RAMIRAN International ConferenceLarge amounts of pig slurry are produced each year in Portugal leading to environmental problems such as water
and air pollution. Previous studies have reported that livestock production is the main source of anthropogenic
ammonia (NH3) emissions in Europe (Kai et al., 2008) and an important source of greenhouse gases (Weiske and
Petersen, 2006). Effluent treatment has been promoted to improve slurry management and to reduce its
environmental impact (Sommer and Hutchings, 2001, Fangueiro et al., 2008a). Solid-liquid separation of slurry is a
useful tool at the farm level producing valuable fractions, a liquid that can be used for direct fertilisation and a solid
fraction that can be composted (Fangueiro et al., 2008b). Alternatively, acidification of slurry has been proposed to
reduce ammonia (NH3) emissions during storage and field application (Kai et al., 2008). Previous works
(Misselbrook et al., 2005; Fangueiro et al., 2008a) reported that higher NH3 emissions occurred during storage of
liquid fraction of slurry or manure with low dry matter content, probably due to a reduced crust formation that
decreases NH3 emissions. Hence, acidification of the liquid fraction of slurry is strongly recommended. Slurry
acidification is common practice in The Netherlands and Denmark (Schils et al., 1999; Eriksen et al., 2008) but this
technology still needs to be improved to avoid hazards. It is expected that this technology will be used in more
countries since the European Directive (2001/81/CE) demands a decrease of atmospheric pollutants such as NH3:
targets for lower NH3 emissions have been already set in Spain (Castrillon et al., 2009). Nevertheless, the
acidification process leads to significant carbon dioxide (CO2) emissions (Vandré and Clemens, 1997). Such CO2
release is problematic when a closed system of slurry acidification is used (when acidified slurry is flushed back to
pig houses) since it may lead to foam formation (Vandré and Clemens, 1997; Borst, 2001). Nevertheless, Fangueiro
et al. (2010) reported that acidification of slurry or derived fractions led to a decrease in CO2 emissions following
soil addition relative to non acidified materials.
The aim of the present work was to measure the CO2 emissions during the acidification process of the
liquid fraction of pig slurry and its subsequent impact during storage and after soil incorporation
