Pillar 6:
Technical and Operational Standards

Executive Summary

Introduction

6.1 Industry-wide best available techniques

6.1.1 Engaging key stakeholders

6.1.2 Developing BAT reference documents (BREFs)

6.1.3 Setting BAT associated emission level (BAT-AELs)

6.1.4 Emissions to air-point source or channelled emissions

6.1.5 Align with environmental permitting

6.1.6 Review and update

6.2 BAT implementation guidance

6.2.1 Set size and feedstock criteria

6.2.2 Develop guidance for planned and operational sites

6.2.3 Make allowance for alternative approaches

6.2.4 Outline a process for deviation based on disproportionate cost vs benefits

6.3 Design standards to control emissions

6.4 Risk-assessment-based plant design

6.4.1 Undertake HAZID and/or HAZOP

6.4.2 Include risk-control measures in design

6.4.3 Implement a source-pathway-receptor model

6.4.4 Include climate change as a risk

6.5 Design and construction standards

6.5.1 Containment systems

6.5.2 Above-ground tanks and bulk storage

6.5.3 Below-ground tanks and pipework

6.5.4 Storage lagoons

6.5.5 Secondary containment

6.5.6 Electrical systems

6.5.7 Pipelines for biogas

6.5.8 Maintenance and repair schedules

6.6 Operational standards for AD operations

6.6.1 Feedstock management

6.6.2 Process monitoring and control

6.7 Management systems and competence

6.8 Quality, management and use of outputs from operations

6.8.1 Export and use of gases and electricity

6.8.2 Digestate quality and management standards

6.8.3 Carbon dioxide capture and use

6.9 Monitoring and control of emissions

6.9.1 Control measures in plant design

6.9.2 Specific techniques for management of noise and vibration

6.9.3 Specific techniques for management of odours

6.9.4 Specific techniques for management of emissions to water

6.9.5 Specific techniques for management of emissions to air

6.9.6 Management plans

6.9.7 Leak detection and repair

6.9.8 Plant decommissioning

6.9.9 Monitoring emissions

6.9.10 Emissions to water

6.10 Emergency response planning

6.10.1 Procedures

6.10.2 Design measures

6.11 Implementation of other technical and quality standards for the industry

Executive Summary

Pillar 6: Technical and Operational Standards presents the best available techniques for preventing or minimising emissions and impacts on the environment. Best available techniques encompass all aspects of installation design, construction, operational standards, technology and methods for decommissioning to allow the rapid development of a high-performing industry that does not cause adverse environmental impacts. By playing an active role in applying technical and operational standards for the biogas industry, 

The biogas industry suffers from its standards having been drawn from a variety of diverse sources, specialisms and legal and policy drivers (e.g. the gas and chemical industry and farming sector). In countries where the industry is well established, a range of standards have emerged that are used to inform ongoing practice and regulation. Aspects of the health, safety and environmental permitting standards are further discussed in Pillar 7: Environmental Regulations and Permitting and Pillar 9: Health, Safety and Environmental Protection Regulation. 

Clear biogas industry specific standards must be developed by countries. This pillar brings together a suite of standards and requirements that can be adopted for plants to meet their performance targets.

Conclusion

This pillar is a guide specific to biogas plant operators and developers to ensure to operational safely, meet performance targets using best available techniques, and maximise their contributions to global climate efforts. The wholistic set of policies in this pillar provide governments a steer on the requirements that are needed for the industry, including for design and construction, ongoing maintenance and risk management, monitoring fugitive emissions.

 

PILLAR 6: Technical and Operational Standards

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Introduction 

Application of technical and operational standards is essential for any industry and the anaerobic digestion (AD) industry is no exception. Clear, recognised standards allow developers to define and scope what will be needed at early plant development stages, allow regulators to set relevant regulatory requirements and help operators optimise plant productivity and safety.

Good technical and operational standards also ensure the environmental performance of the plant, for example, by avoiding leaks to the environment and maintaining AD as a climate-aligned solution. Standards will also ensure that the business model and financial case maintain the continued growth of the industry by preventing failure and the associated risk observed by financial institutions.

Standards must be evidence based and ideally developed in partnership, with contributions from a range of industry stakeholders.

Standards may be minimum benchmarks required for legal operation with a mandate for implementation, or voluntary to achieve quality standards above minimum requirements.

In the AD/biogas industry, technical and operational standards must be established to ensure:

• the health and safety of staff and the public
• protection of the environment including climate mitigation
• protection of animal and plant health
• AD plants are operated to be economically viable, achieving the desired outputs and benefits 
• the requirements for the development and operation of plants are clearly understood so permits are issued in suitable time 
• the same requirements and expectations are applied to all operators to ensure equal opportunities for developers

 

Current AD industry standards have been drawn from a variety of diverse sources, specialisms and legal and policy drivers (e.g. the gas and chemical industry and farming sector). In countries where the AD industry is well established, a range of standards have emerged that are used to inform ongoing practice and regulation. Clear biogas industry specific standards must be developed.

 Aspects of the health, safety and environmental permitting standards are further discussed in Pillar 7 Permitting Policy and Pillar 9 Health, Safety and Environmental Regulations.

 

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6.1. Industry-wide best available techniques

‘Best available techniques’ (BAT), as defined in Europe, are those that are the best for preventing or minimising emissions and impacts on the environment. ¹ BAT encompasses all aspects of installation design, construction, operational standards, technology and methods for decommissioning.

 

EXAMPLES

The Environmental Protection Agency in the USA, using the collaborative programme “AgSTAR: Biogas Recovery in the Agriculture Sector”, has published a handbook that includes best practices for AD. ²

It is crucial that adequate BAT guidance is introduced and followed up to minimise and ultimately prevent biogas plant accidents. ³

The Anaerobic Digestion Certification Scheme International (ADCS-Intl) has been created in line with BAT, stakeholders and other governmental considerations to be used as a technical tool to assist. ⁴

 

The key steps to establishing BAT include:

6.1.1. Engaging key stakeholders

BAT is determined by key stakeholders undertaking industry-wide discussion and analysis of real-life industry practices. Stakeholders include regulators, industry and non-governmental environmental organisations.

6.1.2. Developing BAT reference documents (BREFs)

The discussions with stakeholders and analyses are laid out in BAT reference documents (BREFs). Final BAT conclusions arise from the BREFs and, in turn, they determine the reference points used to set permit conditions for regulated installation sites.

6.1.3. Setting BAT associated emission level (BAT-AELs)

BAT associated emission levels, or BAT-AELs, are specified air and water emissions limits for industrial activities.

6.1.4. Emissions to air-point source or channelled emissions

Standards are applied for point source or channelled emissions to air during plant operation from equipment such as engines, boilers, flares, generators, and extraction and abatement units.

 

EXAMPLE

In the USA, the Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (40 CFR part 50) for six principal pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particle pollution and sulphur dioxide ^5.

 

6.1.5. Align with environmental permitting

Enforcement of BAT is linked with environmental permitting. Large-scale industrial processes that warrant higher degrees of environmental protection are specified installations under environmental regulation. These installations must have a permit to operate and must apply BAT to prevent and minimise emissions.

Any permit application process or template will require the applicant to submit details of the measures proposed to meet BAT and any other specified standards. The suitability of proposed measures will be assessed during the application process and a permit will only be issued if those measures are satisfactory. The proposed measures may also inform the conditions specified in a permit with respect to ongoing monitoring and reporting at the site, permit improvement conditions or additional pre-operational conditions.

6.1.6. Review and update

Industry BREFs are reviewed and updated periodically to ensure that BAT are up-to-date and in line with new industry developments.

 

EXAMPLES

The European Union’s Technical Standards and Regulations Directive 98/34/EC seeks to ensure the transparency of technical regulations and is intended to help avoid creating new technical barriers to trade within the European Community. ⁶

An industry BREF has been published for the waste treatment industry. This document includes final BAT conclusions and BAT-AELs to be applied to all sectors of the waste treatment industry, and specific BAT conclusions and BAT-AELs to be applied to the biological treatment of waste and the AD sector. ^{7 8} 

 

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6.2. BAT implementation guidance

BAT conclusions apply to a range of waste industry sectors. Further guidance and interpretation are needed from the regulator as to how BAT can be deemed to have been implemented in practice in any specific sector.

BAT implementation must consider size and proportionality of cost, and allow for innovation and the development of technology.

6.2.1. Set size and feedstock criteria

The implementation of BAT is enforced on plants that require the relevant permits. This is determined by plant risk factors, such as feedstock types and plant processing capacity, which are linked to permitting processes. For facilities outside the predefined enforcement criteria, BAT provides best-practice benchmarks.

 

EXAMPLES

The UK has introduced a BAT requirement that includes all installations treating less than 100 tonnes of waste daily. ⁹ 

In Denmark, plants treating more than 30 tonnes of feedstock per day should have an environmental permit. ¹⁰

 

6.2.2. Develop guidance for planned and operational sites

The regulator should provide additional guidance at design stage and on operational sites, to specify how BAT is implemented in practice. The regulator may update this guidance to reflect changes in technology or learning outcomes from industry practice. BAT must be considered for functional description and maintenance plans for new built sites.

 

EXAMPLES

The Environment Agency of England and Wales has issued online appropriate measures guidance on implementation of BAT. The online guidance is subject to periodic review and update, and operators must be aware of and adapt to any changes made. ¹¹

The Nordic Council of Ministers and the BAT Group commissioned a “Nordic BAT project on smaller biogas plants in the Nordic countries”, ¹² which led to the development of BAT that will aid the design and management of small AD plants (up to 100 tonnes of feedstock per day) and ultimately reduce the impact plants have on the environment.

 

6.2.3. Make allowance for alternative approaches

Technology is continuously developing, and risk varies from site to site based on distinct factors. Operators can propose alternative techniques that achieve the same degree of environmental protection as those specified in the BAT conclusions. If the regulator agrees that an approach achieves the same degree of environmental protection as a BAT-specified technique, then it can be agreed as BAT-equivalent. ¹³

Where alternative techniques are proposed, there must be early discussions with the regulator to establish if the method is BAT-equivalent. 

 

EXAMPLES

In the EU, the relevant regulations specify what must be considered when deciding whether a technology is BAT-equivalent. ¹⁴

“Emerging techniques”, as described in “BAT in smaller biogas plants in the Nordic countries”, ¹⁵ may be used as a BAT in the future, developed in line with emerging new technologies in the biogas industry.

The United States Environmental Protection Agency has provided an interpretation of alternate approaches that can be accepted as an alternative protocol under biogas regulatory reform rule. ¹⁶

 

6.2.4. Outline a process for deviation based on disproportionate cost vs benefits

Allowance must be made for operators to formally apply to deviate from BAT if they are able to demonstrate that the costs of implementing these techniques are disproportionate to the environmental protection benefits. 

Where disproportionate costs to implementation of BAT can be demonstrated, the operator could implement a method that will not provide equivalent environmental protection to BAT.

There must be a formal process and set of requirements for demonstrating deviation from BAT in this way, and any final decision must be made by the regulator.

 

EXAMPLES

The Environment Agency of England and Wales has developed a cost-benefit analysis tool to help operators present any case for deviation from BAT. ¹⁷

 

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6.3. Design standards to control emissions

Key features of plant design will determine achievable parametres for plant performance and outputs. Where specific standards are set for plant performance and outputs, it is essential that measures are included at the early plant design stage to ensure that these standards can be met when the plant becomes operational.

Retrofitting infrastructure to an existing plant or reconstructing areas of a site to a specified standard can be difficult, costly and, at times, impossible. It is, therefore, important that all relevant standards relating to construction, performance and final outputs are considered at the early design stages.

For example, to meet required standards, plant designers must include features such as:

• secondary containment/bunding for process tanks and liquid stores
• adequate containment and storage capacity for feedstocks
• adequate storage capacity for biogas produced and final digestate
• adequate storage facilities for chemicals, fuels and wastes
• provision of spill containment measures for liquid off-take and delivery points
• necessary equipment for removal of contamination in feedstocks
• the requirement to segregate feedstocks in storage areas
• necessary containment, extraction and abatement systems for management of emissions from the storage and processing of feedstocks and storage and processing of final digestate
• containment and cover arrangements for final digestate stores
• installation of leak detection systems and/or secondary containment for below-ground structures containing potentially polluting substances
• installation of sealed drainage systems in feedstock and digestate process areas
• selection and specification of plant and equipment that will perform to required emissions limits and standards
• installation of suitable accessible sample points to allow process and emissions monitoring
• installation of pasteurisation facilities and maceration to specified areas
• placement/location of plant and equipment at the furthest point from receptors such as watercourses and houses, to minimise potential impacts from emissions
• design of plant control interface and philosophy
• installation of facilities to monitor plant energy efficiency and the use of raw materials, such as electricity metres and flow metres
• inclusion of measures to ensure safe operation of plant and equipment, such as:
  • lightning-protection 
  • fire prevention, detection and response 
  • ATEX rating of equipment ^{18 19}
  • fixed gas detection systems 
  • pressure-relief systems
  • automatic control interlock systems
  • minimum exclusion zones around equipment.
• classification of the areas/parts of installation where combustible gas might arise ²⁰
• inclusion of contingency measures in the event of emergency or plant failure, such as:
  • emergency backup power
  • emergency flares 
  • pressure relief systems 
  • measures to manage unusual plant conditions, e.g. foaming of digestate.
  • consideration of plant decommissioning process at the end of plant operations.

 

 

EXAMPLES

The Environment Agency of England and Wales has issued guidance on plant location, design and capacity as part their published appropriate measures guidance. ²¹

The United States Environmental Protection Agency via the AgSTAR programme has published a “Project Development Handbook” that outlines necessary steps for the evaluation, design and execution of the project. ²²

 

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6.4. Risk-assessment-based plant design

The design of a plant must be based on a robust risk assessment, and control measures must be included at the design stage.

6.4.1. Undertake HAZID and/or HAZOP

A Hazard and Operability Study (HAZOP) or Hazard Identification process (HAZID) must be conducted following the initial design stage. It is important that both HAZOP and HAZID are frequently reviewed and updated to reflect the continuously developing innovative technologies and improvements in the biogas production.

6.4.2. Include risk-control measures in design

Appropriate plant control measures must be identified at the plant design and planning stage by implementing suitable risk-assessment processes through implementation of a HAZID and/or a HAZOP or similar process.

The HAZOP provides a method for a systematic and detailed risk-assessment process for all aspects of plant and operations. The potential for deviation from desired operational standards is considered for each aspect of operations, and the potential of any such deviation being hazardous is assessed. Recommendations are then made to eliminate the possibility of hazardous deviations through plant design and specification controls. The HAZOP assessment must be reviewed whenever any component of plant design or operation is updated or changed.

It is also important that the findings of risk assessments and any subsequently tailored standard operating procedures (SOPs) are shared with the industry to improve the safety of both operators and the public.

 

EXAMPLE

A best practice guide to HAZOP developed by chemical industry experts may be a helpful reference for AD operators and regulators. ²³

 

These measures are further discussed in Pillar 9: Health, Safety and Environment.

6.4.3. Implement a source-pathway-receptor model

Environmental protection measures proposed at the plant design stage must be informed by a detailed environmental risk based on a “source-pathway-receptor” model. This assessment must be based on the specific locational characteristics of the site and the nature and scale of the proposed activities. Additionally, the “fit for purpose” standardisation must be considered to include the geographical location of the plant, available public infrastructure and local permitting requirements.

Detailed impact dispersion modelling assessments may be needed in some instances to allow risk to be assessed before site development. Verification of the assumptions used in any impact modelling assessment before site development is likely to be needed once the plant has been built and operations begun.

 

EXAMPLES

The Environment Agency of England and Wales has developed guidance on completion of environmental risk assessments. ²⁴

The Environment Agency of England and Wales has developed guidance for detailed impact modelling assessments for emissions to air. ^{25 26}

 

6.4.4. Include climate change as a risk

The impacts of a changing climate must also be considered at the initial risk-assessment design stages to allow for an increased frequency of extreme weather events, and to provide additional resilience that may be needed through the lifetime of the plant.

 

EXAMPLE

The Environment Agency of England and Wales has issued guidance on hazards to consider when undertaking a climate-change risk assessment and adaptation plan in different waste sectors, including AD. ²⁷

 

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6.5. Design and construction standards

As large volumes of potentially polluting liquids are stored at an AD facility during day-to-day operations, standards are applied to the design and construction of containment structures – such as storage lagoons, concrete surfaces and sealed drainage systems – and secondary containment measures (bunds). Structures must be designed taking into consideration risk-based factors, such as the materials being processed and annual tonnages/volumes, and local environmental factors, such as the proximity of surface watercourses and the sensitivity of local groundwater.

Additionally, the “fit for purpose” standardisation must be considered, to include the geographical location of the plant, available public infrastructure and local permitting requirements.

6.5.1. Containment systems

The Construction Industry Research and Information Association (CIRIA) ²⁸ have published several construction standards related to the design and construction of containment structures, ²⁹ lagoons, silage clamps and other agricultural buildings, ^{30 31} including the CIRIA 736 standard, which is specified in the UK appropriate measures guidance on the implementation of BAT.

CIRIA 736 includes a ‘source-pathway-receptor’ model risk-assessment approach towards the design and construction of containment systems, which allows the design to be developed in accordance with local conditions. It also outlines standards for other aspects, such as:

• calculating adequate bund capacity
• maintenance measures 
• design and construction of earth bank stores and bunds 
• design and construction of below-ground tanks and transfer systems.

 

EXAMPLE

In the UK, the Silage Slurry and Agricultural Fuel Oil (SSAFO) regulations lay down standards for the construction and maintenance of farmyard slurry stores and silage clamps, ³² and these standards are also implemented as BAT where relevant. 

In the USA, the United States Department of Agriculture have published a conservation practice standard for AD. ³³

 

6.5.2. Above-ground tanks and bulk storage

 All above-ground tanks containing potentially polluting liquids must be:

• on an impermeable surface that is resistant to the material being stored
• secondary contained/bunded/self-contained sealed drainage to prevent spillages leaving the site, or spillages from other areas entering the tank storage area
• shown in context on a detailed site drainage plan
• suitably designed, constructed and maintained for the material being stored
• leakproof and working correctly before first use
• designed with a working capacity that provides a suitable maintained freeboard space at the top of the tank
• gas-tight or covered with gas/displaced air passed through an abatement system before venting to the atmosphere
• compliant with relevant standards, such as:
  • C535 Above-ground proprietary prefabricated oil storage tank systems (where relevant) ³⁴
  • C736 Containment systems for the prevention of pollution ³⁵

The potential for tanks to overflow on filling must be considered at the design risk-assessment stage, and measures to prevent overflow included in the plant design. This is likely to include high-level sensors with interlock input shut-off systems.

For gas-tight tanks, the need for under/overpressure relief systems must also be considered and facilitated at the design stage.

Consideration must also be given to siting and access for maintenance and repair to ancillary equipment inside the tank, such as pumps, mixers and sensors.

6.5.3. Below-ground tanks and pipework

All below-ground or submerged tanks that are used to store, treat or convey waste must be:

• designed and constructed from suitable material resistant to the wastes being contained and the surrounding environment of the tank
• designed, constructed, maintained and leakproof, and working correctly before first use
• secondary contained and/or fitted with a leak-detection system
• fitted with ’shut off’ or isolation facilities to allow access for inspection and repair if needed, and sensors to prevent or detect overfilling and loss of containment
• connected to suitable abatement systems for treatment of releases of displaced air on filling/agitation prior to release to atmosphere.

 

6.5.4. Storage lagoons

Storage lagoons are often a solution for storing final digestate during closed spreading periods. There must be enough storage capacity for digestate to be stored and then used when there is a crop need and spreading conditions are suitable.

Standards for the construction and maintenance of storage lagoons are specified in C736 and C759, ³⁶ and again will depend on the specific risk factors of the location and local ground conditions.

The size of lagoons must take into account:

• the need to always maintain a freeboard space of 750mm at the top of the lagoon
• the need for lagoon covers 
• the potential need for emissions abatement to manage emissions to the atmosphere from the lagoon surface. 

Covers are also needed to prevent rainwater ingress, dilution of the digestate and loss of storage capacity.

Digestate storage must consider factors such as potential residual biogas that maybe present in the material. Residual biogas will be minimal in well operated plants with sufficient retention times in the digester and efficient methodologies

Consideration must be given to the required gas storage capacity to accommodate the residual gas potential in a lagoon. The residual gas obtained from this process must be used where possible, or processed through filtration mechanisms. Certain sizes would bring the site under certain regulation directives, such as Control of Major Accident Hazards (COMAH) ³⁷ in the UK or the SEVESO III Directive. ³⁸

6.5.5 Secondary containment

Secondary containment or bunds must:

• be constructed to CIRIA 736 containment systems for the prevention of pollution guidelines
• be fitted with a high-level probe and an alarm
• have tanker connection points within the bund or provide adequate containment for spillages or leakage
• have regular visual inspections and programmed engineering inspections
• be emptied of rainwater regularly to maintain the containment capacity.

 

EXAMPLES

In the UK, secondary containment systems must be constructed to CIRIA 736 containment standards. ³⁹

In the USA, the United States Department of Agriculture have published conservation practice standards for AD. ⁴⁰

 

 5.5.6. Electrical systems

Electrical equipment is likely to be subject to specific maintenance standards to maintain fitness for purpose. Electrical equipment used in potentially explosive atmosphere zones at the site must be intrinsically safe (ATEX rated). ⁴¹ Items of electrical equipment that are ATEX rated must be listed on an ATEX register.

This area is further detailed in Pillar 9: Health, Safety and Environment.

 

EXAMPLE

 The UK Health and Safety Executive (HSE) has published a summary of the technical standards for the methods of protection for electrical equipment in the UK. ⁴²

 

6.5.7. Pipelines for biogas

The Institution of Gas Engineers and Managers (IGEM) have published standards for the design, construction, testing, operation, maintenance and inspection of steel and polyethylene (PE) pipelines for the transport of biogas. ⁴³

 6.5.8. Maintenance and repair schedules

To comply with construction standards for plant and structures (such as bunds, lagoons, clamps and concrete surfaces) specified maintenance schedules must be implemented.

Maintenance schedules needed to maintain standards of plant and equipment once operational must be developed at the plant design stage for implementation during the lifetime of the plant.

 

EXAMPLE

The CIRIA 759 standard includes guidance on the maintenance and repair of concrete slurry lagoons and tanks, and pre-cast and in situ concrete stores and other farm-based structures. ⁴⁴

 

ATEX equipment must be maintained according to the manufacturer’s recommendations to allow continued assurance of an intrinsically safe status. The need for easy access to relevant equipment must be considered during plant design to allow maintenance access during operations.

Storage tanks must be subject to a suitable schedule of external assessment using non-destructive assessment (NDA) methods. A schedule of internal tank inspection and maintenance must also be specified.

Sedimentation in tanks is likely to need regular removal, and again the practicalities of how and when this must be done must be considered at plant design stage as well as at the operational stage.

An inspection and maintenance programme must be established for all subsurface structures, for example, pressure tests, leak tests, material thickness checks or CCTV checks.

 

EXAMPLE

 The United States Environmental Protection Agency, via the AgSTAR programme, has published an Anaerobic Digester/Biogas System Operator Guidebook, ⁴⁵ which gives a high-level description of the maintenance and inspection requirements at an AD installation.

 

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6.6 Operational standards for AD operations

The design and specification of a plant will largely determine operational capabilities of a given plant. Final plant performance, impacts and productivity will be further determined by how operations are managed at the live site. Further standards are, therefore, needed to determine BAT for day-to-day operational activities over a range of areas including:

• feedstock monitoring, selection and handling
• process monitoring and control
• emissions monitoring and control
• plant maintenance and efficiency
• staff competence and management
• the use of final outputs.

Standards relating to these areas are further discussed below.

6.6.1. Feedstock management

Standards are applied for feedstock materials accepted for processing. This includes the different feedstock types from various industrial processes that are suitable for use in AD, and any restrictions on materials that are either deemed unsuitable or will only be deemed suitable subject to detailed analysis and additional controls.

EXAMPLES

The Environment Agency of England and Wales has issued a number of standard rules permits for AD operations. These permits include a list of pre-assessed waste types with relevant restrictions that are assessed as suitable for use in an AD process operating under the stated permit controls. ⁴⁶

The United States Environmental Protection Agency via the AgSTAR programme has published a Anaerobic Digester/Biogas System Operator Guidebook that provides recommended steps to be taken when accepting feedstock at the AD facility.

 

6.6.1.1. Feedstock pre-acceptance assessment and sampling

Before they are accepted for processing, feedstocks must be assessed to determine their suitability for use in the process, any potential risk to the process associated with them, and any handling or processing requirements associated with the material.

Feedstock sampling must happen as a part of a wider feedstock pre-assessment procedure that takes into account a range of factors, such as:

• the physical form of the waste
• the quantities of the waste that are available
• the process that generated the waste
• the potential for the waste to vary in quantity or characteristics
• any potential hazards associated with the waste or the wider site/process that generated it that must be considered either for handling of the material, or for the potential to impact on the AD plant biology
• the likely age of the waste when it arrives at the site and the potential for it to have become degraded
• the odour potential of the waste
• whether the waste will contain animal-derived materials or not.

Samples of the waste are likely to be needed for analysis to inform the pre-acceptance assessment process. The type of analysis undertaken and the number of samples that must be analysed to gain a representative picture of the material will depend on the characteristics of the material outlined in the previous list.

For example, vegetable offcuts from a vegetable processing factory that produces a single product for human consumption are likely to need fewer samples for characterisation than, for example, sludge arising from effluent treatment plants from a multiple-product processing site with high potential for day-to-day and seasonal variability.

The pre-acceptance assessment will also determine the sampling schedule once the waste has been assessed and accepted for use at the site. Wastes must be reviewed for suitability on at least an annual basis, more often if there are higher risk factors or variability, or if there is any change to the process of production or supply.

The pre-acceptance assessment will also determine any agreed criteria for rejecting wastes on receipt that must be made clear to the supplier before supply begins.

Sampling is required to assess two main aspects of feedstocks:

1. The biogas potential: this affects the operational conditions of the process (e.g. organic loading rate (OLR)) and the design of the tanks (e.g. feedstocks with high biogas potential will require less volume to produce the same quantity of biogas).
2. Contamination with process inhibitors (e.g. antibiotics, high salinity) that can affect biological activities and ultimately stop biogas production.

The frequency of feedstock sampling must be tailored for each site and will depend on the source of feedstocks (e.g. an energy crop such as maize silage will require less frequent sampling than food waste), the condition of feedstocks (e.g. easily decomposing wastes, such as food waste, must be assessed more frequently to allow for proper characterisation) and homogeneity (e.g. feedstocks containing mixed organic materials will have different characteristics depended on the mix). Additionally, any contamination of the feedstock will affect its acceptability for processing.

 

EXAMPLES

The Environment Agency of England and Wales has issued guidance on pre-acceptance assessments of wastes and associated sampling schedules as part of their published appropriate measures guidance.

An example list is available of aspects of a feedstock that must be understood and subject to analysis to determine if a feedstock is suitable for AD. ⁴⁷ This list is not exhaustive but includes, for example, the following:

• particle size distribution and physical contaminants

• total solids and volatile solids

• biogas potential

• total organic carbon (TOC)

• chemical oxygen demand (COD)

• nutrient analysis

• fibre content

• pH and alkalinity

• volatile fatty acids (VFA)

• ammonia and total nitrogen content – carbon to nitrogen (C to N) ratio

• heavy metals and potentially toxic elements (PTEs)

• carbohydrates and lipids.

A framework guidance note, prepared by Jacobs Engineering UK Limited for the UK Environment Agency, provides a framework for assessment of suitability of material for use as an AD feedstock. ⁴⁸

The Anaerobic Digestion Quality Protocol (ADQP) end-of-waste position published by the Environment Agency of England, Wales and Northern Ireland specifies a list of wastes and associated restrictions that are suitable for use in an AD plant producing quality digestate. ⁴⁹

The Environment Agency of England, Scotland and Wales has published a guidance note on the assessment and classification of wastes. ⁵⁰

 

6.6.1.2. Feedstock acceptance, storage and handling standards

Once a waste stream has been pre-assessed as suitable for acceptance at a site, it can be received at the site for use.

Clear criteria for acceptance or rejection of individual loads must be agreed with the supplier before any loads are accepted.

The BAT requirements for receipt, storage and pre-processing of wastes at UK AD operations can be summarised as: ⁵¹

• A schedule of enhanced sampling or monitoring may be needed for initial loads received to allow verification of the pre-assessment itself. This must be determined before receipt, based on the risk factors identified at the pre-acceptance assessment.
• When loads are received, they must be subject to visual and paperwork assessment to ensure the waste received is as expected.
• If any loads do not confirm to the wastes agreed, then a procedure for quarantine and rejection of the waste must be in place.
• Waste reception must be carried out by trained and competent staff as this step is a key control point for feedstock suitability.
• Waste must be received indoors in an enclosed building if there is a significant risk of fugitive emissions when the waste is received, stored or pre-processed before being passed into the AD process, or if it is food waste or waste containing animal-derived materials.
• There must be a schedule in place for the regular cleaning of storage areas designed to manage the risk associated with different feedstock materials.
• Wastes must not be stored in reception buildings for more than five days and must be treated as promptly as possible – within 24 hours if the waste has high risk of generating odours or attracting pests.
• Reception buildings must be fitted with fast-acting roller shutter doors or airlock systems to minimise the release of emissions as vehicles enter or leave the building.
• Reception buildings must be fitted with ventilation systems that ensure a suitable working environment for staff. Air extracted from any ventilation system serving waste reception, storage and handling areas must be passed through an abatement system before being released to the atmosphere.
• A waste tracking system that tracks waste inputs through the process must be set up. The system can be used as a means of ‘stock control’ and traceability, should this be needed.

 

EXAMPLES

The Environment Agency of England and Wales has published standards for waste storage and handling at biowaste facilities. ⁵²

The UK government Animal and Plant Health Agency has issue guidance on storage and labelling of animal by-products (ABPs). ⁵³

In the UK, the Silage Slurry and Agricultural Fuel Oil (SSAFO) Regulations lay down standards for storage of farmyard slurries and silage clamps ⁵⁴

 

6.6.1.3. Processing of animal derived feedstocks

Final digestate arising from AD processes has a valuable use as a biofertiliser for use on food and feed crops. It is, therefore, essential that there are sufficient controls during the process of production to prevent the release of animal and plant diseases into the environmental and food chains when final digestates are spread to agricultural land.

In the EU and UK, specific standards are applied for safe treatment of animal-derived feedstocks, or ABPs. Before an AD facility can process these materials, it must receive specific approval from the regulatory body. Operators must demonstrate that their treatment process includes suitable measures to manage risks to both plant and animal health during the processing of ABPs at AD facilities and the following release of final digestate to land as a fertiliser.

There must be a period of plant validation before full approval for the processing of ABP is granted, to demonstrate and check that the measures in place are reliable and sufficient.

In the UK, ABPs are classed according to distinct categories based on risk, with category 1 materials being higher risk and category 3 materials being lower risk. ⁵⁵ The following types of ABP are suitable for processing in an AD plant:

• category 3 ABP that are not catering waste (in addition to or without catering waste)
• category 2 ABP that has first been pressure rendered at an approved rendering site
• permitted category 2 materials without prior processing for manure, digestive tract and its content, milk, milk-based products, colostrum, eggs and egg products.

The EU standards for processing of ABP in a biogas plant are that a plant must: ^{56 57}

• treat ABPs at 70°C for one hour with a maximum particle size of 12mm
• sterilise category 2 ABPs at 133°C with 3-bar pressure for 20 minutes at an approved plant prior to treatment at the biogas plant (some permitted category 2 materials do not require prior pressure sterilisation)
• anaerobically digest in enclosed digestion tanks approved by the regulator
• include a pasteurisation stage in AD of category 3 ABPs.

 

Once the ABP processing has been approved, operators must regularly monitor the site to ensure that the measures implemented are effectively managing risks. To confirm that any pathogens present at the beginning of the process have been successfully eliminated, regulations require testing of the final material. Although various pathogens may be found in processed digestate, E. coli and Salmonella are used as indicator species because they represent the broader pathogen population and are easy to trace. For monitoring purposes, samples of the digestate must be analysed for these indicators, and any samples that exceed the threshold limits outlined in Table 1 will be considered failed.

Table 1. Pathogen Monitoring Failure Thresholds

Pathogen Tested	The sample will fail if:
Salmonella	Salmonella is detected in any of the sub-sample replicates
E. coli	any of the sub-samples contains more than 5,000 E. coli colonies per gram ormore sub-samples contain more than 1,000 E. coli colonies per gram

 

If a sample fails, the operator must investigate the causes and take corrective actions before any digestate can be released from site.

There are certain higher risk categories of ABPs that are not considered suitable for transformation in a biogas plant, given that final digestate will be used as an agricultural fertiliser and returned for use in feed and food production. Other categories of animal-derived material may only be considered suitable for processing in plants with suitable treatment controls in place.

6.6.1.4. Processes to manage the spread of plant diseases

Similarly, plant material that is known to contain certain plant diseases or injurious or invasive plant species may not be suitable for processing if hazards will persist in the final digestate that will be spread to land.

Operators may also consider any actual or perceived risk from known input feedstocks when considering digestate’s final use; for example, consider whether digestate produced from a plant processing potato waste infected by Phytophthora infestans (oospores)should be spread as a fertiliser on a potato crop. Oospores are resilient structures; AD systems should reach very high temperatures necessary to kill oospores and other resilient pathogen propagules.

6.6.1.5. Physical contamination in feedstock

Elevated levels of physical contamination by materials such as plastics is unacceptable because of the effect this contamination has on the process as contaminants accumulate in digesters, and on the quality of the final digestate that will be spread to land.

Other contaminants, such as stone, metal, sharps and chemicals, may damage plant and equipment and disrupt the process. The capability of any equipment for the removal of any primary packaging associated with feedstocks received must be considered, as must the impact of contaminants on plant, equipment and quality of the final digestate when setting maximum levels for physical contaminants tolerances.

Excessively contaminated feedstock loads must be rejected, and thresholds for rejection must be agreed at the pre-acceptance assessment stage.

6.6.1.6. Pest contamination in feedstocks

Plants processing food waste and other putrescible wastes must implement measures for the detection and management of pests. All waste must be checked for pest infestation on receipt and rejected if infested.

 

EXAMPLE

WRAP has published an interim report on the effects of AD on common agricultural pests and diseases in the UK. ⁵⁸

 

6.6.1.7. Toxic elements in feedstock

Feedstocks must be monitored for levels of potentially toxic elements, phytotoxic substances and other persistent organic pollutants that will not break down in the AD process but persist and accumulate in the environment after digestate applications. The risk of these elements being present in feedstocks must be considered at the waste pre-acceptance assessment stage and, if necessary, sample analysis done to confirm suitability.

 

EXAMPLE

The United States Environmental Protection Agency, under the AgSTAR collaboration programme, has published Increasing Anaerobic Digester Performance with Codigestion, ⁵⁹ which describes the effects feedstock toxicity can have on a digester’s biology, and the means of determining the quality of feedstock.

 

6.6.1.8. Potential inhibitors

Surveillance must also be done for feedstocks containing substances or contamination that might inhibit the AD plant biology and affect the AD plant process and productivity, e.g. cleaning chemicals from another industrial site mixed with feedstocks.

Standards for pre-acceptance assessment of feedstocks are applied to ensure there are sufficient controls to manage the risks described. A summary of current published relevant standards is given in the examples.

 

EXAMPLES

The Environment Agency of England and Wales has:

• specified standards for pre-acceptance and acceptance assessments of feedstocks at biogas plants. ⁶⁰

• published a list of persistent organic pollutants (POPs) that must be disposed of using approved methods. ⁶¹

• published a list of potentially inhibitory substances and thresholds to inform the assessment of feedstock suitability for use in AD. ⁶²

• issued additional control limits on plastic contamination in digestate. These are expected to be introduced for the rest of the UK in the short-to-medium term. ⁶³

The WRAP/BSI PAS110 standard for production of quality digestate outlines standard threshold levels in final digestate for a range of different quality parametres, including potentially toxic elements, pathogens and physical contaminants. ⁶⁴

 

6.6.1.9. Minimum process standards

Standards for suitable minimum retention times in the AD process and pasteurisation of feedstocks or digestate also determine the feedstock characteristics suitable for processing in each AD plant operation.

6.6.1.10.  Feedstock rejection procedures

Feedstock rejection procedures must be developed, including reporting of rejection, quarantine protocols and collection of rejected feedstock.

Aspects of feedstocks policy are further discussed in Pillar 2: Feedstock Policy, and digestate policy in Pillar 4: Digestate Policy.

6.6.2. Process monitoring and control

As a biological waste treatment process, the AD process can become unstable if not managed in a proactive and appropriate way. An unstable process has the potential to lead to a range of safety, environmental and efficiency impacts. Key process indicator variables must be monitored to maintain process stability.

6.6.2.1. Real-time process monitoring

Standards are applied for installation of plant process monitoring and control systems, such as inline monitors for temperature, pressure, tank liquid level and flow rate and gas quality analysis, and the use of Supervisory Control and Data Acquisition (SCADA) control interface systems. The system of controls and interlocks developed will ideally be informed by the HAZOP process. A documented outline of the plant control philosophy, functional design specification and system of alarms and responses would ideally be kept in the site management system.

6.6.2.2. Equipment calibration

Calibration of equipment such as gas analysers, inline/in-tank sensors, gas monitors and lab equipment used for process monitoring and safety surveillance must be done regularly to a given standard. Regular routine calibration of temperature probes on pasteurisation units is a requirement on systems where animal wastes are processed, to ensure that the material is heated to the temperatures required to manage risk.

6.6.2.3. Biological and chemical process management

Standards are applied for the monitoring and management of plant biology to ensure a well-managed and productive process. Staff must have the technical competence to oversee operations. 

On- or off-site labs used for ongoing monitoring and analysis of feedstocks and digester biological health must have suitable accreditation and/or be subject to a schedule of instrument maintenance and calibration.

Industry standards and parametres that are indicative of a stable and productive AD process must be established and maintained.

 

EXAMPLE

The Environment Agency of England and Wales has issued guidance on process monitoring requirements for AD operations, which includes the minimum requirement to monitor the following parametres to demonstrate digester stability: ⁶⁵

• pH and alkalinity of the digester feed

• temperature – continuously

• digester operating temperature

• hydraulic and organic loading rates of the digester feed

• concentration of volatile fatty acids (VFA) and ammonia within the digester

• biogas quantity, composition and pressure – continuously

• liquid and foam levels in the digester

• daily visual inspection looking for scum or floating layers.

If external laboratory providers are used, then analyses must be undertaken to a suitable method and standard, standardised across different providers. 

 In the UK, labs are certified to the UK Accreditation Service (UKAS) standard to ensure quality standards are applied and analysis and techniques are standardised between different providers. ⁶⁶

To prevent and detect foaming in the digester, there must be active management and assessment of digester feed mix and rate. Digester stability must be monitored and foam sensors fitted on digesters for early indication of development of foaming conditions.

 

EXAMPLE

The United States Environmental Protection Agency has indicated the following should be tested daily in the inlet and effluent of the AD facility:

• TS (Total Solids)

• VS (Volatile Solids) 

• alkalinity

• pH

• temperature

 

6.6.2.4. Monitoring plant inputs and outputs

It is recognised best practice to monitor and review the annual consumption of energy, water and raw materials as well as the generation of residues and wastes. Monitoring includes activities such as direct measurements, calculations and recordings, and is broken down at the most appropriate level, i.e. at process or plant/installation level. Any significant changes in the plant/installation level are considered. Opportunities for improvements in energy and water efficiency and waste and resource minimisation must be identified and implemented on an ongoing basis to continuously improve plant efficiency. Outputs such as final digestate must be subject to regular sampling and monitoring to ensure that it has reached the necessary standards for end use.

This has been discussed further in International ADCS Module 4.

6.6.2.5. Biogas management, treatment and storage

Biogas production and storage must be included in the site process monitoring system. Gas volumes in store, flow and pressure conditions must be continuously monitored, as must gas quality and composition. Hydrogen sulphide levels in biogas must be monitored to evaluate the effectiveness of measures in place to manage levels. This is needed to prevent damage to plant and equipment, and to avoid exceeding any permitted emissions limits.

Condensate arising from gas storage and movements systems must be drained via a dedicated sealed collection system. If air or oxygen injection is used for the management of hydrogen sulphide, then oxygen levels must be continuously monitored, with automatic shut-off interface controls to prevent overdosing, which would lead to explosive atmosphere conditions.

Equipment used for the treatment of biogas before combustion or upgrading of biomethane, such as carbon filters, must be monitored to ensure optimum performance. Any additions made to biogas, such as gas odourant or propane needed to raise calorific value, must be subject to monitoring and control.

 

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6.7. Management systems and competence

There must be sufficient resources and technically competent input to for necessary standards to be implemented. It is best practice for all waste management processes to implement and operate according to a comprehensive and fit for purpose environmental management system (EMS).

Provision must be made for training and instructing staff in the measures specified in the EMS, and for risk assessment of activities to develop safe systems of work.

 

EXAMPLE

The UK Control of Substances Hazardous to Health Regulations (COSHH) standards will include control of works by third-party contractors at the site through systems such as the permits to work system. ⁶⁷

 

Necessary competence and resources are identified within the site EMS.

It is recognised best practice to retain written records and documentation of how the EMS was implemented.

Management systems must be tailored to the needs of a specific site and updated and maintained throughout the life of the site. Several reference documents and standards have been published that provide frameworks and guidance on developing an EMS.

 

EXAMPLES

The international ISO 14001 standard provides a framework for developing an EMS to a certifiable standard. ⁶⁸

The Environment Agency of England and Wales has developed guidance on how to set up an EMS. ⁶⁹

The ISO 45001 standard provides a framework or developing a health and safety management system to a certifiable standard. ⁷⁰

The ISO 24252:2021 standard that is one of the first comprehensive works setting criteria for commercial AD systems. ⁷¹

In the UK, waste site operators must demonstrate minimum technical competence for management of wastes at a permitted facility. A formal system of qualifications to demonstrate minimum industry training standards has been established, and it is mandatory that someone who holds a suitable qualification is present on-site. ⁷² Alternatively, technical competence can be demonstrated through establishing a certified competence management scheme to the standard published by Energy and Utility Skills. ⁷³

The Anaerobic Digestion Certification Scheme UK (ADCS UK) in the UK is a published certifiable standard developed by and for the AD industry. It enables operators to demonstrate best practice with respect to environmental and health and safety performance, and a commitment to continuous improvement of plant performance. ⁷⁴

The Biogas Technology and Information Centre (Cambodia), published the “Practical Biogas Plant Development Handbook”, ⁷⁵ which provides guidance on good practices in AD plant operations and the health and safety of biogas projects.

The Occupational Safety and Health Administration (USA) has introduced standards related to safety management of substances that might result in fire or explosion. ⁷⁶

 

Standards relating to development of a complementary health and safety management system are further discussed in Pillar 9: Health, Safety and Environment.

 

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6.8. Quality, management and use of outputs from operations

Product standard and specifications for end products arising from the AD process must be established to ensure they meet minimum requirements and are fit for purpose.

6.8.1. Export and use of gases and electricity

Standards are applied for export and the use of final gas or electricity generated. These are discussed further in Pillar 5: Gas Quality Regulations and Module 10 of the ADCS International.

 

EXAMPLE

In the UK, a number of regulations and guides are in place that specify the requirements in this area under the Gas Safety (Management) Regulations 1996 and its amendments. ^{77 78}

The biomethane quality protocol for end of waste issued by the Environment Agency of England and Wales specifies standards that must be met to achieve end of waste, including compliance with the relevant gas safety standards. ⁷⁹

In India, the standards and specifications for compressed biogas are governed by IS 16087:2016 (Annexure I) of BIS. ⁸⁰

 

6.8.2. Digestate quality and management standards

Final digestate from an AD process has the potential to be a valuable biofertiliser for agricultural use. Standards have been set that define suitable quality parametres for digestate fertilisers to ensure there are no environmental risks from applying the material to land.

 

EXAMPLES

The WRAP/BSI PAS110 standard for production of quality digestate outlines the specification for quality digestate for use in agriculture and field horticulture. ⁸¹

The EU fertiliser regulation lays down common rules on safety, quality and labelling requirements for fertilising products and makes specific provision for specification for end of waste and specification of digestate derived from energy crops and other waste inputs. ⁸²

In Germany, there are limits set for the maximum level of toxic residues as presented in Table 2. ⁸³

 

Table 2. Maximum permitted levels of toxic residue, Germany

Heavy Metal Limit	Mg/kg DM of digestate
Lead	150
Cadmium	1.5
Chrome	100
Copper	100
Nickel	50
Mercury	1
Zinc	400

 

The types of controls needed at the feedstock input selection and characterisation stage to ensure a quality digestate material suitable for agricultural use have been discussed earlier in this document.

Further standards and controls are applied to ensure that the timing, method and quantity of application are determined to achieve maximum agricultural benefit and minimum environmental inputs.

 

EXAMPLE

An EU directive on nitrates limits the amount of nitrogen that can be applied to land during the year  to 170kg N/ha, to help prevent nitrates transfer to surface and ground waters. ⁸⁴

 

Standards are also applied to digestate storage in satellite stores before spreading, to ensure suitable containment and management of emissions to atmosphere.

If digestate spread is derived from materials of animal origin, there are additional standards and requirements for traceability of the digestates spread and restrictions on the use of materials.

Digestate quality standards and controls are discussed in more detail in Pillar 4: Digestate Policy.

6.8.3. Carbon dioxide capture and use

Carbon dioxide separated from biogas during the biogas to biomethane upgrading process may be released into the atmosphere or alternatively subject to capture and recovery for further use, including bioenergy carbon capture and storage (BECCS), which enables negative emissions by permanently storing CO₂ or utilising it in sustainable applications. Final products from carbon dioxide recovery processes can be used for other industrial purposes such as additives or coolants in food manufacturing and supply or cropping aids in indoor farming systems. Final products must meet any required specifications for end uses. 

Regulations for biogas quality is discussed in more detail in Pillar 5: Gas Quality Regulations.

 

EXAMPLES

The European Industrial Gases Association has published a specification for quality standard and verification for food and beverage grade carbon dioxide derived from several sources including biogas AD plants ⁸⁵

The European Biogas Association have published white paper describing the benefits of capturing bio-CO₂, potential markets for it and current standards and regulation that govern the CO₂ market ⁸⁶

 

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6.9. Monitoring and control of emissions

AD plants must be designed and operated in a way that minimises the potential for fugitive emissions from operations, such as:

• dusts
• bioaerosols
• mud
• litter
• pests
• gas leaks
• noise and vibration
• odours 
• contaminated run-off. 

 

The measures in place to control emissions will be specified in the site EMS. Fugitive emissions control is achieved through a combination of plant specification and design, and ongoing process monitoring and control activities during live operations.

6.9.1. Control measures in plant design

Control of fugitive emissions must be considered early, at the plant design and specification stage, and key control measures must be determined early on to achieve effective control. Techniques that are best available for control of emissions must be implemented, including installation of those listed in any industry BAT conclusions. Examples of specific techniques listed in current EU BREF BAT conclusions are listed in the next sections.

6.9.2. Specific techniques for management of noise and vibration

• development and implementation of a noise management plan
• noise reducers
• acoustic and vibrational insulation of equipment
• enclosure of noisy equipment
• soundproofing of buildings
• installation of noise barriers
• location of noise generating plant and equipment away from receptors and doorways or other potential release points
• regularly inspecting and maintaining equipment to ensure optimum performance
• avoiding use of noise-generating equipment at night
• controls for traffic-noise management
• ensuring equipment is operated by experienced, trained and competent staff
• installation of low-noise-rating equipment

 

6.9.3. Specific techniques for management of odours

• installation of abatement systems, such as biofilters or carbon-filtration units
• periodic monitoring of odour emissions
• minimise on-site time of potentially odorous wastes
• minimise diffuse emissions sources for odours
• conduct routine maintenance on key equipment, such as fast-acting doors
• developing cleaning schedules
• implementation of a leak detection and repair programme
• development and implementation of an odour management plan

 

6.9.4. Specific techniques for management of emissions to water

• installation of sealed drainage and leak detection systems
• installation of water efficiency measures, including rainwater recovery and recirculation of contaminated drainage from storage and process areas
• installation of impermeable surfaces for all waste reception, storage and processing areas
• installation of high-level sensors and overflow detectors on tanks and vessels
• installation of secondary containment
• isolation of tanks, vessels and secondary containment
• provision of site drainage, pipework and utilities connections plans
• installation of roofing over storage areas to prevent run-off
• egregation of clean and contaminated water streams
• secondary containment and leak detection installed on below-ground waste-storage vessels
• adequate sizing and capacity of wastewater storage systems

 

6.9.5. Specific techniques for management of emissions to air

• installation of gas pipeline labelling and in-situ gas-detection monitors
• provision of site drainage, pipework and utilities connections plans
• installation of monitoring devices, such as gas detectors, for the detection of emissions
• development of a leak detection and repair plan
• installation of treatment processes, such as wet scrubbing or biofiltration
• prevention of corrosion through the appropriate selection of materials or coatings
• enclosing equipment and buildings for the collection and treatment of emissions

 

6.9.6. Management plans

The proposed control measures for the management and monitoring of fugitive emissions must be specified in documented management plans that the regulator has assessed and agreed to. The type of plans needed and the degree of detail required will depend on the nature and location of operations and the associated risks identified to receptors. Management plans that may need to be developed are as follows:

• noise and vibrations management plan
• odour management plan
• emissions management plan
• pest management plan
• dust management plan
• leak detection and repair plan
• residues management plan
• waste management plan
• energy efficiency plan
• accident management plan

 

EXAMPLES

The Environment Agency of England and Wales has issued standards and guidance on the development and implementation of management plans monitoring and control of emissions. ⁸⁷

The United States Environmental Protection Agency has published, via the AgSTAR collaboration programme, a set of safety practices for on-farm AD systems that aim to help minimise health and safety hazards associated with the AD industry. ⁸⁸

Resources Safety & Health Queensland (Australia), published guidelines that clearly describe the requirements of AD operators to create and maintain a safety management system. ⁸⁹

 

Management plans will also outline measures for responding to complaints and incidents, doing an incident review, and corrective and preventative measures action planning.

6.9.7. Leak detection and repair

Given the significant volumes of gas generated, handled and stored at an AD facility, there is the potential for fugitive emissions of biogas via small leaks from plant, pipelines and equipment. Where emissions from organic compounds are expected, as in this instance, it is best practice according to the European Waste Treatment BREF (BAT 14) ⁹⁰ to set up and implement a risk-based leak detection and repair (LDAR) programme.

An LDAR must take into account the specific site layout, plant and equipment and must link with the site environmental monitoring programme and DSEAR assessment. ⁹¹ A method of surveying the site at least every six months for unknown emissions sources must be developed, and any leaks identified during these surveys must be documented, risk assessed and repaired as soon as possible.

Suitably robust survey methods, such as the use of optical gas imaging (OGI) cameras or sniffing, using organic compound analysers and bag sampling, must be used.

 

EXAMPLES

The Environment Agency of England and Wales has issued guidance on appropriate measures for LDAR for biogas plants. ⁹²

The United States Environmental Protection Agency Office of Compliance has issued a best practice guide on LDAR. ⁹³

 

6.9.8. Plant decommissioning

The potential effects of eventual decommissioning of the plant must also be considered throughout its life. Baseline data of the condition of soil and groundwater before operations start is needed to allow ongoing monitoring of the effect of operations. Remediation measures needed at plant decommissioning will also be informed by this data, and the operator must demonstrate that they have returned the site to its original state before any permit held at the site can finally be surrendered.

The baseline data collated before plant development must be clearly documented in the site EMS, as should any significant changes or events documented throughout the life of the plant once operational.

 

EXAMPLES

The Environment Agency of England and Wales have prepared guidance and a template on preparation of a Site Condition Report  ⁹⁴.

The Government of Ontario, Canada, have published guidance on decommissioning of on-farm biogas systems. ⁹⁵

 

6.9.9. Monitoring emissions

Emissions monitoring for channelled/point source emissions must be conducted to a specified standard. The site environmental permit will specify emission limits for point source emissions and will also specify minimum monitoring requirements and standards.

 

EXAMPLES

Operators in the UK must carry out emission monitoring according to the MCERTS standard. ⁹⁶

The Environment Agency of England and Wales has published a series of standard rules permits that include specified emissions limits, monitoring frequency and monitoring standards that operators must comply with. ⁹⁷

In the EU and UK, emissions limits for a range of combustion plant operating on different fuel types are specified in the Medium Combustion Plant Directive Annex 2 tables. ⁹⁸

For example, emissions limit values specified in the Directive for sulphur dioxide (SO₂) and oxides of nitrogen (NO_x) for new engines and gas turbines operating on biogas are shown in Table 3.

 

Table 3. Emissions Limit Values (mg/Nm³) for new engines and gas turbines as specified in Annex II, Part 2, Table 2 of Directive (EU) 2015/2193. ⁹⁹ 

Pollutant	Type of medium combustion plant	Gaseous fuels other than natural gas
SO2	Engines and gas turbines	15 (other fuels) 40 (biogas)	40 (biogas)
NOx	Engines	190
	Gas Turbines	75

 

Note: Emissions limit values are defined at a temperature of 273.15K, a pressure of 101.3kPa and after correction for the water vapour content of the waste gases and at a standardised O₂ content of 6% for medium combustion plants using solid fuels, 3% for medium combustion plants, other than engines and gas turbines, using liquid and gaseous fuels, and 15% for engines and gas turbines.

BAT-AELs are specified in BAT 34 of the BREF for Waste Treatment ¹⁰⁰ as a specific BAT conclusion for biological waste treatment for channelled emissions to air from abatement equipment, such as biofilters and carbon filtration units used for abatement of dusts, odorous compounds and organic compounds. BAT-AELs specified are shown in Table 4.

Some countries have introduced more stringent limits on chosen pollutants. 

 

EXAMPLE

Germany, under the 44th BImSCHV regulation, ¹⁰¹ sets the limit for NO_x to 100mg/Nm³ in the new combustion engine plants installed after 2018.

 

Table 4. BAT-AELs for channelled ammonia (NH₃), odour, dust, and total volatile organic compounds (TVOC) to air from the biological treatment of waste. ¹⁰²

Parametre	Unit	BAT-AEL (Average over the Sampling Period)	Waste treatment process
NH3a,b	mg/Nm3	0.3–20	All biological treatments of waste
Odour Concentrationa,b	ouE/Nm3	200–1000
a Either the BAT-AEL for NH3 or the BAT-AEL for odour concentration applies. b This BAT-AEL does not apply to the treatment of waste mainly composed of manure.

 

There are also established BAT-AELs for emissions to water from biological waste treatment processes. The monitoring requirements and BAT-AELs are laid out in BAT 7 and BAT 20 of the BAT conclusions for waste treatment.

6.9.10. Emissions to water

Standards are applied for emissions to water to determine when such emissions are acceptable. Emissions may arise from activities such as: 

• discharge of clean rainwater from concrete yards, building roofs and roadways 
• discharge of final effluent from domestic sewage treatment plants or septic tanks 
• dewatering of final digestate. 

For emission to water other than clean water, a site-specific risk assessment is likely to be needed based on the characteristics of the local receiving watercourse and local water quality objectives. Permitted discharges will specify maximum daily discharge volumes and effluent quality emissions limits, with associated monitoring requirements.

 

EXAMPLE

The Environment agency of England and Wales has published guidance on risk assessments and environment quality standards for emissions to water. ¹⁰³

 

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6.10. Emergency response planning

6.10.1. Procedures

Standards are applied for establishing and maintaining emergency preparedness and response procedures for the protection of staff, the public and the environment.

It is recognised best practice to develop an accident management plan that specifies how incidents, accidents and near misses will be managed. This plan must consider the potential for harm to staff and to environmental receptors. The accident management plan must identify potential hazards and mitigation measures that will protect the environment should an event occur.

The accident management plan must clearly specify the roles and responsibilities of staff for the management of incidents and provide clear instructions for responses to different incident types, such as spills of potentially polluting liquids and gas leak detection.

Contingency plans for managing different operational scenarios must also be developed, and incident reporting and post-incident review procedures must be specified in the plan.

It is recognised best practice to include measures such as protection of plant against malevolent acts, e.g. vandalism, the potential for fire and explosion, and other events such as storm and flooding. Given current trends for more extreme weather events, the effects of a changing climate must be considered in any emergency planning process.

The accident management plan must be tested by carrying out mock drills, and proactive emergency services orientation to the site is advisable to ensure all parties are prepared.

 

EXAMPLES

The UK Health and Safety Executive (HSE) has published guidance on Control of Major Accident Hazards (COMAH). ¹⁰⁴

The Environment Agencies of Northern Ireland, Scotland and Wales have published guidance on pollution incident response planning. ¹⁰⁵ 

The Environment Agency of England has published guidance on preparation of an environmental accident management plan. ¹⁰⁶

The Environment Agency of England and Wales has published guidance on the types of hazards that must be considered in an accident management plan at a biowaste treatment facility. ¹⁰⁷

The United States Environmental Protection Agency (via the AgSTAR collaboration programme) has issued guidance that includes emergency action plan information. ⁸⁴

Emergency response planning and accident and incident response with respect to health and safety of staff is further considered in Pillar 9: Health, Safety and Environment.

6.10.2. Design measures

As outlined earlier in this document, essential safety features must be included at the plant design stage, based on a robust risk assessment process such as the HAZOP process to ensure suitable measures are used. Measures that must be used are likely to include:

• emergency flare provision
• emergency backup power provision
• under/overpressure relief systems
• foaming management measures
• lightning protection measures
• fire prevention and detection measures
• fire response procedures, including measures for retention of firefighting waters
• fixed gas detection systems
• automatic control alarm and interlock systems
• DSEAR assessment ¹⁰⁸ and site zoning plans (see Pillar 9: Health, Safety and Environment for further discussion)
• gas leak incident response plan
• secondary containment systems and emergency shut-off safety valves
• spill and incident response procedures
• site security measures
• measures to ensure accessibility and operability of relevant control measures during emergency situations
• built-in contingency to ensure operations are adaptable and flexible during downtime.

 

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6.11. Implementation of other technical and quality standards for the industry

This Pillar has provided a general outline of the areas of an AD operation that are subject to the application of technical and quality standards and is a reference for standards currently applied in the EU and UK. Some of these areas are discussed in more detail in other parts of this document as follows.

• Pillar 4: Digestate Quality
• Pillar 5: Gas Quality Regulations
• Pillar 7: Environmental Permitting
• Pillar 8: Planning Policy
• Pillar 9: Health, Safety and Environment

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FOOTNOTES

1. Best Available Techniques: Environmental Permits, UK Government. https://www.gov.uk/guidance/best-available-techniques-environmental-permits.
2. AgSTAR Anaerobic Digester Project Development Handbook, US EPA. https://www.epa.gov/sites/default/files/2014-12/documents/agstar-handbook.pdf 
3. Hegazy, H., Saady, N.,  Khan, F., Zendehboudi, S., Albayati, T. “Biogas Plants Accidents: Analyzing occurrence, Severity, and Associations Between 1990 and 2023”, Safety Science, 2024, 177, 106597. https://doi.org/10.1016/j.ssci.2024.106597. 
4. International Anaerobic Digestion Certification Scheme, World Biogas Association. https://www.worldbiogasassociation.org/international-anaerobic-digestion-certification-scheme/ 
5. NAAQS Table, US EPA. https://www.epa.gov/criteria-air-pollutants/naaqs-table.
6. Directive (EU) 2015/1535 of the European Parliament and of the Council of 9 September 2015 Laying Down a Procedure for the Provision of Information in the Field of Technical Regulations and of Rules on Information Society Services (Codification). http://data.europa.eu/eli/dir/2015/1535/oj 
7. “Best Available Techniques (BAT) Reference Document for Waste Treatment”, Publications Office of the EU.   https://op.europa.eu/s/zX5K.
8. Commission Implementing Decision (EU) 2018/1147 Establishing Best Available Techniques (BAT) Conclusions for Waste Treatment, European Union. http://data.europa.eu/eli/dec_impl/2018/1147/oj.
9. SR2021 No.7: Anaerobic Digestion facility, Including Use of the Resultant Biogas – Waste Recovery Operation. Environment Agency, UK Government. https://www.gov.uk/government/publications/sr2021-no-7-anaerobic-digestion-facility-including-use-of-the-resultant-biogas-waste-recovery-operation. 
10. Order on approval of listed company, Ministry of the Environment and Gender Equality, Denmark. https://www.retsinformation.dk/eli/lta/2019/1534
11. Biological Waste Treatment: Appropriate Measures for Permitted Facilities, UK Government. 1. When Appropriate Measures Apply, UK Government. https://www.gov.uk/guidance/biological-waste-treatment-appropriate-measures-for-permitted-facilities/1-when-appropriate-measures-apply 
12. BAT in Smaller Biogas Plants in the Nordic Countries, Nordic Council of Minister. https://norden.diva-portal.org/smash/get/diva2:1477056/FULLTEXT01.pdf  
13. Directive 2010/75/EU of the European Parliament and of the Council of 24 November 2010 on industrial emissions (integrated pollution prevention and control).  https://www.legislation.gov.uk/eudr/2010/75/article/14. 
14. Directive 2010/75/EU of the European Parliament. https://www.legislation.gov.uk/eudr/2010/75/article/14. 
15. BAT in Smaller Biogas Plants in the Nordic Countries, Nordic Council of Minister. https://norden.diva-portal.org/smash/get/diva2:1477056/FULLTEXT01.pdf  
16. “Biogas Regulatory Reform Rule Criteria for Qualifying for an Alternative Measurement Protocol Guidance”, US EPA. https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P1019VMC.pdf. 
17. Industrial Emissions Directive Derogation: Cost-Benefit Analysis Tool, UK Government. https://www.gov.uk/government/publications/industrial-emissions-directive-derogation-cost-benefit-analysis-tool. 
18. ATEX Equipment and Explosive Atmospheres, UK Health and Safety Executive. https://www.hse.gov.uk/fireandexplosion/atex.htm#whatatex  
19. ATEX 2014/34/EU Guidelines, European Commission. https://ec.europa.eu/docsroom/documents/59156?locale=en 
20. IEC 60079-10-1:2020 Explosive atmospheres, International Electrotechnical Commission. https://webstore.iec.ch/en/publication/63327
21. Biological Waste Treatment: Appropriate Measures for Permitted Facilities, 4. Site Location, Design and Capacity, UK Government. https://www.gov.uk/guidance/biological-waste-treatment-appropriate-measures-for-permitted-facilities/4-site-location-design-and-capacity 
22. Moreno, V., Guglielmi, D.,  Cozzani, V. “Identification of Critical Safety Barriers in Biogas Facilities”, Reliability Engineering & System Safety, 2018, 169, 81–94. https://doi.org/10.1016/j.ress.2017.07.013. 
23. “HAZOP Guide to Best Practice”, IChemE. https://hsseworld.com/wp-content/uploads/2021/01/HAZOP-GUIDE-TO-BEST-PRACTICE-IChemE-THIRD-EDITION.pdf 
24. Risk Assessments for Your Environmental Permit, UK Government. https://www.gov.uk/guidance/risk-assessments-for-your-environmental-permit 
25. Air Emissions Risk Assessment for Your Environmental Permit, UK Government. https://www.gov.uk/guidance/air-emissions-risk-assessment-for-your-environmental-permit 
26. Environmental Permitting: Air Dispersion Modelling Reports, UK Government. https://www.gov.uk/guidance/environmental-permitting-air-dispersion-modelling-reports 
27. Climate Change: Risk Assessment and Adaptation Planning in Your Management System, UK Government. https://www.gov.uk/guidance/climate-change-risk-assessment-and-adaptation-planning-in-your-management-system 
28. Construction Industry Research and Information Association (CIRIA). https://www.ciria.org/ 
29. Design of Containment Systems for the Prevention of Water Pollution from Industrial Incidents (R164), CIRIA. https://www.ciria.org/CIRIA/Resources/Free_publications/containment_systems.aspx   
30. Livestock Manure and Silage Storage Infrastructure for Agriculture (C759F), CIRIA. https://www.ciria.org/ItemDetail?iProductCode=C759F 
31. BS 5502: Buildings and Structures for Agriculture, BSI. https://doi.org/10.3403/BS5502 
32. Storing Silage, Slurry and Agricultural Fuel Oil, UK Government. https://www.gov.uk/guidance/storing-silage-slurry-and-agricultural-fuel-oil 
33. Conservation Practice Standard: Anaerobic Digester, US Department of Agriculture. https://www.nrcs.usda.gov/sites/default/files/2022-08/Anaerobic_Digester_366_CPS_Oct_2017.pdf 
34. C535: Above-Ground Proprietary Prefabricated Oil Storage Tank Systems, CIRIA. https://www.ciria.org/CIRIA/ProductExcerpts/C535.aspx
35. C736F: Containment systems for the prevention of pollution, CIRIA. https://www.ciria.org/ItemDetail?iProductCode=C736F
36. Livestock Manure and Silage Storage Infrastructure for Agriculture (C759F), CIRIA. https://www.ciria.org/CIRIA/CIRIA/Item_Detail.aspx?iProductCode=C759F    
37. Control of Major Accident Hazards (COMAH), UK Health and Safety Executive. https://www.hse.gov.uk/comah/; 
38. Seveso III Directive, European Union. http://data.europa.eu/eli/dir/2012/18/oj. 
39. C736F: Containment systems for the prevention of pollution, CIRIA. https://www.ciria.org/ItemDetail?iProductCode=C736F
40. Conservation Practice Standard: Anaerobic Digester US Department of Agriculture. https://www.nrcs.usda.gov/sites/default/files/2022-08/Anaerobic_Digester_366_CPS_Oct_2017.pdf 
41. ATEX Equipment and Explosive Atmospheres, UK Health and Safety Executive. https://www.hse.gov.uk/fireandexplosion/atex.htm#whatatex  
42. Technical Standards: What Are the Standards for the Methods of Protection for Electrical Equipment?, UK Health and Safety Executive. https://www.hse.gov.uk/electricity/atex/standards.htm 
43. IGEM/TD/17: Steel and Polyethylene (PE) Pipelines for Biogas Distribution, IGEM. https://www.igem.org.uk/resource/igem-td-17-steel-and-polyethylene-pe-pipelines-for-biogas-distribution.html 
44. Livestock Manure and Silage Storage Infrastructure for Agriculture (C759F), CIRIA. https://www.ciria.org/CIRIA/CIRIA/Item_Detail.aspx?iProductCode=C759F   
45. “Anaerobic Digester/Biogas System Operator Guidebook”, AgSTAR, US EPA. https://www.epa.gov/sites/default/files/2020-11/documents/agstar-operator-guidebook.pdf
46. SR2021 No.6: Anaerobic Digestion Facility, Including Use of the Resultant Biogas – Installations, Environment Agency, UK Government. https://www.gov.uk/government/publications/sr2021-no-6-anaerobic-digestion-facility-including-use-of-the-resultant-biogas-installations/sr2021-no-6-anaerobic-digestion-facility-including-use-of-the-resultant-biogas-installations. 
47. Biological Waste Treatment: Appropriate Measures for Permitted Facilities, 6. Waste Pre-Acceptance, Acceptance and Tracking, UK Government. https://www.gov.uk/guidance/biological-waste-treatment-appropriate-measures-for-permitted-facilities/6-waste-pre-acceptance-acceptance-and-tracking. 
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51. Biological Waste Treatment: Appropriate Measures for Permitted Facilities, 6. Waste Pre-Acceptance, Acceptance and Tracking, UK Government. https://www.gov.uk/guidance/biological-waste-treatment-appropriate-measures-for-permitted-facilities/6-waste-pre-acceptance-acceptance-and-tracking. 
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53. Handling and Storing Animal By-Products, UK Government. https://www.gov.uk/guidance/handling-and-storing-animal-by-products.
54. Storing Silage, Slurry and Agricultural Fuel Oil, UK Government. https://www.gov.uk/guidance/storing-silage-slurry-and-agricultural-fuel-oil. 
55. Animal By-Product Product Categories, Site Approval, Hygiene and Disposal, UK Government. https://www.gov.uk/guidance/animal-by-product-categories-site-approval-hygiene-and-disposal#abp-categories-explained. 
56. Using Animal By-Products at Compost and Biogas Sites, UK Government. https://www.gov.uk/guidance/using-animal-by-products-at-compost-and-biogas-sites.
57. Good Practice Guide How to comply with the EU Animal By-Products Regulations at Composting and Anaerobic Digestion Plants, European Compost Network (ECN). https://www.compostnetwork.info/download/good-practice-guide-comply-eu-animal-products-regulations-composting-anaerobic-digestion-plants/
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59. “Increasing Anaerobic Digester Performance with Codigestion”, AgSTAR, US EPA. https://www.epa.gov/sites/default/files/2014-12/documents/codigestion.pdf. 
60. Biological Waste Treatment: Appropriate Measures for Permitted Facilities, 6. Waste Pre-Acceptance, Acceptance and Tracking, UK Government. https://www.gov.uk/guidance/biological-waste-treatment-appropriate-measures-for-permitted-facilities/6-waste-pre-acceptance-acceptance-and-tracking. 
61. Using Persistent Organic Pollutants (POPs), UK Government. https://www.gov.uk/guidance/using-persistent-organic-pollutants-pops. 
62. Biological Waste Treatment: Appropriate Measures for Permitted Facilities, 13. Bespoke Waste Assessment, UK Government. https://www.gov.uk/guidance/biological-waste-treatment-appropriate-measures-for-permitted-facilities/13-bespoke-waste-assessment. 
63. Regulation of Outputs from Anaerobic Digestion Processes, SEPA. https://www.sepa.org.uk/media/219842/wst-ps-016-regulation-of-outputs-from-anaerobic-digestion-processes.pdf. 
64. BSI PAS 110: Producing Quality Anaerobic Digestate, WRAP. https://www.wrap.ngo/resources/guide/bsi-pas-110-producing-quality-anaerobic-digestate. 
65. Biological Waste Treatment: Appropriate Measures for Permitted Facilities, 8. Waste Treatment, UK Government. https://www.gov.uk/guidance/biological-waste-treatment-appropriate-measures-for-permitted-facilities/8-waste-treatment. 
66. What is Accreditation?, UKAS. https://www.ukas.com/accreditation/ 
67. COSHH: Permits to Work, UK Health and Safety Executive. https://www.hse.gov.uk/coshh/basics/permits.htm. 
68. ISO 14001:2015. Environmental management systems – Requirements with guidance for use, ISO. https://www.iso.org/standard/60857.html. 
69. Develop a Management System: Environmental Permits, UK Government. https://www.gov.uk/guidance/develop-a-management-system-environmental-permits#how-to-develop-your-management-system. 
70. Health and Safety Management Systems, UK Health and Safety Executive. https://www.hse.gov.uk/managing/management-system/iso45001.htm. 
71. ISO 24252:2021. Biogas systems — Non-household and Non-gasification, ISO. https://www.iso.org/standard/78214.html. 
72. CIWM (WAMITAB): Operator Competence. https://ciwmquals.co.uk/competence/. 
73. Competence Management System, Energy & Utility Skills. https://www.euskills.co.uk/about/our-industries/waste-management/competence-management-system/. 
74. What is the ADCS?, Anaerobic Digestion Certification Scheme. https://www.adcertificationscheme.co.uk/what-is-the-adcs/. 
75. “Practical Biogas Plant Development Handbook”, UNIDO. https://downloads.unido.org/ot/25/48/25481236/Biogas%20handbook_English%20version.pdf. 
76. Process Safety Management of Highly Hazardous Chemicals (1910.119), Occupational Safety and Health Administration, US Department of Labor. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.119 
77. A Guide to the Gas Safety (Management) Regulations 1996 (as amended), UK Health and Safety Executive. https://www.hse.gov.uk/pubns/books/l80.htm. 
78. Gas Safety (Management) Regulations 1996, UK Government. https://www.legislation.gov.uk/uksi/1996/551/made. 
79. “Biomethane from Waste”, WRAP. https://assets.publishing.service.gov.uk/media/5a7ca222e5274a38e5755c80/QP_Biomethane_final_to_publish.pdf. 
80. “Environmental Guidelines for Compressed Biogas Plant (CBG)/Bio-CNG Plants”, Central Pollution Control Board, India. https://cpcb.nic.in/uploads/Categorization_Environmental_26102023.pdf. 
81. BSI PAS 110: Producing Quality Anaerobic Digestate, WRAP. https://www.wrap.ngo/resources/guide/bsi-pas-110-producing-quality-anaerobic-digestate.
82. Regulation (EU) 2019/1009 of the European Parliament and of the Council of 5 June 2019 Laying Down Rules on the Making Available on the Market of EU Fertilising Products, European Union. http://data.europa.eu/eli/reg/2019/1009/oj. 
83. Ordinance on the Utilization of Biowaste on Soils 1, 2, §4 (3). Federal Office of Justice, Germany. https://www.gesetze-im-internet.de/bioabfv/__4.html. 
84. Council Directive of 12 December 1991 Concerning the Protection of Waters Against Pollution Caused by Nitrates from Agricultural Sources (91/676/EEC). http://data.europa.eu/eli/dir/1991/676/2008-12-11. 
85. Carbon Dioxide Food and Beverages Grade, Source Qualification, Quality Standards and Verification, EIGA. https://www.eiga.eu/uploads/documents/DOC070.pdf. 
86. “Biogenic CO₂ from the Biogas Industry”, European Biogas Association. https://www.europeanbiogas.eu/wp-content/uploads/2022/10/Biogenic-CO2-from-the-biogas-industry_Sept2022-1.pdf. 
87. Control and Monitor Emissions for Your Environmental Permit, UK Government. https://www.gov.uk/guidance/control-and-monitor-emissions-for-your-environmental-permit. 
88. “Common Safety Practices for On-Farm Anaerobic Digestion Systems”, AgSTAR, US EPA. https://www.epa.gov/sites/default/files/2014-12/documents/safety_practices.pdf 
89. “Guideline for Operating Plant – Biogas”, Resources Safety & Health, Queensland. https://www.rshq.qld.gov.au/resources/documents/petroleum-and-gas/PGI-RSHQ-Biogas-Guideline-June-22.pdf. 
90. Commission Implementing Decision (EU) 2018/1147 Establishing Best Available Techniques (BAT) Conclusions for Waste Treatment, European Union. http://data.europa.eu/eli/dec_impl/2018/1147/oj. 
91. ISO 14001:2015. Environmental management systems – Requirements with guidance for use, ISO. https://www.iso.org/standard/60857.html; The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR), UK Health and Safety Executive. https://www.hse.gov.uk/fireandexplosion/dsear-regulations.htm.
92. Biological Waste Treatment: Appropriate Measures for Permitted Facilities, 11. Emissions Control, UK Government. https://www.gov.uk/guidance/biological-waste-treatment-appropriate-measures-for-permitted-facilities/11-emissions-control. 
93. “Leak Detection and Repair: A Best Practices Guide”, Office of Compliance, US EPA. https://www.epa.gov/sites/default/files/2014-02/documents/ldarguide.pdf. 
94. Environmental Permitting: H5 Site Condition Report, UK Government. https://www.gov.uk/government/publications/environmental-permitting-h5-site-condition-report. 
95. Decommissioning On-Farm Biogas Systems, Government of Ontario. https://www.ontario.ca/page/decommissioning-farm-biogas-systems 
96. Monitoring Emissions to Air, Land and Water (MCERTS), UK Government. https://www.gov.uk/government/collections/monitoring-emissions-to-air-land-and-water-mcerts. 
97. SR2021 No.6: Anaerobic Digestion Facility, Including Use of the Resultant Biogas – Installations, Environment Agency, UK Government. https://www.gov.uk/government/publications/sr2021-no-6-anaerobic-digestion-facility-including-use-of-the-resultant-biogas-installations/sr2021-no-6-anaerobic-digestion-facility-including-use-of-the-resultant-biogas-installations. 
98. Directive (EU) 2015/2193 of the European Parliament and of the Council of 25 November 2015 on the Limitation of Emissions of Certain Pollutants into the Air from Medium Combustion Plants. http://data.europa.eu/eli/dir/2015/2193/oj. 
99. Directive (EU) 2015/2193 of the European Parliament and of the Council of 25 November 2015 on the Limitation of Emissions of Certain Pollutants into the Air from Medium Combustion Plants. http://data.europa.eu/eli/dir/2015/2193/oj.
100. Commission Implementing Decision (EU) 2018/1147 Establishing Best Available Techniques (BAT) Conclusions for Waste Treatment, European Union. http://data.europa.eu/eli/dec_impl/2018/1147/oj. 
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103. Surface Water Pollution Risk Assessment for Your Environmental Permit, UK Government. https://www.gov.uk/guidance/surface-water-pollution-risk-assessment-for-your-environmental-permit. 
104. Control of Major Accident Hazards (COMAH), UK Health and Safety Executive. https://www.hse.gov.uk/comah/ 
105. GPP 21: Pollution incident Response Planning, NetRegs. https://www.netregs.org.uk/environmental-topics/guidance-for-pollution-prevention-gpp-documents/gpp-21-pollution-incident-response-planning/.
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108. The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR), UK Health and Safety Executive. https://www.hse.gov.uk/fireandexplosion/dsear.htm.