Main content area

Carbon dioxide as a carrier gas and biomass addition decrease the total and bioavailable polycyclic aromatic hydrocarbons in biochar produced from sewage sludge

Kończak, Magdalena, Gao, Yanzheng, Oleszczuk, Patryk
Chemosphere 2019 v.228 pp. 26-34
United States Environmental Protection Agency, bioavailability, biochar, biomass, carbon dioxide, gases, polycyclic aromatic hydrocarbons, pyrolysis, sewage sludge, temperature
Organic-solvent extractable (Ctot) and freely dissolved (Cfree) polycyclic aromatic hydrocarbons (PAHs) (US EPA 16 PAHs) were determined in biochars produced from the mixture of sewage sludge and sewage sludge and willow (8:2 or 6:4, w/w). The pyrolysis was carried out at 500, 600, and 700 °C using two different carrier gases (N2 or CO2). Addition of willow and the change of carrier gas from N2 to CO2 reduced Ctot PAHs (from 7.0 to 52%) and Cfree PAHs (15–29%) content. Co-application of willow and SSL and the use of CO2 as a carrier gas also beneficially affected the PAHs profile. The biochars produced with willow addition and/or in a CO2 atmosphere were characterized by a lower (from 9.0 to 62.8%) percentage of 3-6-ring PAHs (Ctot) than the biochars derived from sewage sludge alone in N2 atmosphere. The contribution of individual Cfree PAHs did not differ significantly between biochars. The presence of willow during pyrolysis influenced the direction of the changes in the Ctot PAH content depending on the pyrolysis temperature. For SSL alone, regardless of the carrier gas used, the content of Ctot PAHs was observed to decrease with increasing temperature, whereas in the presence of willow temperature did not affect significantly (P ≥ 0.05) the Ctot PAHs content. The change of carrier gas from N2 to CO2 increased the affinity of the biochars to PAHs as confirmed by the distribution coefficients log KTOC.