1. Ammonia Emissions from Anaerobic Digestion in the UK and Potential Mitigations
Mariana Ghosh (Defra) and Sam Tomlinson (CEH)
11th May 2017
TFEIP-Krakow

2. Outline Introduction: Emissions of Ammonia in the UK
AD: Technological Overview
AD emissions methodology in the UK
The potential mitigation measures
Summary

3. Air Quality: progress so far
There has been a long-term decline in air pollution since 1970.
Between 1970 and 2015, estimated emissions of sulphur dioxide fell by 96%, nitrogen oxides by 69%, NMVOCs by 66%, PM10 by 73% and PM2.5 by 76%. Ammonia emissions from agriculture decreased by 19% between1990 and 2015.
With the exception of ammonia and PM2.5, emissions of all pollutants continued to decrease in 2015.
SOURCE: STATISTICAL RELEASE: 21 DECEMBER 2016
EMISSIONS OF AIR POLLUTANTS IN THE UK, 1970 TO 2015 published on gov.uk

4. Trends in UK ammonia emissions 1980 –2015
Emissions of ammonia from agriculture (dashed line) compared with the total emissions (solid line). Also shown (crosses) are the targets within the National Emissions Ceilings Directive (NECD)
Agriculture (81%) of ammonia emissions (livestock manure management and inorganic nitrogen fertilizer) and AD (3%) of ammonia emissions
Emissions from AD have increased by 70% since 2013
Commitment to reduce ammonia emissions by 8% from the 2005 baseline by 2020.
Ammonia emissions
Ammonia is the only air pollutant that does not reflect the overall trend of long-term reductions. Emissions of ammonia fell at a slower rate than other pollutants between 1980 and 2013 and since 2010 there has been an increase in ammonia emissions of around 3.7%. When emitted into the atmosphere, ammonia has significant negative effects on human health and the environment. It also causes nitrate pollution of freshwaters and accelerates deterioration of polluted water bodies. The Government has a legally binding commitment to reduce ammonia emissions by 8% from the 2005 baseline by This 8% represents the total reduction in ammonia from all sources (mainly agriculture) and will be delivered through the National Emissions Ceiling Directive (NECD).
Ammonia emissions resulting from increasing levels of Anaerobic Digestion (see paragraph below) were not originally included in the statistics when the UK signed up to the directive, and were included in the air quality national statistic for the first time in December 2016.

5. Technological Overview
AD can divert waste from landfill to produce biogas, as source of renewable energy, and “digestate”, a fertilizer
AD can process food waste, manures, sewage sludge and grown-up crops
Example of an AD plant configured to produce energy and biofertiliser from biowaste feedstock (Source: DEFRA 2011)

6. Continuing to live in a changing landscape
Renewable energy growth
Energy demand and consumption
AD needs to evolve
Cost of digestate is a challenge
Renewable energy contributions to meeting the UK's 15% target reduction in total energy consumption by 2020, in accordance with the 2009 EU Renewable Directive, totalled 5.2% in 2013 as measured in accordance with the methodology set out in the Directive.[3] By 2016 provisional calculations show that the figure had risen again to 8.3 per cent of energy consumption (all sources) coming from renewable sources in 2015.[
Increasing amounts of energy from renewable sources including Ad, but Ad is not a cheap way of making electricity. Commentators predict that PV will achieve grid parity in the near future.
Renewables, particularly PV and wind are intermittent so power mix needs to be resiliant – AD with gas grid injection scores well here.
Gate fees show a clear downwards trend
Electricity generated from renewable sources in the United Kingdom between 2000 and 2015 (Source: DECC)

7. Digestate issues Remains a low value product
2013 data shows 98% went to agricultural land
Liquid product difficult to transport
Odour
NH3
SOURCE: WRAP

8. Looking forwards
Need to use innovative thinking and technology to revolutionise the way in which the digestion process and digestate are used
New technology, new processes, new products, new markets
Options appraisal shows potential in some areas but not in others
Need to consider markets as well as products
SOURCE: WRAP

9. UK AD Inventory (NH3) - Overview
Operational AD site database (sources: WRAP, BioGas)
Under development:
Obtaining throughput stats (instead of capacity)
Fractions of co-digestion
Data for waste water
emissions from AD sites
Improve variety of EFs to reflect variety of digestate
Co-digestate
Differing N content
Level of site mitigation
Efficiency vs scale
Quantity of digestate
Going to land
Separated for cleaning
emissions from LS
Basic overview: around 360 or so sites with a capacity of 11m tonnes (8.5m food/manures/crops) (capacity != throughput)
We quantify emissions from the sites themselves (storage and fugitive emissions) and from the landspreading of digestates
Boxes in red represent improvements and researches underway
Land spreading (LS) of digestates

10. Emission Factors for AD in the UK
Site based:
Pre-AD storage: kg NH3 t-1 feedstock
AD process: kg NH3 t-1 feedstock
Post-AD storage: kg NH3 t-1 feedstock
Landspreading:
2.5 kg NH3 t-1 digestate (food-based)
0.83 kg NH3 t-1 digestate (crop-based)
0.83 kg NH3 t-1 digestate (crop/food mix)
(zero emissions from manure digestates and brewery/vegetable washings)
Under development:
Further classification of digestate with EFs
Integration of more application techniques
Our current Efs in the inventory
Efforts to improve estimates are concentrating on landspreading – biggest source of NH3 – in both digestate types and landspreading methods
Currently zero emissions from manure digestate (double counting with ag inv) and zero from brewery/vegetable washings

11. Emissions from AD in the UK
Rapid growth industry
Emissions dominated by the spreading of digestates to land

12. Spatial Distribution Site locations and spreading
Assign emissions by input (t)
Scale by suitable agricultural land
Under development:
Site emissions by feedstock
Landspreading emissions by feedstock
Distance of digestate usage
Quantity of digestate usage
Quantity of liquid fraction treatment
Land types applied to
Spatial distribution tricky due to lack of data – currently scaled by plant capacity size and availability of arable land
Changing to include AD plant type (feedstocks, technologies), digestate type, survey based data, other land types such as grass etc

13. Mitigation Strategies
NH3 stripping
Liquid/solid separation
Acidification
Application techniques
Timing & conditions
Covering
Mitigation reductions are not multiplicative
There are various methods to mitigate against NH3 emissions such as….
Mitigation methods are not necessarily multiplicative: application techniques may be pointless if all N stripped out (especially given cost)
It is possible to remove large quantities of N from digestate but produces and low-use product
There is a balance
NH3 removal can be a balance between utility and environment

14. Summary UK anaerobic digestion industry increasing in size
NH3 emissions increasing with it – now 9.7 kt NH3 (mineral fertiliser = kt)
Developing increased detail into emissions estimations
Spatial distribution improving
Mitigation strategies could substantially decrease landspreading NH3 emissions

15. Thank You!