Anaerobic digestion &
markets for digestates
David Tompkins
Agriculture Sector Specialist
About WRAP
WRAP’s vision is a world without waste, where
resources are used sustainably.
We help businesses, individuals and communities
reap the benefits of reducing waste, developing
sustainable products and using resources in an
efficient way.
FocusWRAP
on food
waste
Main
driver
Reduction and re-use of food and drink wastes
 16Mt of post-farm gate food and drink waste
 5.3 Mt of avoidable household food waste
– Representing over 20 million tonnes of CO2e
– 3% of total UK GHG emissions
– 6% of total UK water footprint
– 1 in 4 cars on the road in the UK
 Ideally this waste would be prevented
– Where this is not possible, it should be recycled
– Composting offers one solution
– AD offers another – with the advantage of
renewable energy
Anaerobic digestion (AD)
Anaerobic digestion (AD)
AD in the UK
107 operational facilities
 44 farm-fed (manures, slurries, crops)
 47 food-waste-fed (households)
 16 industry-fed (distilleries, dairies)
 Total capacity ~5Mtpa
 ~ 230 more plants in planning
Farm-fed
Food-waste-fed
Industrial processes
http://biogas-info.co.uk/maps/index2.htm
Types of digestate
Classification by input:
 Manures and purpose-grown crops
 Waste-derived:
– Source-segregated
– Mixed
 Biosolids and co-digestates
AD can be:
 Wet (<15% DM) or dry
 Mesophilic (35 - 40°C) or thermophilic
(55 - 60°C)
http://www.defra.gov.uk/publications
/files/anaerobic-digestion-strataction-plan.pdf
Digestate is not just digestate…
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Most UK digestates are low dry matter
(<10%)
Can be separated
– Fibre
– Liquor
Different fractions have different
physical and chemical characteristics
– Different potential uses
Digestate regulations
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WRAP focusses on digestates derived from sourcesegregated wastes, including:
– Food processing residues
– Kitchen waste
– Crop processing residues
As soon as a waste is mixed with non-waste, the
whole mix becomes a waste
BUT… there is a way out of this
[Digestates derived from manures and purposegrown crops not normally regulated]
Digestate regulations
To transform ‘waste’ digestates into ‘products’
 Two parts:
– Anaerobic Digestate Quality Protocol
– Approved specification (PAS110)
 If an operator complies with both and is
independently certified to both, then the biofertiliser
is no longer a waste and can be used as a product
 BUT, ADQP lists allowable markets
www.biofertiliser.org.uk
Digestate regulations
PAS110 specification includes limits on:
 E. coli and Salmonella
 PTEs (Cd, Cr, Cu, Hg, Ni, Pb, Zn)
 Digestate stability
 Physical contaminants
PAS110 specification requires tests for:
 pH
 Total nutrients & ammonium-N
 Dry matter
WRAP’s market development work
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>99% digestate is used in agriculture
– Replicated field experiments across the UK
– www.wrap.org.uk/dc-agri
– Biofertiliser Matrix
Other uses
– Brownfield restoration and regeneration
(particularly energy crops)
– Soil manufacture
– Turf establishment
– Sports and amenity turf maintenance
Horticulture pre-feasibility trials
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As an ingredient in growing media
As a liquid feed for containerised strawberry
production
In soil-less hydroponic trials
Key questions:
– Can digestate be used in these applications?
– What are the constraints?
– Can these be overcome?
– Are there business benefits?
– Should the ADQP be changed?
Thank you
David.Tompkins@wrap.org.uk
01295 817896
07703 331947
www.wrap.org.uk