LCA and Risk Assessment of Recycled Phosphorous Fertilisers

Summary

An efficient phosphorus (P) recycling from urban areas is becoming an increasing issue due to the scarcity of natural P deposits. In order to assess the environmental performance of different approaches of P recycling, a LCA assessment and risk assessment studies were carried out. Generally, we found the supply of recycled P-fertilisers (RPFs) to be competitive as compared to conventional sources in terms of LCA results analysed in this contribution: per kg P and with exclusion of infrastructure processes, the highest abiotic depletion potential is shown for conventional mineral fertilisers based on phosphate rocks due to the finite mineral P resources. For fossil primary energy demand, the recycled fertilisers (struvites and an ash-based fertiliser analysed) had highest impacts per kg P. Relatively high acidification and eutrophication potentials
from the supply of P-fertilisers are related to composts, triple-superphosphate and struvites. For the global warming potential per kg P, compost presents the worst results again. However, if co-products of organic fertilisers are considered (i.e. N- and K-contents and the humus sequestration potential), most organic fertilisers are in advantage for a number of indicators – with the exception of conventional composting. The low emission compost and the stabilised sewage sludge present moderate to good overall results. The best relative results for all indicators were found for biogas digestate.
To assess the risk of soil contamination related to the long-term application of RPFs, accumulation scenarios in soil were calculated with a mass balance approach for the potentially toxic elements (PTEs) Cd, Cr, Cu, Ni, Pb, and Zn and for the persistent organic pollutants (POPs) polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH) and polychlorinated dibenzodioxins and dibenzofurans (PCDD/F) in composts, digestates and other RPFs derived from sewage sludge For all calculations, a fertiliser application over 200 years equivalent to 11 kg P ha-1 yr-1 was assumed. Dependent on PTE mobility in soil due to pH and precipitation excess F, an accumulation or depletion compared to the soil background values was found. Highest accumulation was found in scenario pH 7 F 0,1 m yr-1, lowest in scenario pH 5 F 0,3 m yr-1. Fertilisers like composts, with low P content compared to PTE load, had a higher accumulation potential than fertilisers like struvite, meat and bone meal, sewage sludge ash, sewage sludge and digestates, rock phosphate and triple super-phosphate. Only Cd accumulation with TSP was higher than that with compost. For POPs no accumulation risk in soil was found.