Recycling phosphorus by fast pyrolysis of pig manure: Concentration and extraction of phosphorus combined with formation of value-added pyrolysis products

In order to recycle phosphorus from the livestock chain back to the land, fast pyrolysis of concentrated pig manure at different temperatures (400 °C, 500 °C, 600 °C), was undertaken to concentrate the phosphorus in the char fraction for recovery. Results show that 92%–97% of the phosphorus present in the pyrolysis feedstock ends up in the char fraction, while 60%–75% of that can be directly leached as ortho-phosphate, and 90% as total phosphorus. After char combustion, 100% of the phosphorus present can be leached as ortho-phosphate from the ash. Yields, heating values, and properties of the pyrolysis products have been analyzed. Expressed per tonne of fresh pig manure, the char phosphorus value is estimated at 0.81 € t−1–0.86 € t−1, energy application value at 2.4 € t−1–3.6 € t−1 (liquid organic phase) and 0.5 € t−1–0.7 € t−1 (char), and the fertilizer value of the aqueous phase at 0.10 € t−1–0.18 € t−1. Including costs for energy requirement, solid–liquid separation, and drying, pyrolysis costs are estimated around 0.4 € t−1–4.4 € t−1 for pig manure. It is concluded that pyrolysis costs compare positively with pig manure transportation costs of 0.06 € t−1 km−1, while it also offsets phosphorus extraction from the rapidly depleting phosphate rock.