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
566
Life cycle assessment of pig slurry treatment technologies
M. ten Hoeve 1,* , S. Bruun 1 , L.S. Jensen 1 , N.J. Hutchings 2 , R. Jensen 2
1 University of Copenhagen, Faculty of Life Sciences, Department of Agriculture and Ecology, Thorvaldsensvej 40, 1871 Frederiks-
berg C, Denmark.
2 Aarhus University, Department of Agroecology, Blichers Allé 20, 8830 Tjele, Denmark.
Corresponding author. E-mail: mtho@life.ku.dk
ABSTRACT
Animal manure management is associated with negative impacts on global warming, acidification and eutrophication of ecosystems.
In the current study an LCA is used to assess the environmental impacts of treatment of 1000 kg of slurry ex-animal of five different
technologies. These technologies are (a) direct land application (reference scenario), (b) separation by mechanical screw press, (c)
screw press separation and composting of the solid fraction, (d) separation by decanter centrifuge, and (e) decanter centrifuge separation
with ammonia stripping of the liquid fraction. In all separation scenarios, the liquid fraction was land applied close to the farm
and the solid fraction was transported and land applied 100 km from the farm. In general, the treatment technologies analysed in this
LCA show environmental impact potential reduction compared with the reference scenario. The decanter centrifuge scenarios have
equal or lower impact potentials than the screw press scenarios. Relative ranking of scenarios does not change after the sensitivity
analysis, where field emission factors for N2O, NH3 and P were varied within the range observed in literature. Choice of the technology
to implement in any given situation depends on the environmental problem in focus.
Keywords: life cycle assessment, pig slurry, slurry treatment technologies
1. Introduction
Large amounts of animal manure are produced in Europe and its management is associated with a number
of environmental impacts. Impact categories that are mainly affected by animal manure management are (a)
global warming potential, caused by methane and nitrous oxide emissions, (b) acidification potential, induced
by ammonia emissions, and (c) eutrophication potential caused by nitrogen and phosphorus emissions.
These impacts are accentuated because an increasing share of agricultural land in Europe receives excessive
amounts of animal manure. These so-called hotspot areas are characterised by high livestock densities
and insufficient land for manure application. This has resulted in phosphorus surplus in these areas and associated
risks for losses to the environment. In other areas, agricultural fields do not receive sufficient amounts
of nutrients from manure and farmers need to apply mineral fertilisers to their fields. Non-renewable natural
resources like phosphate rock, oil and natural gas, are used for the production of mineral fertiliser and there
are considerable environmental emissions, such as CO2 and phosphate leaching, related to the extraction,
manufacturing and use of these fertilisers. In order to decrease the consumption of mineral fertiliser and
avoid losses from areas with excessive availability of animal manure, geographical redistribution of animal
manure needs to improve.
To enhance nutrient re-distribution, slurry treatment technologies have been developed that focus on the
separation of slurry into a solid and a liquid fraction. The liquid fraction contains most of the easily available
nitrogen but less than half of the phosphorus, so is mainly valued as a nitrogen fertiliser. However, the high
water content in the liquid fraction makes the fraction relatively heavy and less suitable for long distance
transportation. Agricultural land nearby the farm often has been treated with slurry for multiple years, which
implies that phosphorus concentrations in the soil are already sufficiently high to supply the crop demand.
The solid fraction is more transportable, due to its relatively low water content. It has a high concentration of
slowly-available nitrogen and phosphorus, so is mainly valuable as a phosphorus fertiliser. Additional technologies
that are developed to avoid environmental impacts include ammonia stripping from the liquid fraction,
which reduces emissions of ammonia, various technologies for energy extraction and upgrading of the
solid fraction such as composting which may improve the solid fraction as a soil amendment.
The objectives of this study are to determine environmental impact potentials of slurry treatment technologies
in a Life Cycle Assessment (LCA) and to compare impact potentials of treatment technologies with
a reference.
2. Methods
2.1. Model description
The LCA is based on information from literature research. The LCA itself was conducted by using the
GaBi software (www.pe-international.com). The functional unit that forms the basis for the assessment is the
handling of 1000 kg of slurry excreted by pigs. Emissions from slurry, liquid and solid fractions were ana-