Screening LCA of French organic amendments and fertilisers

Abstract

In France, agricultural recycling of organic waste is widespread, but LCIs of organic waste treatments are scarce. This work presents LCIs of the most relevant organic waste treatments yielding residual organic amendments and fertilisers, and organic residue–based industrial processes yielding commercial organic amendments and fertilisers, in France. It also presents the results from a screening LCA performed on these LCIs. LCIs were built from mainly secondary data sources. Four functional units were retained: 1 t fresh mass of final product and 1 t of N, P, or K in fresh mass. Economic allocation was applied, following the French Environment and Energy Management Agency position. The International Reference Life Cycle Data System 2011 suit for impact assessment was retained, and all impacts were expressed as single scores to facilitate comparisons. Organic wastes considered were liquid and solid manures, agro-industrial residues, sewage sludge, green wastes and harvest residues, and biowaste. Treatment steps modelled were stocking, shredding, sieving, and mixing of substrates; anaerobic and aerobic treatments; thickening, dewatering, drying, and pelletising; various biological and physicochemical treatments of phase-separated liquid fractions; and the industrial production of organic amendments and fertilisers. Comparisons were performed among products classified as amendments or fertilisers. LCIs of typical treatment routes are presented, complemented with screening life cycle impact assessment results. Dried sludge and treated solid fractions of agricultural digestates present consistently higher impacts than any other amendment, mainly due to their associated energy use, relatively low N contents, and the use of maize silage as input. These items contribute in average > 50% of the aggregated impacts. Untreated manure and slurry feature the lowest relative impacts for all functional units. Compost-based commercial organic amendments have similar impacts to other composts per t of fresh mass, but slightly lower per t of nutrients or C, due to the inclusion of additional nutrient-rich inputs. Regarding fertilisers, the impact intensity of commercial organo-mineral fertilisers and treated liquid fractions of slurry and agricultural digestate is within similar orders of magnitude. Manure-based digestates feature relatively low impacts per all functional units. Only some digestates and untreated poultry manure feature impacts similar to those of N mineral fertilisers. Energy provision and direct emissions are the main contributors to impacts in organic waste treatments. Modelling choices such as the allocation of impacts to agricultural by-products heavily influence specific impact categories, mainly climate change. Overall, these results represent a needed contribution to background data used in agricultural LCA.