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a b s t r a c tRecent research suggests that anthropogenic nutrient flows may have transgressed the regulatory capacity of the earth. Agrifood systems account for most of the flows, and the food supply is limited more by reducing the excessive flows than by phosphorus (P) reserves or population growth. The food supply is limited primarily by the P flow tolerated by freshwater ecosystems and next by the needed reduction in the conversion of nitrogen (N) to reactive form in fertilizer manufacture, legume cultivation and fossil fuel combustion. The required reduction in P and N flows would reduce the food supply to 250 and 710 kcal capita À 1 d À 1 , respectively, in the current agrifood systems. Dietary changes, waste prevention and nutrient recycling are parts of the necessary transformation.

All life forms require phosphorus (P), which has no substitute in food production. The risk of phosphorus loss from soil and limited P rock reserves has led to the development of recycling P from industrial residues. This study investigates the potential of phosphorus recovery from sewage sludge and manure ash by thermochemical treatment (ASH DEC) in Finland. An ASH DEC plant could receive 46-76 kt/a of sewage sludge ash to produce 51-85 kt/a of a P-rich product with a P2O5 content of 13-18%, while 320-750 kt/a of manure ash could be supplied to produce 350-830 kt/a of a P-rich product with a P content of 4-5%. The P2O5 potential in the total P-rich product from the ASH DEC process using sewage sludge and manure ash is estimated to be 25-47 kt/a, which is significantly more than the P fertilizer demand in Finland's agricultural industries. The energy efficiency of integrated incineration and the ASH DEC process is more dependent on the total solid content and the subsequent need for mechanical dewatering and thermal drying than on the energy required by the ASH DEC process. According to the results of this study, the treated sewage sludge and manure ash using the ASH DEC process represent significant potential phosphorus sources for P fertilizer production.