1. Digestate back to land
16th May 2013
Anna Becvar, Director
Earthcare Technical Ltd
2. What is Anaerobic Digestion (AD)?
•A controlled microbial process where organic
materials are broken down into simpler organic
compounds in the absence of oxygen
• End products:
– Biogas (valuable energy source)
• ~ 60% methane, 40% carbon dioxide
– Semi-liquid organic fertiliser known as
anaerobic digestate or ‘biofertiliser’
3. Digestate availability
• 2009, 17 UK AD plants.
• 2013, 109 + operational
• 10 BSI PAS 110 accredited
Biofertiliser Certification
scheme members
• The majority of digestate is
spread on agricultural land at
present
NNFC AD Plant Map: 8th May 2013
6. Readily available N (RAN) content
of food-based Digestate based on 250 kg N/ha
Organic N
Readily available N
20%
Food based digestate
80% 30%
70%
Pig slurry
Green compost
High readily available N >30% total N (NVZs)
<3%
7. Need to calculate the crop available Nitrogen
• Readily Available N (i.e. Ammonium-N by analysis) is
potentially available for rapid crop uptake
• Organic N is broken down slowly to become available
over months or years
• Crop Available N is the readily available N left for crop
uptake after losses are taken into account
8. Organic materials – N supply and losses
To water (NH4-N, P, FIOs etc).
Nitrogen
gas
Volatilisation
Nitrification
Soil
Organic N
Immobilisation
Nitrous
oxide
gas
Ammonia gas
Organic
N
N
Ammonium
Denitrification
Nitrate
Crop available N
Plant uptake
9. Calculate the Crop Available Nitrogen
1. Location – Rainfall and soil type
2. Timing of application (spring or autumn)
3. Method of application (e.g. surface, dribble bar, injection)
4. Use MANNER NPK to calculate crop available nitrogen
• Should use a FACTS Qualified Advisor
Also need to comply with:
• The CoGAP in England and Wales, PEPFAA in Scotland
•NVZ rules where applicable
11. Trailing hose30%
Trailing shoe40%
Injection -
open slot70%
‘New’ application techniques
Ammonia (odour) emissions, crop contamination
N efficiency, spreading days and accuracy
12. Digestate – NVZs
• Liquid and whole digestate are classed as ‘high readily available
N manures’ (i.e. > 30% of the total N present as readily available
N) and therefore subject to application closed periods.
• High RAN digestate cannot be applied prior to legumes
• If fibre digestate analysis shows < 30% available N it will not be
subject to application closed periods in a NVZ
• N Max:- from Jan 2014 these changes occur
• Total N in all organic manures applied will be counted.
• Most veg crops will have N max values applied. They were
exempt before.
• Livestock manure fraction (%) counts towards Whole Farm Limit
(170 kg N/ha)
14. Digestate
BSI PAS110
‘Waste’ digestate
Standard Permit SR2010No.4
Deployment (England & Wales)
PAS110 in Scotland
(SEPA guidance)
PAS110 + ADQP in England
& Wales a product
Paragraph 7 Exemption in
Scotland
Crop & livestock manure
digestate under farm control
Apply as for farm
manures/slurries
15. In England and Wales waste digestate
• SR2010No4 Mobile Plant land spreading permit (£700
one off EA cost)
• Deployment per 50 ha block of land £760 EA cost
• What you need:
– Spread risk maps of fields
– Up to date soil analysis
– Previous and future cropping
– Soil type
– Up to date digestate analysis (<12 months old)
• 25 working days for the deployment to be assessed
17. BSI PAS110 Input materials
• Input materials: Source segregated biowastes and/or
biodegradable materials
• Shall not include contaminated wastes, products or
materials
• No sewage sludge or its derivatives
• In England and Wales if following ADQP type of waste must
be in the acceptable list
• In Scotland no ADQP but refer to the SEPA Position
statement on classification of outputs
18. BSI PAS110 limits
Pathogens:
E Coli 1000 CFU/g
Salmonella spp Absent in 25g fresh matter
Potentially toxic elements (mg/kg dry matter)
Cadmium 1.5 Lead 200
Chromium 100 Mercury 1.0
Copper 200 Nickel 50
Zinc 400
Physical contaminants
Total glass, metal, plastic
and any other non-stone
>2mm
0.5% m/m dry matter
Stones >5 mm 8% m/m dry matter
20. Good Agricultural Practice when using digestate
• Storage – Covered stores (required for BSI PAS 110) reduce
odour and ammonia loss
• Phosphate- Also a major consideration
• Timing - High readily available N means both whole and
liquid digestates can only be applied outside application
closed periods in NVZs and all digestates should only be
applied when there is crop demand
• Method – Injection or trailing shoe/hose application
equipment will both help minimise odours and conserve N
• Spread Risks - Follow a farm Manure Management Plan
• Work with neighbours - Tell them what you are doing and
spread digestate with an awareness of their concerns/needs
21. Defra/WRAP/Zero Waste Scotland
Digestate and Compost in Agriculture
project, 2010-2014
Objectives
• ‘To quantify the effects of contrasting digestate and
compost applications on soil and crop quality, crop
available nitrogen supply and emissions to the air and
water environments’
22. Field Experiments 2010-2014
WP1 Quantifying effects of contrasting digestate and
compost applications on soil and crop quality
WP2.1 Looking at crop available nitrogen supply
WP2.2 GHG Hubs - effects of digestate and compost
additions (compared to slurry and FYM) on
ammonia (NH3) and Nitrous oxide (N2O)
emissions, and at Wensum site, leaching losses:
nitrate (NO3), soluble P and microbial pathogens
23. Follow the Digestate and Compost in Agriculture
project, and download bulletins: www.wrap.org.uk/dc-agri
Thank you!
anna@earthcaretechnical.co.uk
www.earthcaretechnical.co.uk
