Polycyclic aromatic hydrocarbons in biochar originated from pyrolysis of aseptic packages (Tetra Pak®)

Abstract

Determination of the total yield of polycyclic aromatic hydrocarbons (PAHs) and their derivatives in a Tetra Pak® biochar was the leading target of this study. It was also evaluated the toxicity of Tetra Pak® biochars originated from pyrolysis performed at different temperatures. The relationship between the pyrolysis temperature and the yield of PAHs contained in Tetra Pak® biochars was also investigated. The material (Tetra Pak® packages, aseptic type) was decomposed in a laboratory pyrolysis reaction unit at different temperatures (400 °C, 500 °C, 600 °C, 700 °C). The concentrations of PAHs in Tetra Pak® biochars were determined using the method of pyrolysis gas chromatography combined with mass spectrometric detection. The toxicity of Tetra Pak® biochars was evaluated by Sinapis alba test and calculating of toxic equivalents.The total PAHs concentration in Tetra Pak® biochars oscillated between 79.6 mg/kg and 173.0 mg/kg. The measured concentrations of 16 priority PAHs U.S. Environmental Protection Agency (US EPA) reached the range from 38.4 mg/kg to 73.7 mg/kg. The yields of methylated derivatives of Tetra Pak®-biochar-borne PAHs varied from 5.2 mg/kg to 77.1 mg/kg. A phytotoxicity index of Sinapis alba has shown that biochar produced at temperatures above 500 °C is more likely to have a stimulating effect, supported by the leaching of Ca after the thermal decomposition of calcite and water extractable organic carbon. The stimulating effect of the addition of Tetra Pak® biochar increases with the decreasing concentration of biochar-borne PAHs. Given the financial cost and the minimisation of environmental risk, the addition of biochar in the range of 5–10% can be recommended.