Pyrolysis of municipal sewage sludges in a slowly heating and gas sweeping fixed-bed reactor

• A fixed-bed reactor with sweeping gas was used to mitigate secondary reactions.
• The pyrolysis products reflected the original structures of sludge compositions.
• The slow pyrolysis produced high yields of liquid.
• The oxygen-containing and nitrogenated compounds were the main liquid products.
• The gas and liquid yields correlated with the volatile matter contents in the sludges.

The pyrolysis of three municipal sewage sludges was carried out using a slowly heating and gas sweeping fixed-bed reactor in the temperature range between 300 °C and 700 °C. The study was aimed to characterize the gaseous and liquid products derived from three different sewage sludges and mainly to discuss the varieties of sewage sludges on the yields and compositions of the gaseous and liquid products. The pyrolysis in this reactor was observed to produce high yields of liquid (above 40 wt.% at 700 °C) that contained high proportions of oxygen-containing compounds and nitrogenated compounds, with minor monoaromatics and aliphatic compounds. The gas and liquid yields correlated with the volatile matter contents in the sludges. For all three sewage sludges, the oxygenated compounds were the principal liquid compounds which could be produced at a low temperature of 300 °C, while more of nitrogenated compounds and other compounds were formed at 700 °C depending on the varieties of sewage sludges.