**1. Introduction**

The number of small-scale (< 200 kW electrical capacity) wood gasifiers used for electricity and heat provision in Central Europe is increasing. After the wood gasification process, about 10% of the dry-mass of the wood feedstock input are left in form of wood gasification residues [1] consisting of mixture of char and ash. Inspired by the Terra preta phenomenon and the intention to generate own humus rich black earths [2], especially farmers are interested in the opportunity to use the carbonaceous and nutrient-rich gasification residues produced by their own gasifiers for farm fertilizer production, soil amelioration and for carbon sequestration [3].

However, gasification residues are known for their high content in polycyclic aromatic hydrocarbons (PAH) [4]. PAH are carcinogenic, persistent, accumulate in organisms and partly inhibit reproduction [5]. Due to that, gasification residues with very high PAH contents need to be classified as hazardous waste. As a moderate increase in temperature substantially increases the vapor pressure of PAH, thermal processes can be used to volatize and subse‐ quently remove PAH from background matrixes [6]. To reduce the PAH content in gasification residues, a thermal process – the so called PAH volatilization unit has been developed by a German wood gasifier manufacturer. In the following, a critical assessment of the functional efficiency of this patented process is described.

The research work was carried out with the objective to evaluate the effectiveness of the PAH volatilization unit in reducing the PAH content in gasification residues. This objective was chosen to better assess the environmental suitability of using gasification residues as soil amendment. Our working hypothesis was that it is possible to technically reduce the PAH content in gasification residues to a level which allows for an agricultural use of the gasification

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residues in line with the soil protection regulations in Germany. As a precondition for this evaluation, the suitability of the analysis methods DIN 13877:A and DIN 13877:B for the determination of the PAH content in wood gasification residues had to be checked. Based on the results of [7], our working hypothesis in this regard was that analysis method DIN 13877:B would be more suitable for the analysis task as compared to analysis method DIN 13877:A.
