This document summarizes research testing the biomethane potential of Miscanthus harvested green and stored as silage. The study compares Miscanthus to maize, the control. Preliminary results found that Miscanthus can be stored as silage, especially with additive application, with negligible dry matter losses. Biomethane potential tests are ongoing. The research aims to determine if early harvested and ensiled Miscanthus is a viable substitute for maize in anaerobic digestion plants.

1. #adrdforum @adbioresources
CARLY WHITTAKER
AGRICULTURE SYSTEMS SPECIALIST, ROTHAMSTED RESEARCH
TESTING THE BIOMETHANE
POTENTIAL OF
MISCANTHUS

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…

5. Background

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?

13. The Experiment

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/