Thermal Degradation Behavior of Sewage Sludge in Pyrolysis Processes

Abstract

By considering the growing energy demand internationally, it is necessary to highlight alternate renewable and sustainable resources of fuel such as biomass and domestic waste to produce energy by unconventional methods. Non-lignocellulosic biomass like sewage sludge is the most suitable alternative used instead of fossil fuels because this material has potential to produce both bio-oil and biochar. The current research emphasis on the pyrolysis process of sewage sludge to study the thermal degradation behavior through thermogravimetric analysis and by using lab scale reactor (autoclave pyrolyzer unit) to obtain useful products. Elemental composition of sewage Sludge is determined by ultimate and proximate analysis and existed functional group is identified through FTIR analysis. The Effect of heating rate (5°C/min, 10°C/min and 20°C/min) on thermal degradation behavior is studied by TGA-DTA technique in Nitrogen atmosphere and found the main degradation phase between 200-600°C which is further divided into two phases one from 200-400°C and 400-600°C for the thermal disintegration of different components. The kinetic and thermodynamic parameters are calculated by using model fitting kinetics such as Coats and Redfern method and model free kinetics such as Friedman, KAS, OFW and Popescu is done to describe pyrolysis behavior of sewage sludge by using TGA-DTA data. The effect of temperature (350°C, 400°C and 450°C) is studied through autoclave pyrolyzer unit by keep feedstock, pressure and agitation conditions constant. In lab scale pyrolysis process, highest bio-oil yield was achieved at 450°C. The products such as bio-oil, char and gases are further analyzed by GC-MS, FTIR, TGA and GC-TCD. GC-MS peak area percentage showed that the bio-oil exhibited variety of chemical groups such as acids, carbonyls, furans, phenols, sugars and aromatic hydrocarbon. GC-TCD showed area percentage of methane and carbon dioxide also increased as the temperature increased and area percentage of hydrogen decreased as temperature increased. Various functional group is identified present in char produced at different temperature through Fourier transform infrared spectroscopy.