Page 29 - European Energy Innovation - Autumn 2016 publication
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Autumn 2016 European Energy Innovation  29


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

* 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
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