Untapped potential: phosphorus recovery and reuse options from livestock manure and rendering by-products in the EU-27

Mismanagement of the animal by-products (ABPs) pig slurry, poultry manure and rendered by-products poses serious environmental problems. The need to reduce environmental impacts such as eutrophication caused by livestock farming has prompted European Union (EU) policymakers to introduce policies and strategies for more sustainable management of nitrogen (N) and phosphorus (P) and to improve the recirculation of P in agricultural systems. The above-mentioned ABPs represent an important source of phosphorus for reuse purposes. As a result, there is increasing interest in developing and promoting treatment processes and technologies that sustainably transform ABPs into valuable resources for use as agricultural inputs. This study explores the potential of recirculating P from pig slurry, poultry manure, and rendered by-products through existing treatment processes and technologies that convert ABPs into nutrient-balanced bio-based products (BBPs) such as compost, biochar, ash, struvite, bone ash, and animal bone char. Based on data obtained from relevant literature and databases, we computed the amount of manure and rendered by-products generated annually within the EU 27 from pig slurry, poultry deep litter, and slaughterhouse wastes, and the P derived from these ABPs including the amount of plant-available P in the BBPs. We also analyzed the application rate of the different BBPs in relation to the commonly applied mineral P-fertilizer diammonium phosphate (DAP). The results show that pig slurry and poultry deep litter are important sources of P in the EU-27, yielding annual P output averages of 170,000 tonnes from pig slurry, and 1,067,000 tonnes from poultry deep litter. Furthermore, our modeling shows that the field application rate of animal bone char (ABC) (74–131 kg/ha/yr) is highly comparable with that of traditional DAP (77–107 kg/ha/yr). This is an indication that ABC is an attractive and promising P-fertilizer option to consider from an environmental standpoint in the development of a more sustainable and circular agricultural system that does not depend exclusively on imported inorganic P-fertilizers. However, innovative incentives, techniques, and policies are needed to overcome economic and technical challenges affecting the introduction of ABC to the market.