Formation and toxicity of polycyclic aromatic hydrocarbons during CaO assisted hydrothermal carbonization of swine manure

Abstract

The effects of temperature and CaO introduction on polycyclic aromatic hydrocarbons (PAHs) contents, distribution patterns and toxicity of the products from hydrothermal carbonization (HTC) of swine manure (SM) were investigated in this study for the first time. The results indicated that increasing temperature decreased total PAHs content of the hydrochar, while the PAHs toxicity firstly decreased and then increased during HTC of SM. For the aqueous product, the total PAHs content and toxicity gradually decreased with increasing temperature. CaO introduction during HTC of SM significantly suppressed the PAHs formation and promoted the transformation from higher molecular weight PAHs into lower molecular weight PAHs in HTC products, resulting in the remarkably decreased content and toxicity of PAHs. The lowest total PAHs content (1428.57 μg/kg) and TEQ value (21.33 μg/kg) of the hydrochar were obtained by 15% CaO introduction at 200 °C and 180 °C, respectively, and compared to SM, they were decreased by 73.73% and 79.51%, respectively. Moreover, 3-ring PAHs were the predominant PAHs in HTC products regardless of CaO introduction. The present study demonstrated that CaO assisted HTC at temperature lower than 220 °C was effective to reduce the total content and toxicity of PAHs in SM, and the prepared hydrochar was a promising soil amendment in view of the elimination of PAHs toxicity.

Keywords: CaO introduction; Hydrothermal carbonization; Polycyclic aromatic hydrocarbons; Soil amendment; Swine manure.