2. TESTING THE BIOMETHANE
POTENTIAL OF MISCANTHUS
Carly Whittaker & Ian Shield
Rothamsted Research
14th April 2015
ADBA R&D Forum 2015
3. Alittle bit about
Rothamsted
Research
• Harpenden, Herts
• Long term experiments
• 1843 winter wheat
• 1859 grass/hay
• Hosts National Willow
Collection (~13,000 types)
• Long term (~20 years)
Miscanthus trials
• Home to first approved &
completed GM trial
• Wheat 2013
• Omega-3 Camelina
4. Our experiment:
• To test the biomethane potential of Miscanthus that is harvested green and
stored as silage
• Comparing the results with maize ‘control’
• Main questions:
• Can Miscanthus be stored in silage form?
• Is Miscanthus an adequate displacement of maize in AD?
• Are the environmental credentials more favourable?
• What is the energy yield per hectare?
• We don’t have all the results yet…
6. Miscanthus
• Perennial grass ~ 20 year commercial lifespan
• Propagated via rhizomes – main variety M.
giganteus sterile
• Yields range between 8 and 16 ODT/ha/year
• Contractors – 8 ODT/ha/year
• Average 12 ODT/ha/year
• Our sites up to 19 ODT/ha/year
• Environmental credentials
• High yield with low input – N response debated/site
specific
• Carbon sequestration between 0.5 – 1.5 t C ha-1 year-1
• Up to 65% remaining after termination (little info
available on this)
• LCA- Carbon-negative crop
7. When to Harvest?
Seasonal Changes in Miscanthus
April/May
March September
October
Combustion
Conventionally
harvested in
March
- ~25% m.c
- Low N, P, K
and ash
content
Recycles
nutrients
to rhizome
8. Seasonal Changes in Miscanthus
Combustion
Conventionally
harvested in
March
- ~25% m.c
- Low N, P, K
and ash
content
Biomass yield from the long-term Experiment at Rothamsted (CS/408)
Peak biomass
end Sept
- Lost aerial d.m
27 kg/ha/day
Third of peak
biomass lost
during winter
But drying not an
option
~70% m.c
Dry Matter Yields
9. Recycles
nutrients
to rhizome
April/May
March September
October
Seasonal Changes in Miscanthus
Combustion
Conventionally
harvested in
March
- ~25% m.c
- Low N, P, K
and ash
content
Biomass yield from the long-term Experiment at Rothamsted (CS/408)
Peak biomass
end Sept
- Lost aerial d.m
27.3 kg/ha/day
Third of peak
biomass lost
during winter
But drying not an
option
Recycles
nutrients
to rhizome
10. Seasonal Changes in Miscanthus
April/May
March September
October
Combustion
Conventionally
harvested in
March
- ~25% m.c
- Low N, P, K
and ash
content
Lignocellulosic
ethanol/AD
“Green
harvesting”
Peak biomass
end Sept
- Lost aerial d.m
27.3 kg/ha/day
Third of peak
biomass lost
during winter
But drying not an
option
Green harvesting
issues?
- Starch
reserves?
- N, P & K
recycling?
- Effect on
yield?
- And C seq.?
Recycles
nutrients
to rhizome
11. Seasonal Changes
• N, P & K (Himken et al., 1997)
• N cycling begins early in season
• Harvesting in September means not
quite recovered for next growing
season
• Supplements may be required
• Carbohydrates (Purdy et al., 2014)
• Difficult to supplement this…
• Need some for AD!
• Max carbohydrate content in rhizomes
in November
• But too dry for silaging (40% d.m)
Rhizome Stem
12. Early Harvesting Trials at Rothamsted
• Work by Nicola Yates & Ian Shield
• Early harvesting in October for two
consecutive years – 2009 & 2010
• Treated one plot with additional 50 kg N/ha
0
2
4
6
8
10
12
14
16
Early Late
2009 2010 2013 Early 2013 Late
HarvestedYield(t/ha/year)
Early
Early + N
Conventional
• Higher initial yield
• Early harvest = 50% drop
• After 2 years conventional
harvesting there is no
difference
• Evidence that crop can
‘recover’
• Stagger harvests?
14. The Experiment:
Step 1: Making Silage
• Why do we need to make silage?
• Store green biomass and minimise dry matter losses
• A possible ‘pre-treatment phase’ to boost future biogas production?
• 15% higher biomethane potential from ensiled Miscanthus
• Cellulase additives?
• Challenges
• High dry matter content
• September~35% (25–30% optimal)
• High buffering capacity
• Resists ensilage
• Relatively low carbohydrate content
15. Making Silage
• 30 litre brewing containers
• Maize
• M. giganteus
• M. sacchariflorus
• M. giganteus + 2
additives:
• Homo & heterofermentation
• Designed for high DM crops
• Left for 4 months
16. Homo and Hetero Fermentation Pathways
• Heterolactic
L. brevis and L. fermentum.
Glucose+ ADP→ Lactate + Ethanol+ CO2+ ATP
• Acetic/lactic/ethanol products
• 76% dry matter recovery
• Acetic acid precursor to
methane
• Better feedstock for AD?
• Acetic acid stops breakdown
after opening silo
• Prevent secondary losses in AD
plant?
• Homolactic
L. plantarum, P. acidilactici and L.
paracasei.
Glucose+2 ADP→2 Lactate +2 ATP
• Lactic acid sole acid product
• 100% dry matter recovery
17. Results so far..
• Smelt like silage.
• pH
• Additives significantly improved
silage formation compared to
control
• Dry matter losses
• All negligible except untreated M.
sacchariflorus (2-9% D.M loss)
0
1
2
3
4
5
6
7
pH
Start pH Silage pH
18. Results so far…
• HPLC
• Volatile fatty acid production
shows good lactic acid and acetic
acid formation.
• Biomethane potential
tests currently running
19. Biomethane Potential?
• Mayer et al., 2014 in France
• No yield decline with early
harvesting
• Biogas yield comparative to
maize
• Per tonne volatile solids
• Per hectare
• Miscanthus was best substitute
out of 9 novel feedstocks
• 100% Miscanthus?
• In practice a mix of feedstocks will
be used
20. Conclusions so far
• Early harvesting could be an option for uses in AD
• Staggered early harvests to boost biomass yield and improve suitability for AD
• Miscanthus on it’s own doesn’t silage very well but:
• Miscanthus benefits from additive application to improve silage formation
• Negligible dry matter losses
• pH down to 3.8 with homofermentative silage additive
21. Thank you for listening
• Thanks to
• Nicola Yates
• Richard Webster – Free silage
additives
• Farm Team
• Peter Fruen, Tim Barraclough &
March Castle & Richard Hull
• Chris Hall
• Neil Donovan, Tom
Misselbrook, Andy Retter &
James Hunt at N. Wyke
• carly.whittaker@rothamsted.a
c.uk
• http://www.supergen-
bioenergy.net/
