Feedback on Guidance for Non Waste Anaerobic Digestion

Section 9 "How will SEPA set emission limits in an authorisation?"  sets out the proposed approach to regulating discharges to the water environment from non waste anaerobic digestion over 100 tonnes per days.    

We launched a call for evidence in October 2025 asking operators of non-waste AD plants to benchmark their sites against the requirements of the Waste Treatment Best Available Techniques Conclusions (BATCs), and to provide a gap analysis with supporting evidence. Although stakeholders responded regarding the BAT 20 limits, only limited robust or quantitative evidence was provided.  We have since reviewed these submissions alongside relevant sector data to establish how BAT 20 will define future compliance measures and emission limits for non-waste AD operations.

As a result of this review we will not apply the BAT 20 emission level ranges to direct marine discharges from non-waste AD sites. Instead, we will set emission limits using the standard schedule 10 EASR application processes to discharge effluent to the marine environment.

However, our assessment will still consider all relevant BAT 20 parameters, and any additional parameters which may be capable of causing harm in the marine environment such as metals and ammonia. SEPA will also have regard to the principles of BAT and process optimisation when setting emission limits.

For discharges to inland waters, we will remain aligned with the waste AD sector and set an emission limit within the BAT 20 ranges. We will also consider any additional parameters, including different forms of the BAT 20 parameters, which may be capable of causing environmental harm in the water environment. If our assessment shows that the BAT 20 range is insufficient to protect the local water environment, we will enforce stricter limits.

Adopting a different approach for discharges to the marine environment recognises how much marine and inland receiving environments differ. It allows us to consider each discharge and its specific composition in the context of their receiving environment, setting appropriate limits to prevent environmental harm.

Where we deviate from BAT 20 emission limits, we may require additional environmental monitoring to that set out in BAT 7, such as seabed surveys around long sea outfalls. This data will provide ongoing confirmation that the discharge is not harming the environment.

Operators of non-waste AD activities must provide a robust justification within their permit application that their effluent treatment techniques comply with regulation 9 of EASR. This justification must be informed by any applicable Scottish, UK or EU guidance on the best available techniques for effluent treatment, including those set out in the WT BATC’s.