Enhanced sorption of polycyclic aromatic hydrocarbons by soil amended with biochar

Purpose Polycyclic aromatic hydrocarbon (PAHs) are ubiquitous pollutants in agricultural soils in China. Biochar is the charred product of biomass pyrolysis, which is widely applied to soils to sequestrate atmospheric carbon dioxide and guarantees a long-term benefit for soil fertility. Knowledge about the impacts of various biochars on soil sorption affinity remains obscure. In this study, we evaluated the effects of various biochars on PAHs sorption to biochar-amended agricultural soil. Materials and methods Biochar of pine needle were produced under different pyrolytic temperatures (100°C, 300°C, 400°C, and 700°C, referred as P100-P700) and inputted into a paddy soil with various content. A batch equilibration method was used to determine sorption of PAHs (naphthalene, phenanthrene, and pyrene) in biochar amendment treated and untreated soil. The effects of biochar on PAHs sorption in biochar-amended soil were discussed. Results and discussion Biochars impose different effects on PAHs sorption by biochar-amended soil. P100 added to soil increased the linearity of sorption isotherm due to the linear-type isotherm of P100. While the nonlinearity of sorption isotherm for P300, P400, and P700 amended soil were increased with the increase of biochar content in soil. Biochar produced under high pyrolytic temperature demonstrated high efficiency in improving the sorption affinity of biochar-amended soil, and the total sorption were largely controlled by biochar when P300 content was larger than 0.5%, and P400 and P700 content above 0.1%. The predicted sorption of soil amended with P100 and P300 was consistent with their experimental values. However, for P400 and P700 amended soil, the actual sorption was lower than the predicted. Conclusions The results shown that added biochar into soil may enhance the sorption of PAHs to soil, thus provide a theoretical reference to apply biochar to mitigating the PAHs-contaminated soils through transferring PAHs from soil to biochar.