Conventional methods of sewage sludge disposal are often limited by their environmental impact and economic demands. Pyrolysis has been studied as a viable method for sewage sludge disposal and transformation into usable products. Pyrolytic products may have various uses, and their complex characteristics shall be described to assess their potential for safe utilization. Here, we studied slow pyrolysis of stabilized sewage sludge in a fixed bed reactor at 400–800 °C to describe the composition of the pyrolysis gas and the condensate fraction. We found that condensate elemental composition was practically independent of pyrolysis temperature. On the other hand, the composition of the pyrolysis gas was strongly temperature-dependent regarding both the share of major components (H₂, CO, CO₂, CH₄) and C₂–C₆ hydrocarbons speciation (which as a sum attributed to 7–9 vol. % of the gas). The increase in pyrolysis temperature also resulted in increasing the N₂ content of the gas, whereas the sulfur containing gas compounds were substantially diluted in the increasing gas volume.

Steam can be fully or partially substituted by CO2 as a gasification agent. This substitution affects producer gas composition, char conversion and in-situ tar reforming. Here, wood chips were gasified in a spouting fluidised bed using silica sand and catalytic dolomitic lime as the bed material at 850 °C. The use of a gasifying agent composed of CO2 and H2O was compared to the use of CO2 or H2O alone. It was found that mixtures of CO2 and H2O as the gasifying agent improve char conversion, and that the combined gasification agents are very effective in ensuring the decomposition/destruction of tars when lime based materials are used in the fluidised bed