Mitigating ammonia emissions in Green Gas Support Scheme at the centre of new consultation

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The government is seeking views on proposals for mitigations against ammonia from digestate as part of the Green Gas Support Scheme.

The government’s April 2020 Future support for low carbon heat consultation set out proposals for a new Green Gas Support Scheme to increase the proportion of green gas in the grid, through support for biomethane injection by the process of anaerobic digestion.

In this consultation the government proposes two mitigations against ammonia emissions from digestate, a by-product of anaerobic digestion, for the Green Gas Support Scheme participants.

Digestate is a nutrient rich by-product from anaerobic digestion that can be used as a fertiliser.

Used like this it has ‘many benefits’ but it also releases ammonia when stored or spread on land. It can also lead to water pollution if it is over-applied or used in the wrong place or at the wrong time.

Ammonia is an air pollutant that combines with other chemicals in the atmosphere to form fine particulate matter which has negative impacts on human health.

Ammonia is toxic to some plant species even at low concentrations and sensitive species are currently being impacted by ammonia concentrations across large parts of the UK.

Ammonia deposition also leads to biodiversity loss in sensitive habitats.

Most of the UK’s protected habitats are currently receiving excessive nitrogen and any increase in ammonia emissions will worsen this situation.

The UK government has legally binding targets to reduce ammonia emissions as well as a target to reduce nitrogen deposition in England.

As stated in the Future support for low carbon heat Impact Assessment, ammonia from anaerobic digestion digestate currently accounts for around 5% of all UK ammonia emissions, and biomethane plants are a subset of all anaerobic digestion plants.

Therefore, to maximise carbon savings on the scheme the government must consider all viable ways to mitigate ammonia produced.

In the April consultation the government asked for views on digestate and ways to mitigate ammonia emissions throughout the anaerobic digestion process.

In further engagement with Defra and the Environmental Agency, The Department for Business, Energy and Industrial Strategy (BEIS) have identified some proposals to mitigate emissions on the scheme that would ‘not impact on scheme deployment or present a significant risk to investment.’

In the first proposal, digestate needs to be stored in tanks or lagoons of sufficient size to comply with spreading restrictions to protect water and air quality and ammonia emissions are reduced by installing fixed covers on these new storage units.

The second proposal sets out that digestate should be spread as fertiliser by using low emission techniques.

BEIS welcomes all views but due to the technical nature of the proposals, expects responses mainly from those directly involved in the industry such as anaerobic digestion plant developers and relevant trade associations.

The government’s response to the April consultation will include decisions based on responses to this consultation. The government expects to open the Green Gas Support Scheme scheme in autumn 2021.

This consultation closes at

More information about this consultation and how to take part is available on the government website.