keeping;
• complaint and incident procedures; and
• actions arising from regulator inspections.

A plant may have a valid environmental permit while still suffering from weak inspection, maintenance or record-keeping practices. ADCS is intended to look at how the site is actually managed, not merely whether a permit document exists.

3. Operational performance

Operational performance concerns the ability of the plant to run reliably, efficiently and under control.

This can involve:

• process monitoring;
• feedstock control;
• biogas quantity and quality;
• digestate quality;
• preventive maintenance;
• management of alarms and abnormal conditions;
• critical spare parts;
• inspection and calibration;
• recording plant performance;
• investigating declining output or repeated faults; and
• implementing corrective and preventive actions.

The purpose is not to require every plant to use identical equipment or operating parameters. AD plants differ considerably in scale, design and feedstock. The operator must instead demonstrate that the arrangements are appropriate for the particular plant and its risks.

For an example of why monitoring must come before control, see our explanation of why the digester is only one link in the AD project failure chain.

Who Can Apply for ADCS UK Certification?

The scheme is intended for operators of constructed and operational UK anaerobic digestion plants. It accommodates different sizes and types of plant, including facilities using waste feedstocks and plants using non-waste materials such as crops or crop residues.

According to the current application guidance:

• an applicant does not have to be an ADBA member;
• plants of different sizes can apply;
• each plant is certified separately, even when one operator owns several sites;
• the plant must be available for a site-based inspection; and
• sewage-treatment plants are currently excluded.

The published FAQ also excludes plants co-digesting food waste with sewage sludge under the present scope, reflecting the different regulatory regimes applying to sewage sludge, biosolids and other AD feedstocks.

Developers of plants that have not yet been constructed cannot complete certification, because a site audit is essential. They can, however, use the scheme criteria during design, procurement and construction so that poor decisions are not built into the finished facility.

How to Apply for ADCS UK Certification

The official ADCS UK application guidance sets out the following general process.

1. Review the scheme documents. Read the Scheme Rules and Scheme Criteria and consider the evidence the auditor will require.
2. Assess whether the plant is ready. Identify obvious gaps in procedures, records, training, maintenance or physical infrastructure.
3. Contact an appointed certification body. Obtain the current application form, charges and instructions.
4. Submit the application and fee. The application is registered and given a scheme application number.
5. Provide supporting information. The auditor conducts a desk-based review and requests missing or additional evidence.
6. Agree the site-audit date. All initial certifications require a site-based assessment.
7. Complete the site audit. The auditor examines the facility, speaks to relevant personnel and verifies the submitted evidence.
8. Receive the audit report and decision. The certification body identifies good practice, recommendations and any non-conformances.
9. Close out any non-conformances. Where permitted, the operator supplies evidence of the required corrective actions. A further visit may sometimes be necessary.
10. Receive certification. A successful applicant receives a certificate and permission to use the ADCS UK certification logo, subject to the scheme rules.

At the time of this update, the ADCS UK website identifies Aardvark Certification Limited as the appointed certification body. Applicants should check the official site before applying in case this changes.

How Long Does ADCS Certification Take?

The official FAQ indicates that the period between receipt of a completed application and payment and the audit report is likely to be approximately six to eight weeks.

This is not a guaranteed timeframe. It depends partly on how quickly the applicant supplies complete and usable information.

The time needed to become ready may be much longer if the plant has:

• incomplete records;
• outdated risk assessments;
• unresolved maintenance defects;
• inadequate staff training evidence;
• poorly documented emergency arrangements;
• unresolved permit issues; or
• significant physical deficiencies.

The site-based part of the initial audit is normally expected to take up to one day, although the precise audit requirement will depend on the plant and the evidence requiring verification.

Current ADCS UK Application and Renewal Charges

The ADCS UK website publishes charges based on annual plant throughput. At the time this article was updated, the stated fees were as follows:

Published charges exclude VAT and may change. Additional site-audit work can incur further costs. Always check the current ADCS UK charges page or contact the appointed certification body before budgeting.

The official schedule also publishes multi-site discounts where several sites under common ownership and management are registered and paid for at the same time:

• two to four sites: 10% discount; and
• more than five sites: 15% discount.

Operators should consider not only the application fee but also the internal cost of preparation and any physical, procedural or training improvements required before non-conformances can be closed.

How Long Is ADCS UK Certification Valid?

Under the March 2024 Scheme Rules, an ADCS UK certificate is valid for three years, subject to the operator maintaining the required standards and completing interim reviews.

A full site visit is required at least every three years. Annual reviews take place during the intervening period and may be completed as desk-based surveillance where circumstances permit.

The operator may be asked to supply:

• details of changes to site operation;
• regulator inspection reports from the previous 12 months;
• selected operational and management records; and
• evidence that earlier recommendations have been addressed.

Significant changes can trigger more extensive assessment or recertification. Examples include:

• major changes to plant design or layout;
• a change in the operating company;
• a change in site ownership;
• a major environmental or health and safety incident;
• significant throughput or feedstock changes; and
• other changes affecting regulatory compliance or the validity of previous audit evidence.

What Evidence Should an Operator Prepare?

The official Scheme Criteria document remains the controlling source, but an operator preparing for assessment should expect to assemble organised evidence rather than a last-minute collection of unrelated files.

A practical evidence pack may include:

• a site description and process-flow information;
• responsibility and reporting structures;
• environmental permits and planning conditions;
• risk assessments and safe systems of work;
• DSEAR assessments and hazardous-area information where applicable;
• emergency and incident-response plans;
• staff training and competence records;
• contractor-control procedures;
• feedstock specifications and acceptance records;
• process-monitoring records and operating limits;
• inspection, maintenance and calibration schedules;
• breakdown and corrective-action records;
• gas-quality, leakage and emissions information;
• digestate analysis and outlet arrangements;
• complaint records;
• regulatory correspondence and inspection reports; and
• evidence that management reviews performance and follows up deficiencies.

A common weakness in certification exercises is the gap between written procedure and actual practice. A beautifully written maintenance policy will carry little weight if overdue tasks, recurring failures and missing inspection records show that it is not being implemented.

What Happens If the Plant Does Not Pass?

An unsuccessful initial audit does not necessarily end the application.

The certification body can identify non-conformances, specify the corrective evidence required and set a period for completing improvements. Certification may be awarded once the certification officer is satisfied that the necessary actions have been completed.

Some matters may be closed through documentary evidence. A further site visit may be required when implementation cannot be verified remotely.

The scheme rules also contain appeal and complaint procedures. These are important because ADBA owns and administers the scheme, while the appointed certification body makes individual certification decisions.

Benefits of ADCS Certification

Potential benefits include:

• an independent review by an auditor familiar with the AD sector;
• identification of weaknesses before they develop into serious incidents;
• a structured improvement report;
• comparison against industry-developed criteria;
• greater consistency across several plants operated by one company;
• evidence of management commitment to safe and responsible operation;
• greater confidence among employees and external stakeholders;
• supporting evidence for investors’ or lenders’ due diligence;
• permission to use the ADCS UK certified logo; and
• opportunities for recognition through industry publicity.

Certification may also be relevant during discussions with insurers. However, it would be unwise to promise that every certified plant will automatically receive a lower premium or more favourable policy.

Insurance terms depend on the insurer’s assessment of the individual plant, its loss history, design, operating controls, business-interruption exposure and the wider insurance market. Certification may provide useful evidence of risk management, but it does not compel an insurer to offer a particular saving.

What ADCS Certification Does Not Prove

Certification should not be exaggerated. It does not mean that:

• the plant can never suffer an accident or breakdown;
• all legal and permit requirements outside the scheme’s scope have been independently verified;
• future regulatory compliance is guaranteed;
• every item of plant has been technically inspected;
• the operator no longer needs specialist legal, engineering or safety advice;
• digestate automatically has product or end-of-waste status;
• the biomethane qualifies for every subsidy or sustainability scheme; or
• the plant will necessarily obtain cheaper insurance or finance.

ADCS is a valuable independent assessment framework, but it does not transfer responsibility away from the operator.

ADCS Compared with Other Standards and Certification Schemes

ADCS is sometimes confused with environmental-management, occupational-safety, digestate and renewable-gas certification schemes. These schemes overlap in places, but they do not serve identical purposes.

An operator may therefore hold more than one certification. Existing independently audited systems may also provide evidence relevant to parts of an ADCS assessment and help avoid unnecessary duplication.

ADCS UK Is Not the Same as Digestate Certification

This distinction deserves particular emphasis.

ADCS UK assesses the overall operation of the AD plant. The Biofertiliser Certification Scheme assesses digestate production against PAS 110 and the applicable regulatory framework for achieving end-of-waste status.

An AD plant can therefore require both forms of assurance for different reasons.

ADCS certification does not automatically make digestate a product. Likewise, PAS 110-certified digestate does not prove that every aspect of plant health and safety, maintenance or operational performance meets the ADCS criteria.

For more information about using the material on farms, read our guide to digestate fertilizer and its agricultural use.

What Is ADCS International?

ADCS International is the global development of the AD-specific certification concept. It is owned by the World Biogas Association and is intended to improve the health, safety, environmental and operational performance of biogas plants internationally.

The international scheme addresses a major difficulty: biogas is expanding across countries with very different levels of regulation, technical guidance, operator experience and enforcement.

A scheme based entirely on UK legislation could not simply be exported unchanged. ADCS International instead provides a common framework that can be applied while recognising national legal and regulatory requirements.

Its purpose is not to replace local law. Operators remain responsible for identifying and complying with the rules that apply to their country, region, plant and feedstock.

The 11 ADCS International Modules

The international framework is organised around 11 modules:

1. Site information and understanding
2. Managing health and safety risks
3. Staff training and competence
4. Process monitoring
5. Maintenance of plant, equipment and infrastructure
6. Procuring services
7. Managing environmental risks
8. Animal by-products and preventing cross-contamination
9. Digestate management
10. Biomethane upgrading process
11. Life Cycle Assessment

The addition of biomethane upgrading and Life Cycle Assessment reflects the increasingly important relationship between safe plant operation, methane-emissions control and the claimed climate performance of renewable gas.

Operational Guidance Notes are available for the modules through the official ADCS International guidance and support page. The World Biogas Association states that these resources are available to operators regardless of whether they are participating in certification.

Why an International AD Certification Scheme Matters

Rapid growth in biogas capacity is desirable only if plants perform safely and deliver genuine environmental benefits.

A poorly designed or operated facility can:

• release methane and undermine its climate benefit;
• cause odour and damage community acceptance;
• pollute surface water or groundwater;
• expose workers to toxic or explosive gases;
• produce contaminated or poorly managed digestate;
• suffer low gas yield and excessive parasitic energy demand; and
• damage confidence in the wider biogas industry.

ADCS International provides a means of promoting consistent expectations while allowing implementation to reflect local law and circumstances.

This may be particularly valuable in developing markets where biogas investment is accelerating faster than sector-specific regulatory guidance, operator training or institutional experience.

Early ADCS UK Certification Milestones

The early history of ADCS UK included several important certification announcements:

• Granville EcoPark, Northern Ireland became the first ADCS-certified plant in January 2018.
• Malaby Biogas at Bore Hill Farm, Wiltshire became the first certified plant in England in 2018.
• Rotherdale Farm, operated by Vale Green Energy achieved certification in 2022.
• Bio Capital subsequently achieved certification for several plants, including facilities in Scotland and England.

These announcements helped establish the scheme, but an old press release does not confirm a plant’s current certification status. Certification is maintained through surveillance and reassessment.

Readers seeking current information should consult the official ADCS UK list of certified plants.

A Practical Pre-Audit Readiness Check

Before paying the application fee, an operator should be able to answer “yes” to questions such as:

• Can we produce current permits, procedures and site-specific risk assessments?
• Can we show that operators are trained and competent for their assigned duties?
• Are inspection, maintenance and calibration tasks completed and recorded?
• Do we know which alarms and operating parameters are critical?
• Can staff explain what they would do during a gas leak, spill, fire or biological upset?
• Have outstanding regulator or insurer recommendations been addressed?
• Can we demonstrate control of contractors and visitors?
• Are feedstock acceptance and rejection decisions documented?
• Can we account for the digestate and demonstrate lawful outlets?
• Do managers review incidents, recurring faults and declining performance?
• Are written procedures actually followed on the plant?

If the evidence exists only in the memory of one experienced site manager, the management system is vulnerable. Certification preparation should convert essential knowledge into clear, accessible and routinely used systems.

Frequently Asked Questions

What does ADCS stand for?

ADCS stands for the AD Certification Scheme, with AD meaning anaerobic digestion. The two current forms are ADCS UK and ADCS International.

Is ADCS certification compulsory?

No. ADCS UK is a voluntary industry certification scheme. Legal duties, environmental permits and health and safety requirements remain compulsory whether or not a plant participates.

Is ADCS available to non-ADBA members?

Yes. The published ADCS UK Scheme Rules state that an operator does not have to be an ADBA member to apply.

Can a small farm digester apply?

Yes. ADCS UK is intended to accommodate different plant sizes. The charges are banded by annual throughput.

Can a sewage-treatment AD plant apply?

Not under the currently published UK eligibility information. Sewage-treatment plants and plants co-digesting food waste with sewage sludge are excluded from the present scope.

Can a plant be certified before it is constructed?

No. Certification requires a site-based audit of a constructed plant. Developers can nevertheless use the criteria during design and construction to improve readiness.

How long does certification take?

The official UK FAQ suggests approximately six to eight weeks from receipt of the application and payment to completion of the audit report. Preparation and corrective work can extend the overall period.

How long does an ADCS UK certificate last?

The current Scheme Rules specify a three-year certificate, with annual reviews and a full site visit at least every three years. Significant changes or incidents may require additional assessment or recertification.

Does ADCS guarantee regulatory compliance?

No. It includes checks relevant to its criteria, but it does not replace the operator’s responsibility to comply with every applicable law, permit and regulatory requirement.

Does ADCS certification guarantee cheaper insurance?

No. It may provide useful independent evidence of risk management, but insurance availability and price remain decisions for the insurer based on the individual risk.

Is ADCS the same as PAS 110 certification?

No. ADCS concerns overall AD plant operation. PAS 110 and the Biofertiliser Certification Scheme concern digestate production and quality assurance.

Does ADCS International use UK law?

It draws on the experience and principles behind the UK scheme but is designed for international application. It does not replace the legislation of the country in which the plant operates.

Conclusion

The AD Certification Scheme fills an important gap between generic management standards, legal inspections and the practical realities of running an anaerobic digestion plant.

ADCS UK gives operators a sector-specific, independently audited way to demonstrate their approach to health and safety, environmental protection and operational performance. Its audit report can also provide a practical programme for improvement where deficiencies are found.

ADCS International takes the same underlying objective into a global industry that needs to expand without accepting avoidable methane emissions, accidents, pollution or poorly trained operators as the price of growth.

Certification is not a guarantee that nothing will go wrong, and it cannot transfer legal responsibility away from the plant operator. Its real value lies in requiring the operator to demonstrate—not merely assert—that effective systems are in place and being used.

This article provides general information about the AD Certification Scheme. Scheme documents, charges, appointed certification bodies and eligibility requirements can change. Prospective applicants should consult the current official scheme rules and obtain appropriate professional advice.

[Article first published August 2018. Updated July 2022, August 2022. Rewritten September 2026.]