Thermal treatment of sediments as a function of temperature and reacting atmosphere

Abstract

Samples of polluted sediments were submitted to a two-step thermal treatment either in inert (pyrolysis) or oxidative (combustion) atmosphere. Tests were carried out at 400, 650 and 900°C and a residence time of 2 s. Gaseous effluents were collected on-line and analyzed via GC-MS. A detailed description of the main classes of substances generated as a function of temperature and reacting atmosphere was obtained, and conditions leading to a complete destruction of the evolved pollutants were determined. On increasing the pyrolysis temperature, a cleaner sediment residue was obtained, but the pyrolyzate produced at the highest temperatures was rich in simple and poly aromatic hydrocarbons and other nitrogen-, chlorine- or oxygen-containing products of strong environmental concern. When the thermal treatment was performed in the presence of air, most of these substances were not found in the effluent at 650°C, even though temperatures as high as 900°C, in the presence of a large oxygen excess, were required to achieve a complete destruction of all the organics.