Changes in Wastewater Sludge Characteristics Submitted to Thermal Drying, E-beam Irradiation or Anaerobic Digestion

Changes in organic matter (OM) characteristics of wastewater sludge (WWS) submitted to three handling processes were monitored. Thermal drying, electron beam (e-beam) irradiation and anaerobic digestion were compared. The knowledge of the characteristics of the final residual biomass is essential to improve its valorization. The OM of WWS was investigated at the global scale using elemental analysis, infrared spectroscopy, thermogravimetric analysis and chemical fractionation. Double-shot thermochemolysis coupled with gas chromatography and mass spectrometry (GCMS) was used to compare the diversity and distribution of the molecular contents. A strong influence of thermal drying on lipids and humic-like substances contents was observed through fractionation, which traduced a weakening of the OM. The anaerobic digestion induced an increase in lipids for the hydrolysis phase followed by a decrease which correlates with the volume reduction of sludge by about 30%. E-beam induced change in the distribution of the different pools of organic matter depending on the irradiation dose. At the molecular scale, fatty acids, steroids and aromatics were the main thermochemolysis products in all the samples. The thermal drying induced an increase in fatty acids and in steroids, probably released from the refractory OM. Anaerobic digestion modified exclusively the amount and distribution of fatty acids while e-beam induced a decrease in all the identified compounds including aromatics. Finally double-shot thermochemolysis-GCMS demonstrated that the consequences of the handling process on the molecular contents of WWS should be taken into account for the choice of the final valorization pathway. Studied handling processes