Feedstock recycling of secondary raw materials is the backbone of the Circular Economy (CE). The efficient recovery of resources, energy, along with achieving minimal environmental impact is mandatory for the successful realization of CE. Chicken manure is an interesting waste stream due to its content of nutrients, in particular of phosphorus, which makes it a suitable feedstock for fertilizer applications. However, the contamination caused by antibiotics, organic pollutants, and sanitary aspects demand the manures treatment before further recycling. Thermochemical treatment based on intermediate pyrolysis targets decentral application to produce carbonized solids for fertilizer application. This work evaluated pyrolysis char from the pyrolysis of chicken manure in comparison to the original feedstock using state-of-the-art thermal treatment, i.e., combustion in grate furnaces. The samples were evaluated in terms of chemical and mineralogical composition by applying several analytical techniques. Bio-availability of the main nutrients (NPK) was assessed by adopting standard methods. Additionally, the effect on toxicity was discussed by means of heavy metals analysis, as well as of pot tests. Results showed, that pyrolysis had a far more positive effect on nutrient availability compared to combustion, and it provided a suitable method for the thermal treatment of contaminated feedstocks.