Microwave pyrolysis of sewage sludge:: analysis of the gas fraction

Four wet sewage sludges from different waste water treatment plants were dried and pyrolyzed (in a single process) at laboratory scale, using a multimode-microwave oven. The gases obtained from these pyrolysis experiments were analyzed and compared with those from a more conventional pyrolysis employing an electrical furnace. The results help to explain the complex mechanisms that take place during the pyrolysis of sewage sludge. This process produces a considerable amount of gases with potential value as fuels due to the fact that they have relatively high calorific values. Upon comparing the two pyrolysis processes, it was found that microwave pyrolysis takes a much shorter time than when using the electrical furnace. It was also found, that while microwave pyrolysis gives rise to a gas with a high content (up to 62%) of CO and H-2 (synthesis gas), conventional pyrolysis generates a gas with an elevated proportion (ca. 25%) of hydrocarbons of high calorific value. (C) 2003 Elsevier B.V. All rights reserved.