PCDD/Fs in wet sewage sludge pyrolysis using conventional and microwave heating

• Most volatile matters were released before 600 °C in FTIR analysis of pyrolysis of wet sludge.
• Distillation effects explained the congener profiles of 17 toxic PCDD/Fs well.
• Both CP and MWP of wet sludge had effects of distillation and dechlorination of PCDD/Fs.
• CP presented more prominent dechlorination and distillation effects than MWP.

TG-FTIR was carried out to investigate gas evolution during pyrolysis of wet sewage sludge from Shanghai, China. Weight lost 85% in the temperature range 25–600 °C while the main volatile matters were released before 600 °C.To get emission characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during pyrolysis processes, conventional pyrolysis (CP) by electric heating and microwave pyrolysis (MWP) by microwave heating were separately conducted on two set of batch reactors.Both CP and MWP evolved no more than 5% of concentration of 17 toxic PCDD/Fs in untreated sewage sludge while corresponding ratios of International Toxicity Equivalents (I-TEQ) were around 30%. The ratios of difference congeners can be well explained by distillation effect. Homologue profiles of the total PCDD/Fs indicated presence of dechlorination and distillation effects during the two processes while the effects in CP were more prominent than in MWP though the latter got higher temperature. Other to that, MWP produced equivalent quantity of PCDD/Fs compared with CP indicating the absence of “nonthermal” effect in MWP on PCDD/Fs evolution.