The document discusses the use of digestate from anaerobic digestion in agriculture. It notes that digestate comes from a variety of substrates and its composition can vary significantly depending on the substrate and digestion process. Digestate is commonly applied as fertilizer due to its nutrient content. However, its use faces challenges related to quality standards, environmental effects, and nutrient management. The document explores these challenges and the effects of digestate application on soil properties like pH, organic matter content, and microbial activity. While digestate application can promote soil health, the impacts are complex and depend on the digestate type, soil characteristics, and agricultural management practices. More research is still needed to understand these relationships.

1. Digestate
u*liza*on
in
agriculture
(a
holis*c
analysis)
E.
Hartung
Ins*tute
of
Agricultural
Engineering
-­‐
Kiel
University
Agenda:
• Mo+va+on
&
Challenges
• Substrate
variability
&
AD
effects
• Fer+lizer
use
&
effect
on
Soil
proper+es
• GHG
&
…
• “Other”
u+liza+on
• Conclusions

2. Mo*va*on
Development
biogas
plants
in
Germany
plants
installed
electrical
output
(GW)
Substrate
Input
of
German
biogas
plants
48
%
NaWaRo
2
%
bio-­‐waste
6
%
residual
materials
44
%
solid
&
fluid
manure
Substrate
Output
/
Digestates

3. “Mo*va*on”
-­‐
2
Statements
Today,
the
general
op*ons
for
the
digestate
use
are:
• landscaping,
• combus*on
• and
fer*liza*on
(mostly
in
agriculture),
the
last
of
which
is
oVen
the
most
aWrac*ve
op*on
due
to
organic
and
nutrient
content
(Hahn
&
Hoffstede,
2010).
The
common
applica*ons
of
digestate
include
• fer*lizers,
• growing
media,
• soil
improvers,
• combus*on
and
• landfill
(Jansen,
2011).

4. Challenges
Origin,
composi*on
&
pre-­‐/post-­‐treatment
of
digestates
/
type
of
diges*on
process:
• nutrients,
pH
&
heavy
metals,
organic
dry
maWer
content
• chemical,
physical
&
biological
contaminants
Legisla*on
of
digestate
u*liza*on
in
agriculture
as
fer*lizer:
• quality
criteria
&
threshold
defini*ons
• applica*on
limits
(*me
periods,
maximum
nutrient
loads,
minimum
storage
capaci*es,
etc.)
• fer*liser
applica*on
plan/management
&
applica*on
techniques
Environmental
effects
of
applied
digestates:
• effects
on
soil
proper*es,
• odour,
ammonia
&
GHG-­‐emissions,
pathogens
• leaching
of
nutrients
&
contaminants
Substrate
Quality
Legisla+ve
Limits
Environmental
Effects

5. Challenges
Addi*onal
challenges:
• area
used
for
the
cul*va*on
of
energy
crops
is
in
general
not
enough
for
the
applica*on
of
the
digestates
-­‐>
high
demand
for
“addi*onal
applica*on
areas”
• low
dry
maWer
(poor
transportability)
and
low
&
strongly
varying
nutrient
content
• high
storage-­‐,
transporta*on-­‐
and
applica*on
–costs
• high
pH,
instable
fer*lising
effect,
loss
of
nutrients
Substrate
Quality
Legisla+ve
Limits
Environmental
Effects
Nutrients
present
in
plant
&
animal
products
Lukehurst
et
al.,
2010;
hWp://www.en.esbjerg.aau.dk/digitalAssets/80/80457_task37_digestate_brochure9-­‐2010.pdf

6. Substrate
variability
Substrates
used
for
biogas
produc*on
(can)
include
(Al
Seadi,
et
al.,
2008):
• Animal
manure
and
slurry;
• Agricultural
residues
and
by-­‐products;
• Diges*ble
organic
wastes
from
food
and
agro
industries
(vegetable
and
animal
origin);
• Organic
frac*on
of
municipal
solid
waste
(MSW)
and
from
catering
(vegetable
and
animal
origin);
• Sewage
sludge
(WWTP);
• Dedicated
energy
crops
(e.g.
maize,
miscanthus,
sorghum,
clover);
and
• Organic
waste
from
other
industries
e.g.
paper,
leather
and
tex*le
industries.
Lukehurst
et
al.,
2010;
hWp://www.en.esbjerg.aau.dk/digitalAssets/80/80457_task37_digestate_brochure9-­‐2010.pdf

7. Substrate
variability
Makádi
et
al.,
2012;
hWp://cdn.intechopen.com/pdfs-­‐wm/31331.pdf

8. Substrate
variability
&
AD
effects
Due
to
anaerobic
diges*on
(AD)
part
of
the
organic
nitrogen
supplied
with
the
feedstock
is
converted
to
ammonium,
although
the
total
nitrogen
content
in
digestate
remains
the
same
as
in
the
feedstock
(Lukehurst
et
al.,
2010).
Lukehurst
et
al.,
2010;
hWp://www.en.esbjerg.aau.dk/digitalAssets/80/80457_task37_digestate_brochure9-­‐2010.pdf

9. Fer*lizer
use
&
Effect
on
Soil
proper*es
Lukehurst
et
al.,
2010;
hWp://www.en.esbjerg.aau.dk/digitalAssets/80/80457_task37_digestate_brochure9-­‐2010.pdf

10. Substrate
variability
&
AD
effects
The
amounts
of
organic
dry
maWer
and
the
carbon
content
of
digestate
are
decreased
by
the
decomposi*on
of
easily
degradable
carbon
compounds
in
digesters
(S*nner
et
al.,
2008)
Makádi
et
al.,
2012;
hWp://cdn.intechopen.com/pdfs-­‐wm/31331.pdf

11. Fer*lizer
use
&
Effect
on
Soil
proper*es
Effect
of
digestate
on
soil
pH:
• in
case
of
long
term
digestate
applica*on
monitoring
of
soil
pH
is
necessary
• soil
acidifica*on
due
to
digestates
seem
to
depend
on
soil
type/texture
• loamy
soils
will
show
rather
a
pH
decrease
compared
to
sandy
soils
Effect
of
digestate
on
soil
organic
maWer
(OM)
content:
• inconsistent
results
with
respect
to
soil
organic
maWer
decrease/increase
• tendency
that
OM
losses
duet
to
intensive
cul*va*on
of
energy
crops
can
not
be
“compensated”
by
digestate
applica*on
(limited
by
maximum
nutrient
loads)
• but
digestates
have
advantages
compared
to
the
ini*al
(input)
substrate
• higher
lignin
content
in
digestates
leads
to
increased
reten*on
*me
in
soil

12. Fer*lizer
use
&
Effect
on
Soil
proper*es
Effect
of
digestate
on
soil
organic
maWer
(OM)
content:
• inconsistent
results
with
respect
to
soil
organic
maWer
decrease/increase
• tendency
that
OM
losses
duet
to
intensive
cul*va*on
of
energy
crops
can
not
be
“compensated”
by
digestate
applica*on
(limited
by
maximum
nutrient
loads)
• but
digestates
have
advantages
compared
to
the
ini*al
(input)
substrate
• higher
lignin
content
in
digestates
leads
to
increased
reten*on
*me
in
soil
plant
material
slurry
digestates
material
dry
maLer
%
humus
reproduc+on
kg
Humus-­‐C
(t
substrate)-­‐1
straw
green
fer*lizer
cupngs
pig
caWle
fluid
VDLUFA,
2005
solid

13. Fer*lizer
use
&
Effect
on
Soil
proper*es
type
of
digestate
Percentage
of
total
N
slow
biodegradable
(humus
reproduc+on
effec+ve)
easily
biodegradable
fast
biodegradable
Liebetrau
et
al.,
2013;
hWps://www.dbfz.de/web/fileadmin/user_upload/Referenzen/Abschlussberichte/Endbericht03KB027_final_TIB_31_07_2013.pdf

14. Fer*lizer
use
&
Effect
on
Soil
proper*es
Effects
of
a
commonly
prac*ced
humus
supply
with
500
Häq
(kg
Humus-­‐C)
ha-­‐1
a-­‐1
of
different
digestates
&
composts
(1
Häq
is
equivalent
to
1
kg
of
produced
soil
carbon
due
to
humifica*on
per
t
of
supplied
substrate)
type
of
digestate
Limit
120
kg/ha
Limit
170
kg/ha
N-­‐Amount
in
kg/ha
slow
biodegradable
(humus
reproduc+on
effec+ve)
easily
biodegradable
fast
biodegradable
Liebetrau
et
al.,
2013;
hWps://www.dbfz.de/web/fileadmin/user_upload/Referenzen/Abschlussberichte/Endbericht03KB027_final_TIB_31_07_2013.pdf

15. Fer*lizer
use
&
Effect
on
Soil
proper*es
Effect
of
digestate
on
soil
pH:
• in
case
of
long
term
digestate
applica*on
monitoring
of
soil
pH
is
necessary
• soil
acidifica*on
due
to
digestates
seem
to
depend
on
soil
type/texture
• loamy
soils
will
show
rather
a
pH
decrease
compared
to
sandy
soils
Effect
of
digestate
on
soil
organic
maWer
(OM)
content:
• inconsistent
results
with
respect
to
soil
organic
maWer
decrease/increase
• tendency
that
OM
losses
duet
to
intensive
cul*va*on
of
energy
crops
can
not
be
“compensated”
by
digestate
applica*on
(limited
by
maximum
nutrient
loads)
• but
digestates
have
advantages
compared
to
the
ini*al
(input)
substrate
• higher
lignin
content
in
digestates
leads
to
increased
reten*on
*me
in
soil
Effect
of
digestate
on
microbiological
ac*vity
of
soil:
• should
be
a
sensi*ve
indica*on
of
changes
in
physical
&
chemical
soil
proper*es
• digestates
are
supposed
to
promote
microbiological
ac*vity
e.g.
due
to
higher
amounts
of
easy
degradable
carbon
• digestates
contain
growth
regulators
&
influence
enzyme
ac*vi*es

16. Fer*lizer
use
&
Effect
on
Soil
proper*es
Effect
of
digestate
on
microbiological
ac*vity
of
soil:
• should
be
a
sensi*ve
indica*on
of
changes
in
physical
&
chemical
soil
proper*es
• digestates
are
supposed
to
promote
microbiological
ac*vity
e.g.
due
to
higher
amounts
of
easy
degradable
carbon
• digestates
contain
growth
regulators
&
influence
enzyme
ac*vi*es
• But
Makádi
et
al.,
2012;
hWp://cdn.intechopen.com/pdfs-­‐wm/31331.pdf
effects
depend
very
much
on
type
of
digestate,
soil
texture,
crop
rota+on
and
fer+lizer
management,
…
;
much
more
systema+c
research
in
long
+me
experiments
are
necessary!

17. GHG
&
Ammonia
emissions
&
…
General
Ques*ons?
• focus
on
processes
&/or
applica*ons
• focus
on
whole
produc*on
chain
(e.g.
energy
&
nutrient
balances,
LCA
studies)
• which
model,
included
boundary/limi*ng
condi*ons
&
set
values
are
used
• which
assump*ons
were
made

18. GHG
&
Ammonia
emissions
&
…
Input
substrate]
CO2-­‐eq/Mg
GHG
emissions
[kg
different
fermenta*on
processes
/
facili*es
digestate
applica+on
digestate
storage
compos+ng
/
post
roo+ng
emissions
past
bio-­‐
filter
electricity
demand
BGP
&
CHP
emissions
fermenter
emissions
CHP
credit
digestate
credit
heat
recovery
credit
electricity
Balance
Liebetrau
et
al.,
2013;
hWps://www.dbfz.de/web/fileadmin/user_upload/Referenzen/Abschlussberichte/Endbericht03KB027_final_TIB_31_07_2013.pdf

19. GHG
&
…
Odour:
• diges*on
reduces
significantly
many
odour
compounds
(unpleasant
odours)
Ammonia
emissions
&
N
leaching
depends
on:
• type
of
digestate
&
nutrient
content
• storage
&
applica*on
technique,
pre-­‐/post-­‐treatment
of
digestate
• soil
type
&
soil
moisture,
crop
rota*on
&
crop
yield
• *me
&
amount
of
applica*on,
weather
condi*ons,
etc.
….
Veterinary
Safety,
Plant
pathogens
&
Weed
seeds:
• anaerobic
diges*on
(AD)
is
very
effec*ve
in
lowering
pathogen
loads
with
respect
to
veterinary
safety
• few
studies
show
a
reduc*on
poten*al
for
pant
pathogens
due
to
(mesophilic)
AD
• few
studies
show
a
reduc*on
poten*al
of
the
viability
of
weed
&
crop
seeds
due
to
(mesophilic)
AD

20. GHG
&
…
Veterinary
Safety,
Plant
pathogens
&
weed
seeds:
• anaerobic
diges*on
(AD)
is
very
effec*ve
in
lowering
pathogen
loads
with
respect
to
veterinary
safety
• few
studies
show
a
reduc*on
poten*al
for
pant
pathogens
due
to
(mesophilic)
AD
• few
studies
show
a
reduc*on
poten*al
of
the
viability
of
weed
&
crop
seeds
due
to
(mesophilic)
AD
Lukehurst
et
al.,
2010;
hWp://www.en.esbjerg.aau.dk/digitalAssets/80/80457_task37_digestate_brochure9-­‐2010.pdf

21. GHG
&
…
Veterinary
Safety,
Plant
pathogens
&
weed
seeds:
• anaerobic
diges*on
(AD)
is
very
effec*ve
in
lowering
pathogen
loads
with
respect
to
veterinary
safety
• few
studies
show
a
reduc*on
poten*al
for
pant
pathogens
due
to
(mesophilic)
AD
• few
studies
show
a
reduc*on
poten*al
of
the
viability
of
weed
&
crop
seeds
due
to
(mesophilic)
AD
Lukehurst
et
al.,
2010;
hWp://www.en.esbjerg.aau.dk/digitalAssets/80/80457_task37_digestate_brochure9-­‐2010.pdf

22. “Other”
u*liza*on
Separa*on
before
or
past
anaerobic
fermenta*on:
• separa*on
efficiency
depends
very
much
on
type
of
digestate
&
type
of
separa*on
technique
• high
investment
costs,
energy
efficiency
of
separa*on
process
needs
to
be
improved

23. “Other”
u*liza*on
Separa*on
before
or
past
anaerobic
fermenta*on:
• separa*on
efficiency
depends
very
much
on
type
of
digestate
&
type
of
separa*on
technique
• high
investment
costs,
energy
efficiency
of
separa*on
process
needs
to
be
improved
Lukehurst
et
al.,
2010;
hWp://www.en.esbjerg.aau.dk/digitalAssets/80/80457_task37_digestate_brochure9-­‐2010.pdf

24. “Other”
u*liza*on
Separa*on
before
or
past
anaerobic
fermenta*on:
• separa*on
efficiency
depends
very
much
on
type
of
digestate
&
type
of
separa*on
technique
• high
investment
costs,
energy
efficiency
of
separa*on
process
needs
to
be
improved
digestate
post
processing
(high
treatment
&
investment
costs):
• solid-­‐liquid
separa*on:
• solid
frac*on
compos*ng
-­‐>
soil
improver-­‐growing
material
(SIGM)
• liquid
frac*on
-­‐>
Liquid
fer0lizer
• stripping
(ammonium
sulphate
fer0lizer)
• pelle*zing
(fer0lizer
pellet/solid
fuel)

25. “Other”
u*liza*on
digestate
post
processing
(high
treatment
&
investment
costs):
• solid-­‐liquid
separa*on:
• solid
frac*on
compos*ng
-­‐>
soil
improver-­‐growing
material
(SIGM)
• liquid
frac*on
-­‐>
Liquid
fer0lizer
• stripping
(ammonium
sulphate
fer0lizer)
• pelle*zing
(fer0lizer
pellet/solid
fuel)
Primary
energy
demand
in
kWh/t
raw
digestate
GHG
emissions
in
kg
CO2eq/t
raw
digestate
Haverinen,
2014,
hWps://aaltodoc.aalto.fi/bitstream/handle/123456789/13544/master_Haverinen_Aleksi_2014.pdf?sequence=1

26. “Other”
u*liza*on
Separa*on
before
or
past
anaerobic
fermenta*on:
• separa*on
efficiency
depends
very
much
on
type
of
digestate
&
type
of
separa*on
technique
• high
investment
costs,
energy
efficiency
of
separa*on
process
needs
to
be
improved
digestate
post
processing
(high
treatment
&
investment
costs):
• solid-­‐liquid
separa*on:
• solid
frac*on
compos*ng
-­‐>
soil
improver-­‐growing
material
(SIGM)
• liquid
frac*on
-­‐>
Liquid
fer0lizer
• stripping
(ammonium
sulphate
fer0lizer)
• pelle*zing
(fer0lizer
pellet/solid
fuel)
• ion
exchange,
struvite
precipita*on
• membrane
filtra*on
• drying
• soil
improver
(carboniza*on,
biochar
produc*on)

27. Conclusions
• U*liza*on
of
digestates
in
agriculture
is
a
very
broad
field/topic
• Up
to
now
most
digestates
are
used
as
fer*lizer
&
effect:
• environment
• soil
proper*es
• Alterna*ve
digestate
u*liza*on
are
mostly
characterized
by
high
treatment
&
investment
costs
• Future
goals:
• Achieve
more
knowledge
on
effects
of
digestate
applica*on
• Op*mize
(automated)
side-­‐
&
plant-­‐specific
applica*on
• Improve
cost-­‐effec*ve
separa*on
and
carboniza*on
techniques
• U*lize
fluctua*on
of
renewable
energy
produc*on
for
digestate
treatment

28. Digestate
u*liza*on
in
agriculture
(a
holis*c
analysis)
E.
Hartung
Ins*tute
of
Agricultural
Engineering
-­‐
Kiel
University
Agenda:
• Mo+va+on
&
Challenges
• Substrate
variability
&
AD
effects
• Fer+lizer
use
&
effect
on
Soil
proper+es
• GHG
&
…
• “Other”
u+liza+on
• Conclusions