In relation to the use of non-renewable energy the two scenarios
strongly differ. In the treatment scenario there is a net consumption
of energy, especially during the treatment process (Fig. 4), whereas
the transfer scenario represents an energy saving strategy, as the
energy needed for the production and transport of avoided chemical
fertilisers is larger than that needed for the transport and
injection of slurry (Table 4). In the treatment scenario most energy
consumed is in the form of electricity for the treatment process
itself which, in the French situation, comes mainly from nuclear
power plants. Oil in the form of diesel is also an important source of
energy used for transport of slurry and compost and for the
construction of the treatment station. In the transfer scenario, most
energy consumed is in the form of diesel during the transport of
slurry and its injection, however, energy savings from natural gas
used for the production and transport of fertilisers are higher. In
fact, for a slurry with the characteristics of that used in this study
(i.e. from finishing pigs, Table 1), a transport distance of up to 87 km
for its injection into crop land would allow maintaining an energy
balance close to equilibrium.