Page 29 - European Energy Innovation - Autumn 2016 publication

Autumn 2016 European Energy Innovation 29
250 kg CO2eq of avoided emissions from
manure storage under conventional
practice (being higher than the CO2eq
reduction when only looking at the
renewable energy component!). As
indicated, annually 1.27 billion tonnes
of manure are produced in Europe,
offering both a burden as well as a
huge potential. Member states such
as Denmark have indicated they aim
for 50% of manure being digested by
2020 before being spread on land.
We estimate that throughout Europe
approximately 3.3% of all manure is
being digested, equalling ALREADY
avoided GHG emissions of 10.5 million
tonnes of CO2eq. If we were to move
to a level of 33%, the avoided GHG
emissions would amount to 105 million
tonnes of CO2eq. The GHG emission
abatement by avoided emissions when
collecting manure and converting it to
energy, indicates that this technology
can significantly outperform other
renewable energy approaches when
scoring against tonnes CO2eq per MWh
energy.
Biofertilizer production
Biogas installations do not only
generate energy but also produce
digestate. This is the residual part of
organic matter treated by AD, and is
rich in plant available nutrients. The
microbial processes which convert
biomass into bio-energy, also convert
mineral nutrients (N, P, K, …) to a
more plant available form. When
substituting synthetic mineral fertilizer abatement via sequestration in the
N by mineral nitrogen from biobased
renewable sources, GHG emissions can
be reduced by up to 6 kg CO2eq per
kg mineral N replaced (FP-7 Improved
Nutrient and Energy Management
through Anaerobic Digestion;
www.inemad.eu). In the EU-28, current
* EBA – European Biogas Association, Rue d’Arlon 63, 1040 Brussels, Belgium
a Ghent University, Coupure Links 653, 9000 Ghent, Belgium
b AKB - Austrian Biogas Association, Landstraße 11, 4020 Linz, Austria
c CzBA - Czech Biogas Association, Na Zlaté stoce 1619, 370 05 České Budějovice, Czech Republic
www.europeanenergyinnovation.eu
synthetic mineral N use corresponds
with 11 million t synthetic N, leaving
a huge potential for GHG reduction
when moving to a circular approach for
mineral N fertilizer use.
CARBON SEQUESTRATION
In addition to mineral fertilizers which
can be refined / extracted from biogas
operations, also the residual organic
fraction has considerable value as a
soil enhancer. The fraction which resists
microbial breakdown in an AD reactor
is considered to be recalcitrant and
adds to the soil organic matter and
therefore sequesters carbon from the
anthropogenic C-cycle. On average
(based on product degradability),
approximately 30-50% of organic
matter is not broken down in the
reactor. Subsequently, in the soil a
fraction will break down and mineralise
in the first year whereas a significant
portion will resist humification and
can rightfully be considered as a kind
of C-sink. At the moment, each year
approximately 237 million t digestate
is produced in the EU and used as an
organic soil enhancer. Which portion
of the organic carbon in digestate
could be considered as recalcitrant to
mineralisation over prolonged time
periods and which could therefore be
argued as being removed from the
anthropogenic C-cycle, would require
further assessment. Nevertheless,
the pathway in which digestate and
AD contribute to CO2eq emission
soil is evident from a qualitative
perspective. COP21 should encourage
countries to implement soil organic
carbon restoration plans, increasing the
current soil organic carbon from <2%
to ~ 3% AND to take into account the
net difference as sequestered carbon.
BIOGAS
Carbonate buffer capacity
Additionally, the microbiological
biogas process produces CO2eq and
CH4 in secluded tanks, the CO2eq is
continuously converted in significant
amounts to carbonate and precipitated
to CaCO3, MgCO3 which itself increases
the chemical buffer capacity and
provides the digestate endproduct
with liming characteristics. This carbon
is not yet taken into account but
provides a consistent sink for carbon
sequestration as organic carbon is
firstly converted to CO2eq and finally to
CaCO3, MgCO3 being thus successfully
removed from atmospheric carbon.
Under natural withering conditions
carbonates can be re-released into
the atmosphere as CO2. However, the
rate at which this occurs can be lower
than the rate of annual addition of
carbonates via consistent fertilization
with digestate (derivatives). Further
research is therefore required to
identify the significance of this
potential contribution.
In conclusion, AD has four ways of
reducing GHG emissions of which
only the replacement of fossil fuels
is well known and considered. The
abovementioned additional GHG
reductions should be fully
recognized and accounted for in
national action plans to reduce GHG
emissions and to make European
agriculture more sustainable. This
also implies that the AD business
model could and should enjoy
benefits coming out of the European
Trading System (ETS) on CO2eq
certificates in reflection of the logic
that this technology reduces more
GHG emissions than can merely be
attributed to the substitution of fossil
energy by renewable energy. l