Effect of incineration temperature on phosphorus availability in bio-ash from manure

In the near future phosphorus (P) will be a limited resource in high demand. This will increase the incentives for recycling P in animal manure. In this study the dry-matter-rich fraction from slurry separation was incinerated and the P availability of the ash fraction examined. The aim was to adjust incineration temperature to support a high plant-availability of P in ash. The plant-availability of P was approximately halved when the incineration temperature was increased from 400 to 700 degrees C. This decrease in plant-availability was probably due to the formation of hydroxyapatite. Incineration temperatures should therefore be kept below 700 degrees C to ensure a high fertilizer efficiency of P in ash. This may conflict with the energy production, which is optimal at temperatures above 800 degrees C. An alternative to incineration may therefore be thermal gasification of the dry-matter-rich fraction, which can be carried out efficiently at lower temperatures.