Study on Nitrogen Transformation during Sewage Sludge Pyrolysis at Low Temperatures

Abstract

The nitrogen conversion with attention to the intermediates and NOx precursors has been investigated during the primary pyrolysis of sewage sludge by using Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetric analyzer (TGA) coupled with Fourier transform infrared spectrometry (FTIR). The results indicated that 75.4% of total nitrogen exists in the forms of protein in the sewage sludge. Amine compounds and nitrogen heterocyclics were found to be the main nitrogenated intermediates during the pyrolysis process in the temperature range of 250-400 °C. As the dominant nitrogenated compounds, the relative proportions of amine compounds were above 52% in all cases. And since the decomposition of sewage sludge was promoted by high temperature, the relative proportion of amine compounds increased by 24.6% when the temperature raised from 300 to 400 °C. Moreover, the generation of NH3 at 250 oC was mainly derived from the decomposition of ammonium salt, while the deamination of amine compounds led to a significant increase of NH3 at 300 °C.