Pyrolysis of municipal sewage sludge for bioenergy production: Thermo-kinetic studies, evolved gas analysis, and techno-socio-economic assessment

In this study, a comprehensive investigation was conducted to use municipal sewage sludge (MSS) as a promising feedstock for bioenergy production via pyrolysis process. Using thermogravimetric analysis (TGA), MSS was subjected to thermal decomposition experiments at four different heating rates of 5, 10, 30 and 50 degrees C/min. TGA curves were divided into three distinctive stages, namely drying zone (T ( )<= 200 degrees C), active pyrolysis zone (200 < T < 600 degrees C), and char decomposition zone (T >= 600 degrees C). Moreover, the data were used to analyze thermokinetic parameters through Flynn-Wall-Ozawa (FWO), Kissenger-Akahira-Sunose (KAS), and Starink methods, where the average values of E-a (126.62-136.92 kJ/mol), Gibbs free energy (159.19-159.61 kJ/mol), and calculated high heating value (HHV, 16.47 +/- 0.03 MJ/kg) showed the considerable bioenergy potential of the low-cost biomass. The low difference between E-a and Delta H (similar to 5 kJ/mol) showed that product formation was favorable during pyrolysis. In addition, for the first time, the comparative study of the results predicted from support vector regression (SVR) model and the experimental data, showed a satisfactory agreement (R-2 > 0.9999) and accurate results regarding different train-test data categories. Further employed was Pyrolysis-Gas Chromatography/Mass Spectroscopy (Py-GC/MS) at 700 degrees C to characterize the potential chemical products, which indicated the presence of a range of aromatic and aliphatic hydrocarbons, nitrogen-containing compounds, alcohol, furans and sulfur compounds. Finally, three alternative scenarios associated with the planned project were presented and techno-socio-economic assessment (TSEA) of the alternative scenarios were evaluated, for the first time, by means of economic indexes and considering social aspects. Net present value (NPV) of all alternative scenarios of the pyrolysis plant over the 20-year plant lifetime was positive compared to the base case, indicating that the project was feasible. Sensitivity analysis of the optimistic scenario showed that the profitability of pyrolysis plant was highly dependent on bio-oil selling price and total production cost.