Residual perfluorochemicals in the biochar from sewage sludge

Biochar has been recently considered as a candidate for soil amendment and soil remediation. Some pollutants have been screened in the biochar for safety purposes except for perfluorochemicals (PFCs). In this study, the contamination of biochars from plant residues and sewage sludge with perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) was examined. The total residual concentrations of PFOA and PFOS in the sludge biochar were 15.8-16.9 ng/g and these values did not decrease significantly after pyrolysis. On the other hand, these PFCs were not found in the biochar from plant sources. In conclusion, the use of the sludge biochar in the agricultural environment should be re-evaluated, since the concentrations of PFCs in the sewage sludge showed no significant decrease after thermal process.