Effect of pyrolysis temperatures on freely dissolved polycyclic aromatic hydrocarbon (PAH) concentrations in sewage sludge-derived biochars

The aim of this study was to evaluate the effect of sewage sludge pyrolysis on freely dissolved (C-free) polycyclic aromatic hydrocarbon (PAH) contents in biochars. Four sewage sludges with varying properties and PAH contents were pyrolysed at temperatures of 500 degrees C, 600 degrees C or 700 degrees C. C-free PAH contents were determined using polyoxymethylene (POM). The contents of C-free PAHs in the sludges ranged from 262 to 294 ng L-1. Sewage sludge-derived biochars have from 2.3- to 3.4-times lower C-free PAH contents comparing to corresponding sewage sludges. The C-free PAH contents in the biochars ranged between 81 ng L-1 and 126 ng L-1. As regards agricultural use of biochar, the lower contents of C-free PAHs in the biochars compared to the sewage sludges makes biochar a safer material than sewage sludge in terms of PAH contents. (C) 2016 Elsevier Ltd. All rights reserved.