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  • Non-waste anaerobic digestion less than 100 tonnes per day

Non-waste anaerobic digestion less than 100 tonnes per day

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This activity applies to the anaerobic digestion of non-waste materials and associated feedstock and digestate handling and storage.

Anaerobic digestion of non-waste materials is a new regulated activity made law in the Environment Authorisations (Scotland) Regulations 2018 (EASR). This activity has a ‘sunrise date’ of 1 April 2028; this means that it will not be regulated by SEPA until this date. Digestate and containment requirements as per Schedule 9 of EASR must still be adhered to. More information on how and when to apply will be provided prior to the new activity being regulated.

We will publish updated and new guidance documents to account for the changes in waste and non-waste anaerobic digestion. The guidance states that digestate produced using only non-waste materials (e.g. energy crops grown specifically for anaerobic digestion) when used directly on agricultural land will not be regulated as waste.

This activity is found in Schedule 26 Part 3 Paragraph 69 of the Environmental Authorisations (Scotland) Regulations. 

Authorisation level

Registration

Fit and Proper Person tests

Fit and Proper Person tests apply to this activity. You will be asked in your application if you have any relevant convictions held by you or any additional persons.  

Read more about Fit and Proper Person tests

Fees and charges

An application fee applies to the application of a new authorisation for this activity.

Band Threshold/Description Fee

An application fee applies to the application for a new authorisation for this activity.

For detailed information on application, annual activity fees, and fees related to transferring, varying, or surrendering an authorisation, please refer to our charging information.

Standard conditions

The set of Standard Conditions for this activity has the following reference EASR-SC-001.

Your registration application will only be granted if you can confirm you are able to comply with the standard conditions set out below.

If you carry on an activity under a registration authorisation you must comply with the standard conditions. It is an offence if you do not comply with the conditions.

SEPA will not authorise this activity if it poses an unacceptable risk to the environment.

  1. All potentially odorous materials must be stored within suitable closed containers or covered to prevent odour.

  2. All storage and processing of feedstock, digestate and effluent must take place on an area with a sealed drainage system.

  3. All liquid feedstock, digestate and effluent must be kept within a liquid storage and management system.

  4. The liquid storage and management system must be designed, constructed, maintained, managed and of sufficient capacity to prevent any emissions.

  5. The liquid storage and management system must be constructed as detailed in the liquid storage and management system engineering plans.

  6. Liquid digestate storage lagoons with walls made of earth must not be filled to a level that results in less than 750 millimetres of freeboard.

  7. Liquid digestate storage tank(s) must not be filled to a level which results in less than 300 millimetres of freeboard.

  8. Non-liquid feedstock must not be stored above the height of the vessel it is stored in once is has been compacted.

  9. Liquid feedstock, digestate and effluent storage lagoons with walls made of earth must:

    1. be lined with an impermeable sheet material; and
    2. have suitable leak detection.

  10. The impermeable liner at the mixing and filling zones of any earth-banked liquid feedstock, digestate or effluent storage lagoons must be protected with a layer of concrete.

  11. All biogas condensate must be:

    1. collected and contained; or
    2. recirculated back to the digester.

  12. Pressure, temperature and flowrate in the pressure system must be monitored and recorded via telemetry 24 hours a day.

  13. The pressure relief and vacuum systems must be:

    1. inspected to ensure they are correctly seated; and
    2. linked to an alarm system(s) which is connected to 24-hour telemetry.

  14. All reasonable steps must be taken to minimise:

    1. emissions of unburned biogas;
    2. any activation of a PRV; and
    3. the operation of the auxiliary flare.

  15. Any activation of the flare, must be recorded and reported as an environmental event.

  16. Point source emissions to air from the authorised activities must only be made from the gas engine and/or the combined heat and power (CHP) plant stack(s).

  17. Any gas engine and/or combined heat and power (CHP) plant stack height associated with the authorised activities must be:

    1. greater than or equal to 3 metres above the roof ridge height of the building on which it is located; or,
    2. greater than or equal to 3 metres above the ground if it is located separate to any building; and
    3. greater than or equal to the height of any part of a building which is located within a distance of 5 times the uncorrected stack height.

  18. Emissions of substance(s) to the air from the gas engine and/or CHP plant stack(s) must not exceed the specified emission limit value specified in Table 1.

  19. Air must not be added to dilute emissions in order to achieve emission limit values specified in Table 1.

  20. The emission of any substance, not specified in Table 1, from the authorised activities must not cause environmental harm.

    Table 1 Emissions to air from gas engine and/or CHP: limits

    Substance Emission Limit Value
    Dust 50mg/m3
    Oxides of Nitrogen (NOx) 190mg/m3
    Suplhur Dioxide 15 mg/m3
    Total Volatile Organic Compounds 20 mg/m3
    Carbon Monoxide 1000 mg/m3

  21. Monitoring of emissions of substances to air must be undertaken at the gas engine and/or combined CHP plant stack(s) at the sample port, frequency and using the monitoring standard specified in Table 2.

  22. Sample points must be installed, maintained and appropriately identified so that representative samples may be safely obtained.

  23. Monitoring must be undertaken:

    1. during normal operation;
    2. under stable conditions; and
    3. at a representative, even load.

  24. The first monitoring of emissions must be undertaken within four months of the start of operations.

    Table 2 Emissions to air from gas and/or CHP: monitoring requirements

    Substance/parameter Emission Point Reference Monitoring frequency Monitoring standard (1)
    Dust Sample port determined in accordance with BS EN 15259 Manufacturer's guarantee OR annually BS EN 13284-1
    Oxides of Nitrogen (NOx) Sample port determined in accordance with BS EN 15259 Annually BS EN 14792
    Sulphur Dioxide Sample port determined in accordance with BS EN 15259 On commissioning of a new plant OR a new feedstock is introduced to the process BS EN 14791
    Total Volatile Organic Compounds Sample port determined in accordance with BS EN 15259 Annually BS EN 12619
    Carbon monoxide Sample port determined in accordance with BS EN 15259 Annually BS EN 15058
    Biogas flare temperature (°C) Sample port determined in accordance with BS EN 15259 Continuous BS EN 16911-2

  25. All releases to the air from the authorised activities during normal operation, other than condensed water vapour, must be free from visible emissions.

  26. Measures must be taken to prevent, or where that is not practicable, minimise:

    1. dust;
    2. odour;
    3. noise
    4. the presence of vermin;
    5. biogas emissions; and
    6. heat emissions

    from the authorised activities.

  27. Dust from the authorised activities, which has a significant impact on the environment, people or property, must not be emitted beyond the boundary of the authorised place.

  28. Offensive odours from the authorised activities as perceived by a SEPA officer must not be emitted beyond the boundary of the authorised place.

  29. Noise from the authorised activities, which has a significant impact on the environment, people or property, must not be emitted beyond the boundary of the Authorised Place.

  30. SEPA must be notified via its pollution hotline contact telephone number as soon as reasonably practicable, and in any case within 24 hours of identification of an event, of any of the following:

    1. an event that has caused or could cause adverse impact to the environment or harm to human health;
    2. an event that results, or could result, in an emission to the environment that is not authorised; and
    3. an event that has caused a breach of a condition of this authorisation.

    In this condition, the meaning of 'event' is as defined in the Glossary of Terms.

  31. All measures that are reasonably practicable must be taken to stop an event and to minimise its effect on the environment.

  32. Within 14 days of an event a report must be submitted to SEPA detailing:

    1. the reason(s) for the event;
    2. the action(s) taken to stop the event and minimise the impacts; and
    3. the action(s) taken to prevent the event from reoccurring.

  33. All information recorded, kept or submitted to SEPA in accordance with a condition of this authorisation must be:

    1. true and accurate; and
    2. kept for a minimum of six years; and provided to SEPA upon request.

  34. Records must be kept of all monitoring results and verification of compliance with the emission limit values specified in Table 1.

  35. The results of the monitoring of emissions, as described in condition 22, must be submitted to SEPA within eight weeks of the date the monitoring took place via email to registry@sepa.org.uk

Digestate

Material remaining after anaerobic digestion of biodegradable feedstock including whole digestate (mixture of liquor and fibre), liquor, and separated fibre.

Dust

Suspended solid particles and liquid droplets suspended in air which may be deposited on surfaces and may cause air pollution and/or nuisance.

Effluent

A mixture consisting wholly of or containing liquid produced from the storage of any forage crop or other feedstock, the storage of digestate, and rainwater or groundwater emanating from an effluent collection system or drain.

Emission

The direct or indirect release of substances or heat from individual or diffuse sources in the authorised activities into air, water or land.

Emission limit value

The mass, expressed in terms of specific parameters, concentrated or level of an emission, which may or may not be exceeded during one or more periods of time.

All emission limit values are defined at:

  1. a temperature of 273.1K;
  2. a pressure of 101.3kPa:

without correction for water vapour content.

Environmental harm

  1. harm to the health of human beings or living organisms,
  2. harm to the quality of the environment, including:
    1. harm to the quality of the environment taken as a whole,
    2. harm to the quality of air, water or land, and
    3. other impairment of, or interference with, ecosystems,
  3. offence to the senses of human beings,
  4. damage to property, or
  5. impairment of, or any interference with, amenities or other legitimate uses of the environment.

Event

  • any accident which has caused or could cause environmental harm; or
  • any malfunction, breakdown or failure of plant, infrastructure or techniques which has caused or could cause environmental harm; or
  • force majeure or action taken to save human life or limb.

Feedstock

The non-waste materials to be treated in anaerobic digestion plant.

Forage crop

Any crop grown as food for livestock or for use in energy production.

Freeboard

The vertical distance between the crest of a tank, container or lagoon and the digestate surface.

Gas engine

An internal combustion engine which operates according to the Otto cycle and uses spark ignition to burn fuel.

Impermeable

A surface constructed of impermeable material to a standard sufficient to prevent the transmission of liquids beyond the surface. Should be read in conjunction with the term ‘sealed drainage system’.

Impermeable sheet material

  1. synthetic rubbers, EPDM (ethylene propylene diene monomer rubber) and butyl,
  2. plastics, including polyvinyl chloride, low density polyethylene and high density polyethylene, and
  3. reinforced geomembranes.

Leak-proof

To be constructed of impermeable material of sufficient strength and structural integrity such that it is unlikely to burst or leak in its ordinary use.

Liquid

Any aqueous material but excluding sludge.

Liquid storage and management system

An impermeable system designed to contain liquid, comprising the base(s) and walls of liquid feedstock, digestate or effluent storage tank(s), lagoon(s), pit(s), vessel(s), tower(s) plus any connected channels, pipes and valves which:

  1. has sufficient capacity to accommodate contaminated run-off (including any rainfall) that directly or indirectly enters the liquid storage and management system and the volume of digestate produced during periods when application is not authorised under activity 18 of column 1 of Schedule 9 of the Regulations or would not comply with the requirements of the Action Programme for Nitrate Vulnerable Zones (Scotland) Regulations.
  2. has an effluent tank which is at least:
    1. for a feedstock storage tank, lagoon, pit, vessel or tower with a capacity of less than 1,500m³, 20 litres for every 1m³ of silo capacity; or
    2. for a feedstock storage tank, lagoon, pit, vessel or tower with a capacity of 1,500m3 or greater, 30,000 litres plus 6.7 litres for every 1m3 of silo capacity over 1,500m3;
  3. is protected against corrosion in accordance with paragraph 7.2 of the Code of Practice on Buildings and Structures for Agriculture published by the British Standards Institution and numbered BS 5502-50:1993+A2:2010;
  4. is capable of withstanding characteristic loads calculated on the assumptions and in the manner as set out in paragraph 5 of the Code of Practice on Buildings and Structures for Agriculture published by the British Standards Institution and numbered BS 5502-50:1993+A2:2010;
  5. where the system incorporates a system of pumps and sumps, it must be fitted with an automatic overfill prevention device with a dedicated electrical supply and an alarm;
  6. if new, reconstructed or enlarged on or after 1 January 2022, has a life expectancy of at least 20 years, with proper maintenance, from its construction, reconstruction or enlargement;
  7. Where the liquid digestate storage tank is fitted with a drainage pipe—
    1. There must be two valves in series on the pipe and each valve must be capable of stopping the flow of liquid digestate through the pipe and must be kept shut and locked in that position when not in use;
    2. Sub-paragraph (g)(i) does not apply in relation to a liquid digestate storage tank which drains through the pipe into another liquid digestate storage tank of equal or greater capacity or where the tops of the tanks are at the same level.

Normal operation

Operation of authorised activities excluding start-up and shut-down periods.

Point source emissions

Single, identifiable source of emission.

Sealed drainage system

A drainage system with impermeable components and surfaces which does not leak and which will ensure that:

  1. no liquid will run off the surfaces otherwise than via the system; and
  2. except where they may be lawfully discharged, all liquids entering the system are collected in a sealed sump.

SEPA Officer

Any person who is authorised in writing by SEPA under section 108 of the Environment Act 1995.

Sludge

A by-product of the anaerobic digestion process with a suspension having a high solids content.

Storage tank

Includes a lagoon, pit (other than a reception pit), vessel or tower used for the storage of feedstock, digestate and effluent.

Sump

In relation to a sealed drainage system, the container in which all liquid collects which must:

  1. hold at least:
    1. for a single container, 110% of its capacity;
    2. or for two or more containers, the greater of:
      1. 110% of the capacity of the largest container; or
      2. 25% of the capacity of all containers together.
  2. catch all spills from the container(s) and related parts;
  3. be leak-proof;
  4. be located, and/or protected, to prevent damage as far as reasonably practicable; and
  5. have any spills and/or rainwater removed as soon as reasonably practicable.

Uncorrected stack height

The stack height before any required increases in height are made to account for any nearby buildings.

Water environment

All surface water, groundwater and wetlands.

How to apply

It is not possible to apply for this activity at this time.

The new digital application service for this activity will be launched in December 2027. Information on how to apply for this activity will be shared here ahead of the launch.

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