Characterization of the macromolecular organic content of sewage sludges by thermally assisted hydrolysis and methylation-gas chromatography–mass spectrometer (THM-GC/MS)

Abstract

The aim of this study is to determine a methodology enabling us to simplify the information generated by thermally assisted hydrolysis and methylation (THM)-pyrograms of sludges and to provide an insight into the sludges according to their chemical composition. The insoluble organic fractions of 48 sewage sludges originating from industrial (food-processing and paper mill) and domestic (urban, small urban and rural) wastewater-treatment plants (WWTP) of the region of Lorraine (northeast of France) were characterized by THM-GC/MS. A relative quantification of the pyrograms by integration of the major peaks was then carried out. The results of this integration were plotted in a triangular diagram defined by the poles corresponding to the three major families evidenced in the pyrograms (lignin-derived, lipid-derived and nitrogenous compounds). This type of representation enables us to separate paper-mill sludges from the others, because they are characterized by high amounts of lignin-derived compounds. The majority of domestic sludges and food-processing sludges are gathered and characterized by an intermediate composition in lipid-derived, lignin-derived and nitrogenous compounds, but seven urban sludges show an evolution of their chemical composition towards the lipid pole. The domestic sludges can be separated from the others on the basis of their molecular nitrogenous distribution. Such a methodology is complementary with the qualitative analysis of pyrograms and makes it possible to approach the chemical composition of sludges, which governs their reactivity once they are disposed on soil.