Evaluation of sewage sludge and slow pyrolyzed sewage sludge-derived biochar for adsorption of phenanthrene and pyrene

The present study investigated the sorption of phenanthrene (PHE) and pyrene (PYR) by sewage sludges and sewage sludge-derived biochars. The organic carbon normalized distribution coefficient (log KOC for Cw = 0.01 Sw) for the sewage sludges ranged from 5.62 L kg−1 to 5.64 L kg−1 for PHE and from 5.72 L kg−1 to 5.75 L kg−1 for PYR. The conversion of sewage sludges into biochar significantly increased their sorption capacity. The value of log KOC for the biochars ranged from 5.54 L kg−1 to 6.23 L kg−1 for PHE and from 5.95 L kg−1 to 6.52 L kg−1 for PYR depending on temperature of pyrolysis. The dominant process was monolayer adsorption in the micropores and/or multilayer surface adsorption (in the mesopores), which was indicated by the significant correlations between log KOC and surface properties of biochars. PYR was sorbed better on the tested materials than PHE.