Classification and characterization of bio-oil obtained from catalytic and non-catalytic pyrolysis of desludging sewage sample

Abstract

Sewage sludge is a very harmful waste when improperly discharged into the environment because of its inherent abundant pathogens, organic pollutants, and heavy metal constituents. The pyrolysis of sewage sludge is viewed not only to reduce pollutants associated with it but also one of the viable alternative sources for renewable energy or biofuel production. In this study, the effect of catalyst and temperature on the yield and composition of bio-oil obtained from the catalytic and non-catalytic pyrolysis of desludging sewage samples (DSS) was investigated. Modified pyrolysis reactor was used to pyrolyze the DSS at temperature ranges of 300–400,400–500,500–600 and 600–700 ℃ with and without the use of zeolite-Y catalyst. The 'heterogeneous' catalysis reaction yielded 20.9 wt% bio-oil, while the reaction without catalyst yielded 18.2 wt% bio-oil. Pyrolysis of the DSS favored char yield of between 55.4 and 76.6 wt%. The X-ray Fluorescence (XRF) analysis showed high silica (46 and 56.1 wt%), calcium (20.9 and 15.50 wt%), and low organic matter (12 and 12.87 wt%) contents present in the desludging feedstock before and after pyrolysis respectively. The gas chromatography–mass spectrometry (GCMS) analysis indicated the presence of nitrogen-containing compounds (between 20 and 50 wt%), mono-aromatics (18 and 28 wt%) and oxygenated compounds, in the form of carboxylic acids, aliphatics, ketones, ethers, esters and aldehydes in the bio-oils. Pyrolysis process development is, therefore, essential to clean the environment of pollutants from sewage sludge, by its conversion to more useful chemicals. In contrast, sewage sludge with high silica content may be tailored to the production of building materials.

Keywords

• pyrolysis
• sewage sludge
• heterogeneous catalysis
• bio-oils
• zeolite-y