Life cycle assessment of biological pig manure treatment versus direct land application - a trade-off story

Excess manure can have two common fates: to be exported and applied to agricultural land, or to be treated, possibly with resource recovery (i.e. energy and/or nutrients). In this study, the environmental performance of a treatment system of pig manure (centrifugation and subsequent biological nitrogen removal from the liquid fraction and composting of the solid fraction) has been assessed using life cycle assessment (LCA) with the ReCiPe method to assess environmental impacts at midpoint and endpoint level. Such treatment system is typical for Flanders (Belgium), a region characterized by a manure excess. The performance of this treatment-scenario has been compared to the direct field application of untreated manure (no-treatment-scenario) to gain insight in the environmental trade-offs between them. The hotspots dominating the environmental impact for manure treatment were the field application of compost and the effluent from the biological treatment, and the electricity needed to run the treatment facility. The substitution of synthetic fertilizers played an important role in both scenarios (mitigation of potential damaging impacts). The comparison between the two manure management scenarios showed that the treatment scenario scores better in some categories and vice versa. Manure treatment does prevent marine eutrophication and must be carried out in nitrate-vulnerable zones, such as the studied region of Flanders. Finally, the use of single score through normalization and weighting of midpoint impacts was evaluated. This underscores a policy direction towards manure treatment, but this message should be interpreted with care as the approach of normalization and aggregation can be questioned.