Removal of pyrene by agricultural straw-derived biochar/persulfate system via both adsorption and advanced oxidation process: performance and mechanism

The biomass in agricultural and forestry waste has a high value for resource utilization. In this study, biochar materials were prepared for treating wastewater containing polycyclic aromatic hydrocarbons (PAHs). To eliminate pyrene rather than transfer it onto the adsorbent, this study employed a chemical oxidation method to degrade pyrene using persulfate as the oxidant and biochar as the activator. When the pH of the solution was 3 and the dosage of biochar was 0.9 g/L, the biochar (BC1, BC2 and BC3) prepared from sawdust, coconut shells and agricultural straw reduced the C/C0 value to 0.12, 0.09 and 0.05 respectively, indicating that the biochar had a good adsorption effect on pyrene. BC3 was chosen to activate persulfate to degrade pyrene, and under the conditions of solution pH of 3, persulfate concentration of 10 mM, and BC3 dosage of 1.5 g/L, the C/C0 value decreased to 0.04 and the removal efficiency of pyrene was 96%. In the BC3/persulfate oxidation system, oxidative degradation played a dominant role in the removal of pyrene. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FITR) analyses demonstrated that the catalysis of persistent free radicals (PFRs) on the biochar surface was the main mechanism for the activation of persulfate to produce SO4•- for the degradation of pyrene.