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AD, ammonia emissions and clean air

Prior to speaking at ADBA National Conference 2021, Angela Bywater, Environmental Biotechnology Network Co-Manager at Southampton University, funded by UKRI, shares a blog with us on AD, ammonia emissions and air quality.

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In the world of air quality, of major concern is ammonia emissions, where around 88% of UK ammonia emissions come from agriculture[1]. These emissions remain stubbornly above 2008 levels whilst other air quality indicators – particularly sulphur dioxide, oxides of nitrogen and non-methane volatile organic compounds – have fallen[2].

A benefit of anaerobic digestion (AD) is that it produces a fertiliser where much of the nitrogen can readily be taken up by plants since it is in ammonium form (NH4+). However, this readily available nitrogen (RAN) can also easily be released to air as ammonia (NH3) during the separation, storage and application of digestate and separated digestate products. Allowing the nitrogen to be emitted as ammonia translates directly to a monetary loss through the loss of digestate fertiliser quality.  It also reduces the positive environmental value of AD technology. It therefore makes sense for operators to reduce ammonia emissions as much as possible.

Although AD forms a small part of these ammonia emissions, there is increasing scrutiny on the industry, including specific mention of the technology in the 2019 Clean Air Strategy report[3], which includes a proposed requirement to store slurry/digestate in covered stores by 2027 as well as mandated utilisation of low-emission spreading equipment by 2025. Using gas-tight digestate covers also minimises fugitive methane emissions, identified as a major emissions source[4].

An article, coordinated by the BBSRC Environmental Biotechnology Network (https://ebnet.ac.uk/), which details an excellent case study on digestate acidification to reduce ammonia emissions and carried out by Dr Stephen Temple can be found on pages 33-34 of ADBA’s latest magazine, and our session at the ADBA National Conference will explore this important topic in more depth. 

By Angela Bywater

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Hear more from Angela at 4pm on 16th Febraury at ADBA National Conference 2021. Click here to book your ticket.

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[1] https://www.gov.uk/government/publications/code-of-good-agricultural-practice-for-reducing-ammonia-emissions/code-of-good-agricultural-practice-cogap-for-reducing-ammonia-emissions

[2] https://www.gov.uk/government/publications/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-1970-to-2018-summary#long-term-trends-in-emissions-of-air-pollutants

[3] https://www.gov.uk/government/publications/clean-air-strategy-2019

[4] https://www.ieabioenergy.com/wp-content/uploads/2018/01/Methane-Emission_web_end_small.pdf

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