Abstract: Biochar adsorption and surfactant washing were used to remediate PAHs contaminated soil. Rice husk biochar prepared at 700 ℃ was added to examine the effect of biochar addition on the washing of PAHs by nonionic surfactant TX-100. The underlying mechanism of biochar adsorption combined with TX-100 washing was examined by simulating contaminated soil with pyrene-containing kaolin after aging. The results of enhanced washing remediation showed that when the concentration of TX-100 was 10 g·L^-1, washing time was 16 h, the ratio of solid to liquid was 1∶10, and the rotating speed was 150 r·min^-1, a desorption rate of 66.2% was obtained for the contaminated soil with PAHs concentration of 94.97 mg·kg^-1. After the rice husk biochar with 1% soil mass was added and stabilized for 14 days, the desorption rate of PAHs by TX-100 increased from 66.2% to 80.6% (P<0.05), and the desorption rate of tetracyclic PAHs was the highest (42.1%). Kaolin simulation results showed that after adding biochar 1% of soil mass for 14 days, the content of pyrene in kaolin decreased from 50 mg·kg^-1 to 27.77 mg·kg^-1. TX-100 could effectively wash out pyrene adsorbed on biochar, with desorption rate reaching 82.4%. Scanning electron microscope and spectroscopic analysis showed that biochar could adsorb TX-100, while the adsorbed TX-100 occupied part of the pores of biochar, and the absorption vibration peaks of C=O and C=C at 1600 cm^-1 and C-O-C at 1103-1025 cm^-1 were obviously weakened, which further led to the migration of PAHs from solid phase to liquid phase. Therefore, before using surfactants for washing and remediation, biochar addition can significantly improve the desorption rate of soil PAHs.

Key words: biochar, surfactant, PAHs, interface migration.