LCA Food 2012 in Saint Malo, France! - Manifestations et colloques ...

PARALLEL SESSION 6C: POULTRY AND PORK PRODUCTION SYSTEMS 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
3. Results and discussion
3.1. Main model
A comparison of the treatment scenarios with the reference scenario is done for four impact potential
categories. The reference scenario is set to 100%. For the treatment scenarios, values higher than 100% imply
that the environmental impact is higher in the treatment scenario than in the reference scenario. Figure 1
provides an overview of the relative climate change potential. The screw press with composting scenario has
an impact potential that is 11.5% higher than the reference scenario due to CO2 (24.2 kg CO2-eq), CH4 (33.1
kg CO2-eq), and N2O (2.7 kg CO2-eq), emissions during the composting process. All other treatment scenarios
have a lower global warming potential than the reference. The decanter centrifuge scenario show the
lowest impact potential.
All treatment scenarios show a lower freshwater eutrophication potential than the reference scenario, see
Figure 1. For the two screw press scenarios, this reduced impact potential is approximately 24% smaller than
in the reference, while for the decanter centrifuge with ammonia stripping scenario, this reduced impact potential
is approximately 55% smaller than in the reference.
Application of phosphorus from the liquid fraction in the centrifuge scenario is lower than the plant-need.
71% of the phosphorus in slurry ends up in the solid fraction after centrifuge separation. Consequently, 29%
of the initial phosphorus ends in the liquid fraction. Nitrogen separation is less efficient, resulting in a relatively
larger share of nitrogen in the liquid fraction compared to phosphorus. As field application is assumed
to follow application limit of 170 kg N ha -1 yr -1 for nitrogen, a smaller amount of phosphorus in the liquid
fraction is spread in the centrifuge scenario. Another explanation for the negative contribution to freshwater
eutrophication for the two centrifuge scenarios is that the production of mineral fertiliser contributes to
freshwater eutrophication. The production of mineral phosphorus fertiliser is replaced in the scenarios where
the solid fraction is applied to fields that are low in phosphorus. In the decanter centrifuge scenarios, a large
share of phosphorus is in the solid fraction, 71%, and thus replacing 0.45 kg P2O5 (mineral phosphorus fertiliser).
After screw press separation, only 17% of initial phosphorus is in the solid fraction, implying a replacement
of 1.95 kg P2O5 (mineral phosphorus fertiliser).
Looking at Fig. 1, it can be seen that all treatment scenarios have a lower contribution to marine eutrophication
than the reference scenario. In the ReCiPe2008 method, marine eutrophication potential is calculated
from the emissions of nitrogen, because growth in saltwater bodies is assumed to be limited by nitrogen.
Reductions range from 29% less for the screw press with composting scenario to 39% for the centrifuge with
ammonia stripping scenario. This is mainly caused by the assumed mineral fertiliser replacement efficiency
for the different slurry fraction. With 45%, the lowest replacement efficiency is assumed for the screw press
with composting scenario, while the highest is assumed for the stripped ammonia, with 100%.
The relative acidification potential ranges from 86% for the centrifuge with ammonia stripping scenario,
to 102% for the screw press with composting scenario. The main contribution in all scenarios is caused during
storage under the partly-slatted flours in the pig housing. As the storage during housing is similar in all
scenarios and treatment first takes place after this stage, differences in acidification potential for the scenarios
are mainly caused after field application of the slurry. For the centrifuge with ammonia stripping scenario,
emissions during treatment are higher than in any other scenario due to increased pH. However, this
increase during treatment is more than compensated for after field application, leading to a net reduction in
ammonia loss from the complete stripping process. The increased acidification potential in the screw press
with composting scenario is due to the addition of rape straw during composting, increasing the total amount
of nitrogen.
A noticable difference between this research and that of others is that biogenic carbon is included in the
analysis in this study but not in the others (De Vries et al., 2012; Lopez-Ridaura et al., 2009; Prapaspongsa et
al., 2010). Both De Vries et al., (2012) and Prapaspongsa et al., (2010) show a negative contribution to climate
change field, which implies that the use of mineral fertiliser has a higher impact on climate change than
the use of pig slurry. Lopez-Ridaura et al., (2009) and the current research show the opposite.
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