Fate of organic pollutants in sewage sludge during thermal treatments: Elimination of PCBs, PAHs, and PPCPs

Abstract

The use of biochar and hydrochar, the solid by-product from thermal treatments of biomass, as organic soil fertilizers is becoming increasingly popular. However, few studies have examined the fate of organic pollutants in these organic amendments such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pharmaceuticals and personal care products (PPCPs). In this study, we investigated pyrolysis process and hydrothermal carbonization (HTC) as promising methods to treat organic pollutants in two raw sludges (stabilized sewage sludge and sludge cake). Biochars (pyrolysis temperatures of 450 °C and 600 °C) and hydrochars (HTC temperature of 180 °C) produced from two raw sludges, and resulting chars were analyzed for the presence of three organic pollutants groups including PCBs, PAHs, PPCPs. During the HTC process, the reduction in concentration of pharmaceuticals was higher than the other groups. Most of these compounds were removed during the pyrolysis process at 450 °C, however; at 600 °C (≥99.9%) all organic pollutants were removed from the produced biochars. These results confirm the usefulness of a pyrolysis process at above 600 °C for the elimination of organic pollutants from biochars to produce chars with little or no organic pollutants as a safe amendment to improve degraded soils.