Comparison between hydrogen-rich biogas production from conventional pyrolysis and microwave pyrolysis of sewage sludge: is microwave pyrolysis always better in the whole temperature range?

To investigate the influence of the pyrolysis temperature on biogas production from sewage sludge, conventional pyrolysis and microwave pyrolysis were carried out in the temperature range from 600 degrees C to 900 degrees C and all products were analyzed. With the temperature increasing, the product yields for conventional pyrolysis varied significantly, while those for microwave pyrolysis changed quite slightly. In conventional pyrolysis, the yield of H-2 increased from 1.26 mmol/g at 600 degrees C to 9.07 mmol/g at 900 degrees C, while it was varied only from 1.84 mmol/g to 3.67 mmol/g in microwave pyrolysis. Under microwave pyrolysis, a high ratio of H/C indicated that more hydrogen atoms converted directly to tar instead of being released into biogas, which was caused by side reactions (such as the hydrogen transfer reaction). More aromatic compounds in the tar during microwave pyrolysis illustrated that the hydrogen transfer reaction was enhanced by microwave at the higher temperatures. It has been found that the sludge microwave pyrolysis had some drawbacks for the hydrogen-rich biogas production, because it could promote some side reactions to suppress the H-2 production, especially the hydrogen transfer reaction. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study investigated the influence of pyrolysis temperature on biogas production from sewage sludge using conventional pyrolysis and microwave pyrolysis. Results showed that with increasing temperature, the product yields varied significantly for conventional pyrolysis, while the changes were minimal for microwave pyrolysis. Microwave pyrolysis resulted in more hydrogen atoms converting into tar instead of being released into biogas, indicating the enhancement of hydrogen transfer reactions at higher temperatures.