Anaerobic digestion permitting explained

Regulation of anaerobic digestion plants in the UK is sometimes considered a complicated process, however this does not have to be the case. Katie Edwards and Debbie Howes from environmental consultancy RPS explain the process and how it works.

Farmers wishing to operate anaerobic digestion (AD) plants will need to obtain either a suitable exemption from permitting or an environmental permit to operate within the requirements of environmental law in the UK. The type and nature of the authorisation will depend on the size of the processing facility and the feedstock proposed for treatment.

Who are the regulators?

Within England the Environment Agency (EA) is the primary regulator for AD facilities, in Scotland it is the Scottish Environmental Protection Agency (SEPA) and in Wales, on 1 April 2013, Natural Resources Wales became the principal regulatory authority.

For the purposes of AD, the above regulators consider manure and slurry, when used as feedstock, to be wastes. If manures and slurries are digested together or with specifically grown energy crops, then the digestate output may not be considered a waste.

If the facility adheres to the PAS 110 quality standard for AD then the resulting digestate will be considered a product and not a waste. However, if the facility does not, the digestate output is also considered a waste and may also require authorisation for spreading to land etc.

PAS 110 is a voluntary quality protocol that was developed by waste resource agency WRAP and the EA for anaerobic digestion facilities. It specifies quite a bit of detail from the input materials to the monitoring and sampling completed throughout the process, and as such can be quite onerous on operators to achieve compliance with in the eyes of the EA. However, once compliance is achieved it does reduce the regulatory burden for the output materials drastically, which means that end markets are easier to find.

What are permits and exemptions?

AD plants are regulated under several regulatory mechanisms; although the authorisations required are broadly similar across the UK as a whole, there are variations depending on what part of the country the AD plant is found. Within England and Wales, environmental permits and waste exemptions are available, while in Scotland, waste management licences (WML), pollution prevention and control (PPC) permits and exemptions are available.

Exemptions from permitting cover low-risk AD activities and can be registered online in England and Wales for free and by submission of a notification form in Scotland for a small fee.

Generally, exemptions are limited to small scale facilities only; <1,240m3 of manure and slurry or <50m3 of food waste for storage and treatment with resultant biogas engines of <0.4MW thermal input in England and Wales. In Scotland the limits are set by the thresholds for WMLs and PPC permits, but are still considered low / small scale.

Environmental permits cover the medium- to high-risk AD facilities and can be either standard or bespoke permits; standard permits consist of a pre-defined set of standard conditions that have already been risk-assessed and evaluated by the regulator and as such require less information to be provided when they are applied for, cost less and take less time to be issued.

However, bespoke permits are defined on a site-specific basis and as such are more expensive to apply for. As they need to be fully risk-assessed on application and evaluated by the regulator, they take longer to be approved and generally contain tighter conditions for the operator.

In Scotland, all permits are assessed on a site-by-site basis and are therefore all considered bespoke.

In addition, permits also classify facilities according to the regulations that apply to them, as either waste operations (WMLs in Scotland) and installations (PPC permits in Scotland).

Facilities considered as waste operations are subject to the Waste Framework Directive only. However, installations are also subject to the requirements of the Industrial Emissions Directive and cover those AD facilities that either dispose of more than 50 tonnes of non-hazardous waste a day or recover (or a mix of recovery and dispose of) more than 100 tonnes of non-hazardous waste a day.

Facilities regulated as ‘installations’ are required by law to implement best available techniques (BAT) for the operation of their facility. BAT represents a European Union-wide set of standard requirements for the operation of the facility, ranging from waste acceptance requirements to containment and drainage.

What else do I need to do?

Compliance with the various regulatory mechanisms varies, and more is required of operators with more complicated, larger-scale facilities.

However, in all instances farmers will be required to have an environmental management system (EMS) in place to cover their facility.

An EMS is a system that will set out the procedures by which the facility will be operated and what information will be recorded and why, in order to prevent environmental impact. In general, farmers should keep records of all materials being processed through the facility and all digestate etc leaving the facility and where it goes. They must ensure that any final spreading sites also have appropriate authorisation.

What can we learn from the AD leak at Harper Adams?

The recent leak at the Harper Adams AD facility resulted in not just the leakage of digestate from a storage tank, but also a bund failure resulting in digestate leaking into a nearby field. The Environment Agency has stated that “there were no serious environmental impacts arising from the leak”, predominantly due to the contingency measures in place and swift actions to put these into operation.

Accident planning and being prepared for emergencies are important considerations during the planning, permitting, building and operational phase of any waste activity such as an AD plant. You can never be too prepared for the unexpected and the permitting process requires operators to conduct a risk assessment during the application.

This ensures that potential risks such as tank failure are considered and measures such as bunding are put in place to manage the risks. Bunds need to be designed and constructed in line with current guidance. CIRIA, the construction industry research and information association, produces guidance to improve safe working practices and assists operators to engineer and build infrastructure that not only meets industry standards, but is fit for purpose.

Sitting alongside the build, design operators are also required to write an accident management plan, which must be available and put into action should an incident occur. Staff will also need to be trained to undertake regular plant and equipment checks and be able to respond to an emergency.

More on this topic

New permitting rules for anaerobic digestion

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