Effect of moisture content on the characterization of products from the pyrolysis of sewage sludge

•High moisture content was conducive to the production of hydrogen rich fuel gas.•The steam involved in gasification and reforming reactions has a saturation value.•The toxic effect of tar decreased with the increase of moisture content.•The ejection of volatile matter was intensified by high moisture content.

Sewage sludge samples with moisture contents of 0%, 31%, 47% and 80% were pyrolyzed at 1000 °C in a tubular furnace to evaluate the effect of moisture content on the pyrolysis process. The evaporation of water accelerated the evolution of porosity in the solid char and hence contributed to the devolatilization of sewage sludge, leading to an increase in the gas fraction and a decrease in the solid fraction. The steam-rich atmosphere generated by the high moisture content of sewage sludge favored the steam reforming reactions of volatile compounds and the steam gasification of solid char, enhancing the production of hydrogen rich fuel gas. A saturation value was also observed for the steam involved in the gasification and reforming reactions. GC–MS analysis showed that the increase of moisture content not only promoted the reduction of the species in the tar, but also improved the production of light aromatics, as a result, the toxic effect of tar decreased considerably. The decrease in the peak areas of organic functional groups of solid char demonstrated that the participation of steam promoted the ejection of volatile matters of sewage sludge during the pyrolysis process.